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Unusual design concerns resulting in hot battery terminals with LiFePO4 batteries. Pro Power 12V 306Ah Lithium Batteries

Chris Down Under

New Member
Joined
Jan 11, 2023
Messages
19
Location
Victoria, Australia
Hi everyone,
Newbie here, but have been off grid since 2009. As part of the regular checks of the system I noticed that the battery terminals for my Pro Power 12V 306Ah LiFePO4 batteries were running hot - hot enough that you would burn your fingers if you left them there for a few minutes. Four of them are connected in series so as to power a 48V inverter. The maximum charge current from the solar panels is around 110A, but rarely are the batteries receiving such charge. Having been off grid a long time the batteries are rarely drawn down 20%, so most mornings they're more than 80% full - every day. I've used these batteries for about three years now and they are out of warranty. They still work, but the terminals are hot whilst the current for either charge or discharge is beyond 60A.
Being something of an old school tech geek, I cracked the case open so as to see what was going on inside causing the hot terminals.
Here's what I found:
IMGP0757.JPG

I never in my wildest dreams expected to see six 10AWG (6mm2) wires soldered onto the bottom of the battery terminal. And observant readers will note that the drizzle of glue indicates that the epoxy got hot enough that the terminal has now rotated. All very exciting stuff, and not something you'd want to see. The plan at this stage is to drill a hole in the top of the battery case, cut the wires, pull them through, lug them properly with M8 lugs and connect the lot to a 300A rated bus bar which will be attached to the lid of the battery. Not pretty, but it should work and the buss bar has 4x M8 lugs so that should spread the current a lot better.
The combination of metals in the current arrangement is probably bonkers. And soldering... Yikes!
I'm curious to hear if any of the readers have any thoughts as to this fix.
The inside of the battery surprised me too because it is a 6P/4S configuration and there are no less than six BMS systems inside the battery. You can count them. I really never expected to find this. Oh well. Here's a photo of the guts of the thing.
IMGP0758.JPG
At this stage, I will retire these batteries and use them in a less demanding system than the house power system. If anyone can recommend replacement 48V around 400A batteries I'd be appreciative. I like the look of the 100A rack mount batteries.
Thanks, and I'd appreciate any and all thoughts in this matter.
Cheers
Chris
 
Hi everyone,
Newbie here, but have been off grid since 2009. As part of the regular checks of the system I noticed that the battery terminals for my Pro Power 12V 306Ah LiFePO4 batteries were running hot - hot enough that you would burn your fingers if you left them there for a few minutes. Four of them are connected in series so as to power a 48V inverter. The maximum charge current from the solar panels is around 110A, but rarely are the batteries receiving such charge. Having been off grid a long time the batteries are rarely drawn down 20%, so most mornings they're more than 80% full - every day. I've used these batteries for about three years now and they are out of warranty. They still work, but the terminals are hot whilst the current for either charge or discharge is beyond 60A.
Being something of an old school tech geek, I cracked the case open so as to see what was going on inside causing the hot terminals.
Here's what I found:
View attachment 129015

I never in my wildest dreams expected to see six 10AWG (6mm2) wires soldered onto the bottom of the battery terminal. And observant readers will note that the drizzle of glue indicates that the epoxy got hot enough that the terminal has now rotated. All very exciting stuff, and not something you'd want to see. The plan at this stage is to drill a hole in the top of the battery case, cut the wires, pull them through, lug them properly with M8 lugs and connect the lot to a 300A rated bus bar which will be attached to the lid of the battery. Not pretty, but it should work and the buss bar has 4x M8 lugs so that should spread the current a lot better.
The combination of metals in the current arrangement is probably bonkers. And soldering... Yikes!
I'm curious to hear if any of the readers have any thoughts as to this fix.
The inside of the battery surprised me too because it is a 6P/4S configuration and there are no less than six BMS systems inside the battery. You can count them. I really never expected to find this. Oh well. Here's a photo of the guts of the thing.
View attachment 129016
At this stage, I will retire these batteries and use them in a less demanding system than the house power system. If anyone can recommend replacement 48V around 400A batteries I'd be appreciative. I like the look of the 100A rack mount batteries.
Thanks, and I'd appreciate any and all thoughts in this matter.
Cheers
Chris
Hi Chris - thanks for the show and tell. That is pretty fascinating. Having individual BMS is pretty wild. The wiring is much thicker than Inwould have guessed. My 48v, 16s BMS uses very thin wire to cut power to various cells.

