LifePo4-Request for advice about cell balancing?

[Samro]

But the delta ran away even at 13.8V?

 

[Raul a/3]

But the delta ran away even at 13.8V?

That shows imbalance, it only shows when cells start to fill up, from 3.45v up.
Have a search on YouTube for Andy’s Off grid garage , from Australia. That guy has a ton of tests and I mean lots with real life data and busting myths. Browse trough his videos, and pay attention how you balance a pack, and what are the voltages mean.
There is another guy Up North and personal,

I have built 5 packs so far, the longest to balance was one of the 280ah 16cell I built, and it was done within 3 days, just with the bms and active balancer. The second I had trouble with, was a 12v pack with 300ah B grade cells, I had to re do the buss bars as I had a bad contact/ high resistance on one terminal. That was throwing the balance off.

 

[Samro]

I have done much research. Take a look at this:

 

[Raul a/3]

Sorry that link does not work for me.

 

[Samro]

Had a moment where I turned into my dad! I've edited the link to work.

 

[Raul a/3]

That’s the guy, make sure you don’t get confused with the early findings, what he does, he tests for different scenarios.

 

[Samro]

I'll post a screenshot at 14.2V. Hopefully showing a better aligned set of cells.

 

[Raul a/3]

To help your balancer, make sure you don’t overwhelm it with a high charging rate. From 13.8v if there is a imbalance, ideally current should be small under 0.05C so it doesn’t trigger the HVD. If it does trigger it, it will slow the balancing process.

 

[Samro]

I've been charging at 10A for as long as I can remember with an absorption voltage of 13.8V to prevent the HVD. Tye delta has always been higher than 0.3V at the end of the 60 minute Absorption time. I will set my absorption voltage to 14V and see where I am at, but hoping the delta will be much reduced following my recent action. You have now made me worry that this won't be the case!

 

[Raul a/3]

Only one way to find out, under pressure.

 

[Samro]

Well that's annoying...Woke up this morning to this!

 

[Samro]

.....and yes Raul. I did follow your advice not to exceed 0.05C.
I am unsure if I am more annoyed that I posted what I've done on a public forum, or the fact that I've now got to remove the battery to resolve properly!

 

[Raul a/3]

Don’t worry, I have seen worse, cell 4 it’s full, and it will peak until the rest will catch up. Remind me what’s the capacity of this battery?
Xioxiang app indicates a JBD bms, if that’s correct, balancing 100ma, or 10hrs of balancing for one Amp to be shaved off.
Can you open the battery? A second best option is to fit a Heltec active balancer, with a manual switch.

 

[Samro]

It's a JBD BMS. 200Ah. I think the balancer is only 50ma.
The switched belted active balancer sounds like it would be the way ahead.
In the meantime I have changed the BMS settings to hopefully balance out the pack.

 

[Samro]

BTW.. What does the "belted" bit mean?
Do you have a suggested active balancer that you know to be reliable?

 

[Raul a/3]

Sorry was a autocorrect mistake, I meant Heltec, it’s the make of the balancer. You can get a 4s 2A quite cheaply now, or even a 5A for large capacities. If it’s only 200ah, a 2A will do the job.

With the 50ma balancing, 2% missing, that would be 4ah , approximately 80hrs of balancing with the existing setup. Look for a Heltec active balancer 2 or5A. Even if you remove it after you done it’s worth it.

Something like this

1.2A/5A 3S 4S 7S 10S 13S 17S Active Equalizer Balancer Lifepo4/Li-ion Battery | eBay

1x 1.2A LED Active Equaliser (choose the number of cells above). 1 Active Equaliser. Universal; suitable for LiPo, Li-Ion, LiFePO4 and LTO batteries. The build-up of waste heat may also limit the rate at which equalisation can occur.

www.ebay.co.uk

 

[Samro]

Sorry was a autocorrect mistake, I meant Heltec, it’s the make of the balancer. You can get a 4s 2A quite cheaply now, or even a 5A for large capacities. If it’s only 200ah, a 2A will do the job.

With the 50ma balancing, 2% missing, that would be 4ah , approximately 80hrs of balancing with the existing setup. Look for a Heltec active balancer 2 or5A. Even if you remove it after you done it’s worth it.

Something like this

1.2A/5A 3S 4S 7S 10S 13S 17S Active Equalizer Balancer Lifepo4/Li-ion Battery | eBay

1x 1.2A LED Active Equaliser (choose the number of cells above). 1 Active Equaliser. Universal; suitable for LiPo, Li-Ion, LiFePO4 and LTO batteries. The build-up of waste heat may also limit the rate at which equalisation can occur.

www.ebay.co.uk

Placed the order on e-Bay for the Heltec 4s 5A.
I suppose it will now be a case of removing the front seat to access the battery. The battery is a Roamer Gen 1 under-seat battery. I'll be interested to work out how i use this new device when it arrives.

