Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Mr. Sharkey via EV]

Not to draw this topic out too far, but I thought I'd post an image 
that shows what I inherited when I bought the conversion truck and 
began removing the cells for installation in my car.


This is large image, but I left it in the original resolution after 
cropping so that the details wouldn't be lost:


http://www.westlanetv.org/~sharkey/evgfx/Old_Thundersky_Installation.jpg

This looks like a Sunday Funnies "How many problems can you spot in 
this picture?" puzzle. The strap that I just operated on is one of 
the two shown in the photo.


The controller in this rig was set to limit current to 350 amperes. 
Even with that, there were burned spots where some of the straps 
contacted the tarnished/oxidized cell terminals. The general fit and 
finish of the installation invited problems. No particular effort was 
expended to make connections low resistance, or even to produce a 
close fit. Look at the distortion on the left hand strap end where 
the copper has been pulled up by the oversized BMS ring terminal 
being compressed by a stainless flat washer under the terminal bolt. 
Or the interface of the other end of the strap with the rectangular 
copper bar that runs through the Hall effect current sensor.


All of this is a testament as to why Tesla chose to have robots weld 
their battery cell connectors.


That said, at least NEC fabricated the Leaf cells with copper 
contacts that are backed up by steel captive nuts so that the bus 
bars can be drawn down tight. The copper contacts have a little bit 
of "float" in the module cases so that they have at least a limited 
amount of position adjustment when the modules are assembled into a battery.


>> Bob Rice used to weld his connections

Some years back, I was contacted by a new owner of an SCT conversion 
like mine. He described his lead-acid pack as having copper braid 
soldered to the battery terminal posts as jumpers. I thought it was 
some kind of desperation move by a previous owner, but given the 
"super cooled liquid" that lead terminals represent, it was probably 
a good move. Glad to be past that phase of EV technology. I can't see 
ever going back to lead.


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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Lee Hart via EV]

Mr. Sharkey via EV wrote:

In an EV, we usually only get a single bolt and a flat mating
surface the diameter of a nickle to make a successful connection. In
building battery packs, we get to repeat that  a hundred times over.
Seems unfair, but I think I said it previously, we got to work with what
we are given.


Yes, it's a poor situation for making a good connection. But one we are 
stuck with on cheap Chinese prismatic cells. I don't think they know or 
care about making reliable high-current connections.


Industrial batteries always have welded inter-cell jumpers. My old 
friend Bob Rice used to weld his connections, too. He figured the only 
time they will ever have to be disturbed is if the battery fails; and 
then there's no problem in cutting it off the dead cell.


His technique was to use a very hot torch, wrap a wet rag around the 
outside of the terminal, and then quickly weld to the top of the post. 
If you can do it in a second or two, the post and terminal have enough 
thermal mass to keep the heat from spreading and damaging the seal.


It is possible to weld aluminum. I've often wondered if an experienced 
welder with the right equipment could weld the inter-cell jumpers to a 
lithium cell without damaging the seal. It seems like it's such a 
massive slug of aluminum that a spot welder might be able to do it.


Lee Hart
--
There is a computer disease that anybody who works with computers knows
about. It's very serious, and interferes completely with your work. The
trouble with computers is that you 'play' with them! (Richard Feynman)
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Mr. Sharkey via EV]

>> It is possible that the Noalox had become separated in the bottle
>> but as a long term industrial electrician who has never used
>> the stuff before, I decided to use the tried and tested method of having
>> bright clean (tight) connections.

That's always my first choice also, bright and tight. When working 
with aluminum conductors, and worse, mixing aluminum with other 
materials and alloys, some form of anti-oxidant is a good idea.


I stopped using NoAlOx for battery terminals quite a long time ago in 
favor of the NoOxID product. NoAlOx seems to "creep" from where it's 
applied, and eventually any excess gets spread around and catches the 
inevitable dirt and dust. NoOxID is a thicker paste-like compound 
that seems to stay put. It is also less likely to stain anything it gets on.


More concerning, I don't like the idea of grinding sintered aluminum, 
suspended in the NoAlOx product, into terminals and conductors. Seems 
counter productive to put any solid materials between conductive 
surfaces that are supposed to be making contact, especially if the 
total surface area of the contact is important. Drawing tension into 
the joint by tightening the fastener can only cause the aluminum to 
be pressed into the conductors, or else the conductors are held apart 
by the solid material. Neither is what I'm after.


I suppose NoAlOx is OK for it's intended purpose, protecting aluminum 
wiring that is used in circuit breaker panels and other service 
equipment, I still use it for that purpose. Most AHJ's (electrical 
inspectors) expect to see it and will not approve work that doesn't 
use it where required.


In industrial electrical work, circuits that pull the kind of current 
we see in EV's have large contact areas where conductors meet, 
perhaps with multiple fasteners and pressure connectors that can 
really be pulled tight. In an EV, we usually only get a single bolt 
and a flat mating surface the diameter of a nickle to make a 
successful connection. In building battery packs, we get to repeat 
that  a hundred times over. Seems unfair, but I think I said it 
previously, we got to work with what we are given.


It also helps to pay attention. I didn't and I got a chance to do it 
over. That's luck at work.


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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Russ Sciville via EV]

 So good to read that you found it was caused by being simply forgetful. I go 
over all the terminals two or three times as it is so easy to miss one in a 
couple of hundred.
Previous posts mentioned using Noalox paste. I used to use it as advised on 
various forums but have been burning out the odd Orion BMS inputs over the past 
few years on my two home builds.For the recent rebuild of the traction battery 
and again repaired BMS I cleaned up the connections with wire wool and alcohol. 
You could see on the links where the contact had been poor and I suppose caused 
a rise in voltage across the sensing circuit.They have been faultless since.
It is possible that the Noalox had become separated in the bottle but as a long 
term industrial electrician who has never used the stuff before, I decided to 
use the tried and tested method of having bright clean (tight) connections.
On Thursday, 3 October 2019, 00:19:03 BST, Mr. Sharkey via EV 
 wrote:  
 
 Well, it looks like this issue may have been one of my own making. 
When I went to remove the cell interconnect strap, both bolts into 
the cell terminals were "just snug", not tight. Apparently I got 
distracted when completing the BMS card swap, and didn't torque the bolts.

