Batteries vs Cold ☃

General Discussion about electric vehicles.
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DrkAngel
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Re: Batteries vs Cold

Post by DrkAngel » Dec 13, 2011 9:30 am

Sorry for the mess!


My eBike subject-thread got folded into this eVehicle Forum thread.
Everything transferred, is specifically, and best applicable, to smaller eBike packs ...
But it wasn't my doing ...
Trying to clean it up a bit!
Last edited by DrkAngel on Nov 12, 2017 9:53 pm, edited 1 time in total.
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Re: Batteries vs Cold

Post by Kin » Dec 14, 2011 12:32 am

If C rating is reduced...Doesnt that simply mean the internal resistance will increase as you ask for higher C...meaning that it will shortly warm up as necessary?

I would assume the issue is really with LiPo, which are liable to never warm up enough to reach their potential. But if heat retention is an issue, I suggest wrapping the batteries in bubble wrap. It's a very good insulator, and also protects them.

But my problem is probably that I'm not fully wrapping my head around how cold of a temperature people are trying their batteries at [I've done cold winters, just not with any e-transportation]. I'm in NC right now, and this is not what I would call cold.
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Re: Batteries vs Cold

Post by whatever » Dec 14, 2011 3:36 am

on the positive side of cold:
there are reports on youtube, of laptop cells being revived by puting them in a freezer for 15hours or so,
i have one in the fridge now, will see how it goes

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Re: Batteries vs Cold

Post by DrkAngel » Dec 17, 2011 8:35 am

Heating pads advertise 3W usage @ 12V.
3W/12V=.25A
11.1V 5000mAh (5A) RC Lipo pack should power heating pads for ~20 hours.

A "DC Step-Down Adjustable Converter Power Module" could power multiple sets of pads for a full weekend, from the full bike pack, with minimal pack drain.
Nice extra is that the voltage is "trimmable"
"input 4.5V-40V"
"Output 1.5V-35V"
"2Amp, 3Amp w\heatsink"
DC Step-Down Adjustable Converter Power Module - $2.18

Could also be used to power:
12V lighting, horns, turn signals, small 12V accessories ...
~3.8V LED lighting
etc.

DC Step-Down Adjustable Converter Power Module - "trimmed" to maintain voltage-charge on 11.1V Lipo pack, or 12V SLA, could power higher demand 12V devices.

Also, will test to confirm, that these modules can be run in parallel! (higher amperage!)
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Re: Batteries vs Cold

Post by miuan » Dec 18, 2011 6:16 pm

Kin wrote:If C rating is reduced...Doesnt that simply mean the internal resistance will increase as you ask for higher C...meaning that it will shortly warm up as necessary?

I would assume the issue is really with LiPo, which are liable to never warm up enough to reach their potential. But if heat retention is an issue, I suggest wrapping the batteries in bubble wrap. It's a very good insulator, and also protects them.
It's beating a dead horse here. What more do we need than a battery that heats itself up as necessary thanks to this inevitable inbuilt feature of temperature dependant IR? Are you suggesting we are damaging our 20C lipo by riding it at 1 to 3C average? I doubt that.

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Re: Batteries vs Cold

Post by DrkAngel » Dec 18, 2011 7:33 pm

This thread is designed for all those who despair at the loss of speed, power and capacity, due to the cold.
It seems to be a universal complaint ...

Most vocal, seem to be the new eCar owners.

Some Chevy Volt owners complain of 50% Winter range!

Nisson Leaf, very similar.

Chevy and Nisson, both promise improved, "cold weather packages", for 2012!

2012 Electric Ford Focus
The 2012 Electric Ford Focus will employ a liquid heating system:
"On cold days, heated liquid warms the batteries, gradually bringing the system’s temperature to a level that allows it to efficiently accept charge energy and provide enough discharge power for expected vehicle performance."

eBikes batteries might suffer more from the cold!
The small mass, with larger, relative, surface area means they will cool very fast.

The use of insulation, combined with auxiliary, or self contained heating elements, seems to be the most reasonable countermeasure.
Last edited by DrkAngel on Dec 19, 2011 9:25 am, edited 2 times in total.
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Re: Batteries vs Cold

Post by mistercrash » Dec 19, 2011 8:21 am

This blows my mind about Chevy and Nissan. Is this true!? After millions spent in R&D, advertisement and manufacturing development to finally put these cars on the market, only now do they wake up and think, oh d'uh! These batteries don't do well in d'uh cold!

I hope we don't see a new movie coming out in a couple years, ''Who killed the electric car II''. Old man winter --------- GUILTY!
Is it ready yet?

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Re: Batteries vs Cold

Post by chrisvw » Dec 21, 2011 6:29 pm

I noted a comment/question about whether the self heating that occurs from the voltage droop you get when cold will correct the problem. I was riding in 25 deg F ( -4 deg C) weather last night where the bike had been parked outside for several hours (returning from the city council meeting where they banned ebikes on the trails!) and after 9 miles, still no improvement in performance. It clearly felt like a C rate limitation. I thought my battery was going dead early, but it never died like it does when the battery is exhausted. I had used 6ah of the 8ah I normally get from the batteries (on a 10ah Li pack). From my limited data point, self-heating would be insufficient to help. The battery heaters sound like a great idea.
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Re: Batteries vs Cold

Post by DrkAngel » Dec 22, 2011 5:47 pm

Received "Heaters" today ... 11 days shipping time.
Not self adhesive.
2 pads run in parallel use 1.2A
12V x 1.2A = 14.4 watts
8V x .8A = 6.4 watts

Rigged in series
12V x .3A = 3.6 watts
Batheater s.JPG
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Re: Batteries vs Cold

Post by neptronix » Dec 22, 2011 7:58 pm

chrisvw wrote:I noted a comment/question about whether the self heating that occurs from the voltage droop you get when cold will correct the problem. I was riding in 25 deg F ( -4 deg C) weather last night where the bike had been parked outside for several hours (returning from the city council meeting where they banned ebikes on the trails!) and after 9 miles, still no improvement in performance. It clearly felt like a C rate limitation. I thought my battery was going dead early, but it never died like it does when the battery is exhausted. I had used 6ah of the 8ah I normally get from the batteries (on a 10ah Li pack). From my limited data point, self-heating would be insufficient to help. The battery heaters sound like a great idea.
Battery heating depends entirely on what type of chemistry you're running at what C rate.
Trying to pull 3C out of my 20C capable lipo pack results in no battery heating, and the sag isn't that bad at all.
Run your 2C lifepo4 pack at 1-2C, and yeah it's gonna heat itself up due to the regular amount of waste heat that it generates.

And for the record, i find that allowing the controller to keep the batteries fairly warm works damn well.
15F out here, been riding for a few miles.. managed to get the controller nice and hot pumping all sorts of amps to get through the snow.. the batteries are 50F, the controller is 90F.. both are encased in a FalconEV bag with plenty of padding. Almost the equivalent of putting a blanket over your battery.. works for me.. just keep the temps under control if you have a controller that is more of a space heater than anything else ;)
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Re: Batteries vs Cold

Post by DrkAngel » Dec 22, 2011 8:28 pm

DrkAngel wrote:Received "Heaters" today ... 11 days shipping time.
Not self adhesive.
2 pads run in parallel use 1.2A
12V x 1.2A = 14.4 watts
8V x .8A = 6.4 watts

Rigged in series
12V x .3A = 3.6 watts
Looks like 1 pair, rigged in series, might run safely from a higher voltage pack ... ?
2S2P - 4 pads, should cover and heat my 25.9V pack nicely!
Will have to do some experimenting ...
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There, shallow draughts intoxicate the brain,
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Re: Batteries vs Cold

Post by DrkAngel » Dec 23, 2011 12:11 pm

DrkAngel wrote:
DrkAngel wrote:Received "Heaters" today ... 11 days shipping time.
Not self adhesive.
2 pads run in parallel use 1.2A
12V x 1.2A = 14.4 watts
8V x .8A = 6.4 watts

Rigged in series
12V x .3A = 3.6 watts
Looks like 1 pair, rigged in series, might run safely from a higher voltage pack ... ?
2S2P - 4 pads, should cover and heat my 25.9V pack nicely!
Will have to do some experimenting ...

Oops! Sorry!
I found the double sided adhesive tape.

More test results:
2 pads run in series:
25.9V pack - 29V
.7A 1- 13.5V 1- 15.5V = 20Watts ... 15.5V noticeably warmer ... too hot?
Reversed voltage showed same pad running at higher V.

3 pads run in series
.5A 8.6V 9.1V 10.7V = 14.5Watts
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Re: Batteries vs Cold

Post by DrkAngel » Jan 01, 2012 2:34 pm

DrkAngel wrote:Received "Heaters" today ... 11 days shipping time.
With self adhesive tapes.
2 pads run in parallel use 1.2A
12V x 1.2A = 14.4 watts
8V x .8A = 6.4 watts

2 pads rigged in series
12V x .3A = 3.6 watts
Batheater s.JPG
More test results:
2 pads run in series:
25.9V pack - 29V
.7A 1- 13.5V 1- 15.5V = 20Watts ... 15.5V noticeably warmer ... too hot?
Reversed voltage showed same pad running at higher V.

3 pads run in series
.5A 8.6V 9.1V 10.7V = 14.5Watts

25.9V pack - 29.2V
4 pads run in series 25.9V pack - 29.2V
Covers the main exterior surfaces of my LiPo packs.
All pads near 7V - about 3W each
Looks to be ideal for me, with batts placed in insulated pack.

37V pack - ~42V 6pack "Cool Cell" pack should work nicely with 6 pads in series.
(6 pads covering vertical surfaces nicely.)
Stats should be nearly identical to 4 pad 29.2V pack.
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Re: Batteries vs Cold

Post by DrkAngel » Aug 02, 2013 7:49 am

My recycled laptop build runs very well at 80ºF.
At 60ºF, one chilly morning, there was a noticeable speed-acceleration decrease.

This has me wondering ... at what temperatures are speed and acceleration optimal-degraded, and to what extent?

So ...
At various temperatures, 90ºF, 80ºF, 70ºF, 60ºF, 50ºF, 40ºF, 30ºF, 20ºF etc. ...
With same eBike and identically fresh charged battery, tire pressure etc. ...
I will test voltage sag, acceleration and top speed.

Acceleration test will be determined by resultant speed from full throttle over a measured distance. It will be run in 2 directions and the results combined, (to minimize wind as a factor).
Top speed will be similarly determined on a level course with 2 direction runs.

Voltage sag will be measured at initial full throttle, end of acceleration run and top cruising speed. Should also note amp draw at same cruising speed at all temperature (16mph?).

This will be a long term project but 50ºF - 60ºF - and 70ºF should be attainable this weekend.
Last edited by DrkAngel on Dec 01, 2013 4:19 am, edited 1 time in total.
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Re: Batteries vs Cold

Post by DrkAngel » Oct 08, 2013 9:59 am

Some company - SONY, finally graphed a discharge-temperature graph!

Graphite (US18650GR) - SONY
Lithium ion rechargeable batteries with lithium cobalt oxide cathodes and graphite anodes
SONY 18650GR temp.jpg
SONY 18650GR temp.jpg (28.41 KiB) Viewed 2552 times
Compare with their various C-rate discharge graph
SONY 18650GR discharge.jpg
SONY 18650GR discharge.jpg (32.67 KiB) Viewed 2552 times
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Re: Batteries vs Cold

Post by DrkAngel » Oct 08, 2013 12:04 pm

Found a pile of similar
1st 2 are Li-ion
Li-ion temp.jpg
Li-ion temp.jpg (29.99 KiB) Viewed 2522 times
lithium-battery-temperature-vs-capacity.jpg
lithium-battery-temperature-vs-capacity.jpg (61.72 KiB) Viewed 2522 times
2nd 2 appear to be LiFePO4
LiFePO4 cap.jpg
LiFePO4 cap.jpg (23.37 KiB) Viewed 2522 times
LiFePO4 temp.jpg
LiFePO4 temp.jpg (18.95 KiB) Viewed 2522 times
All show tragic losses in output and capacity!
So!
Keep your battery warm!
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Re: Batteries vs Cold

Post by friendly1uk » Oct 08, 2013 12:23 pm

Looking it the post above, the first graph seems right, but the second does not resemble anything


I picked up a few facts recently. My lipo's Ah rating might shift 5% through the winter here, and model plane owners pre-heat their packs to avoid waiting for the IR to cause self heating. Of course self heating of this magnitude requires high IR, so it can't make the high IR go away, or the heating would go away. It is a balancing act that means few lipo powered planes fly in the coldest of weather.

As a lot of lipo has discharge rates way above what people demand, lipo users shouldn't suffer much. What we are looking at is the typical slowing down of reactions seen in colder conditions. There would need to be a lot of slowing before I noticed, as I only use a 7th of my max C rate anyway. A rate taken at 30 degree's C. I don't have a big pack either, at 5ah is is actually amongst the smallest.

If you use low C rate chemistry to begin with, you could suffer badly. Some batteries can barely meet 250w requirements at the best of times. It really boils down to how well matched your batteries are to your controller. (Something not measured in Ah like many seem to think}
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Re: Batteries vs Cold

Post by DrkAngel » Oct 08, 2013 1:27 pm

friendly1uk wrote:Looking it the post above, the first graph seems right, but the second does not resemble anything
2nd demonstrates that excessive heat, above 25ºC, is bad ... also.
Performance loss is similar to cold.