I bought the EG4 LifePower4 100 Ah rack batteries and are so far happy with the build quality. Only time will tell if they last the 7000 rated cycles. If I can get 10 years will be happy with new technology by then. I think the price point is good enough to not mess with serial 12V solutions.

Cheers,
-Jay
 
Hi Jay. Thanks. Yeah, opening the case was an interesting exercise and I was considering doing a YouTube how-to clip showing how I did that step by step (with disclaimers, lot's of disclaimers - don't do this at home kids!) Do you have any thoughts about that?

Those were the exact batteries I had in mind, so I really appreciate the feedback. Unfortunately they're not available in Australia but are in the process of being certified. In the tear down videos on those EG4 batteries it looked like 16mm2 6AWG cable from the batteries to the terminals to me. Out of curiosity, have you ever noticed the cables or terminals running hot from your EG4?

I agree about the price point, and likewise am now only considering 48V options.

Cheers,
Chris
 
Hi everyone,
I fixed up the first of five batteries today and thought that a picture of the fix tells more than a thousand words ever could:
IMGP0802.JPG

As you can see, the 6 BMS wires now feed into a 300A bus bar all with M8 bolts which is attached to the battery lid. There are now only 2x BMS cables to each lug and the lug closest to the now defunct battery terminals is the main feeder and battery inter-connector point. Ran 50A through the bus bar to get some charge into the battery for about half an hour, and everything ran cool. What a relief that the fix works. A person shouldn't have to modify batteries, but then they are made to a price point. I have no idea how long these cells and BMS modules will last? Don't know, but problems after only three years of use - and gentle use too - are not good.

Incidentally, the thin wire is for the battery charger, the battery inter-connectors used in the house power system are 1AWG 50mm2.

It might be wise to get a couple of 48V 16 connector BMS modules and eventually convert the lot to a 48V 50A battery. Should be possible. Does anyone have any thoughts as to that option? The bus bars to the cells aren't welded from what I could see.

Cheers

Chris
 
Hi Jay. Thanks. Yeah, opening the case was an interesting exercise and I was considering doing a YouTube how-to clip showing how I did that step by step (with disclaimers, lot's of disclaimers - don't do this at home kids!) Do you have any thoughts about that?

Those were the exact batteries I had in mind, so I really appreciate the feedback. Unfortunately they're not available in Australia but are in the process of being certified. In the tear down videos on those EG4 batteries it looked like 16mm2 6AWG cable from the batteries to the terminals to me. Out of curiosity, have you ever noticed the cables or terminals running hot from your EG4?

I agree about the price point, and likewise am now only considering 48V options.

Cheers,
Chris
I will check the temps today and report back. Been meaning to pull out my thermal measuring device anyway.
 
I find the multiple BMS setup totally bonkers. Like what is the purpose? current sharing? You'd think one high amperage BMS would be cheaper than 6 low amperage units ?‍♂️
 
Hi Jay. How did you go?
As an update, finished adding the bus bars to the three other 12V batteries last night, and now I'm going to try balancing them all during the next week or two, whilst using them at the same time. Should be interesting! After the work involving the battery fix and swapping in and out of the spare battery, the balance of the pack of four batteries is a mess. The plan is to charge them at a slightly lower voltage to avoid over voltage and then draw off a couple of % charge each night from the battery with the highest state of charge for the next couple of weeks. Note to self: purchase a second lot of 51.2V batteries so that they can be removed and parallel balanced whilst the other bank drives the system. It's the things you don't think about which cause you to come unstuck. Cheers. Chris
 
Hi SparkyJJO. Mate, it's not just you, I didn't expect to find that arrangement inside the battery either. I'm coming around to the point of view that the batteries either need clear cases so that you can see what's inside, or have easily removable lids for inspection. The tear down videos from the host of this website are far more valuable than most people would realise. Cheers. Chris
 
Hi Jay. How did you go?
As an update, finished adding the bus bars to the three other 12V batteries last night, and now I'm going to try balancing them all during the next week or two, whilst using them at the same time. Should be interesting! After the work involving the battery fix and swapping in and out of the spare battery, the balance of the pack of four batteries is a mess. The plan is to charge them at a slightly lower voltage to avoid over voltage and then draw off a couple of % charge each night from the battery with the highest state of charge for the next couple of weeks. Note to self: purchase a second lot of 51.2V batteries so that they can be removed and parallel balanced whilst the other bank drives the system. It's the things you don't think about which cause you to come unstuck. Cheers. Chris
Hey Mate!