The straps are made up of four .025" "leaves" of copper stock, with a 
little hickey bend in the center for mechanical relief between the 
cells. A sleeve of heat shrink tubing  protects the center of the 
completed strap, and holds it together for assembly on the pack. This 
was one that I had disassembled to repair, probably because it had 
been intentionally bent by the previous owner to do something that it 
wasn't intended to do.

When I took it off, it didn't look at all unusual on the top, and the 
bottom looked fine, it had been in complete contact with the cell 
terminals by the appearance of the anti-corrosion grease.

Inside was a different matter. I cut the heat shrink off and found this:

http://www.westlanetv.org/~sharkey/evgfx/Hot_Strap.jpg

The four leaves from right-to-left are top-to-bottom, respectively, 
and the bottom of the photo is the end that was connected to the 
too-warm cell in the IR photo.

I wish I had been able to use some brand name green abrasive pads 
instead of the dollar-store pretend ones, cleaning the discoloration 
out of the straps would have been much easier. Afterwards, I hit them 
with real white Scotchbrite, then gave them a shine with Brasso for 
good measure. A wash with denatured alcohol, and I put them back on 
the cells. I'm going to go all over the battery and check all the 
fasteners for proper torque before putting the cover back on the pack.

In the long term, I think I might build a new strap. If this one was 
so abused that I needed to take it apart to use it again, there may 
be some issues with the leaves not making as complete of a contact 
with each other as new, flat straps made from new stock. I don't have 
any .025 stock, so I use five leaves of .020 copper to build new straps.

I hope to have another session with the IR camera next week to see if 
my efforts to correct this little screw-up have been successful.

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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Pestka Dennis via EV]

I torque my CALB 180's to 14.75 ft lbs, or 20 NM.
This is per EVTV specs.

Dennis

From: EV  on behalf of jim--- via EV 

Sent: Wednesday, October 2, 2019 10:18 PM
To: Electric Vehicle Discussion List 
Cc: j...@k6ccc.org 
Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

Mr. Sharkey said (in part):

> Soft aluminum and copper make me queasy when I have to test the
> threads. I played it safe and only torqued to 8 ft.lbs. Anyone know
> the official torque spec on Thundersky's?

No idea on the Thundersky.  The large Telecomm batteries we use at work are 110 
inch pounds - or about 9 foot pounds.  We torque them all correctly.

73
-
Jim Walls - K6CCC
j...@k6ccc.org


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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Lee Hart via EV]

Cor van de Water via EV wrote:

The leaves do not need to contact each other in any other point than at the 
battery terminal screw which compresses them into one flat ring.


Ah yes; good point. Sometimes they are actually insulated from each 
other, such as in high current switchmode power supplies. The "skin 
effect" causes high frequency currents to flow predominantly in the 
surface of thick conductors. So, they laminate buss bars or use 
insulated strands of wire to keep the thickness small.


I should also mention that it is important that the layers *do* make 
good contact at the ends. It is all too easy for only the bottom surface 
of the bottom leaf to make good contact with its terminal. The others 
have extra "contact" resistance, and so carry proportionately less 
current. The top leaf carries the least current.


You might think the bolt will conduct current up to the top leaf. But 
the bolt is often steel (or worse, stainless steel), which has very high 
electrical resistance.


Thermal imaging is a quick easy way to evaluate connectors. But for a 
more accurate indicatin, I prefer to draw a known current, and measure 
the voltage drop with a multimeter. This can readily show you the 
resistance of the bolt, current variations between leafs, etc.


Lee Hart

--
There is a computer disease that anybody who works with computers knows
about. It's very serious, and interferes completely with your work. The
trouble with computers is that you 'play' with them! (Richard Feynman)
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[jim--- via EV]

Mr. Sharkey said (in part):

> Soft aluminum and copper make me queasy when I have to test the 
> threads. I played it safe and only torqued to 8 ft.lbs. Anyone know 
> the official torque spec on Thundersky's?

No idea on the Thundersky.  The large Telecomm batteries we use at work are 110 
inch pounds - or about 9 foot pounds.  We torque them all correctly.

73
-
Jim Walls - K6CCC
j...@k6ccc.org


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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Mr. Sharkey via EV]

>> Glad you found something!

Yeah, me too. I went all around the battery and tested torque on the 
rest of the 74 bolts, and only found a few that needed an extra 
foot-pound or two. The threads have been coated with anti-seize, so 
there is good lubrication, but I'm really gun-shy (wrench-shy?) about 
pulling down too hard and yanking the threads out of the cell posts. 
Soft aluminum and copper make me queasy when I have to test the 
threads. I played it safe and only torqued to 8 ft.lbs. Anyone know 
the official torque spec on Thundersky's?


>> The leaves do not need to contact each other...

Yes, I did know that, but I had some concern that the ends of the 
leaves were still a little wrinkly, and might not be flattening 
enough. Looking at the patterns in the "Bad_Straps.jpg" image, it 
looks like there  was pretty good contact area going on, just not 
enough pressure.


I guess the good news in all this is I only made one run into town 
and back with loose hardware, and the cell terminal posts looked 
fine, in spite of the straps getting a little scorched.


Thanks everyone for the suggestions. Maybe next I'll launch into a 
tale about what happens when you short out a pair of series connected 
Leaf modules by putting the bus bars on wrong (surprising outcome!).


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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[jim--- via EV]

Mr. Sharkey said (in part):
> Well, it looks like this issue may have been one of my own making. 
> When I went to remove the cell interconnect strap, both bolts into 
> the cell terminals were "just snug", not tight. Apparently I got 
> distracted when completing the BMS card swap, and didn't torque the bolts.

That was the important part.  The next few paragraphs were not the issue.  Just 
snug was your issue.

Glad you found something!

Jim Walls




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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Cor van de Water via EV]

The leaves do not need to contact each other in any other point than at the 
battery terminal screw which compresses them into one flat ring.

