Re: [EVDL] LiFePO4Charging

[tomw via EV]

That's a big voltage drop. Even when I charge at 70A DC my DVM on the pack
terminals agrees to within a tenth of a volt with the voltage readout on the
charger taken at it's output. I would suspect a loose connection inside the
charger or at the charger leads on the pack.



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Re: [EVDL] LiFePO4Charging

[Buddy Mills via EV]

>But thenyou say the charger reads 334 - 335V, which is way different than
the 231V
>you say the string is at, so I'm confused. What charger are you using? Does
>it read 334 - 335V at the same time you measure 231V across the charger
>leads at the pack?

Tomw,
 
 Thanks for catching that.  I missed typed it should have been 234 to 235
volts.  But to answer your question the 234-235 volts is when I tell the BMS
to restrict the total voltage higher to see if the cells will ever reach
3.5v.  So I guess from reading other comments, the lost is from the
resistance in my interconnect.  I did not realize that the draw from my
connections would have this much drop on charge.
  To answer the other questions my charger is an eltek Valere with a Orien
BMS.  The measure voltage on each cell and the total pack is via the BMS
after the balance but before the fully charged phase.

So at this point I assume that turning off the total pack restrictions to
allow for loss and limiting each battery to 3.45 (was 3.5) is my best
charging regiment. 

Thanks,
Buddy
 





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Re: [EVDL] LiFePO4Charging

[tomw via EV]

I have 132 60AH batteries in 2P66S.  So I am going to call this 66 batteries
at 120AH.  Specs call for 3.6 volts max,  so 66 in serial is 237.7 volts.  I
don't want to push them so I set the max voltage at 231volts charge which
brings me to approx 3.5 volts per battery.  Now in real life once it is at
this 231 volts for the string each individual battery voltage is approx 3.34
volts +/- 0.10 volt.  Even at the plus side of that each battery would be
3.44 volts or 227.04 volts for the string.  So how is it that my charger
string voltage is reading 334 - 335 volts while each battery is reading
3.34?  Does it matter if the total voltage is over the max (66 X 231) as
long as the individual voltage is less 3.5 volts?  Should I set my BMS
charge voltage cutoff higher and just leave each cell set at the 3.5 volts
max.

You say that when you charge to 231V each individual pair of cells is
actually at 3.34V +/-0.10V, so I assume you did indeed measure the voltage
on all the pairs, and measured them with the same voltmeter you measured
231V with so if the voltmeter has some % error, it should be similar in both
measurements.  If so, there must be a source of resistance causing the
voltage difference of about V = 231 - 66*3.34 = 10.56V near end of charge,
or, perhaps you are measuring the cells' rest voltages a bit after charging,
and not at the end of charge while the charger is still running? But then
you say the charger reads 334 - 335V, which is way different than the 231V
you say the string is at, so I'm confused. What charger are you using? Does
it read 334 - 335V at the same time you measure 231V across the charger
leads at the pack?



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Re: [EVDL] LiFePO4Charging

[Cor van de Water via EV]

That, or your meter is not very accurate in measuring the voltages.
The voltage of all 66 series cells (plus cable losses) should add up
exactly 
to the voltage that the charger is supplying.
It has been said before that charging to 3.45V is sufficient, so about
228V,
but make sure that all cells (esp the lowest and highest) do charge to
the same voltage.
Do you use a BMS to make sure all cells are at the same limit and stay
below 3.5V each?

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: cwa...@proxim.com Private: http://www.cvandewater.info
Skype: cor_van_de_water Tel: +1 408 383 7626


-Original Message-
From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of John Lindsay
via EV
Sent: Thursday, September 25, 2014 6:29 PM
To: Buddy Mills; Electric Vehicle Discussion List
Subject: Re: [EVDL] LiFePO4Charging

Read the voltage drop across the cables connecting the batteries.

The missing volts equal the charge current multiplied by the total
resistance in the connections and cables. Otherwise known as Ohms Law. 

You may have some bad connections. 

John Lindsay

> On 26 Sep 2014, at 10:50 am, Buddy Mills via EV 
wrote:
> 
> I thought I understood how to charge my 9 month old LiFeP04 but know I
am
> doubting my process.  So I will lay it out and see what feedback the
battery
> gurus here can suggest.
> 
> I have 132 60AH batteries in 2P66S.  So I am going to call this 66
batteries
> at 120AH.  Specs call for 3.6 volts max,  so 66 in serial is 237.7
volts.  I
> don't want to push them so I set the max voltage at 231volts charge
which
> brings me to approx 3.5 volts per battery.  Now in real life once it
is at
> this 231 volts for the string each individual battery voltage is
approx 3.34
> volts +/- 0.10 volt.  Even at the plus side of that each battery would
be
> 3.44 volts or 227.04 volts for the string.  So how is it that my
charger
> string voltage is reading 334 - 335 volts while each battery is
reading
> 3.34?  Does it matter if the total voltage is over the max (66 X 231)
as
> long as the individual voltage is less 3.5 volts?  Should I set my BMS
> charge voltage cutoff higher and just leave each cell set at the 3.5
volts
> max.   Hope I am making sense.
> 
> 
> 
> Thanks in advance for any feedback,
> 
> 
> 
> Buddy Mills
> 
> <mailto:buddymi...@cox.net> buddymi...@cox.net
> 
> 
> 
> Look mom, no gas.  <http://www.evalbum.com/2887>
http://www.evalbum.com/2887
> 
> 
> 
> Disclaimer:  No animals were harmed or killed in the process of
writing this
> email.  Any stories to the contrary are, for the most part, either
fictional
> or greatly exaggerated. 
> 
> 
> 
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Re: [EVDL] LiFePO4Charging

[John Lindsay via EV]

Read the voltage drop across the cables connecting the batteries.

The missing volts equal the charge current multiplied by the total resistance 
in the connections and cables. Otherwise known as Ohms Law. 

You may have some bad connections. 

John Lindsay

> On 26 Sep 2014, at 10:50 am, Buddy Mills via EV  wrote:
> 
> I thought I understood how to charge my 9 month old LiFeP04 but know I am
> doubting my process.  So I will lay it out and see what feedback the battery
> gurus here can suggest.
> 
> I have 132 60AH batteries in 2P66S.  So I am going to call this 66 batteries
> at 120AH.  Specs call for 3.6 volts max,  so 66 in serial is 237.7 volts.  I
> don't want to push them so I set the max voltage at 231volts charge which
> brings me to approx 3.5 volts per battery.  Now in real life once it is at
> this 231 volts for the string each individual battery voltage is approx 3.34
> volts +/- 0.10 volt.  Even at the plus side of that each battery would be
> 3.44 volts or 227.04 volts for the string.  So how is it that my charger
> string voltage is reading 334 - 335 volts while each battery is reading
> 3.34?  Does it matter if the total voltage is over the max (66 X 231) as
> long as the individual voltage is less 3.5 volts?  Should I set my BMS
> charge voltage cutoff higher and just leave each cell set at the 3.5 volts
> max.   Hope I am making sense.
> 
> 
> 
> Thanks in advance for any feedback,
> 
> 
> 
> Buddy Mills
> 
>  buddymi...@cox.net
> 
> 
> 
> Look mom, no gas.   http://www.evalbum.com/2887
> 
> 
> 
> Disclaimer:  No animals were harmed or killed in the process of writing this
> email.  Any stories to the contrary are, for the most part, either fictional
> or greatly exaggerated. 
> 
> 
> 
> -- next part --
> An HTML attachment was scrubbed...
> URL: 
> 
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