If you're interested in having the JBD/Overkill BMS activate and disable an external active balancer at certain cell voltages, have a look at the work we've been doing over on this thread: https://diysolarforum.com/threads/active-balancer-make-it-smart-💡.40192/post-731612
Problems with keeping 302Ah in balance
- Thread starter T3TRIS
- Start date
T3TRIS
New Member
- Joined
- Feb 22, 2022
- Messages
- 28
Alright, new update. I've installed the 5A balancer (so easy!!!) and I think it works, at least the little diode is on.
I put a 25A load on the batter for 20min or so to try to shave off some of that cell saturation, then re-connected the charger. The charger chugged along at 30A, as expected, until cell #3 reached 3.65V. The rest of the cells were at #1: 3.606V, #2: 3.533V (119mV behind) and #4: 3.567V
Total voltage of the pack was 14.35V. The charger is set to AGM, so my assumption is that it will spit out however many amps the battery asks for until they kinda reach some saturation.
If the balancer is working, it would seem that 5A is not enough to even out the cells for the amps coming from the charger to taper down, as it's supposed to do in the charging profile. That's mostly what bothers me... This battery is much more likely to be charged at 100% than to be discharged to 0%. If that 100% happens often, I'd rather have the charger stop the charge than rely on the BMS's mosfet (wouldn't want one of those to fail).
Maybe I'll look into the voltage sense relay that someone else suggested. That'd stop the charge, but again, ideally I'd like the charger to do that as it was designed!
I started a 25A capacity test last night too and got around 281Ah before the BMS triggered (set the value to 2.65V).
Now I'm charging the battery again at 30A. That discharge and the following charge are done with the active 5A balancer. We'll see how that goes.
I did tip the battery briefly and heard quite a bit of gurgling! Got me panicked for a minute until I read a few posts saying that it's mostly normal... Still weird though.
Several questions then:
1. Is Redarc wrong in making their Lithium charge voltage 14.5V?
2. Is there an easy way to check if this works properly?
3 bonus question: Am I still chasing perfection? I'm just not really happy with the end of 100% charge being controlled by the BMS rather than the charger.
I put a 25A load on the batter for 20min or so to try to shave off some of that cell saturation, then re-connected the charger. The charger chugged along at 30A, as expected, until cell #3 reached 3.65V. The rest of the cells were at #1: 3.606V, #2: 3.533V (119mV behind) and #4: 3.567V
Total voltage of the pack was 14.35V. The charger is set to AGM, so my assumption is that it will spit out however many amps the battery asks for until they kinda reach some saturation.
If the balancer is working, it would seem that 5A is not enough to even out the cells for the amps coming from the charger to taper down, as it's supposed to do in the charging profile. That's mostly what bothers me... This battery is much more likely to be charged at 100% than to be discharged to 0%. If that 100% happens often, I'd rather have the charger stop the charge than rely on the BMS's mosfet (wouldn't want one of those to fail).
Maybe I'll look into the voltage sense relay that someone else suggested. That'd stop the charge, but again, ideally I'd like the charger to do that as it was designed!
I started a 25A capacity test last night too and got around 281Ah before the BMS triggered (set the value to 2.65V).
Now I'm charging the battery again at 30A. That discharge and the following charge are done with the active 5A balancer. We'll see how that goes.
I did tip the battery briefly and heard quite a bit of gurgling! Got me panicked for a minute until I read a few posts saying that it's mostly normal... Still weird though.
Several questions then:
1. Is Redarc wrong in making their Lithium charge voltage 14.5V?
2. Is there an easy way to check if this works properly?
3 bonus question: Am I still chasing perfection? I'm just not really happy with the end of 100% charge being controlled by the BMS rather than the charger.
Last edited:
5 amp balance would need 500 mV cell differential. At those number closer to 800mA would be the balance current and it will take some time. You are charging 40+ times faster than the balancer can compensate.
Give it a couple weeks at least. Then check in with some new numbers. Or get out that balancing power supply back out and charge the full battery at 1 amp for the last 5% overnight.