Sent from Mail for Windows 10

From: Mr. Sharkey via EV
Sent: Wednesday, October 2, 2019 4:18 PM
To: ev@lists.evdl.org
Cc: Mr. Sharkey
Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

Well, it looks like this issue may have been one of my own making. 
When I went to remove the cell interconnect strap, both bolts into 
the cell terminals were "just snug", not tight. Apparently I got 
distracted when completing the BMS card swap, and didn't torque the bolts.

The straps are made up of four .025" "leaves" of copper stock, with a 
little hickey bend in the center for mechanical relief between the 
cells. A sleeve of heat shrink tubing  protects the center of the 
completed strap, and holds it together for assembly on the pack. This 
was one that I had disassembled to repair, probably because it had 
been intentionally bent by the previous owner to do something that it 
wasn't intended to do.

When I took it off, it didn't look at all unusual on the top, and the 
bottom looked fine, it had been in complete contact with the cell 
terminals by the appearance of the anti-corrosion grease.

Inside was a different matter. I cut the heat shrink off and found this:

http://www.westlanetv.org/~sharkey/evgfx/Hot_Strap.jpg

The four leaves from right-to-left are top-to-bottom, respectively, 
and the bottom of the photo is the end that was connected to the 
too-warm cell in the IR photo.

I wish I had been able to use some brand name green abrasive pads 
instead of the dollar-store pretend ones, cleaning the discoloration 
out of the straps would have been much easier. Afterwards, I hit them 
with real white Scotchbrite, then gave them a shine with Brasso for 
good measure. A wash with denatured alcohol, and I put them back on 
the cells. I'm going to go all over the battery and check all the 
fasteners for proper torque before putting the cover back on the pack.

In the long term, I think I might build a new strap. If this one was 
so abused that I needed to take it apart to use it again, there may 
be some issues with the leaves not making as complete of a contact 
with each other as new, flat straps made from new stock. I don't have 
any .025 stock, so I use five leaves of .020 copper to build new straps.

I hope to have another session with the IR camera next week to see if 
my efforts to correct this little screw-up have been successful.

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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Mr. Sharkey via EV]

Well, it looks like this issue may have been one of my own making. 
When I went to remove the cell interconnect strap, both bolts into 
the cell terminals were "just snug", not tight. Apparently I got 
distracted when completing the BMS card swap, and didn't torque the bolts.


The straps are made up of four .025" "leaves" of copper stock, with a 
little hickey bend in the center for mechanical relief between the 
cells. A sleeve of heat shrink tubing  protects the center of the 
completed strap, and holds it together for assembly on the pack. This 
was one that I had disassembled to repair, probably because it had 
been intentionally bent by the previous owner to do something that it 
wasn't intended to do.


When I took it off, it didn't look at all unusual on the top, and the 
bottom looked fine, it had been in complete contact with the cell 
terminals by the appearance of the anti-corrosion grease.


Inside was a different matter. I cut the heat shrink off and found this:

http://www.westlanetv.org/~sharkey/evgfx/Hot_Strap.jpg

The four leaves from right-to-left are top-to-bottom, respectively, 
and the bottom of the photo is the end that was connected to the 
too-warm cell in the IR photo.


I wish I had been able to use some brand name green abrasive pads 
instead of the dollar-store pretend ones, cleaning the discoloration 
out of the straps would have been much easier. Afterwards, I hit them 
with real white Scotchbrite, then gave them a shine with Brasso for 
good measure. A wash with denatured alcohol, and I put them back on 
the cells. I'm going to go all over the battery and check all the 
fasteners for proper torque before putting the cover back on the pack.


In the long term, I think I might build a new strap. If this one was 
so abused that I needed to take it apart to use it again, there may 
be some issues with the leaves not making as complete of a contact 
with each other as new, flat straps made from new stock. I don't have 
any .025 stock, so I use five leaves of .020 copper to build new straps.


I hope to have another session with the IR camera next week to see if 
my efforts to correct this little screw-up have been successful.


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Re: [EVDL] LiFePO4 Thermal Imaging Opinions? (common mistake)

[Cor van de Water via EV]

Correct.
In the forum post, also a remark is made how the power supply stays so cool.
If you look closely, you see the orange color from every opening in the
metal enclosure, but the reflection of the metal enclosure shows you that
the room is cool, because that is what is seen by the FLIR, not the temp of
the metal case itself.
Cor.

On Tue, Oct 1, 2019, 11:35 PM Robert Bruninga via EV 
wrote:

