Re: [EVDL] 18650 cell level fuse wire

[Cor van de Water via EV]

Hi Justin,
Thanks for chiming in – very useful info.
Another issue and I suspect you have noticed this also: smoke and smell.

Somewhere around 1995 I had a colleague who was involved in cost reducing a 
product design and he too had the same idea of testing PCB traces as fuses to 
see if he could characterize them enough to become useful fuses.
So, he grabbed an existing high density board that he had the layout files of, 
so he could verify the trace width of a certain trace on the board, then solder 
2 wires onto the mounting pads of the components on the ends of the trace 
section to run current through it and experiment what trace width would blow at 
what current.
He was amazed at the current that was needed to cause the traces to open. He 
only used low voltage as this was for a handheld terminal that worked from 6V 
battery, so the highest voltage in the system was the battery charger which 
supplied 9V.
The other thing (as his lab was across from the break room) was the amount of 
smoke generated by heating up traces.
Even (or especially) traces that warmed up without blowing, caused a lot of 
nasty smells of evaporating PCB chemicals.
Traces that did (eventually) open caused smoke to pour out of the PCB, to the 
point that he stopped testing and evacuated his lab for a while, because he 
thought it unsafe to filter all those chemicals through his lungs. Many 
colleagues were not so happy that they were now “second hand smokers” with the 
results of his experiments slowly dissipating through the building halls.
Several hardware colleagues came running when the smell reached their office, 
as this was recognized as the typical “the magical smoke was released” signal, 
so they wanted to know what device had blown up so spectacularly to cause this 
cloud.
This all to say that if you design PCB “fuses” that are run so that they have a 
chance to break the circuit, that means that they will cause a lot of heat at 
rated load, which will not only constitute a loss but also likely release nasty 
smells in operation.
If this is for a battery, you can likely contain the smoke and smell in an 
enclosure, just like the Leaf battery pack has a very characteristic Lithium 
smell when first opened, due to the deteriorating cells emitting vapors. 
Occasionally I smell this when walking through the parking lot with vehicles 
charging, apparently a battery occasionally “burps” and emits this same smell 
while charging.
But I worry about deterioration of the PCB when regularly exposed to elevated 
temperatures, I have worked a lot with TVs in my past of repairing TVs as hobby 
and I have seen the results of not properly rated components that were running 
hot for years and resulting PCB deterioration: charring and deformation and the 
failures associated with hot solder joints cracking due to mechanical stress, 
corroding and pushing / pulling leads free from solder pads. That is why so 
many old TVs need regular “percussive maintenance” to work again for some time.
Deliberately accelerating this process by heating up a PCB with traces designed 
for fuses does not sound like a good idea to me, even though you could 
carefully design a small section of the trace to be thinner and concentrate all 
the heat in an area that is not so affected by this heat – the smell, smoke and 
charring problems still remain.
There is a reason that all commercial products use discrete fuses or safety 
resistors, designed for the job.
Going back to the original question of wire to act as cell fuse in paralleled 
cell packs like Tesla – yes, apparently they are able to characterize it well 
enough.
NOTE that you rely on the BMS to detect when one or more cells have 
“disappeared” so that a pack can be repaired before too many fuses blow and you 
start blowing the remaining ones, not because there is a cell failure but 
because you are overloading them. That is one of the reasons why EVs limit 
drive power when detecting a battery balancing problem.
Regards,
Cor.

Sent from Mail for Windows 10

From: Justin Kenny via EV
Sent: Monday, January 21, 2019 3:26 PM
To: ev@lists.evdl.org
Cc: Justin Kenny
Subject: Re: [EVDL] 18650 cell level fuse wire

I'm the owner of the Leaf Rex channel Cor mentioned earlier. I highly
caution against using PCB fuses in general, I've done testing on those
also: https://youtu.be/CMlpCX0bug8 If you have a relatively large open
circuit voltage in the system you are trying to protect, it will
create a conductive plasma and char the PCB, leaving behind a
"resistor" which can continue to burn, though hopefully
self-extinguish in keeping with the "flame retardant" part of FR-4.

- Justin

On Mon, Jan 21, 2019 at 1:09 PM  wrote:
> Message: 13
> Date: Mon, 21 Jan 2019 15:25:38 -0500
> From: Martin Klingensmith 
> To: Lee Hart via EV 
> Subject: Re: [EVDL] 18650 cell level fuse wire
> Message-ID: <623a4924-a24a-52f3-b720-2ee3c2f69...@nnytech.net>
> Content-Type: text/plai

Re: [EVDL] 18650 cell level fuse wire

[Michael Ross via EV]

The open air fuses of Tesla packs eliminate the sort of creepage failure
that Justin has recounted.where aerosol deposits from the vaporizing of the
fuse leave traces for further arcing and leakage.