Give it a couple weeks at least. Then check in with some new numbers. Or get out that balancing power supply back out and charge the full battery at 1 amp for the last 5% overnight.
houseofancients
Solar Wizard
lower your charging amps to about 5-10a and give it about 1 hour.
furthermore remember not to leave the balancer connected.
manually start the balancer when cells hit 3.45 high, disconnect it after done.
you could solder an on-off switch to it to make that a bit easier
sunshine_eggo
Happy Breffast!
3.533-3.650V is a pretty insignificant imbalance.
Lower absorption to 14.2V and increase time to 1 hour.
Lower absorption to 14.2V and increase time to 1 hour.
T3TRIS
New Member
- Joined
- Feb 22, 2022
- Messages
- 28
Ok, I read that before. Some people say to leave it running all the time and some others say only while charging and above 3.4V. The balancer I got isn't all that fancy... Is it really a problem to leave these connected 24/7? This is an oversized battery for the application.
As far as adjusting the charging voltage, I don't have that luxury. It's controlled by the Redarc Manager30 which can only define charging profiles based on battery chemistry. I wrote some of the details here but I can't control output current or voltage (safe for saying its GEL/AGM at 14.4V charge and 13.5V float, or Lithium at 14.5V charge and 13.6V float). I'm not sure what the charger does in the background, but it happily fed 30A to the battery in either mode, as if the cells were just thirsty for it!
timselectric
If I can do it, you can do it.
- Joined
- Feb 5, 2022
- Messages
- 18,551
Internal cell resistance changes with SOC.
A Balancer working at a lower SOC actually increases the delta at the higher SOC. It works against the goal.
A Balancer working at a lower SOC actually increases the delta at the higher SOC. It works against the goal.
houseofancients
Solar Wizard
and badly too
Alkaline
Solar Wizard
good on the balancer, I say leave it connected and see how you like it. They made different versions of this the only I have stops working any time the average voltage goes below 2.9v.
I never had an issue with the AB as long as I would fully charge the battery. it works best on the upper SOC range when they are 3.6v. I never had an issue leaving it on it basically does nothing in the 3.3v range.
Note you may have small additional draw on your cells, but at 300AH I doubt it makes any difference.
So yeah keep it on and keep the charger on they will all balance out.
I never had an issue with the AB as long as I would fully charge the battery. it works best on the upper SOC range when they are 3.6v. I never had an issue leaving it on it basically does nothing in the 3.3v range.
Note you may have small additional draw on your cells, but at 300AH I doubt it makes any difference.
So yeah keep it on and keep the charger on they will all balance out.
Alkaline
Solar Wizard
You need to hit the 3.6v ranges for it to work, when the cell is 3.4 and the others are 3.3 it basically does nothing. It only works when the voltage difference is big and you only get that when 1 of the cells is full.
Just leave it plugged in and see how you like it vs plug in and off (pain in the ?) I'm sure you could get may be a little better balancing flipping it on/off but for me I would just fully charge my pack once a month and it would balance all the cells it usually took 2 hours or so to balance even shaddy grade B/C xuba cells.
houseofancients
Solar Wizard
not used to you giving bad advise on cells alkaline..
do have to add, if OP has one that stops at 3.9 , it wouldnt matter as you said, but i think they only made that for a specific aussie reseller.
the other option would be a neey , but that would mean a reorder
Alkaline
Solar Wizard
Go to alibaba and has contact the hankzor store they have a version that stops at 2.9v its the same price they also have a version that stops at 1.8v available to anyone.
Alkaline
Solar Wizard
To clarify, that Active balancer will not stop if ANY SINGLE cell falls below 2.9v, only when the average voltage in the capacitors falls to this level. So if you have a situation where 1 cell is say 2.5 and the other 3.3 it will still keep working because the average voltage would be like (3.3 + 3.3 + 3.3 + 2.5 )/ 4= 3.075v
timselectric
If I can do it, you can do it.
- Joined
- Feb 5, 2022
- Messages
- 18,551
They need to offer one that stops at 3.4v
Who drains their cells to 2.9?
It's basically never off.
Who drains their cells to 2.9?