> > ...a couple years ago I used a thermal imaging camera to demonstrate
> > how hot a lighting controller board got under heavy load.
> >
> http://forums.lightorama.com/topic/45960-how-warm-does-a-sandevices-e682-g
> et/
> <http://forums.lightorama.com/topic/45960-how-warm-does-a-sandevices-e682-get/>
>
> Warning!
>
> A common mistake.  The "heat" visible on the eithernet connector has
> nothing to do with that connector.  That is nothing but a reflection of
> something hot (maybe the person taking he picture).  Notice how in every
> view, there is variation in the "heat" image of that shiny connector.
>
> This is because SHINY METAL does not radiate heat very much but it does
> provide excellent specular reflection.  So all you ever see of a shiny
> metallic component is what it is reflecting, nothing at all about its own
> temp.
>
> A very common mistake.
>
> The Thermal emissivity of everything in view is *assumed* to be about 0.9.
> The operator has to know enough to discount any reading of any material
> this is not 0.9 ish.  True, most things are, but definitely NOT shiny
> metal!  Aluminum is 0.03 or 30 times less emissivity.  (that is why we
> wrap it around a baked potato!).
>
> Hold up a baking tin, it acts like a thermal mirror to everything in the
> room.  You are seeing nothing about its own temperature.
>
> Bob, WB4AAPR
>
> -Original Message-
> From: EV  On Behalf Of jim--- via EV
> Sent: Tuesday, October 1, 2019 2:21 PM
> To: Electric Vehicle Discussion List 
> Cc: j...@k6ccc.org
> Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?
>
> Yes.  Heat is going to conduct better through the metal plates of the
> batter vs the electrolite.  Therefore, the heat if generated at the
> connector is going to conduct along the metal plates.  Assuming that the
> plates in that battery are vertical, I would expect something similar to
> what is being seen.
>
> Also note that the strap is FAR hotter than the portion of the strap
> visible at the left edge of the IR image, and that the right end of the
> strap and the top of the cell on the right that is connected to that strap
> is also warm.  There is a lot of heat being generated in the strap or more
> likely the connection between the left end of the strap and the top of the
> battery.
>
> We use IR images using similar equipment here at work for checking
> electrical connections quite regularly.
>
> For a little entertainment, a couple years ago I used a thermal imaging
> camera to demonstrate how hot a lighting controller board got under heavy
> load.  I posted the results on a Christmas Lighting forum.  You should be
> able to read it - although you can't post a reply unless you are a member
> of that forum.
> http://forums.lightorama.com/topic/45960-how-warm-does-a-sandevices-e682-g
> et/
> <http://forums.lightorama.com/topic/45960-how-warm-does-a-sandevices-e682-get/>
>
>
> Jim
>
>
> -Original Message-
> From: "Peri Hartman via EV" 
> Sent: Tuesday, October 1, 2019 10:53
> To: "Electric Vehicle Discussion List" 
> Cc: "Peri Hartman" 
> Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?
>
> Wow, hat's a great observation. Question: is it significant that the IR
> image also shows heat emanating vertically, appearing to be relatively
> uniform ?
> Peri
>
> -- Original Message --
> From: "jim--- via EV" 
> To: "Electric Vehicle Discussion List" 
> Cc: "j...@k6ccc.org" 
> Sent: 01-Oct-19 10:36:24 AM
> Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?
>
> >>  A close-up of the cell, looking from the front of the pack. It's been
> photoshopped to blend the IR image with the visible image to provide some
> perspective of the actual appearance:
> >>
> >>  http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg
> >
> >Carefully check the connection on that cell that is closest to the
> camera.  Note that only the one end of the cell is warmer - not both ends.
> I would suspect that the connection is marginal and causing the heat.  The
> heat has conducted into that end of the cell.
> >
> >73
> >-
> >Jim Walls - K6CCC
> >j...@k6ccc.org
> >
> >
> >__

Re: [EVDL] LiFePO4 Thermal Imaging Opinions? (common mistake)

[Robert Bruninga via EV]

> ...a couple years ago I used a thermal imaging camera to demonstrate
> how hot a lighting controller board got under heavy load.
>
http://forums.lightorama.com/topic/45960-how-warm-does-a-sandevices-e682-g
et/

Warning!

A common mistake.  The "heat" visible on the eithernet connector has
nothing to do with that connector.  That is nothing but a reflection of
something hot (maybe the person taking he picture).  Notice how in every
view, there is variation in the "heat" image of that shiny connector.

This is because SHINY METAL does not radiate heat very much but it does
provide excellent specular reflection.  So all you ever see of a shiny
metallic component is what it is reflecting, nothing at all about its own
temp.

A very common mistake.

The Thermal emissivity of everything in view is *assumed* to be about 0.9.
The operator has to know enough to discount any reading of any material
this is not 0.9 ish.  True, most things are, but definitely NOT shiny
metal!  Aluminum is 0.03 or 30 times less emissivity.  (that is why we
wrap it around a baked potato!).

Hold up a baking tin, it acts like a thermal mirror to everything in the
room.  You are seeing nothing about its own temperature.

Bob, WB4AAPR

-Original Message-
From: EV  On Behalf Of jim--- via EV
Sent: Tuesday, October 1, 2019 2:21 PM
To: Electric Vehicle Discussion List 
Cc: j...@k6ccc.org
Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

Yes.  Heat is going to conduct better through the metal plates of the
batter vs the electrolite.  Therefore, the heat if generated at the
connector is going to conduct along the metal plates.  Assuming that the
plates in that battery are vertical, I would expect something similar to
what is being seen.

Also note that the strap is FAR hotter than the portion of the strap
visible at the left edge of the IR image, and that the right end of the
strap and the top of the cell on the right that is connected to that strap
is also warm.  There is a lot of heat being generated in the strap or more
likely the connection between the left end of the strap and the top of the
battery.

We use IR images using similar equipment here at work for checking
electrical connections quite regularly.

For a little entertainment, a couple years ago I used a thermal imaging
camera to demonstrate how hot a lighting controller board got under heavy
load.  I posted the results on a Christmas Lighting forum.  You should be
able to read it - although you can't post a reply unless you are a member
of that forum.
http://forums.lightorama.com/topic/45960-how-warm-does-a-sandevices-e682-g
et/


Jim


-Original Message-
From: "Peri Hartman via EV" 
Sent: Tuesday, October 1, 2019 10:53
To: "Electric Vehicle Discussion List" 
Cc: "Peri Hartman" 
Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

Wow, hat's a great observation. Question: is it significant that the IR
image also shows heat emanating vertically, appearing to be relatively
uniform ?
Peri

-- Original Message --
From: "jim--- via EV" 
To: "Electric Vehicle Discussion List" 
Cc: "j...@k6ccc.org" 
Sent: 01-Oct-19 10:36:24 AM
Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

>>  A close-up of the cell, looking from the front of the pack. It's been
photoshopped to blend the IR image with the visible image to provide some
perspective of the actual appearance:
>>
>>  http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg
>
>Carefully check the connection on that cell that is closest to the
camera.  Note that only the one end of the cell is warmer - not both ends.
I would suspect that the connection is marginal and causing the heat.  The
heat has conducted into that end of the cell.
>
>73
>-
>Jim Walls - K6CCC
>j...@k6ccc.org
>
>
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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Mr. Sharkey via EV]

Thanks everyone for the thoughtful replies. I'm very hopeful that the 
problem is something external that I have control over, rather than 
internal, which I don't. I'll be putting lots of attention into that 
terminal, strap and hardware tomorrow. It will be embarrassing if it 
turns out to be something simple. I did withhold some information, 
which is that I swapped out the BMS card on that cell, and the one 
immediately to the right (in the "front/composite image") after the 
balancing. Could be that I missed torquing the bolt on that one, 
although it should be very snug even without the click wrench applied.