 

[Raul a/3]

Placed the order on e-Bay for the Heltec 4s 5A.
I suppose it will now be a case of removing the front seat to access the battery. The battery is a Roamer Gen 1 under-seat battery. I'll be interested to work out how i use this new device when it arrives.

I can guide through, its easy and straight forward.

 

[Samro]

Good news! Whilst waiting for the battery balancer to arrive from eBay, I happened to leave my van on charge last weekend and I noted that the cells all balanced within 3mV at the end of the absorption stage. (Delta of 0mV to 1mV when in float!)

The charger absorption voltage had been set at 13.8V and the BMS settings had been set "Not to balance when charging". (Since @Raul a/3 and @Ajpepe72 suggested this change yonks ago.)

However, this weekend there was a difference in the charger settings - I had made an inadvertent change to my Multiplus setting, where the absorption duration was set to 8 hours with a repeat every 0.25 days. This extended absorption duration (In conjunction with the low absorption voltage and BMS setting), seems to be what was finally caused the cells to balance .

After noting the balanced cells, I discharge the battery fully and charged up again at 30A and the Delta remained nice and small, never exceeding 10mV.

I then reduced the "Delta to balance" from 10mV to 5mV and again discharged the battery and recharged and the Delta is now even closer to zero whilst charging and at rest.
I repeated this, gradually creeping the absorption voltage up to 14.2V, and the Delta did not run away, but reduced from 24mV to 15mV by the end of the absorption duration at 14.2V.

So, the mere threat of a cell balancer made my problem go away!

I now have questions for @Raul a/3:

1. Should I reduce the absorption duration from 8 hours to 1 hour as per Roamer Batteries recommended settings?
2. If so, should I now change the BMS setting to only balance on charging?

It is unusual to have my battery on charge for expended periods and so realistically the cells will spend more time balancing when driving (From DC-DC charger). I rarely drive for longer than 3 - 4 hours and so I'm concerned that if I now leave the BMS to only charge when no current flows the cells will get out of balance again. If I set the absorption voltage for the DC-DC charger at 13.8 Volts to reduce battery wear, and set the BMS to "Only balance when charging", the cells will spend more time balancing. Is this correct?

BTW - The battery only ever charges to 14.2 Volts if plugged into to shore power. Both Solar and DC-DC charge to 13.8V with a absorption of 1 Hour.

I would appreciate your views on this?

 

[Raul a/3]

Good news! Whilst waiting for the battery balancer to arrive from eBay, I happened to leave my van on charge last weekend and I noted that the cells all balanced within 3mV at the end of the absorption stage. (Delta of 0mV to 1mV when in float!)

The charger absorption voltage had been set at 13.8V and the BMS settings had been set "Not to balance when charging". (Since @Raul a/3 and @Ajpepe72 suggested this change yonks ago.)

However, this weekend there was a difference in the charger settings - I had made an inadvertent change to my Multiplus setting, where the absorption duration was set to 8 hours with a repeat every 0.25 days. This extended absorption duration (In conjunction with the low absorption voltage and BMS setting), seems to be what was finally caused the cells to balance .

After noting the balanced cells, I discharge the battery fully and charged up again at 30A and the Delta remained nice and small, never exceeding 10mV.

I then reduced the "Delta to balance" from 10mV to 5mV and again discharged the battery and recharged and the Delta is now even closer to zero whilst charging and at rest.
I repeated this, gradually creeping the absorption voltage up to 14.2V, and the Delta did not run away, but reduced from 24mV to 15mV by the end of the absorption duration at 14.2V.

So, the mere threat of a cell balancer made my problem go away!

I now have questions for @Raul a/3:

1. Should I reduce the absorption duration from 8 hours to 1 hour as per Roamer Batteries recommended settings?
2. If so, should I now change the BMS setting to only balance on charging?

It is unusual to have my battery on charge for expended periods and so realistically the cells will spend more time balancing when driving (From DC-DC charger). I rarely drive for longer than 3 - 4 hours and so I'm concerned that if I now leave the BMS to only charge when no current flows the cells will get out of balance again. If I set the absorption voltage for the DC-DC charger at 13.8 Volts to reduce battery wear, and set the BMS to "Only balance when charging", the cells will spend more time balancing. Is this correct?

BTW - The battery only ever charges to 14.2 Volts if plugged into to shore power. Both Solar and DC-DC charge to 13.8V with a absorption of 1 Hour.

I would appreciate your views on this?

1. Yes, 1hr is more than enough absorb at 14.2v. I absorb 40mins at 14v, and get fully charged, and balanced.

2. No, it should balance all the time, the two triggers for balance should be: cell start balance 3.45v and cell delta 5mv. That’s it, and let it balance all the time. Once the delta comes down below 5mv, it will stop balance, and will only start if a cell exceeds 3.45v.
After a while, you will see the cells will be staying in balance better.