20 AH LiMnO2 "overheating" drawing 20 amps??

My new 24 volt 20 AH LiMnO2 battery powers my 600 watt BMC motorized e-bike great, drawing 20 amps of current for 33 minutes before it cuts out at 25 volts, all data obtained by "shunt" tests in real time, on the bike, while at full throttle on flat terrain and no peddling. I sent the battery back to the makers, and they said it was due to the battery BMS shutting off the battery due to "overheating". They're not sure why....yet. When hooked up to my other e-bike with a 400 watt BMC motor, actually 370 watts, it does not cut out at 25 volts, presumably not overheating. The battery is in a plastic "Currie e-ride" case, with no vents, made for SLA's. Would "venting" the plastic case help, or does it sound like bad cells? Any theories about this problem?

Venting the case may or may not solve the overheating problem, but it sure won't hurt. If the controller is also in the case, move it to the outside. I'd probably just bypass the bms for discharge and only use it as a balancer for charging. But I don't like bms's anyway and don't use them.

Depending on the BMS, it could overheat if there is no air flow for it. If you ran it for 10 minutes then felt the FETs on the BMS, you could tell if they are getting hot. Zipped up in a bag there is really no place for the heat to go.

Thanks for the replies- the builder is going to run the battery off 20 amps while OUTSIDE the battery case. If it still cuts out, I guess that will remove "overheating" as the culprit. I'll let you know....

In the previous thread, I must have misunderstood. I thought you said the battery was overheating.

A bms overheating is different. You have to let at least some cooling air get on the bms in hot weather.

In my hot climate, my ping bms's would heat up and shut down if I smothered the battery in a closed bag. Unzipping the bag, and letting some breeze into the bms on a warm to hot day solved the problem.

Usually I carried the batteries in a metal toolbox. I cut enough of the top away facing forward to scoop in just a tiny bit of cooling air for the bms. Never had the cutout with the vent working. In winter, the metal box allowed the battery to cool too much. Smothering the battery in some extra insulation in freezing weather was not a problem.

Dogman, here's where we're at with trying to troubleshoot why the BMS is battery is kicking off my new 24 volt LiMnO2 battery. ElectricRider has duplicated my tests- when they draw 20 amps from the battery it cuts out at 25 volts or thereabouts, in the plastic case. They believe it's due to "overheating". Now they will do the same test OUT OF THE PLASTIC CURRIE E-RIDE BATTERY CASE. If it still kicks off, then VENTING will not be a cause of it overheating. Their theory is that the plastic container is providing a closed nonventilated chamber producing an over heating situation.....If it doesn't kick off in an open environment, then venting will rectify the problem, at least at a 20 amp draw. Unfortunately, I draw up to 35-38 amps up hills for a few minutes, so that will be the next test- to see if it kicks off drawing higher amps.

Entirely possible you have multiple problems. Hot bms getting hotter when the cells themselves get pretty warm pulling hard up that hill. But it's no solution to say, "just ride in the winter". I find it hard to believe your pack loves a 5c discharge. Doing it in tests is one thing, loving doing it out on the road is another. I bet the pack warms up noticeably discharging 40+ amps. My 20 c lipo does. I'm positive a larger pack would help.

VERY COOL that Electric Rider is working with you on this.

Imagine if you bought that battery from a china vendor. Even with the best of vendors, you'd still be fixing it yourself. Can't send it back to china.

dogman said:

Entirely possible you have multiple problems. Hot bms getting hotter when the cells themselves get pretty warm pulling hard up that hill. But it's no solution to say, "just ride in the winter". I find it hard to believe your pack loves a 5c discharge. Doing it in tests is one thing, loving doing it out on the road is another. I bet the pack warms up noticeably discharging 40+ amps. My 20 c lipo does. I'm positive a larger pack would help.

VERY COOL that Electric Rider is working with you on this.

Imagine if you bought that battery from a china vendor. Even with the best of vendors, you'd still be fixing it yourself. Can't send it back to china.

Click to expand...

Just want to "+1" for electricrider. Very good experience with them.