The battery in the conversion truck I bought had been cared for in 
terms of loading and balancing, and had a PFC-20 with conservative 
settings, but the installation was somewhat careless, no 
anti-corrosion compound on anything, lots of tarnished terminals and 
straps, corrosion, arcing on cell terminals, odd bits of bent-up 
copper being used as conductors between sub packs and fuses, shunts, 
etc. The whole thing had been exposed to under-hood water splash, 
salt-air/costal marine environment, road dirt, etc, etc.


I did a meticulous clean-up, restoration, and installation, filing 
the cell terminals flat when needed, digging out arced pit spots in 
the terminals (very hard metal compounds produced there, couldn't be 
simply filed away). All of the straps were flattened and filed when 
needed. The cell terminals and strap ends were random-orbital sanded 
with two grades of Scotchbrite abrasive discs, and NoOxID (my 
preference instead of NoAlOx) applied immediately afterwards (yes, I 
am aware how quickly aluminum oxidizes, but I have to work with what 
I got. Remember that only the positive cell terminals are aluminum, 
the negs are copper.)


As for having a "proper BMS", well, sure, but I'm a little stuck on 
the cost, being almost twice what I paid for the whole conversion 
truck, complete with battery,  Warp 11, PFC-20, Zilla 1K, etc. This 
was an economy Li conversion for me, and since the cells were nearly 
free, well, you get the idea... (if anyone is looking for a motor, 
controller, HEPA pedal, contact me off-list, I'd like to reclaim some 
more of my garage floor).


Details tomorrow after the tear-down. I may have access to the IR 
camera again next week, although now that I have pinpointed the warm 
cell, it's possible to do a rough investigation by simply touching. 
The jumper straps on all of the other cells were dead-cold, while 
this one was slightly warm to the touch.


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Re: [EVDL] LiFePO4 Thermal Imaging Opinions? Amazing

[Robert Bruninga via EV]

Thermal imaging is amazing!

I was playing with one in the basement, looking at pipes and then I saw a
big white spot in the area of the stove up in the kitchen.  Worring that
something was wrong (no heat source should be there) I ran upstairs to
find a cat asleep on the rug in front of the stove.

This was a glaring big, bright white spot.  But, I was seeing it through a
thick braided rug, 3/8" of ceramic tiles, 3/4" plywood underlayment and
then 3/4" of tong-and-grove flooring.  Amazing.

I also used  such a  camera to find hidden angled studs behind very thick
100 year old plaster and lath walls.  Simply put a 1000W light on the far
side, came back in an hour, and it was like xray vision.  I could clearly
see all the complexity of the studs.

Bob

-Original Message-
From: EV  On Behalf Of Peri Hartman via EV
Sent: Tuesday, October 1, 2019 1:53 PM
To: Electric Vehicle Discussion List 
Cc: Peri Hartman 
Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

Wow, hat's a great observation. Question: is it significant that the IR
image also shows heat emanating vertically, appearing to be relatively
uniform ?
Peri

-- Original Message --
From: "jim--- via EV" 
To: "Electric Vehicle Discussion List" 
Cc: "j...@k6ccc.org" 
Sent: 01-Oct-19 10:36:24 AM
Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

>>  A close-up of the cell, looking from the front of the pack. It's been
photoshopped to blend the IR image with the visible image to provide some
perspective of the actual appearance:
>>
>>  http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg
>
>Carefully check the connection on that cell that is closest to the
camera.  Note that only the one end of the cell is warmer - not both ends.
I would suspect that the connection is marginal and causing the heat.  The
heat has conducted into that end of the cell.
>
>73
>-
>Jim Walls - K6CCC
>j...@k6ccc.org
>
>
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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Alan Arrison via EV]

If you had a proper BMS like the Elithion system that I have, it would 
show you the exact temperature of each cell and warn you of over 
temperature.



On 9/30/2019 11:57 PM, Mr. Sharkey via EV wrote:

Time to turn up the dial on the technical channel.

After converting my car to a lightly-used set of Thundersky 160's, 
I've finally gotten around to having some thermal images taken of the 
cells after running the car up to temperature. My purpose was to make 
sure that none of my cell interconnect wiring (copper strap stock) was 
heating up. What I found was somewhat unexpected. One of the 38 cells 
was showing an elevated temperature from the rest.




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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[jim--- via EV]

Yes.  Heat is going to conduct better through the metal plates of the batter vs 
the electrolite.  Therefore, the heat if generated at the connector is going to 
conduct along the metal plates.  Assuming that the plates in that battery are 
vertical, I would expect something similar to what is being seen.

Also note that the strap is FAR hotter than the portion of the strap visible at 
the left edge of the IR image, and that the right end of the strap and the top 
of the cell on the right that is connected to that strap is also warm.  There 
is a lot of heat being generated in the strap or more likely the connection 
between the left end of the strap and the top of the battery.

We use IR images using similar equipment here at work for checking electrical 
connections quite regularly.  

For a little entertainment, a couple years ago I used a thermal imaging camera 
to demonstrate how hot a lighting controller board got under heavy load.  I 
posted the results on a Christmas Lighting forum.  You should be able to read 
it - although you can't post a reply unless you are a member of that forum.
http://forums.lightorama.com/topic/45960-how-warm-does-a-sandevices-e682-get/


Jim


-Original Message-
From: "Peri Hartman via EV" 
Sent: Tuesday, October 1, 2019 10:53
To: "Electric Vehicle Discussion List" 
Cc: "Peri Hartman" 
Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

Wow, hat's a great observation. Question: is it significant that the IR 
image also shows heat emanating vertically, appearing to be relatively 
uniform ?
Peri

-- Original Message --
From: "jim--- via EV" 
To: "Electric Vehicle Discussion List" 
Cc: "j...@k6ccc.org" 
Sent: 01-Oct-19 10:36:24 AM
Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

>>  A close-up of the cell, looking from the front of the pack. It's been 
>> photoshopped to blend the IR image with the visible image to provide some 
>> perspective of the actual appearance:
>>
>>  http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg
>
>Carefully check the connection on that cell that is closest to the camera.  
>Note that only the one end of the cell is warmer - not both ends.  I would 
>suspect that the connection is marginal and causing the heat.  The heat has 
>conducted into that end of the cell.
>
>73
>-
>Jim Walls - K6CCC
>j...@k6ccc.org
>
>
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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Peri Hartman via EV]

Wow, hat's a great observation. Question: is it significant that the IR 
image also shows heat emanating vertically, appearing to be relatively 
uniform ?

