acdoctor
Solar Enthusiast
On my 280s from 3.55 to 3.65 is only a few minutes, virtually no capacity difference. So if most were at 3.55 and 1 hit 3.65 I don’t think it would bother me.
I don't charge that high, I have bulk set to 55.4 or so I think, Used to be higher but backed it off a while back for longevity (hopefully).On my 280s from 3.55 to 3.65 is only a few minutes, virtually no capacity difference. So if most were at 3.55 and 1 hit 3.65 I don’t think it would bother me.
The alligator clip leads from the power supply might explain that. Numerous reports of people having problems that are easily resolved with a larger gauge wire and ring terminals.Hmm, the max output of that supply as 10a and it never got close to that, hence why it took so long to top balance the pack.
I upgraded those after reading the same which is how I got it up to about 6a, ran double leads to test also, I think it was just the supply.The alligator clip leads from the power supply might explain that. Numerous reports of people having problems that are easily resolved with a larger gauge wire and ring terminals.
0.05v in the JK BMS, which I think is 50mv and seems to be based on what i am seeing from the BMS and balancing trigger at the moment?
What's accepted as OK cell differences?
i would set this may be a bit lower as the heltec balancer, and make it stop at the point where the bms active balancer comes on ..I also see the Heltec has some pads that can be wired for a switch, meaning I could put a relay on it and only have it turn on when pack is above X volts which is another option is it's a higher amp balancer.
What do people consider acceptable cell delta's in larger capacity packs like this?
Active balancer that is active below 3.4v will unbalance your cells. Stop already with the Heltec. Make sure your JK does not balance below 3.4v. You need to top balance again (just the JK will work, but patience is required). Get all of the cells above 3.6v, let the active balancer portion of the BMS work and you will be good. The Heltec tries to balance your cells all of the time and has undone your original top balance. Looks also like you have some minor connection problems from the readings on the resistance of your BMS wiring.- That pic is the first day it went in to service, so there was no additional balancer then. the red wires are the BMS sense/balance leads.
- I used both balancers for a few months, but prior to that it has lived with 1 balancer it's whole life, it's back to 1 balancer now, the Heltec stand alone.
- Washers are only on the top of the last fitting between it and the nut, that comment is just to say they are where they should be.
- No rating was given on the bus bars, but I was advised that double stacking reduced any risk of overloading them, I guess it also allows the potential for increased and uneven resistances between the cells?
- The heltec specs imply it's always on above 3v, but current ramps up as the voltage differences increase.
3S-21S 5A Capacitive active equalization/Active Balancer
[vc_row][vc_column][/vc_column][/vc_row]heltec-bms.com
- I had the BMS balancer originally only working above 3.3v but with any cell delta above .05 it would be working, so basically all the time.
In my head though, to see a cell going HVD and LVD means it just has less capacity than those around it yes? Unless there is something to the resistance comment I made earlier, those cells have higher resistances and all have increased (bad internal resistance/failing cells etc).
Quite true. Once you get above 3.45v the power stored above that is at most 1 or 2 amp hours, and above 3.55v you are talking maybe 0.1 amp hours.On my 280s from 3.55 to 3.65 is only a few minutes, virtually no capacity difference. So if most were at 3.55 and 1 hit 3.65 I don’t think it would bother me.
There might be more too it as the problem continues. Last night under a 2.7kw load I had cell 12 dipping noticeably so went down with the Fluke 325 and checked that cell and confirmed it was genuinly a solid .1 .2 v below the other cells under load 3-3.1v vs 3.2-3.3v in adjacent cells. So either the balance is WELL out or I do have some actual cell issues, the thing that gets me is if it was a cell problem why does the problem cell move around so much.Active balancer that is active below 3.4v will unbalance your cells. Stop already with the Heltec. Make sure your JK does not balance below 3.4v. You need to top balance again (just the JK will work, but patience is required). Get all of the cells above 3.6v, let the active balancer portion of the BMS work and you will be good. The Heltec tries to balance your cells all of the time and has undone your original top balance. