How to keep LiFePO4 warm in cold climate?

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shizzzon
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How to keep LiFePO4 warm in cold climate?

Post by shizzzon » Nov 24, 2017 9:36 am

I am currently running tests by placing a sample pack of A123 AHR32113s 4S1P in the refrigerator in a project box to simulate trying to warm these up from cold climate and am having difficulties.

These cells will be placed in a vehicle on a much larger scale that are not easily removable. The temperatures here can drop well below 32F which causes much concern if the car is started under this temperature because cells are not suppose to be charged under 32F.

The alternator sizing to cell pack will allow the alternator to charge these around 2.4-3C. They are rated for 5C max.

Anyways, our project box has 1 layer of Reflectix insulation material. It's aluminum wrapped around bubble wrap.
We have 1 layer of this in a cardboard box. We have the primary + and - wire coming out of the box and ran outside the door.

We let it sit for 12hrs. (someone has the frig set to high too, lol)
Temperature inside the refrigerator is 45-48F

Temperature of the Cells at rest is 42F.

Fully charged about 2 weeks ago.
Voltage showing 13.12vDC

We put a 2.7C load on it. After about 3-4 minutes, voltage had dropped to 11.60v and starting dropping a little faster showing capacity has dropped massively due to colder temperature.

But.. even with a 2.7C load, the temperature of the cells on this load only went up to 44.5F after 3-4 minutes.

I have read of people warming their cells up in a vehicle by putting a load on them for a minute and warm them up.. but not these cells.

These cells take a LOT of amps to get warm and that's not going to work in this application to warm them up.

In our normal testing, it took a 29F increase over ambient (79F to 108F) running a 15.2C test to near death.

But doing 1-7C tests to near death, it warms from 79F less than 10F.


What i am seeing is this-

Our thermal insulation is keeping the cells COLDER than the rest of the refrigerator..

I thought it would keep them warmer?

I can add a heating element.. but that's last resort for right now.

Curious on some sort of thermal insulation method to keep the cells warmer than surrounding ambient temps or is heating element only way?

markz
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Re: How to keep LiFePO4 warm in cold climate?

Post by markz » Nov 25, 2017 4:50 am

nichromium wire can be used, I just bought some from Fast Tech.

Do a little calculation as to what kind of watts you require, digital multi meter the resistance of the wire and using the formula's apply appropriate voltage. You could encase the battery pack into a well sealed box made of 1/2" wood and it would retain the heat quite well I'd assume. I would keep the temprature to around ideal temps, which have been listed elsewhere here on Endless Sphere.

When the battery is in use, the battery pack will generate its own heat.

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RebelRider.Mike
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Re: How to keep LiFePO4 warm in cold climate?

Post by RebelRider.Mike » Nov 30, 2017 3:13 am

This is an interesting thread.

I have an issue that seems similar. I bought a drop-in LiFePO4 starter battery replacement for my motorcycle. Works great in the summer. Seems like it discharges in cold temperatures. I was assured when I bought it that it wouldn't have any issues with cold. Absolutely false! Around 40F or less at night, and the battery is dead the next day. Like around 10V dead.

I keep mine on a LiFePO4 maintainer/charger when the weather is cold. Seems to work fine. I'm not sure if it keeps the battery warm, but it at least is fully charged, (13-ish Volts) and it will turn the engine over fine. I don't know if maintaining the battery at cold temperatures would be causing damage or not.

I suppose another way to keep the battery maintained in the winter would be to somehow make an easy disconnect and keep the battery indoors when not in use. That would be pretty inconvenient though if you use it everyday. I've also got a LiIon battery booster to "jump" the battery when I forget to put the maintainer on. Works good in a pinch, but the maintainer is really better.

Not sure if any of that helps, but that's been my experience. I look forward to seeing your test results. :)
Mike

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dogman dan
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Re: How to keep LiFePO4 warm in cold climate?

Post by dogman dan » Nov 30, 2017 6:15 am

That sounds like more voltage drop because its cool, than it should be. I suspect you have a drop because of the cool, and, some other issue, like a trickle discharge situation overnight.

If you were talking well below freezing, different story. But not working in 40F is worse than you should expect.

Lots of neat plug in your car heating devices for gas, but not so many for electric. One off the shelf option out there for gentle heat, and waterproof, is a reptile heater. Warm, but not hot enough to cook a battery like some heating ideas could be.

If you don't need so waterproof, a regular hot pad from a pharmacy works similarly, but larger for a large car battery. Those are used by most hot air balloon pilots to gently warm propane tanks, so you have good pressure in the tank when flying in sub zero weather. Plug in overnight, and the tank is warm in the morning. Plumbing heat tape tends to overcook the tank, causing problems when the tank vents from overpressure.

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Re: How to keep LiFePO4 warm in cold climate?

Post by dustNbone » Nov 30, 2017 11:05 pm

I agree, 40F shouldn't be causing that kind of voltage drop. I'd say that's around the point that I start to notice some reduced performance at 25A, but I'm talking maybe 2V off the 52V I'd expect to see pulling that much current in "normal" conditions.

Things really don't start to suffer till maybe 25F or so, at that point I'll suffer a fair bit of range reduction due to hitting LVC much sooner.

I don't think it's really that it discharges, the chemistry just is reluctant to give up it's stored energy. If I bring the battery which is hitting LVC inside long enough to warm it back up, it will work as normal, and I'll get pretty much the same Wh from the initial charge (charged at room temperature) as I normally would.

Of course I'm talking about a specific type (A123 AMP20 pouches) of cell. I have no experience with any other LiFePo4.

markz
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Re: How to keep LiFePO4 warm in cold climate?

Post by markz » Nov 30, 2017 11:18 pm

Alternator tops up the battery in cars and trucks, so motorcycles must have an alternator because lights at night would deplete battery quickly especially on high beam - So what do you need to do to the alternator when you install lithium?

https://www.lithiumpros.com/how-does-co ... batteries/
As winter sets in and the weather gets colder, we get lots of calls and questions about how our batteries perform in winter weather, and what steps need to be taken to maintain them. ALL batteries will perform poorly in cold weather, regardless of whether they are lithium or lead-acid. In fact, a lithium battery will still outperform a comparably-sized lead-acid when the temperature drops. However, since most people try to run the smallest and lightest lithium battery possible, there are some things to be aware of: For a daily-driven car… …almost no extra effort is required. On a very cold morning, however, one might find that the cranking performance of the battery is not as strong as usual; if it is very cold and the car has been sitting for a while, the car might not crank fast enough to start. This does not mean that your battery is dead.

Simply turn on the headlights or rear defroster for a few minutes to drain some energy from the battery. As a result, the battery will warm up internally and gain enough “juice” to start the car.
For ease I would install a heating system and with the flick of a switch it would turn it on, and be powered by a small pocket sized battery. Still a hassle. Why are you using lithium battery to begin with?

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dogman dan
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Re: How to keep LiFePO4 warm in cold climate?

Post by dogman dan » Dec 02, 2017 8:11 am

I'd want to know if the battery is balanced. Of course, they likely made checking that impossible.

If there is a bms, then putting it on the trickle charger a few nights likely did balance it. Keeping it on trickle daily could kill it.

You don't trickle charge lithium. Its not like lead, that loves a nightly trickle charge.

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