48v Lipo pack 13s temperature

[userix]

I have a max amps 48v 13s 44Ah 40C pack.

After 40 min or so of aggressive riding, I notice the pack does get hot, around 109F degrees on the exterior. Not sure the temp deep within the pack. Peak amp draw is around 300A but nothing much higher as shown on my ammeter I have connected. The power cable get very warm during high current use as well.

Is 109F measured on the outer surface of the pack too hot to continue to use? I thought 300A peak and 100A continuous is well within the 40C rating of my pack.

I also notice a total pack voltage drop of 8v from 50v to 42v during the peak current draws.

 

[john61ct]

Mfg ratings are fiction.

Have you got an Ah counter?

What cells comprise the pack?

How many cycles have they seen?

 

[amberwolf]

I have a max amps 48v 13s 44Ah 40C pack.

40C? I wouldn't believe that even for RC LiPo. :/

If 300A is the max, then 300A / 44Ah = 6.8C.

Presumably the average current is much lower than 300A, so your pack is really only likely seeing say, 3-4C.

If it's in the 100A range, then it's actually only seeing 2C most of the time, and that's a pretty low rate; a 40C capable pack shouldn't even rise in temperature noticeably at that kind of rate.

If it's heating up that much for that low a rate, it'd probably burst into flames if run at 40C. :lol: (kidding, but seriously, it shouldn't heat up that much if it was really capable of that rate)

My guess is it's common 18650 generic whatever cells, that are at best 1C, possibly only 0.5C max.

The power cable get very warm during high current use as well.

Sounds like these are probably way too thin for the current. What gauge are they? (or rather, how wide is the actual conductor itself, since lots of cheap "clone" wire is mismarked significantly incorrectly. )

Is 109F measured on the outer surface of the pack too hot to continue to use? I thought 300A peak and 100A continuous is well within the 40C rating of my pack.

If it was actually a 40C pack, then it sure would be. But I don't think it remotely close to that capability based on your results. Sounds like you might've been scammed by the seller, whoever this "max amps" is.

I think you might want to measure the temperature inside the pack, because if it's that hot outside, it's probably *really* hot inside.

 

[userix]

Mfg ratings are fiction.

Have you got an Ah counter?

What cells comprise the pack?

How many cycles have they seen?

I don't have an Ah counter, just an ammeter. The cells are max amps brand lipo pouch cells, combined together to get the 13S 44Ah size. It weighs around 14kg. Pack is made with brand new cells, so 3 cycles. The pack averages about 1-2 Ohms per cell.

The power cables are 8awg, which I think is too small as well.

I would think as a "40 C" pack, it shouldn't be heating up that much under heavy current use, especially with the highest current I see being pulled is 300A.

Does discharging the pack in a lipo safe bag make it runner hotter too?

 

[john61ct]

Completely forget about the seller C rating.

You need more Ah to safely get the amps you need.

Maybe need to tear down & rebuild the wiring?

Afraid you may have been ripped off.

Best to stick to packs sold by trusted vendors recommended here, ideally built with known-good cells with high-C test results published by members.

 

[Balmorhea]

The power cables are 8awg, which I think is too small as well.

If your power cables were the main problem, it would be the cables that got hot, and not the pack.

 

[userix]

The pack does get hot too. It's not just the cables that get hot. Would running the pack in a lipo safe bag make it run hotter?

 

[Inductonaut]

I'm curious what your exact configuration is? Is this multiple packs connected just in series or is it a parallel/series configuration? Trying to think of how one might build such a 13s 44ah pack with common rc lipos... sometimes a common mistake is adding AH capacity of a series only setup and having the impression of more capacity than is really there.

Yes adding any amount of insulation including the lipo bag would increase temps to some degree. As the others have said though, a pack of that size really shouldn't heat that much. I run a much smaller 18s 5ah pack around 100amp continuous and temperature of the middle cells hasn't risen above 95F yet.

Going out on a limb here, is it one of these
https://www.maxamps.com/lipo-22000-6s-22-2v-battery-pack

and one of these in series?
https://www.maxamps.com/lipo-22000-7s-25-9v-battery-pack

 

[amberwolf]

The pack averages about 1-2 Ohms per cell.

*OHMS*? That's why it's getting so hot. That's a TERRIBLE internal resistance that even practically dead old abused cells will beat. :/

The power cables are 8awg, which I think is too small as well.

Actual 8, or just marked as 8?

Either way, you' probably want something more like 0 or bigger for 300A.

I would think as a "40 C" pack, it shouldn't be heating up that much under heavy current use, especially with the highest current I see being pulled is 300A.

That's the point--it's not a 40C pack if it's getting that hot, if it has that kind of cell resistance.

 

[userix]

The pack averages about 1-2 Ohms per cell.

*OHMS*? That's why it's getting so hot. That's a TERRIBLE internal resistance that even practically dead old abused cells will beat. :/

The power cables are 8awg, which I think is too small as well.

Actual 8, or just marked as 8?

Either way, you' probably want something more like 0 or bigger for 300A.

