Do LiFePO4 Batteries Get Hot?

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engr_scotty
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Do LiFePO4 Batteries Get Hot?

Hi,

I've been around NiCD and NiMH batteries and they get hot when they are used heavy, like in ebike applications.

I am going to move to Life batteries and need to know if they get hot like the NiCDs/NiMHs, so that I can design a suitable enclosure, etc. Anybody out there have experience with heavily taxed Life's?

Thanks,
Scott

alnvilma
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Re: Do LiFePO4 Batteries Get Hot?

I have a big brick of a LiFePO4 and my controller/wiring in a rack box. I have just started riding around but I have detected no additional heat beyond ambient temps.

HCT
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Re: Do LiFePO4 Batteries Get Hot?

Prediction : Word " IMPEDANCE " will becomes as familiar as Amp/Hour or Volts in the near future .
It determine efficiency ,loss ,heat creation , all the detrimental things that shorten life and kill batteries .

In general Nickel based batteries pack have lower impedance than equivalent LiFePO4 .It is the impedance that determine the loss or heat creation both in the charging and discharge mode .

In fact the NiCd and NiZn based will cool off as they are charged ,the NiMh do not, they heat up .

A lot of the nickel based charger rely on the temperature rise function to turn of or turn down the charger (whether they use DV/DT or DT/DT the change depend on temperature changes.

The lithium chemistries like the lead acid depend on batteries reaching a certain preset voltage and monitored the declining current through the batteries , a much softer and slower process.

Case material ( plastic or metal )of the batteries pack will influence heat detection of the pack .

Taking identical impedance batteries whether lithium or Nickel Based will created the same loss ( heat ), however in the Nickel Based pack the case temperature will rise much faster and will be close to the contact post , whereas in the lithium based the case will rise at much slower rate , however the posts will get hotter ( reflecting heat generated inside the cell )

In closing , heat is the number one battery killer, and the amount being created in any pack is directly related to impedance , the lower the impedance , less heat .

HEAT & LOSS & INEFFICIENCY RELATED DIRECTLY to IMPEDANCE

dogman
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Re: Do LiFePO4 Batteries Get Hot?

Once my collarbones healed, I spent half the summer riding up a very steep hill in 105 F heat everyday. I was very concerned about heat affecting my new duct tape battery from Li Ping. So needing to protect it anyway, I used a large aluminum cookie sheet, cut and folded in the corners to make a very tight fitting pan wrapped around the pack. Coming in the house with a 105 F battery, I wanted it to cool some before I recharged it, and it worked good, cooling the battery much faster to room temp. Of course while outide, it would be at the 105 ambient temp. I never had the pack overheat once all summer. About 400 miles later, my motor melted to pieces, but the battery is fine.

This battery is being used normaly, with 99% of its use between 1 and 1.5c. Of course if you overdischarge the heck out of one, like a phoenix motor on a 10ah duct tape battery, I would think it could get hot. My experience is, if the lifepo4 battery is hot, you got too much motor. Warm yes, but not hot. Once I thought it through what it's operating range was in farenheight, I stopped worrying about charging the battery warm. 70 centigrade is toasty.

Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global

engr_scotty
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Re: Do LiFePO4 Batteries Get Hot?

Thanks !

I may see if I can get Ping to create a battery that will drop into an aluminum Bud box for both protection and whatever heat release is needed. He seems pretty flexible with the dimensions. I think I'm looking at a 16Ah size too. I think that should work well with the 400W BL-36 @48V. Got some rolling hills here in MN and I can just pedal some on the steeper ones. Sounds like you use a Cycle Analyst or similar. Seems like a person could just use a clip on amp meter from radio shack too...but I digress...

thanks!

alnvilma
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Re: Do LiFePO4 Batteries Get Hot?

I just took my plastic box/batt out in 80ish heat full throttle with some hills and one short killer;
No discernable temps from the batt or controller. The motor was very warm to the 5 second touch!
My CA said it routinely drew 20+ amps and bursts above 40. Also lots of 800-1000 watts and pegged at 1200!
Here are my first photos if they load...well, that didn't work. Maybe over at bike forum...

dogman
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Re: Do LiFePO4 Batteries Get Hot?