On Mon, Jan 21, 2019 at 10:05 PM Justin Kenny via EV 
wrote:

> I'm the owner of the Leaf Rex channel Cor mentioned earlier. I highly
> caution against using PCB fuses in general, I've done testing on those
> also: https://youtu.be/CMlpCX0bug8 If you have a relatively large open
> circuit voltage in the system you are trying to protect, it will
> create a conductive plasma and char the PCB, leaving behind a
> "resistor" which can continue to burn, though hopefully
> self-extinguish in keeping with the "flame retardant" part of FR-4.
>
> - Justin
>
> On Mon, Jan 21, 2019 at 1:09 PM  wrote:
> > Message: 13
> > Date: Mon, 21 Jan 2019 15:25:38 -0500
> > From: Martin Klingensmith 
> > To: Lee Hart via EV 
> > Subject: Re: [EVDL] 18650 cell level fuse wire
> > Message-ID: <623a4924-a24a-52f3-b720-2ee3c2f69...@nnytech.net>
> > Content-Type: text/plain; charset=utf-8; format=flowed
> >
> >
> > IIRC I've seen "fusible links" on PCBs. They're a short section of
> > copper trace that is much narrower than the rest of the trace. My
> > understanding is that they're used for an extra level of protection or
> > where the designer thinks they're really clever. For all modern PCB
> > materials it's not *too* unsafe because they aren't (supposed to be)
> > flammable.
> >
> > -
> >
> > Martin K
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Re: [EVDL] 18650 cell level fuse wire

[Justin Kenny via EV]

I'm the owner of the Leaf Rex channel Cor mentioned earlier. I highly
caution against using PCB fuses in general, I've done testing on those
also: https://youtu.be/CMlpCX0bug8 If you have a relatively large open
circuit voltage in the system you are trying to protect, it will
create a conductive plasma and char the PCB, leaving behind a
"resistor" which can continue to burn, though hopefully
self-extinguish in keeping with the "flame retardant" part of FR-4.

- Justin

On Mon, Jan 21, 2019 at 1:09 PM  wrote:
> Message: 13
> Date: Mon, 21 Jan 2019 15:25:38 -0500
> From: Martin Klingensmith 
> To: Lee Hart via EV 
> Subject: Re: [EVDL] 18650 cell level fuse wire
> Message-ID: <623a4924-a24a-52f3-b720-2ee3c2f69...@nnytech.net>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
>
> IIRC I've seen "fusible links" on PCBs. They're a short section of
> copper trace that is much narrower than the rest of the trace. My
> understanding is that they're used for an extra level of protection or
> where the designer thinks they're really clever. For all modern PCB
> materials it's not *too* unsafe because they aren't (supposed to be)
> flammable.
>
> -
>
> Martin K
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Re: [EVDL] 18650 cell level fuse wire

[Martin Klingensmith via EV]

On 1/21/2019 2:12 PM, Lee Hart via EV wrote:



Wire of any kind or size is not an adequate substitute for a fuse.


Most fuses *are* a piece of wire of adequate size. :-) The trick is in 
the choice of wire, and in how it is packaged.




IIRC I've seen "fusible links" on PCBs. They're a short section of 
copper trace that is much narrower than the rest of the trace. My 
understanding is that they're used for an extra level of protection or 
where the designer thinks they're really clever. For all modern PCB 
materials it's not *too* unsafe because they aren't (supposed to be) 
flammable.


-

Martin K


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Re: [EVDL] 18650 cell level fuse wire

[Lee Hart via EV]

EVDL Administrator via EV wrote:

On 21 Jan 2019 at 1:18, ken via EV wrote:


What is a 10ths wire?


ten thousands


Wire of any kind or size is not an adequate substitute for a fuse.


Most fuses *are* a piece of wire of adequate size. :-) The trick is in 
the choice of wire, and in how it is packaged.


The choice of wire is important. Normal wire sizes aren't that precise; 
the variation in cross-sectional area is around %5. Then, due to high 
high metal prices, vendors tend to "cheat" (since they know consumers 
won't measure it). It's not uncommon to find cheap wire that is 2 or 3 
sizes smaller than the package claims.


