Battery heat problem - What is this resin?

[tigger_na]

Dear Forumites

Heat kills batteries, that's a fact. According to my battery supplier, my battery will last for 5,000 cycles at 80% DOD/25°C and 3,000 cycles at 80% DOD/45°C. That is a massive difference. But how do you keep batteries cool if they are in an unventilated enclosure, with an ambient temperature hitting 35°C on a regular basis? My previous battery, a 48V 100Ah Akkutech (also looks like a Leoch design) lasted all of 2 months before they started to deteriorate rapidly, before they became entirely useless after another 2. They expanded so severely that they bulged the steel enclosure, according to my supplier a sure sign of overheating. 

When I opened up the enclosure of my new battery, to see if there is anything I can do, I found this, I don't know, sticky, rubbery, grey goo spread over the side of the batteries. I don't understand its reason - My understanding would be that you need heat to dissipate as fast as possible, and spreading an insulating material over the side of the battery would definitely go counter to that.

The next problem is the control board, which, according to the BMS, is a good 3°C warmer than the batteries themselves. Now why would you put batteries into a steel enclosure, and then add a heater to it? Why is the space of the control board not separate from the space of the batteries?

Any advice?

[Greglsh]

Not 100% sure just my 2c worth, but maybe the "grey goo" is like a heat transfer paste which transfers the heat of the batteries to the metal case to act as a heat sink?

[madness_za]

5 minutes ago, Greglsh said:

Not 100% sure just my 2c worth, but maybe the "grey goo" is like a heat transfer paste which transfers the heat of the batteries to the metal case to act as a heat sink?

That would be my guess as well

[tigger_na]

There's a sticky plastic mat that sticks on this filler, then there's a large air gap, then there's the casing/steel housing. I'm inclined to agree with you about the filler haveing thermal conductive properties, but air is a good thermal insulator, so I doubt if any heat from the batteries will reach the casing if it's constructed this way.

Here my battery temp today, I have no idea how this is supposed to last. The PCB temperature is 39.9°C now, while the graph (reported by the BMS, must be an average of different sensors) shows 36.9°C. Peak was when the charge cycle was complete at 38.8°C. All through the night, the temperature dropped to 29.9°C. Don't know how cool it was during the night, but definitely less than 20, so this thing is an effective heater box.

I added a Peltier cooler, recirculating and cooling the air in the casing, can't see that it makes much of a difference, don't know it's rating either - best guess is 60W.

[Greglsh]

21 hours ago, tigger_na said:

There's a sticky plastic mat that sticks on this filler, then there's a large air gap, then there's the casing/steel housing. I'm inclined to agree with you about the filler haveing thermal conductive properties, but air is a good thermal insulator, so I doubt if any heat from the batteries will reach the casing if it's constructed this way.

Here my battery temp today, I have no idea how this is supposed to last. The PCB temperature is 39.9°C now, while the graph (reported by the BMS, must be an average of different sensors) shows 36.9°C. Peak was when the charge cycle was complete at 38.8°C. All through the night, the temperature dropped to 29.9°C. Don't know how cool it was during the night, but definitely less than 20, so this thing is an effective heater box.

I added a Peltier cooler, recirculating and cooling the air in the casing, can't see that it makes much of a difference, don't know it's rating either - best guess is 60W.

Okay, from the picture it looked like the case was touching the "grey goo" , if it has an air gap then it wont be very effective at all.

[PsyCLown]

My first thoughts was also a thermal paste of sorts, although that does not make sense.

Perhaps it is more of a fire retardant paste?

 

With regards to the temps, well, not too much one can do about that here in South Africa. Unfortunately it gets hot here in summer and a lot of people (myself included) have their equipment installed in their garages and my garage gets really hot - I even installed an extraction fan to help remove hot air from the garage and draw in some cooler air and allow for some air movement within the garage and this does help a little but temps still get uncomfortable at times.

 

My view is that you can only do what is reasonably practicable, installing an aircon in the garage just to keep the inverter and batteries cool does not make sense as the electricity cost will be far greater than a replacement battery would be over a few years. Not to mention the initial aircon purchase & installation cost.

Fans only do so much, bringing the temperature below ambient temperature is unlikely.

 

Therefore, it is just what it is and having multiple batteries and/or reducing the loads and strain on the batteries will help keep them cool and help extend their lifespan.

 

With all of this being said, the lifespan of you Akkutech battery does not seem right, way too short of a lifespan. Also is the area you keep your batteries in reaching 45C? That is really hot! I can believe the cells could reach 45C for a bit while under a heavy load for a bit of time but that is unlikely to be for extended periods of time.