Peri

-- Original Message --
From: "jim--- via EV" 
To: "Electric Vehicle Discussion List" 
Cc: "j...@k6ccc.org" 
Sent: 01-Oct-19 10:36:24 AM
Subject: Re: [EVDL] LiFePO4 Thermal Imaging Opinions?


 A close-up of the cell, looking from the front of the pack. It's been 
photoshopped to blend the IR image with the visible image to provide some 
perspective of the actual appearance:

 http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg


Carefully check the connection on that cell that is closest to the camera.  
Note that only the one end of the cell is warmer - not both ends.  I would 
suspect that the connection is marginal and causing the heat.  The heat has 
conducted into that end of the cell.

73
-
Jim Walls - K6CCC
j...@k6ccc.org


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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[jim--- via EV]

> A close-up of the cell, looking from the front of the pack. It's been 
> photoshopped to blend the IR image with the visible image to provide some 
> perspective of the actual appearance:
> 
> http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg

Carefully check the connection on that cell that is closest to the camera.  
Note that only the one end of the cell is warmer - not both ends.  I would 
suspect that the connection is marginal and causing the heat.  The heat has 
conducted into that end of the cell.

73
-
Jim Walls - K6CCC
j...@k6ccc.org


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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[paul dove via EV]

I have always thought temperature could be used in this way.

Sent from my iPhone

> On Oct 1, 2019, at 1:30 AM, Gary Krysztopik via EV  wrote:
> 
> Sorry, no help to you but I always wondered if thermal imaging could be
> used for a cheaper/simpler? BMS (assuming one had a clear visual of the
> entire pack).
> 
> On Mon, Sep 30, 2019 at 9:08 PM Mr. Sharkey via EV 
> wrote:
> 
>> Time to turn up the dial on the technical channel.
>> 
>> After converting my car to a lightly-used set of Thundersky 160's,
>> I've finally gotten around to having some thermal images taken of the
>> cells after running the car up to temperature. My purpose was to make
>> sure that none of my cell interconnect wiring (copper strap stock)
>> was heating up. What I found was somewhat unexpected. One of the 38
>> cells was showing an elevated temperature from the rest.
>> 
>> First, the IR image of the right-hand half of the pack, taken from
>> behind the car. the suspect cell is at the center cross-hairs:
>> 
>> http://www.westlanetv.org/~sharkey/evgfx/IR_0677.jpg
>> 
>> A close-up of the cell, looking from the front of the pack. It's been
>> photoshopped to blend the IR image with the visible image to provide
>> some perspective of the actual appearance:
>> 
>> http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg
>> 
>> The car ran a 15 mile trip at about 55 MPH, pulling 100 - 125 amperes
>> most of the way. A couple of 275 - 300 amp sprints pulling out into
>> traffic, etc.  Photos were taken immediately thereafter.
>> 
>> All of the cells had been carefully (manually) balanced a few days
>> before the photos were taken. During balancing, this cell was about
>> 15 ampere-hours lower than most of the rest of the pack, but not the
>> lowest of the 8 cells that needed attention. It came right up with a
>> balancing charge. None of the other cells showed any variance in
>> temperature in this series of photos.
>> 
>> Questions for the list:
>> 
>> The cell isn't actually "hot" but it's obviously warmer than the
>> rest. What's everyone's take on this one cell warming up? Can I just
>> assume that it may have higher internal resistance, and therefore
>> more heating under load? Is the heating indicative of a coming
>> (perhaps spectacular) failure?
>> 
>> I've got about 1,600 miles on this new pack, and it seems to be
>> performing well. I'd like to keep using it in this configuration, but
>> if it seems risky to continue loading this one cell, it ~could~ be
>> jumpered out of the pack (not my first choice).
>> 
>> Opinions or advice?
>> 
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>> 
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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[paul dove via EV]

I had a loose connection on my pack. It heated the cell to failure before I 
found it.

Sent from my iPhone

> On Sep 30, 2019, at 10:57 PM, Mr. Sharkey via EV  wrote:
> 
> Time to turn up the dial on the technical channel.
> 
> After converting my car to a lightly-used set of Thundersky 160's, I've 
> finally gotten around to having some thermal images taken of the cells after 
> running the car up to temperature. My purpose was to make sure that none of 
> my cell interconnect wiring (copper strap stock) was heating up. What I found 
> was somewhat unexpected. One of the 38 cells was showing an elevated 
> temperature from the rest.
> 
> First, the IR image of the right-hand half of the pack, taken from behind the 
> car. the suspect cell is at the center cross-hairs:
> 
> http://www.westlanetv.org/~sharkey/evgfx/IR_0677.jpg
> 
> A close-up of the cell, looking from the front of the pack. It's been 
> photoshopped to blend the IR image with the visible image to provide some 
> perspective of the actual appearance:
> 
> http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg
> 
> The car ran a 15 mile trip at about 55 MPH, pulling 100 - 125 amperes most of 
> the way. A couple of 275 - 300 amp sprints pulling out into traffic, etc.  
> Photos were taken immediately thereafter.
> 
> All of the cells had been carefully (manually) balanced a few days before the 
> photos were taken. During balancing, this cell was about 15 ampere-hours 
> lower than most of the rest of the pack, but not the lowest of the 8 cells 
> that needed attention. It came right up with a balancing charge. None of the 
> other cells showed any variance in temperature in this series of photos.
> 
> Questions for the list:
> 
> The cell isn't actually "hot" but it's obviously warmer than the rest. What's 
> everyone's take on this one cell warming up? Can I just assume that it may 
> have higher internal resistance, and therefore more heating under load? Is 
> the heating indicative of a coming (perhaps spectacular) failure?
> 
> I've got about 1,600 miles on this new pack, and it seems to be performing 
> well. I'd like to keep using it in this configuration, but if it seems risky 
> to continue loading this one cell, it ~could~ be jumpered out of the pack 
> (not my first choice).
> 
> Opinions or advice?
> 
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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Bill Dube via EV]

I agree with Marco that it is quite likely a dirty/corroded connection 
between the strap and the cell. This is more common than most folks realize.