I would think as a "40 C" pack, it shouldn't be heating up that much under heavy current use, especially with the highest current I see being pulled is 300A.

That's the point--it's not a 40C pack if it's getting that hot, if it has that kind of cell resistance.

Sorry. It’s 1-2 milli-ohms (m-ohms). Not ohms.

 

[amberwolf]

Ah, well, that's much more realistic.

If their internal resistnace, per cell group, is really that low (actually measured, not just a specification provided by the seller), then it's comparable to my aging EIG 40Ah 14s battery pack's resistance, whcih is in the mid-30's milliohm range (as estimated by the Cycle Analyst; I don't have anything that can directly measure it).

The EIG cells, when *new*, are 5C cells. Nowadays, I'd probably call the ones I'm using 2-3C cells, as I see a fair bit of sag drawing only 85-90A, especially when they're not still fully charged. As they get closer to empty than full, the sag gets even worse.

They don't heat up like yours, but I'm also not even drawing 0.5C (18-20A or so) from them constantly, and the 2C+ peaks (85-90A) are only a few seconds at a time, a couple dozen times or so during a 10-minute commute.

So...I still don't think you have a 40C pack.

 

[userix]

Yeah the resistance is measured from my Graupner polaron pro charger. It’s able to show the resistance for each cell of my pack.

On my kart application. I do pull on average 90-120A throughout the duration of my drive, which is almost constantly. And very often full throttle 300A peak from a stop throughout a total of 50min of driving.

 

[userix]

Ran into a weird issue while charging.

I notice it wasn’t able to reach full charge of 4.2v per cell. During charging the Ir as shown on my graupner polaron charger is around 2-6 mOhms. But once it get close to full charge, it gets stuck around 4.15v per cell and the IR then shoots up to 80-90 mohms per cell. One cell is at 4.2v but it should be balance charging? It’s consistent across all cells and not just one cell that is faulty. The charger isn’t able to finish the charging cycle because it’s not reaching the set 4.2v voltage per cell, so it just keeps charging at very low amps, trying to reach4.2v for the rest of the cells, until the safety timer kicks in.

 

[amberwolf]

I notice it wasn’t able to reach full charge of 4.2v per cell. During charging the Ir as shown on my graupner polaron charger is around 2-6 mOhms. But once it get close to full charge, it gets stuck around 4.15v per cell and the IR then shoots up to 80-90 mohms per cell. One cell is at 4.2v but it should be balance charging? It’s consistent across all cells and not just one cell that is faulty. The charger isn’t able to finish the charging cycle because it’s not reaching the set 4.2v voltage per cell, so it just keeps charging at very low amps, trying to reach4.2v for the rest of the cells, until the safety timer kicks in.

Depending on how the system is designed, it *should* shut off primary charging current once any cell reaches it's HVC.

At that point, it may either leave all current off, until that cell is drained down past whatever it's balancing point is, or it may simply hold charging current down to the limit that hte balancing system is capable of (usually a few milliamps, a few dozen at most, except for large systems like big EV batteries).

You'd have to check it's manual for what it's designed behavior is in this situation (it may not even say; it's such a common design behavior to do the above).

Basically, that's normal behavior for the charging system, when confronted with unmatched cells that don't behave identically during charging/discharging.


Regarding the Ri, it's normal for it to go up with SoC. By how much, depends on the specific cell. If you can get the manufacturer's spec sheet for the cell, it should have charts for this stuff. Without that info, you can only guess at what's "good" results for these cells.

But at the measurements youv'e given so far, they're not really suitable for the use you have for them.

 

[john61ct]

Stop trying to get the whole pack to 4.2V, fool's errand that.

Can you set your balancer to start balancing at a lower voltage, e.g. say 4.05V ? Call that X.

Find out what the balance current is, let's say 0.5A per cell max, call it Y.

Get the pack charged so that some cells are over X, and some are under.

Then set the charger to a termination voltage of X+0.05V, so here 4.10V,

and also a very low current rate, but over Y, here maybe 1A.

You may need to wait a very long time, but hopefully you won't need to do this again for a while. If too long, consider balancing via a unit with a higher Y rate.

Once they are all balanced at that X voltage, keep that as your start-balance setpoint but this time raise the target to 4.15V and set the current rate to faster, say 0.5C, or whatever you usually use.

If successful, do a few full cycles that way see how you go.

Do not return to 4.2Vpc unless for occasional testing, capacity benchmarking etc.

 

[Dulel]

Hi friend,
Your average current draw must be lower than 90÷120amps, otherwise you would be unable to drive 50mins from 44Ah pack.
Anyway voltage drop tells a lot. 8V drop on 13S battery means that load is too high. I have small ebike workshop (made around 300 ebikes and batteries so far) and never allow more than 0.3V voltage drop per cell. For 13s battery it means 4V drop. When batteries get older drop increases, you know that for sure.
In your case during transients power heating battery is approx 8V x 300A, whopping 2.4kw. If you wan't any decent battery life consider halving load or battery redesign.
Best regards Dusan Latinovic

 

[john61ct]

When batteries get older drop increases

And lower quality cells, right out of the box