Sorry I slacked off and didn’t get your your temp report. I was helping my cousin run a new 100A service.Hope to do tomorrow.

You have more patience than me on balancing those batteries. Sounds like it will work out well.

Cheers!
-Jay
 
Are those BMS glued down directly to the cells without any insulation sheets between BMS and the cells?
What they have done is putting 6 battery packs into one case, and poor workmanship despite calling it 'Pro'.
I wonder how you would know if one or more BMS have gone into shutdown, the other BMS will have to carry the load when that happens.
 
Hi Jay,
Yeah, no worries at all mate. 100A is something which requires, err, a persons full attention.
Look forward to hearing about your experience with the temperatures on those terminals. It's something I've been wondering about.
Still balancing the batteries today. Taking off 10Ah at a time from the highest voltage battery. This job will take some time.
Cheers
Chris
 
Hi Bud,

Thanks for your thoughts with this issue. The 6x BMS were glued to the cells, and the cells were wrapped in some sort of blue clear-ish plastic. I was unable to determine whether a further layer of insulating material had been placed between the plastic and the underside of the BMS. My gut feeling suggests that the answer is NO. Not how I would have set the battery arrangement out.

And that was my exact thinking too. The large battery is actually six smaller batteries. Makes you wonder if the manufacturer simply scaled up the design from a 50A battery? Unfortunately, what I've learned over the years with off grid solar power is that scaling up a system works until new issues become apparent. Then you have to redesign the now larger arrangement to accommodate the new issues.

I'd also been wondering about that issue with the BMS setup. At the moment the multi-BMS arrangement seems to be working - and I tested a battery for over voltage - which is what I worry about most of all. And with the new bus bar, everything is running cool.

That's certainly possible if one of the BMS goes into shutdown, and I wouldn't know either. How could you?

The batteries are out of warranty and if I knew back then what I know now, I wouldn't have bought them. But there's no point chucking them into the bin either. Just have to get some additional battery storage for redundancy if and when one of the BMS modules fails, with 24 of them between four batteries, something will go wrong sooner or later don't you reckon?

I couldn't see any thermal sensors either, or thermal cut off switch. However, it may be on the BMS board for all I know, maybe.

Cheers. Chris
 
As a bit of an update, the four batteries survived the modification process and the terminals, lugs and cables and are now running cool.

IMGP0816.JPG

Those are 50mm2 cables linking the batteries and the markings on the green case are reflections. It ain't pretty, but it works.
 
If they did not put the insulation sheet between BMS and the cell bodies, if they did not trim those wires that are soldered to the BMS properly, I.E. the wire is trimmed but has pointy sharp end, and not short enough, they may be making contact with the cells but is being insulated by thin layer blue wrap for now, if your in mobile setup, the wires can cut through the blue wrap and short circuit by the shell metal body.
I would use them but keep close eyes on them.
 
As a bit of an update, the four batteries survived the modification process and the terminals, lugs and cables and are now running cool.

View attachment 129533

Those are 50mm2 cables linking the batteries and the markings on the green case are reflections. It ain't pretty, but it works.
they look a lot nicer than original picture to me at least from a safety standpoint for sure
 
Hi Bud,
Yes, not good. Fortunately the batteries won't be moved around at all, although removing the lid did require a bit of force.
Your comment got me wondering, and looking closely at the image it appears that the manufacturer used blobs of silicone as a glue between the BMS and the cells. However it does look like there is also some sort of beige material between the BMS and the cell.
A zoom in of the photo shows this:

BMS.jpg

Cheers. Chris
 
Hi labeeman,

The batteries are only three years old and out of warranty. I'm pretty sure that you could get high amp BMS circuits three years ago. If someone had done a tear down video of one of these batteries beforehand, I'd never have purchased the things (knowing what I know now). The tear down videos and these sorts of discussions are highly valuable to prospective purchasers of the equipment.

Cheers

Chris
 
Hi labeeman,

The batteries are only three years old and out of warranty. I'm pretty sure that you could get high amp BMS circuits three years ago. If someone had done a tear down video of one of these batteries beforehand, I'd never have purchased the things (knowing what I know now). The tear down videos and these sorts of discussions are highly valuable to prospective purchasers of the equipment.

Cheers

Chris
Yep you could get high amp BMS 3 years ago too bad you did not get to see a teardown of them before purchase I would not have bought them either
 

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