Remove the strap. Clean both surfaces with Scotchbright. Apply a thin 
coating of NoAlOx to the terminal and to the bus bar. Reassemble.


You shouldn't wait too long between the cleaning step and the reassembly 
step. These should be done in the same work session as corrosion will 
form on the freshly cleaned surface.


    My two cents.

    Bill D.

On 10/1/2019 7:09 PM, Ing. Marco Gaxiola via EV wrote:

Are you sure it is an internal cell failure and not just a loose or dirty 
connection within the bussbar?  The heat on that image looks only on one area 
from the whole cell. Keep in mind that those ‘prismatic’ cells comes on tens or 
hundreds of thin rectangular layers with the same shape of the plastic 
enclosure. And a high internal resistance developed in cell chemistry would 
probably show up an evenly hot across the enclusure. (Please correct me of 
wrong).

Why don’t you try first to check for a poor electrical contact at that spot, 
clean it, re-tighten it and repeat your test?

Marco Gaxiola


Sent from my iPhone


On Sep 30, 2019, at 8:57 PM, Mr. Sharkey via EV  wrote:

Time to turn up the dial on the technical channel.

After converting my car to a lightly-used set of Thundersky 160's, I've finally 
gotten around to having some thermal images taken of the cells after running 
the car up to temperature. My purpose was to make sure that none of my cell 
interconnect wiring (copper strap stock) was heating up. What I found was 
somewhat unexpected. One of the 38 cells was showing an elevated temperature 
from the rest.

First, the IR image of the right-hand half of the pack, taken from behind the 
car. the suspect cell is at the center cross-hairs:

http://www.westlanetv.org/~sharkey/evgfx/IR_0677.jpg

A close-up of the cell, looking from the front of the pack. It's been 
photoshopped to blend the IR image with the visible image to provide some 
perspective of the actual appearance:

http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg

The car ran a 15 mile trip at about 55 MPH, pulling 100 - 125 amperes most of 
the way. A couple of 275 - 300 amp sprints pulling out into traffic, etc.  
Photos were taken immediately thereafter.

All of the cells had been carefully (manually) balanced a few days before the 
photos were taken. During balancing, this cell was about 15 ampere-hours lower 
than most of the rest of the pack, but not the lowest of the 8 cells that 
needed attention. It came right up with a balancing charge. None of the other 
cells showed any variance in temperature in this series of photos.

Questions for the list:

The cell isn't actually "hot" but it's obviously warmer than the rest. What's 
everyone's take on this one cell warming up? Can I just assume that it may have higher 
internal resistance, and therefore more heating under load? Is the heating indicative of 
a coming (perhaps spectacular) failure?

I've got about 1,600 miles on this new pack, and it seems to be performing 
well. I'd like to keep using it in this configuration, but if it seems risky to 
continue loading this one cell, it ~could~ be jumpered out of the pack (not my 
first choice).

Opinions or advice?

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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Gary Krysztopik via EV]

Sorry, no help to you but I always wondered if thermal imaging could be
used for a cheaper/simpler? BMS (assuming one had a clear visual of the
entire pack).

On Mon, Sep 30, 2019 at 9:08 PM Mr. Sharkey via EV 
wrote:

> Time to turn up the dial on the technical channel.
>
> After converting my car to a lightly-used set of Thundersky 160's,
> I've finally gotten around to having some thermal images taken of the
> cells after running the car up to temperature. My purpose was to make
> sure that none of my cell interconnect wiring (copper strap stock)
> was heating up. What I found was somewhat unexpected. One of the 38
> cells was showing an elevated temperature from the rest.
>
> First, the IR image of the right-hand half of the pack, taken from
> behind the car. the suspect cell is at the center cross-hairs:
>
> http://www.westlanetv.org/~sharkey/evgfx/IR_0677.jpg
>
> A close-up of the cell, looking from the front of the pack. It's been
> photoshopped to blend the IR image with the visible image to provide
> some perspective of the actual appearance:
>
> http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg
>
> The car ran a 15 mile trip at about 55 MPH, pulling 100 - 125 amperes
> most of the way. A couple of 275 - 300 amp sprints pulling out into
> traffic, etc.  Photos were taken immediately thereafter.
>
> All of the cells had been carefully (manually) balanced a few days
> before the photos were taken. During balancing, this cell was about
> 15 ampere-hours lower than most of the rest of the pack, but not the
> lowest of the 8 cells that needed attention. It came right up with a
> balancing charge. None of the other cells showed any variance in
> temperature in this series of photos.
>
> Questions for the list:
>
> The cell isn't actually "hot" but it's obviously warmer than the
> rest. What's everyone's take on this one cell warming up? Can I just
> assume that it may have higher internal resistance, and therefore
> more heating under load? Is the heating indicative of a coming
> (perhaps spectacular) failure?
>
> I've got about 1,600 miles on this new pack, and it seems to be
> performing well. I'd like to keep using it in this configuration, but
> if it seems risky to continue loading this one cell, it ~could~ be
> jumpered out of the pack (not my first choice).
>
> Opinions or advice?
>
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> http://groups.yahoo.com/group/NEDRA)
>
>
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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Ing. Marco Gaxiola via EV]

Are you sure it is an internal cell failure and not just a loose or dirty 
connection within the bussbar?  The heat on that image looks only on one area 
from the whole cell. Keep in mind that those ‘prismatic’ cells comes on tens or 
hundreds of thin rectangular layers with the same shape of the plastic 
enclosure. And a high internal resistance developed in cell chemistry would 
probably show up an evenly hot across the enclusure. (Please correct me of 
wrong). 

Why don’t you try first to check for a poor electrical contact at that spot, 
clean it, re-tighten it and repeat your test?  