I had a 36v 10ah Ping pack a few years ago that would get hotter than hell on the bms pack as I would keep it fully charged and murder it with a cyclone 35 amp controller
I temporarily fixed the heating fets by soldering a copper braid/strip to the BMS board.

One more interesting point- after initally installing the battery onto my Synergy e-bike with that 600W motor, it would CONSISTENTLY cut out at about the same point along my route. At about the 7th to the 8th mile, fully throttled, it would cut out. This route, unlike the flat controlled test route that got me 11 miles/33 minutes, had a few mild to moderate hills, but the route was consistent and cut out at about the same point. This indicates that it cut out at the same voltage, although I didn't confirm this finding with an "on-board" test. Anyway, my theory is that the BMS is cutting out prematurely for "UNKNOWN" reasons. It'll be interesting to see what electricrider says next......Yeah, they're great working with me.....so far.

i doubt if the BMS is cutting out 'prematurely'. it is cutting out for a reason and the reason is voltage sag of the limn2o4 cells. we have not seen the cell voltages while charging so there is no way to tell you which one is causing the cut out.

wimpy cells.. wimpy bms.. either ways, it's underrated for the task you're trying to get it to do.

Batteries are best at about half or a fourth of their rated C rate. That goes for RC Lipo, lifepo4, etc.

Neptronix, tell me what 24 volt Amp-Hour storage LiMnO2 battery I should have gotten to power my 600 watt BMC motor, that draws 20 amps continuously with 2-3 minute bursts of 35-40 amp draws on hills? And what C-rating would have met the challenge? I suspect you are correct about this battery being insufficient for the job, because when I connect it to my 370 watt BMC, it doesn't cut out at all.....

Dnmun, what causes "voltage sag" in the cells of a LiMnO2 battery. Does it have anything to do with "overworking" the battery or is it something else?

doubledipsoon said:

Neptronix, tell me what 24 volt Amp-Hour storage LiMnO2 battery I should have gotten to power my 600 watt BMC motor, that draws 20 amps continuously with 2-3 minute bursts of 35-40 amp draws on hills? And what C-rating would have met the challenge? I suspect you are correct about this battery being insufficient for the job, because when I connect it to my 370 watt BMC, it doesn't cut out at all.....

Click to expand...

Oh you need to turn those amps down to about 25-30A max..

I don't know much about premade limno2 batteries. I use 20C RC Lipo at 2C and have barely any noticeable voltage sag at all - way overspecced for the job! You could go with a larger battery of the same type and get less voltage sag; for example, if you had a 40AH battery, you'd cut the voltage sag in half and the heat in half, given that you were putting the same load on it.

I just received an e-mail from ElectricRider- FIRST TEST: they ran my 24 volt 20 AH LiMnO2 battery delivering 20 amps and it cut out while in the plastic unvented battery case, with the battery still at 25 volts, all due to "overheating". SECOND TEST: they ran it drawing 20 amps and it did not cut out while OUTSIDE the plastic case, running until it drained a total of 20.1 AHs...Does this solve the problem, or am I still headed for more malfunctions due to "HIDDEN VARIABLES" (low C-ratings, underrated battery to load ratios, wimpy overworked cells, etc. etc. etc.? I mean, should I throw the towel and just get a 40 AH battery?

not much you can do since they will return the pack for you to use since it does work. by using a low voltage current source it takes a lot more current to provide the same power to the motor.

i still don't understand where the heat is coming from. is it the battery itself or the mosfets in the BMS?

if the mosfets in the BMS get hot that usually means they are shorted so it would not cut off like it did. so i am kinda stumped.

the voltage sag would be from the internal resistance of the cell causing a voltage drop across the cell as the current was pulled out of it. this is where needing high current causes the sag to be higher than it would be for the same power from a 48V pack.

Well, going into winter, you shouldn't have as many problems with the battery, but it will become a problem in summer again, even outside the case.

No prebuilt battery should require air cooling though, lol..

Can't say what the problem is, other than it is underperforming for the job it's being given.

And we still don't know if it's the battery getting hot, or just the bms, or both.

