Cold Weather Performance?

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Paul9
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Cold Weather Performance?

Post by Paul9 » Mon, 04 Jul 2016, 19:35

Hi people,

I am wondering how much (if at all?) cold weather affects the performance of lithium batteries?

I installed my 100ah CALB about two years ago but the car was off the road for most of last winter while we hunted around for a new gear box.

We are now in the middle of this winter and in Sydney the daily temps range from 3 degreesC to 17-18 degreesC. I am noticing that the pack voltage is consistently lower than it has been for a long while.

First thing in the morning, fully charged, pack voltage is about 113v to 113.5v. This is still the case. However the pack voltage at various current draws used to be as follows:

50amp draw = 105v pack voltage
100amp draw = 100v pack voltage
150amp draw = 95v pack voltage

Now, however, the same figures are as follows:

50amp draw = 103v pack voltage
100amp draw = 97v pack voltage
150amp draw = 92v pack voltage

I also appear to be using about 10% more amp hours for my trips.

Is this just normal in winter or could something else be wrong?

Thanks in advance,
Paul

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Richo
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Cold Weather Performance?

Post by Richo » Mon, 04 Jul 2016, 20:39

Are you using a heater for the interior / windows?
So the short answer is NO but the long answer is YES.
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Paul9
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Cold Weather Performance?

Post by Paul9 » Mon, 04 Jul 2016, 21:01

Hi Richo

I have a demister installed but because of the power drain I never use it.

Thanks

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Johny
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Cold Weather Performance?

Post by Johny » Mon, 04 Jul 2016, 21:31

That about fits with my summer/winter variation.

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Richo
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Cold Weather Performance?

Post by Richo » Tue, 05 Jul 2016, 20:42

So to quantify that's a pack impedance of 100mR during summer and 110mR during winter.
Not too sure if you have 30 or 31 cells?
But we are talking about a 300uR per cell variation.

Doesn't seem like much.
But that is assuming that it is divided equally.
No way of telling unless each cell was individually tested under load.

Have you tried putting that conductive goop on each terminal?
So the short answer is NO but the long answer is YES.
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Richo
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Cold Weather Performance?

Post by Richo » Tue, 05 Jul 2016, 20:49

here is the link to the terminal grease thread
viewtopic.php?title=battery-grease-noal ... 053#p49394
So the short answer is NO but the long answer is YES.
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Richo
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Cold Weather Performance?

Post by Richo » Tue, 05 Jul 2016, 20:52

Another thing to look at would be the DC/DC to 12V system.
If the 12V battery is on it's last legs the DC/DC could be pumping lots of current into it for no benefit.
So the short answer is NO but the long answer is YES.
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Paul9
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Cold Weather Performance?

Post by Paul9 » Tue, 05 Jul 2016, 23:03

Thanks Johny - your reply reassures me a bit.

Thanks Richo - I don't think I used the conductive goop you mention. I will check the links listed in the Noalex thread and get some.

The DC_DC probably is not the problem as the aux battery is recharged from a flex solar panel on the roof. The panel and the DC-DC are both routed through a regulator and the DC-DC is switched on or off via a switch on the dashboard. I normally only use the DC-DC once a month or two as the panel keeps the aux battery filled up.

Thanks for the advice guys.
Paul

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Johny
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Cold Weather Performance?

Post by Johny » Tue, 05 Jul 2016, 23:50

Really foggying the waters with this talk of grease. I get 83km summer and 73km winter - no heater. You're doing well with that small variation. Check my blog. Label "range" for time-of-year range.

Edit: foggying
Last edited by Johny on Tue, 05 Jul 2016, 13:54, edited 1 time in total.

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coulomb
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Cold Weather Performance?

Post by coulomb » Wed, 06 Jul 2016, 14:58

Johny wrote: Really foggying the waters with this talk of grease.

Not to mention that the grease is not conducting. A thin layer is applied, and when the joint is completed the grease is displaced from between the conducting metal parts. The intention is to exclude air and water to prevent corrosion. You could well eventually end up with better conductivity than you would have ended up with, but no more than you would start with if you didn't use the grease.

So it doesn't enhance conductivity, it prevents conductivity from worsening due to corrosion.
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Richo
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Cold Weather Performance?

Post by Richo » Wed, 06 Jul 2016, 21:11

coulomb wrote:Not to mention that the grease is not conducting.


You do realise that some of them are copper loaded.
Even the blurb says "assists conductivity".

Now that the DC/DC is eliminated.
the choices are:
1. Slightly worn cells.
2. One more worn cell.
3. Bad connections.
4. Natural drift of cell performance over temp.

Johny and Coulomb are suggesting 4.
I have suggested 3 - which can be tested for a small cost.
1 and 2 can be tested too

Let see automotive environment, temp drift - no must be just the cells ignore it....