Similar concept to taking your car to redline every now and then vs driving it while its bouncing off the rev limiter constantly. It is not continuous heat or strain on the battery.

 

My batteries do have some vents in the enclosure to help allow for hot air to escape, how much of a difference it makes I am not sure. It does not bother me all that much as there is little I can do about it high temps are not constant.

[tigger_na]

Thanks PsyCLown. The supplier boasts that their batteries are developed for African conditions, something I find hard to believe, looking at how little effort is done with cooling. No, we don't get 45°C. Yet. 38 is just about the maximum, and that usually hits in the afternoon, after the battery is fully charged. I'm surprised that you say that ventilating your garage helped. Well, if your battery case has ventilation holes, it would, rather, this proves that having a ventilated case does help.

What I plan to do now is to divide the battery case, force ventilate the front part where the PCB is housed, and cool the rear of the case with Peltier plates, and, if I can, limit the charging current. My thinking, less power pumped into the batteries will mean less heating, but over a longer period of time. If it works, then a better control solution than a thermostat will have to be designed. Peltiers are inefficient under the wrong conditions, so they're not something that should run at night, and constantly ventilating the PCB is not the brightest of ideas in freezing conditions either.

I'll keep the forum updated.

Edited March 6 by tigger_na

[GMAC]

2 month only 4 month max does not sound possible for even operating temp of around 40c .

There must be something more going on there than just temp . 

I would keep an eye on how the inverter charges the batterys 

[TaliaB]

On 2024/03/04 at 8:13 PM, tigger_na said:

They expanded so severely that they bulged the steel enclosure, according to my supplier a sure sign of overheating. 

I agree with @GMAC temps of 40° very unlikely to cause the severe bulging and short lifespan of the cells, but high charge/discharge rates can and will and also push up the cell temprature. The supplier spec for these 48V 100Ah Akkutech batteries is 0.2C 20 amps. For interest sake what is your charge/discharge current set to?

[tigger_na]

I'm here to learn. The BMS of the Akkutech is not user configurable, so if it was indeed subjected to high charge or discharge currents, then it was the BMS that fried the battery, no? It was connected to a Kodak inverter, battery type wat selected as Lib, so I just let the BMS do what it's supposed to do.

[GMAC]

As I said best to keep an eye on how your setup is charging .

For example 

Just yesterday got a guy that phone for help his humble is lasting only 2 or 3 hours were it used to last up to 8 hours with same load 

We did not do the instillation .

Long story short the inverter was not communicating with the battery but did not give error so the Inverter was charging up to bulk charge which was higher than the bms allowed and was then cutting charging till the battery volts settled to a point the bms allowed charging again,  could hear the relay switching in the battery . This was happening every 3 minutes 24/7 for an year +

Don't think this did the battery very good long term . 

So don't just keep an eye on volts but also how the inverter charges .

 

 

[tigger_na]

I divided the battery case with a plastic sheet, ventilated the front part, where the PCB is housed, with a filtered air supply, and the back, where the batteries are housed, with a recirculating 120W Peltier cooler. Then I installed a ventilation fan to the whole solar equipment alcove. Problem solved. The ventilation fan for the alcove had the most effect, the Peltier system comes last in effect. In the graph below, the system came online on the 19th of March. Before, peaks of 38°C where commonplace, I now have those down to 33°C.

As to the charging or discharging behaviour, it mostly stays below 40A. I do not like that high absorption voltage (58.6V) and the long periods it is kept there. I've asked my supplier whether I can adjust the Enersol Lithium 48 – 100 BMS to charge to 95% SOC instead of a 100%. No answer yet...

[Beat]

My humble comment on your descriptions is this:

The battery charging voltage is way too high, even for a 16 cells pack. That causes high currents and those cause heat. Remember, internal resistance and high current cause high voltage drop (Ohms law). Voltage times current is power in W. That is the power that heats the battery internally. My recommendation for long battery life is to stay away from 1C currents. Limit to exceptional 0.5C but regular 0.2C currents. My LEOCH 48100TB packs have almost 4 years of duty with over 1200 cycles and still 100% reported SOH. If your system duty requires such high currents, it would be a wise thing to add packs. It improves system performance and extends battery life as the currents are shared between the packs. Set the charging voltage on the inverter/charger according to battery specs.

[tigger_na]

Thank you Beat, I think exactly the same. My current draw spikes happened when my concentration slipped, so I can easily avoid those, but those charging currents are too high for my liking. Sadly, until now at least, I have no way of limiting either charge current or absorption voltage, as anything I program into my Kodak inverter is promptly overwritten by the BMS. Sadly, EnerSOL isn't too keen on answering my queries, but we live in (unsubstantiated) hope.

[P1000]

20 hours ago, tigger_na said:

Enersol Lithium 48 – 100 BMS to charge to 95% SOC instead of a 100%.

That won't make much of a difference in longevity with LiFePO4, except that it will make your SOC drift and possibly make your cells not balance. Just keep the temperature and charge rates down.

[TaliaB]

2 hours ago, tigger_na said:

Sadly, until now at least, I have no way of limiting either charge current or absorption voltage, as anything I program into my Kodak inverter is promptly overwritten by the BMS.

Why don't you disconnect the comms between battery and inverter then setup the voltage and charging current under USE. THEN: As you know your way around the guts of the battery remove the bms and replace with JK bms from Lithuim Cells then you have full control over the bms settings seeing you get no joy from the supplier. At the current voltage of 58.6v(3.66v/cell) you are going to damage the lfp cells.

https://lithium-cells.co.za/detail/429357?gad_source=1&gclid=Cj0KCQjwzZmwBhD8ARIsAH4v1gX6oX8_R0IvbkBt_vqg1-cSRHUBiVaFIiZ6UyN2_9cKoFDvryfa324aAu-REALw_wcB

[tigger_na]

23 hours ago, P1000 said:

That won't make much of a difference in longevity with LiFePO4, except that it will make your SOC drift and possibly make your cells not balance. Just keep the temperature and charge rates down.

I accept your obvious expertise and thank you for it, I'm just offering three use cases where a lower maximum SOC is backed and even required by the manufacturer:
• My Samsung phone has a setting for limiting max SOC to 85% in favour of increased longevity.
• The manufacturer of my drone guarantees their batteries for 400 cycles, if and only if they werent stored at 90%+ SOC for a cumulative total of more than x days.
• The manufacturer of my electric pruning shears has a special storage charging procedure, and they will also not entertain guarantee claims if the battery has not been stored at that specific SOC.

[tigger_na]

22 hours ago, TaliaB said:

Why don't you disconnect the comms between battery and inverter then setup the voltage and charging current under USE. THEN: As you know your way around the guts of the battery remove the bms and replace with JK bms from Lithuim Cells then you have full control over the bms settings seeing you get no joy from the supplier. At the current voltage of 58.6v(3.66v/cell) you are going to damage the lfp cells.

https://lithium-cells.co.za/detail/429357?gad_source=1&gclid=Cj0KCQjwzZmwBhD8ARIsAH4v1gX6oX8_R0IvbkBt_vqg1-cSRHUBiVaFIiZ6UyN2_9cKoFDvryfa324aAu-REALw_wcB

Thank you, that is a suggestion I never even considered. I have reservations though, I cannot imagine that a third-party BMS will regulate my battery as well as a manufacturer-designed and supplied BMS. The same goes for the inverter, which will cetainly not. But both together? Maybe. Then again, this "manufacturer designed and supplied" BMS is obviously programmed wrong, so if they missed that, what else did they miss?

As to the manufacturer's guarantee, I doubt that they will honour that, ever, as my battery casing now looks like swiss cheese. Know that little sticker "warranty void if opened"? I scraped it off as good as I could, but the idea is still there. Now, if I come to them with a warranty claim with a third-party BMS, they won't only not honour the warranty, they may actually shoot me on the spot. I would, a customer like that.

[Scorp007]

5 hours ago, tigger_na said:

Thank you, that is a suggestion I never even considered. I have reservations though, I cannot imagine that a third-party BMS will regulate my battery as well as a manufacturer-designed and supplied BMS. The same goes for the inverter, which will cetainly not. But both together? Maybe. Then again, this "manufacturer designed and supplied" BMS is obviously programmed wrong, so if they missed that, what else did they miss?

As to the manufacturer's guarantee, I doubt that they will honour that, ever, as my battery casing now looks like swiss cheese. Know that little sticker "warranty void if opened"? I scraped it off as good as I could, but the idea is still there. Now, if I come to them with a warranty claim with a third-party BMS, they won't only not honour the warranty, they may actually shoot me on the spot. I would, a customer like that.

I think based on what you have done so far there should be nothing left of a warranty. I am sure @TaliaB based his suggestion on that fact. I also use the JK and at times we have to accept the fact that companies designing great BMSes can produce a much better BMS than what manufacturers put in their batteries at the lowest cost. 

[Beat]

9 hours ago, tigger_na said:

Then again, this "manufacturer designed and supplied" BMS is obviously programmed wrong, so if they missed that, what else did they miss?