But we do know that 10 ah is a tad small for 40 amps spikes. It's just gotta hate those. My 20c pack of 10 ah gets pretty warm if I give it 40 amps much. More size would help the cells themselves stay cooler. You know that towards the end of a discharge, the c rate the battery can handle gets less?

That's part of where I get that cut the expected c rate in half rule. Most of your ride won't ever be fully charged, and lowest internal resistance.

Since ElectricRider has confirmed that the battery can put out 20 amps continuous without cutting out, I'll attempt to reproduce those findings on flat terrain, OUT of the plastic case, taking voltage readings off the battery every mile or so....then I'll attempt to test the battery with my "routine 9 mile round trip", with 7 of its miles flat (pulling 20 amps) and 2 of its miles mild to moderately uphill (pulling 30-35 amps). If it works out, I'll thank the gods, if it cuts out, it's back to ElectricRider for more of the same....Like Dave from ER has said, "It's live and learn"....

Maybe turn down the amp draw to 28 amps from 35a.

you can add another battery in series to get the power you need without damaging this one more. you should lay off these high current draws until you can do that. it eats up the battery fast.

Well, my two cents: I think if you want to run at that power level with that battery at that voltage, you need a bigger (more Ahr) battery. 24v is going to need a lot of current for a given power level. A 24V, 20 Ahr battery is the size of a 10 Ahr 48v battery, which is what I have and the same chemistry also. I have it current-limited to 25A, which is still 2.5C for this battery. I do pull 25A from it, but only for very short periods of time, less than a minute. Most of the time, I am under 1C. I would get another pack the same size and, if your controller/motor will take it, put it in series and lower the current at a particular power level. Or put it in parallel and run each battery at half the C rating one battery is currently seeing. Personally I don't think a battery that needs to be out of its shrink-wrap to pull its stated continuous current draw is working up to its specifications but I do think electricrider.com has their heart in the right place. If their LiMn battery won't do it, you are not likely to find one comparable that will. Would be good to know what is causing the overheating; the BMS is supposedly rated to 50 A so to cut out early at 20A is not up to stuff, in my opinion.

The other option is to go with a higher C rated chemistry. RC LiPO will be cool as cucumber at that C rating, right up to the point when it goes out in a blaze of lithium-fueled glory (just kidding, LiPO-heads. But seriously, if you go LiPO, make sure you know what you are doing.)

dnmun, I thought the whole purpose of a battery "BMS" is to safeguard the battery from any kind of abuse- overheat, overamperage, etc, by having it cut out. My 9 mile round trip is 90% at 20 amps, and 10% at 33-35 amps, not a very huge amp draw from a 20 AH battery. So, why sweat it? Besides I've got a 100% warranty for the first 6 months. My policy is to believe ElectricRider about my battery being OK, and then "going for it". I mean, it's really amazing to pay $460 for a LiMnO2 battery and have to "baby it". I can't wait to get it back, because I've got a nice workout for it. Hey, Like the HAL 9000 computer told Dave in 2001: A Space Odyssey, "Put the unit back in and let it fail, and then replace it"....I'll keep you all posted, but something tells me that I'm headed for another cutout/failure leading to a refund or another replacement battery. And why not?
s

pdf, yes, it would be good to know why it is overheating. You have hit the nail on the head. According to the vibes from ER, (and I'm paraphrasing) "the battery is OK, but needs venting." Now this is interesting because my first impulse was still "so why is it overheating?"....and "why have I never heard about batteries needing to be vented".....As far as the C- rating goes, I assumed that this particular LiMnO2 battery had a higher than normal "C-rating" because ER advertizes about their batteries being able to take high current draws. I mean that's what they do. Of course, "assuming" has gotten me into problems before. Besides the guys that are into these BMC/MAC "finned" motors, Andy from ElectrikMotion, and Scott from EVDeals recommended them for batteries for my specific motor. So there you have it. They're the pros, and I'm the trusting customer. Never mind the specific info I gave ER about what I was powering, doesn't seem to make much difference now. So, a warranty is a wonderful thing, huh?