First battery in the series voltage low

[nezek88]

Hi guys,

I've got a 15kw offgrid system from China, cheap unbranded stuff and now, of course, I'm having issues...

So right now it feels as if the battery are running WAY to fast..
I have a 96V system with a paralleled series of 8 AGM 12v280AH(total16)

I've ran few tests with the batteries and what caught my attention is the first battery, closest to the Inverter load..

Below is the plan and all the readings I recorded:

Here is an unfinished chart of my layout (I'm waiting for information from the installer to complete the chart, as I have additional issue where breaker trip when connect the grid to the inverter).












1. Does this mean the battery is dead?
2. Can you guys spot any mistakes with this setup?
3. Anything better I could do?

Thanks,

Nezek

 

[sunshine_eggo]

1. It means your bank is out of balance. It might mean there's a problem with that battery. You will need to routinely monitor your bank, break it down and individually charge the 12V. Hopefully, you individually charged all the 12V before you put them in series.
2. It's a 96V system. Fundamentally, that's a mistake.
3. Break the banks down and charge the 12V individually. You'll probably need to do this regularly.

 

[Supervstech]

12.48 resting is a bad sign… what is the equalization schedule on them? What size cables are you using? How good are the connections?

Can we see some photos of your build? I have never seen someone parallel banks at a breaker junction…
That might be a place to start.

 

[12VoltInstalls]

1. Does this mean the battery is dead?

Answer:

1. It means your bank is out of balance. It might mean there's a problem with that battery.

before you declare an autopsy the batteries balance as indicated.
Monitor results.
(EDIT: deleted erroneous info i mindlessly typed pertaining only to parallel batteries)

2. Can you guys spot any mistakes with this setup?

You don’t mention cable size.
Or I missed it.

 

[Supervstech]

Basically, batteries in series need nigh perfect cables. Everything needs to be sized for minimum voltage drop, and be EQUAL in length. Perfectly clean, and very well maintained.
96V lead acid is going to be tricky to maintain.

 

[sunshine_eggo]

Answer:

before you declare an autopsy the batteries balance as indicated but mark the questioned battery. Put it on the other end on reassembly. Monitor results.
Long series runs hit the end batteries harder on charging and may lower effective charge on the middle batteries. On discharge, the end batteries take the brunt. Your 1KWh load may be presenting lower static voltage on the end battery because you’re reading the drop?

This is false. All batteries in a series circuit carry exactly the same current. That's how electricity works.

What you're saying is applicable to >2 STRINGS in parallel where end strings may share more of the current than middle strings, but again, each of the batteries in each string carry the exact same current.

String position can matter from a thermal perspective if the battery is tightly packed. End elements can have a thermal gradient across them (lead on one side, air on the other), which can degrade performance if the gradient is significant.

I would discourage the OP from shuffling the order of the batteries in strings. There is nothing to be gained.

You don’t mention cable size.
Or I missed it.

Good point. All connections should be checked as well.

 

[12VoltInstalls]

This is false. All batteries in a series circuit carry exactly the same current. That's how electricity works.

Yes. Hoo boy ?
I lost focus of the 96V and typed off the cuff. I deleted. ?
Thank you for pointing that out.

would discourage the OP from shuffling the order of the batteries in strings. There is nothing to be gained.

️

 

[justgary]

And this is exactly why I'm switching from 4s2p AGM to 16s LFP. Lack of a decent BMS for AGM batteries makes it very hard to run a system for an extended period without lots of manual tinkering and fidgeting.

 

[sunshine_eggo]

And this is exactly why I'm switching from 4s2p AGM to 16s LFP. Lack of a decent BMS for AGM batteries makes it very hard to run a system for an extended period without lots of manual tinkering and fidgeting.

There are 12V balancers that work very well. I have them on my 4S2P 48V Trojan bank. Every time I check them at any state, they are never more than 0.1V deviation among the 8. Following the initial full charge of the individual 12V prior to installation 18 months ago, I've never had to deal with a battery balance issue with these installed.

They're about $25 each, but it was completely worth it for me.

 

[justgary]

There are 12V balancers that work very well. I have them on my 4S2P 48V Trojan bank. Every time I check them at any state, they are never more than 0.1V deviation among the 8. Following the initial full charge of the individual 12V prior to installation 18 months ago, I've never had to deal with a battery balance issue with these installed.

They're about $25 each, but it was completely worth it for me.

Thank you for posting the link to that balancer.

 

[sunshine_eggo]

For 24V/48V systems, there are cheaper options. Search for "48V balancer." There are single units with multiple wires to the individual 12V that are about 1/4 to 1/2 the price. I've just used this brand on Lithium and have an inherent trust in it.

 

[Weldman]

So lining up about 12 of these should help the forklift battery I own ?‍

 

[sunshine_eggo]

So lining up about 12 of these should help the forklift battery I own ?‍

Only if you need it, and I doubt you do.

Since you're dealing with single cells, they tend to be a little more manageable. When dealing in 12V, you're only seeing the "net" of the 6 cells inside.