This BMS is obviously killing your battery. I go along with TaliaB and strongly suggest to disconnect the inverter from the BMS. That's the only way to save what's ever left of that battery. And as Scorp007 mentioned there is likely nothing left of the guarantee anyway.

I'm one of those who advocate to let the inverter manage the charging without BMS connection. Important are the charge voltage settings according to battery specs. I have done so now for almost 4 years with very good result. I use the BMS only for monitoring the batteries. LEOCH does not put any BMS connection condition on their guarantee.

 

[Tinbum]

1 hour ago, Beat said:

 

I'm one of those who advocate to let the inverter manage the charging without BMS connection. Important are the charge voltage settings according to battery specs.

 

And I'm the opposite. I'd advocate getting a decent inverter instead of making do with some of the rubbish on the market..

[Nexuss]

17 hours ago, tigger_na said:

I accept your obvious expertise and thank you for it, I'm just offering three use cases where a lower maximum SOC is backed and even required by the manufacturer:
• My Samsung phone has a setting for limiting max SOC to 85% in favour of increased longevity.
• The manufacturer of my drone guarantees their batteries for 400 cycles, if and only if they werent stored at 90%+ SOC for a cumulative total of more than x days.
• The manufacturer of my electric pruning shears has a special storage charging procedure, and they will also not entertain guarantee claims if the battery has not been stored at that specific SOC.

You are comparing Lipo to LFP chemistry ,they are very different. LFP need to be charged to 100% regularly to keep cells balanced. 

[TaliaB]

11 hours ago, Tinbum said:

And I'm the opposite. I'd advocate getting a decent inverter instead of making do with some of the rubbish on the market..

I think you are missing the point. There is absolutely nothing wrong with the Kodak inverters, in fact there are 1000 of Kodak inverters installed across SA with no problems. The point @Beatis trying to make is that the bms in the battery has failed causing the bloated cells. The bms gives the inverter instructions on charging profiles not the other way around. What happened in this case the bms failed and most probably gave an incorrect charge profile to the inverter and there was no way of telling the bms is faulty until you discover one expensive damaged lfp battery module. 

Edited March 31 by TaliaB

[Tinbum]

2 hours ago, TaliaB said:

I think you are missing the point. There is absolutely nothing wrong with the Kodak inverters, in fact there are 1000 of Kodak inverters installed across SA with no problems. The point @Beatis trying to make is that the bms in the battery has failed causing the bloated cells. The bms gives the inverter instructions on charging profiles not the other way around. What happened in this case the bms failed and most probably gave an incorrect charge profile to the inverter and there was no way of telling the bms is faulty until you discover one expensive damaged lfp battery module. 

I'm not missing the point at all. As I understand it @Beat doesn't believe in have communication at all, not just in this case.

I know how exactly how a BMS works. If the BMS is giving the wrong settings to inverter then the battery should be returned as being unfit for use. It shouldn't have been taken apart as they are not going to accept it back like that.

Many people on here have problems with batteries going over voltage and most of the time it is either a cheap inverter, BMS communication not being set up correctly or wrong settings when their is no communication.

Removing BMS communication is not generally the correct solution. The BMS normally incorporates protection features to shut down the inverter if something is wrong before the BMS has to activate its own protection. In this case yes it could be a solution as the OP has removed the option of returning the battery but even then I wouldn't be happy at all to run it with a faulty BMS. The better solution is to replace the BMS with something like a JK.

The point I was making is that a BMS has excellent protection features that control inverters and they should be used not disconnected.

Edited March 31 by Tinbum

[Scorp007]

19 hours ago, Tinbum said:

I'm not missing the point at all.

Many people on here have problems with batteries going over voltage and most of the time it is either a cheap inverter, BMS communication not being set up correctly or wrong settings.The BMS normally incorporates protection features to shut down the inverter if something is wrong before the BMS has to activate its own protection. In this case yes it could be a solution as the OP has removed the option of returning the battery but even then I wouldn't be happy at all to run it with a faulty BMS. The better solution is to replace the BMS with something like a JK.

We all seem to be on the right track. It's just a matter of a faulty BMS and not the inverter that cased this problem based on what we know. Not a cheap inverter. The inverter did not get the correct instruction from the BMS. 

Most BMSes in the battery has no means to apply the right settings. That is as far as I have seen. Their settings are set by the factory. 

We just need to look at how many of a certain make of battery never switches off or stops charging when over voltage. This is also the reason the cells bulge but the manufacturer always blames the inverter and hardly ever accepts responsibility that it is the BMS that did not action its own protection before damage. 

Edited April 1 by Scorp007