When was the last time any of the connections where checked for tightness?

As a matter of course isn't it worth testing 1,2,3 before just flat out saying it's 4 and ignoring the rest?
Especially since the cost is low.
So the short answer is NO but the long answer is YES.
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Cold Weather Performance?

Post by Paul9 » Thu, 07 Jul 2016, 14:48

Thanks guys,

How can I test for weak/bad connections?

Thanks
Paul

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Richo
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Post by Richo » Thu, 07 Jul 2016, 20:46

Test the voltage of each cell under load.
A poor connection will make the voltage droop more under load.
A BMS that reports or logs the voltage of each cell can do this.
This needs to be paired up with a current reading.
Manually testing it under load still in the car would be a bit more difficult

Removing the battery doesn't test the connection in situ.

What's your BMS like?
So the short answer is NO but the long answer is YES.
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Cold Weather Performance?

Post by Paul9 » Fri, 08 Jul 2016, 17:17

Thanks Richo

I do have 4 resistors that I used in the past to test cells to determine weak cells. I assume I could use those again to test cells in situ?

I use the EV Power BMS which gives me:

a) When charging - a "Battery Fault" message when any cell goes over 4.0v but it doesn't tell me which cell,

b) When charging - a "Battery Overvolt" message when the pack voltage reaches a preset level,

c) When charging - Turns the charging process off as soon as a) or b) happens,

d) When discharging - gives me a "Battery Fault" message when any cell goes below 2.5v but doesn't tell me which cell

e) When discharging - 30 seconds after the above "Battery Fault" message appears the BMS turns the car off.

The BMS does not appear to do any more than the above.

I have recently had the pack voltage down to 92v while driving which, with 34 cells, gave me an average cell voltage of 2.7v. I did not receive a "Battery Fault" message at 92v which I think(?) means no cell was below 2.5v while the average cell voltage was 2.7v.

If using the resistors is the best way to test for weak cells I will go ahead with that.

Thanks again,
Paul

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Johny
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Cold Weather Performance?

Post by Johny » Fri, 08 Jul 2016, 19:42

Paul9 wrote:...
I have recently had the pack voltage down to 92v while driving which, with 34 cells, gave me an average cell voltage of 2.7v. I did not receive a "Battery Fault" message at 92v which I think(?) means no cell was below 2.5v while the average cell voltage was 2.7v.
That would have exposed any weak cells if you had them.

Edit: too much bold...
Last edited by Johny on Fri, 08 Jul 2016, 09:42, edited 1 time in total.

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Richo
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Cold Weather Performance?

Post by Richo » Fri, 08 Jul 2016, 21:09

Paul9 wrote: I do have 4 resistors that I used in the past to test cells to determine weak cells. I assume I could use those again to test cells in situ?


Possible
So it would go.
1. Test the voltage of the cell unloaded.(VO)
2. Connect power resistors (RL) across the cell and measure voltage again(VL).
3. Repeat for each cell.

Make sure the the resistors stay about the same temp during the tests.
ie let them cool between cell tests.

RI = (VO - VL) / (VL / RL)
This should give you the impedance of the cell in Ohms.
Multiply by 1000 to get Milliohms (mR).
You should be getting around 3.5mR for each cell.

The absolute value isn't critical but if there are 1 or 2 that are different to the rest could indicate a weak cell.


So the short answer is NO but the long answer is YES.
Help prevent road rage - get outta my way!

Paul9
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Cold Weather Performance?

Post by Paul9 » Sat, 09 Jul 2016, 16:21

Thanks Johny - I tended to think along the same lines.

Thanks Richo - I will try what you suggest just in case.

Cheers
Paul

Peter C in Canberra
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Cold Weather Performance?

Post by Peter C in Canberra » Sat, 10 Sep 2016, 02:55

Replying to the original question, yes, I always get more voltage sag under load in winter with my >7 year old thunder sky LiFePO4 cells. Their internal resistance is higher when cold.
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Re: Cold Weather Performance?

Post by fffffred » Mon, 27 May 2019, 11:03

I come across this article which was an interesting read:
https://www.nxtbook.com/nxtbooks/sae/19 ... tid=26#/12

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Richo
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Re: Cold Weather Performance?

Post by Richo » Tue, 28 May 2019, 12:44

Well not really.
They all had apples in them and found all the apples froze at cold temps.
What a surprise - another waste of money research.

Mitsubishi use the Toshiba SCiB cells in the Japanese version of the iMieV because it gets cold in Japan.
I can still hear Tony saying "How did you solve the icing problem?"
https://www.youtube.com/watch?v=hHgkVOOTl_Y
Simple - don't put F'ing apples in'em... :idea:

It would have skewed the results if there was an orange in the research. :arrow:
So the short answer is NO but the long answer is YES.
Help prevent road rage - get outta my way!

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