 

[nezek88]

1. It means your bank is out of balance. It might mean there's a problem with that battery. You will need to routinely monitor your bank, break it down and individually charge the 12V. Hopefully, you individually charged all the 12V before you put them in series.
2. It's a 96V system. Fundamentally, that's a mistake.
3. Break the banks down and charge the 12V individually. You'll probably need to do this regularly.

Hi sunshineeggo , thanks for replying and assisting..

1. how should I charge them individually? I have a 96v mppt charge controller
2. could you recommend reading material? why is it a fundamental mistake
a. should I change to a 48v? would I still be able to use all these batteries? from my understanding paralleling further will cause additional problems
3. again, how am I meant to charge them individually and how often would you recommend that I do that?

Also, you were recommending a load balancer to someone here, would that be something I could use too?

 

[nezek88]

2.48 resting is a bad sign… what is the equalization schedule on them? What size cables are you using? How good are the connections?

Can we see some photos of your build? I have never seen someone parallel banks at a breaker junction…
That might be a place to start.

I'm not sure how the equalization work, it seems to have a setting for it in the MPPT and I can contact the seller for more information as the owner manual doesn't say anything about it :-(

There are the settings:


I'm using 25mm cables for everything you see in the original draw. MPPT to Combiner and panels are all 10MM
For the connections I'm using 25-12 LUG that bolts on the battery so that's ok I spouse?


build photos follow by breaker junction:

 

[Supervstech]

Ah…
Your pictures show everything…

All cells in series need EXACTLY the same length conductors between each battery… impossible with the rack you have,
Each set needs to be paralleled with cable able to flow the ENTIRE amp load without voltage drop.
You need a rack where you can set the series run batteries directly against each other.

 

[sunshine_eggo]

Hi sunshineeggo , thanks for replying and assisting..

1. how should I charge them individually? I have a 96v mppt charge controller

With a 12V battery charger.

2. could you recommend reading material? why is it a fundamental mistake

Victron's Wiring Unlimited in the Resources section.

To elaborate, it is critical that all components of a series battery be as identical as possible - brand, model, age and especially... stage of charge.

A 96V charger only knows how to charge 96V. Its not going to know or care if some of the batteries are 11V and others are 13V. It's going to do its thing. The ones that are higher voltage are likely going to be overcharged and damaged, and the ones that are lower voltage are likely undercharged and damaged.

The fact that you don't have a 12V charger says you didn't fully charge them prior to putting them in series. This project has had some level of doom from the start.

a. should I change to a 48v? would I still be able to use all these batteries? from my understanding paralleling further will cause additional problems

Changing to 48V would necessitate replacing your inverter/MPPT.

8S is double the issue that 4S is.
4S4P is easier to manage than 8S2P. You only have to worry about 4 series strings.

3. again, how am I meant to charge them individually and how often would you recommend that I do that?

See #1.

As often as they need it.

Also, you were recommending a load balancer to someone here, would that be something I could use too?

That would work for you, but it would potentially be another $400 you didn't need to spend, BUT it could also be used if you decide to switch to 48V.

I'm not sure how the equalization work, it seems to have a setting for it in the MPPT and I can contact the seller for more information as the owner manual doesn't say anything about it :-(

AGM generally shouldn't be equalized in the traditional sense. Flooded lead acid (FLA) are more over-charge tolerant and can have their electrolyte replenished if it boils off. FLA can be taken to higher voltages safely and equalization can allow the lagging batteries to "catch up."

AGMs are sealed. If they lose electrolyte, it's permanent. In some cases AGM batteries have limited equalization that is far less aggressive than the typical flooded style.

I'm using 25mm cables for everything you see in the original draw. MPPT to Combiner and panels are all 10MM
For the connections I'm using 25-12 LUG that bolts on the battery so that's ok I spouse?

Given the high battery voltage, thinner conductors is likely not a concern.

I do have concern with how you've wired the banks. Once you read the Wiring Unlimited concerning paralleling batteries, you'll either realize you did it right, and I can't tell from the pictures, or you did it wrong.

 

[12VoltInstalls]

AGM generally shouldn't be equalized

I noticed that the settings posted seemed to be an ok range for AGM - 116.8 is 14.6 equalize versus 14.5V “constant charge.”
Is that correct?

settings:

I'm using

 

[sunshine_eggo]

I noticed that the settings posted seemed to be an ok range for AGM - 116.8 is 14.6 equalize versus 14.5V “constant charge.”
Is that correct?

Shouldn't be too harmful if at all. EQ with AGM is not particularly effective. Some batteries actually spec it out at a higher voltage, but it's something that should be done very carefully and infrequently.

 

[nezek88]

Shouldn't be too harmful if at all. EQ with AGM is not particularly effective. Some batteries actually spec it out at a higher voltage, but it's something that should be done very carefully and infrequently.

I'm getting a 12v charger tomorrow, I'm basically just charging them, individually, one by one - equalizing them for about 5 hours? @ about 14.5V?