Actually I don't have a cycleanalyst, but have read enough from those who do to have a good Idea of what different sise motors draw with stock controllers. And here's another, from alnvilma. Was that the controller plagued WE you were riding?

I have always figured that most 500-600 watt motor kits draw between 15 and 25 amps most of the time. More of course on a big hill. Figuring that for the batteries from Li Ping, the 1c rate is one amp per amp hour of sise, my 20 ah, will discharge at 1c when it puts out 20 amps. That is why i keep pounding on and on to get the 20. That way you will only momentarily reach 2c on hills, but not ride all day at 2c. For my Ping 1.0 its a bit more important, since I expect 1000 cycles to 80% only if I keep the battery below 1c most of the time. For the new cells, you can expect 1500 cycles to 80%, but you won't get all 1500 if you discharge at rates above 1c all the time.

So with a 16 ah battery, if you run 25 amps a lot of the time, you are at about 1.75 c and spiking close to 2.75c. Untill somebody does some testing, we don't know how many cycles to expect at that rate. Some evidence is starting to come in that the Ping 1.0 cells degrade pretty quick when used at 2c rates, but no real data, just anecdotal stuff so far. Bear in mind that only one of the 4 pouches in a cell needs to go bad to cut your batterys usable ah to 75% I think the only way to make inexpesive lifepo4 a cheap battery is to use it right, at rates as close to 1c as possible. My pack has now done 1400 miles and still has ever bit of range it had when I bought it. I ride hard enough to melt motors, but my 20 ah is just fine.

Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global

engr_scotty
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Re: Do LiFePO4 Batteries Get Hot?

Dogman,

I appreciate your concern, and I may bite the bullet for a 20ah, but for now, can you help me with the math? I'm new to this stuff, so maybe I'm off somewhere...

Ok, this is an older BL-36 kit, 400W. P=IE so nominal current draw @48V is: 400W/48V = 8.3A. Of course, that's on the high-side since the LiFe batt's run typically >50V.

OK, so up a hill.. say the BL is heavily taxed, which it will be, and is putting out 800W. 800/48 = 16.7A, or slightly over 1C. This is the part I don't get, and it may depend on the kit and many other factors. Maybe there's a thread on the BL and current draw, etc. But just doing the math ---assuming certain wattage output, which may be totally wrong---it looks as though the 16ah will work....Anybody know about this? Do you think I should start a new thread?

Thanks,
Scott

dogman
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Re: Do LiFePO4 Batteries Get Hot?

Forget the 400 watt claim along with the range on a 7 ah sla claim.

Basicly you have a controller that will put out such and such ammount of amps X 48 volts. I believe the older WE brusless kits had a 25 amp controller, so you may be lookin at 1200 watts of power at the peak. This is what it will put out when starting up on an uphill grade for instance. The motors are all the same, whatever wattage they call em, but the 400 watt kit may have been a 24v, so if you have the 24v controller you could have a problem with the 48 v battery. I don't know how to identify the different controllers, I have only seen my brushed ones.

Anyway, from reading a lot of posts from guys with wattmeters and such, your motor will be drawing 15-20 amps when cruising at full throttle. So buying a battery that will provide that amperage easily will last longer than one that is doing it at a higher c rate. For the 20 ah battery 1c, is 20 amps discharge, which is how they get the rated amperage. It will put out a lot more, and the 16 ah battery will power your bike fine. For me, I do serious mileage, and expect to wear out a ping pack in three years or less, so the lifespan is more important to me. I also need every watt, or I get to peadle up a nice big hill when I run out coming home. If you live on flat ground, or it's downhill to home, this could be a lot less important to you. I haven't heard one post yet saying I wish I'd bought smaller, but plenty wishing they bought bigger. I made the same mistake, buying the 36v 20 ah when I could have got the 48v. As it turned out, I still have enough range, but had I bought the 48v, I would have had even more, and a shorter commute time.

Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global

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