Image
Last edited by DrkAngel on Dec 01, 2013 4:19 am, edited 1 time in total.
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Re: Batteries vs Cold

Post by wb9k » Oct 08, 2013 4:14 pm

The apparent loss of capacity and performance is due to a rise in cell impedance at lower temps. Cool batteries don't perform as well, but they last longer. I'd be far more concerned with keeping cells cool than warm unless it's below freezing. Most of the range loss in winter driving with the Volt is due to the fact that the car's heat is sourced by the HV battery, not because of capacity rise. The car's liquid "cooling" system can also preheat the battery while the car is plugged in. Owners I know say their EV range falls from about 40 to about 28 miles--well short of 50% loss. While the issue is not yet licked, it's grossly unfair to accuse the OEM's of ignoring thermal considerations.
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Re: Batteries vs Cold

Post by friendly1uk » Oct 08, 2013 7:26 pm

DrkAngel wrote:
friendly1uk wrote:Looking it the post above, the first graph seems right, but the second does not resemble anything
2nd demonstrates that excessive heat, above 25 C, is bad ... also.
Performance loss is similar to cold.

Image
But that is not right is it? Warmer cells have higher Ah capacity and higher voltage. They're more active.

I believe:
The first drawing shows these cells need a 0.2c discharge rate to deliver the full Ah rating.
The second drawing shows at 1c they only achieve 92% but also shows the ~10% can be regained by warming to 60 centigrade.
The labels are wrong.
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Re: Batteries vs Cold

Post by DrkAngel » Oct 10, 2013 9:22 am

All sources insist that battery temperature, during charge and discharge, is optimally in the 20-25ºC range.
Every source I've seen states that high temperature is a major damaging-destructive force!

Storage temperature seems optimal towards 0ºC.
Last edited by DrkAngel on Dec 01, 2013 4:20 am, edited 2 times in total.
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Re: Batteries vs Cold

Post by mistercrash » Oct 14, 2013 4:15 pm

Hobby King has a new device which might be interesting. A battery warmer with programmable temperature and works on 12V source. I'm thinking that maybe undo the sides to make a mat that can be wrapped around a larger battery.

http://www.hobbyking.com/hobbyking/stor ... y%20warmer
Is it ready yet?

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Re: Batteries vs Cold

Post by DrkAngel » Nov 28, 2013 11:52 am

Found some oem test specs for Sanyo 18650 cells.
Specs and graph show a 2C discharge rate capability. (Not recommended for best life-survivability!!)
Discharge Rate.jpg
Discharge Rate.jpg (47.47 KiB) Viewed 2166 times
2nd graph clearly demonstrates how performance and usable capacity suffer during Winter use!
Discharge Temperature.jpg
Discharge Temperature.jpg (46.72 KiB) Viewed 2166 times
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Re: Batteries vs Cold

Post by DrkAngel » Nov 28, 2013 12:33 pm

Image

Right now it is about -10ºC = 14ºF, I've left my bike out in weather like this and it just does not run well.
Initial start-sag voltage from my 25.9V LiPo:
at 20ºC (68ºF) battery provides 27.3V
At -10ºC (14ºF) battery outputs a pitiful 23.4V

Fortunately ... I am building a 33.3v 42.3Ah LiPo pack in an insulated 6 pack cooler.
I am using an AC plug quick connect and intend on storing pack right near a heater vent that outputs a balmy 80-85ºF.
Large 33.3V pack will be used on my 36V eZip Mountain Trailz.

eZip Mountain Trailz (Winterized)
36V controller (upgraded from 24V oem)
oem gearing (provided 16mph) - 33.3V pushes to legal 20mph with max watt output near 10-12mph, great for mushing through slush & snow!)
A Klondike XT tungsten carbide studded tire on the rear, and
Homemade Studded Tire on the front, (I quick swap to mountain tread when road clears)

The 33.3V will also work on my comfort cruiser during the Summer for extra torque-speed when needed.
25.9V w\16T mod pushes it along at ~20mph but controller works with 22.2V - 36V+.

I am limiting charge to 4.05V per bank ... anticipating a ~300% usable life!
Last edited by DrkAngel on Dec 01, 2013 4:22 am, edited 2 times in total.
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Re: Batteries vs Cold

Post by DrkAngel » Nov 30, 2013 9:58 am

50% capacity, when the temperature sounds reasonable but ...
The 50% capacity is at a much lower voltage.
So, performance, speed, torque etc. are all diminished a great degree.
Samsung 3000mAh 3.7V (18650)
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A little learning is a dangerous thing;
Drink deep, or taste not the Pierian spring:
There, shallow draughts intoxicate the brain,
And drinking largely, sobers us again.

I enjoy enlightening ... and enlivening the spirit of the innovators.

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