It's basically never off.
houseofancients
Solar Wizard
exactly..
one would want one to start at 3.45, and stop latest at 3.37.
ideally on would want the bms to control that like the jk does, or that custom one from australian
with the neey one can set that up as it is "smart"
Alkaline
Solar Wizard
3.4? You would never balance anything my guy... most of my cells chill out at like 3.35v just idling, Like as soon as I take them off the charger with in like 10-20 mins they are in 3.35 range and stay there.
I think 3.1 - 3.65 is fine the only mode I would like is for the AB to be off when battery is discharging no other mode, during discharging is where you can have voltage difference as high as 100-200 milivolt and this is where the AB makes the situation worse because it has no idea the batt is under a load.
timselectric
If I can do it, you can do it.
- Joined
- Feb 5, 2022
- Messages
- 18,551
You're not top balancing below 3.4v. You're actually un-balancing.
I do agree that you should only be balancing while charging.
12VoltInstalls
life passes by too quickly to not live in freedom
That may be merely your mindset. Other experienced folks say not to worry, and ‘nominal’ is a good word. The customer should never run the extremes you did and I personally have the opinion you are delivering 100% of what you promised.
Don’t let your OCD bring you to the point of discounting your good work.
T3TRIS
New Member
- Joined
- Feb 22, 2022
- Messages
- 28
Thanks again for all the inputs and the OCD reality check 
Here's where my OCD seems to pay though... I swapped the 302Ah CATL cells for the 280Ah EVE cells that I had laying around. Did a top balance on those followed by a quick capacity test (around 274Ah). The cells' voltages were never more that 5mV apart during the capacity test (except at the extreme of course) and during the following recharge.
I've now set my power supply to 14.48V at the end of the leads and cranked it up to 50A. Those 280Ah cells are doing just fine and now have just been "sipping" current and balancing themselves at the top end. It's been like that for a good 20 minutes now and no over-voltage was triggered. All the cells are above 3.600V and the 5A active balancer is disconnected... And that's also despite cell #4 being behind by almost 70mV at some point...
I'm going to deliver this battery with these 280Ah cells instead of the 302Ah. The 302Ah didn't test any better than these anyway and these seem to work MUCH better. I'm happy with this functioning like this instead of having the BMS limit the upper threshold of charging.
So... yeah. Not too sure what to make of all this except that my 302Ah cells seem to definitely NOT be "grade A" (I know it's kind of a made up term). I'm definitely OCD, yes... but this different result is tough to argue.
By the time I finished writing this, the batteries were still taking a charge and balancing using ONLY the Overkill Solar tiny bleed resistors:
Cell 1: 3.635V
Cell 2: 3.636V
Cell 3: 3.606V
Cell 4: 3.617V
Apparently these tiny bleed resistors are enough to balance 280Ah when they are matched and top balanced properly.
Here's where my OCD seems to pay though... I swapped the 302Ah CATL cells for the 280Ah EVE cells that I had laying around. Did a top balance on those followed by a quick capacity test (around 274Ah). The cells' voltages were never more that 5mV apart during the capacity test (except at the extreme of course) and during the following recharge.
I've now set my power supply to 14.48V at the end of the leads and cranked it up to 50A. Those 280Ah cells are doing just fine and now have just been "sipping" current and balancing themselves at the top end. It's been like that for a good 20 minutes now and no over-voltage was triggered. All the cells are above 3.600V and the 5A active balancer is disconnected... And that's also despite cell #4 being behind by almost 70mV at some point...
I'm going to deliver this battery with these 280Ah cells instead of the 302Ah. The 302Ah didn't test any better than these anyway and these seem to work MUCH better. I'm happy with this functioning like this instead of having the BMS limit the upper threshold of charging.
So... yeah. Not too sure what to make of all this except that my 302Ah cells seem to definitely NOT be "grade A" (I know it's kind of a made up term). I'm definitely OCD, yes... but this different result is tough to argue.
By the time I finished writing this, the batteries were still taking a charge and balancing using ONLY the Overkill Solar tiny bleed resistors:
Cell 1: 3.635V
Cell 2: 3.636V
Cell 3: 3.606V
Cell 4: 3.617V
Apparently these tiny bleed resistors are enough to balance 280Ah when they are matched and top balanced properly.
Similar threads