The purity of the metal is also important. Copper is not a good choice. 
Tiny amounts of impurities in copper cause a huge change in its 
resistance. Copper also work-hardens; its resistance increases as a 
result of flexing. When held near its melting point for long periods 
(like a fuse that doesn't quite blow), it crystalizes and develops 
stress cracks that significantly alter its resistance. Silver is a 
better choice for fuse wire.


The packaging is important. Just like food, if you don't package it 
correctly, it will go bad before you can use it. A wire in open air is 
subject to being cooled by moving air, heated by surrounding parts, 
corroded so its diameter shrinks, and even mechanically stressed if its 
ends can move (like a wire between cells that move as they expand and 
contract). The ends of the wire matter as well; they can act as a "heat 
sink" to pull heat away from the center, so it takes more current to 
melt it. So proper fuses are packaged to create a controlled environment 
around it.


--
The belief that there is only one truth, and that oneself is in
possession of it, is the root of all evil in the world. (Max Born)
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] 18650 cell level fuse wire

[Cor van de Water via EV]

I once did a Leaf battery swap for someone planning to add exen more range.
Some of his wire and pcb fuse tests are on Youtube, look for Leaf Rex.
Cor.

On Mon, Jan 21, 2019, 9:10 AM EVDL Administrator via EV  On 21 Jan 2019 at 1:18, ken via EV wrote:
>
> > > What is a 10ths wire?
> >
> > ten thousands
>
> Wire of any kind or size is not an adequate substitute for a fuse.
>
> David Roden - Akron, Ohio, USA
> EVDL Administrator
>
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Re: [EVDL] 18650 cell level fuse wire

[EVDL Administrator via EV]

On 21 Jan 2019 at 1:18, ken via EV wrote:

> > What is a 10ths wire?
> 
> ten thousands

Wire of any kind or size is not an adequate substitute for a fuse.

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: [EVDL] 18650 cell level fuse wire

[ken via EV]

> What is a 10ths wire?

ten thousands

 If it was #10 AWG, then that is way,way to big.
>
>
> Bob
>
>
> On Sun, Jan 20, 2019 at 3:52 PM ken via EV  wrote:
>
>
>> I cells are 2600 mah average reclamed / tested .  lion  . what or which
>>  size wire should I use.  I tryed a 10 ths 3 inch wire shorted across
>> the cell and it turned red 5 seconds but did not blow. I'd call my load
>> low as I'm working runing a ryboi blower  with  my 5s x 5p pack . I've
>> not measured the laod for the blower yet .
>>
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Re: [EVDL] 18650 cell level fuse wire

[Robert Bruninga via EV]

What is a 10ths wire?  If it was #10 AWG, then that is way,way to big.

Bob

On Sun, Jan 20, 2019 at 3:52 PM ken via EV  wrote:

>  I cells are 2600 mah average reclamed / tested .  lion  . what or which
> size wire should I use.  I tryed a 10 ths 3 inch wire shorted across the
> cell and it turned red 5 seconds but did not blow. I'd call my load low
> as I'm working runing a ryboi blower  with  my 5s x 5p pack . I've not
> measured the laod for the blower yet .
>
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Re: [EVDL] 18650 cell level fuse wire

[Michael Ross via EV]

You have two options, make the wire you have thinner, or select an alloy
the melts at a lower temperature.

Actually there is a possible third option - put some insulating material
around it fo keep convective cooling from slowing down the blow. You would
want a clear material or you would not be able to see blown links.

These are the basics that any fuse designer would be concerned with and
have as options.  Those folks have to worry about other stuff like creepage
(the distance along solid surfaces from link end to link end)  and
clearance (length of air gap between link ends) of faults, and arc
suppression, etc. You might want to consider them as well. with a lot of DC
voltage and current you can definitely have a fault arc.

Tesla battery packs I have seen images of used bare wires in air.  Maybe
you can find out what alloy they use.

On Sun, Jan 20, 2019 at 3:52 PM ken via EV  wrote:

>  I cells are 2600 mah average reclamed / tested .  lion  . what or which
> size wire should I use.  I tryed a 10 ths 3 inch wire shorted across the
> cell and it turned red 5 seconds but did not blow. I'd call my load low
> as I'm working runing a ryboi blower  with  my 5s x 5p pack . I've not
> measured the laod for the blower yet .
>
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[EVDL] 18650 cell level fuse wire

[ken via EV]

 I cells are 2600 mah average reclamed / tested .  lion  . what or which
size wire should I use.  I tryed a 10 ths 3 inch wire shorted across the
cell and it turned red 5 seconds but did not blow. I'd call my load low
as I'm working runing a ryboi blower  with  my 5s x 5p pack . I've not
measured the laod for the blower yet .

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