Marco Gaxiola 


Sent from my iPhone

> On Sep 30, 2019, at 8:57 PM, Mr. Sharkey via EV  wrote:
> 
> Time to turn up the dial on the technical channel.
> 
> After converting my car to a lightly-used set of Thundersky 160's, I've 
> finally gotten around to having some thermal images taken of the cells after 
> running the car up to temperature. My purpose was to make sure that none of 
> my cell interconnect wiring (copper strap stock) was heating up. What I found 
> was somewhat unexpected. One of the 38 cells was showing an elevated 
> temperature from the rest.
> 
> First, the IR image of the right-hand half of the pack, taken from behind the 
> car. the suspect cell is at the center cross-hairs:
> 
> http://www.westlanetv.org/~sharkey/evgfx/IR_0677.jpg
> 
> A close-up of the cell, looking from the front of the pack. It's been 
> photoshopped to blend the IR image with the visible image to provide some 
> perspective of the actual appearance:
> 
> http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg
> 
> The car ran a 15 mile trip at about 55 MPH, pulling 100 - 125 amperes most of 
> the way. A couple of 275 - 300 amp sprints pulling out into traffic, etc.  
> Photos were taken immediately thereafter.
> 
> All of the cells had been carefully (manually) balanced a few days before the 
> photos were taken. During balancing, this cell was about 15 ampere-hours 
> lower than most of the rest of the pack, but not the lowest of the 8 cells 
> that needed attention. It came right up with a balancing charge. None of the 
> other cells showed any variance in temperature in this series of photos.
> 
> Questions for the list:
> 
> The cell isn't actually "hot" but it's obviously warmer than the rest. What's 
> everyone's take on this one cell warming up? Can I just assume that it may 
> have higher internal resistance, and therefore more heating under load? Is 
> the heating indicative of a coming (perhaps spectacular) failure?
> 
> I've got about 1,600 miles on this new pack, and it seems to be performing 
> well. I'd like to keep using it in this configuration, but if it seems risky 
> to continue loading this one cell, it ~could~ be jumpered out of the pack 
> (not my first choice).
> 
> Opinions or advice?
> 
> ___
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> 
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Re: [EVDL] LiFePO4 Thermal Imaging Opinions?

[Cor van de Water via EV]

How much warmer is that cell than surrounding ones?
1 or 2 deg is no reason for panic, just keep an eye on it. 10 degrees and
it is wise to replace it soon.
Internal resistance is one of the best indicators of future failure.
Cor.

On Mon, Sep 30, 2019, 9:08 PM Mr. Sharkey via EV  wrote:

> Time to turn up the dial on the technical channel.
>
> After converting my car to a lightly-used set of Thundersky 160's,
> I've finally gotten around to having some thermal images taken of the
> cells after running the car up to temperature. My purpose was to make
> sure that none of my cell interconnect wiring (copper strap stock)
> was heating up. What I found was somewhat unexpected. One of the 38
> cells was showing an elevated temperature from the rest.
>
> First, the IR image of the right-hand half of the pack, taken from
> behind the car. the suspect cell is at the center cross-hairs:
>
> http://www.westlanetv.org/~sharkey/evgfx/IR_0677.jpg
>
> A close-up of the cell, looking from the front of the pack. It's been
> photoshopped to blend the IR image with the visible image to provide
> some perspective of the actual appearance:
>
> http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg
>
> The car ran a 15 mile trip at about 55 MPH, pulling 100 - 125 amperes
> most of the way. A couple of 275 - 300 amp sprints pulling out into
> traffic, etc.  Photos were taken immediately thereafter.
>
> All of the cells had been carefully (manually) balanced a few days
> before the photos were taken. During balancing, this cell was about
> 15 ampere-hours lower than most of the rest of the pack, but not the
> lowest of the 8 cells that needed attention. It came right up with a
> balancing charge. None of the other cells showed any variance in
> temperature in this series of photos.
>
> Questions for the list:
>
> The cell isn't actually "hot" but it's obviously warmer than the
> rest. What's everyone's take on this one cell warming up? Can I just
> assume that it may have higher internal resistance, and therefore
> more heating under load? Is the heating indicative of a coming
> (perhaps spectacular) failure?
>
> I've got about 1,600 miles on this new pack, and it seems to be
> performing well. I'd like to keep using it in this configuration, but
> if it seems risky to continue loading this one cell, it ~could~ be
> jumpered out of the pack (not my first choice).
>
> Opinions or advice?
>
> ___
> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> ARCHIVE: http://www.evdl.org/archive/index.html
> INFO: http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> Please discuss EV drag racing at NEDRA (
> http://groups.yahoo.com/group/NEDRA)
>
>
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[EVDL] LiFePO4 Thermal Imaging Opinions?

[Mr. Sharkey via EV]

Time to turn up the dial on the technical channel.

After converting my car to a lightly-used set of Thundersky 160's, 
I've finally gotten around to having some thermal images taken of the 
cells after running the car up to temperature. My purpose was to make 
sure that none of my cell interconnect wiring (copper strap stock) 
was heating up. What I found was somewhat unexpected. One of the 38 
cells was showing an elevated temperature from the rest.


First, the IR image of the right-hand half of the pack, taken from 
behind the car. the suspect cell is at the center cross-hairs:


http://www.westlanetv.org/~sharkey/evgfx/IR_0677.jpg

A close-up of the cell, looking from the front of the pack. It's been 
photoshopped to blend the IR image with the visible image to provide 
some perspective of the actual appearance:


http://www.westlanetv.org/~sharkey/evgfx/Hot_Cell_2.jpg

The car ran a 15 mile trip at about 55 MPH, pulling 100 - 125 amperes 
most of the way. A couple of 275 - 300 amp sprints pulling out into 
traffic, etc.  Photos were taken immediately thereafter.


All of the cells had been carefully (manually) balanced a few days 
before the photos were taken. During balancing, this cell was about 
15 ampere-hours lower than most of the rest of the pack, but not the 
lowest of the 8 cells that needed attention. It came right up with a 
balancing charge. None of the other cells showed any variance in 
temperature in this series of photos.


Questions for the list:

The cell isn't actually "hot" but it's obviously warmer than the 
rest. What's everyone's take on this one cell warming up? Can I just 
assume that it may have higher internal resistance, and therefore 
more heating under load? Is the heating indicative of a coming 
(perhaps spectacular) failure?


I've got about 1,600 miles on this new pack, and it seems to be 
performing well. I'd like to keep using it in this configuration, but 
if it seems risky to continue loading this one cell, it ~could~ be 
jumpered out of the pack (not my first choice).


Opinions or advice?

___
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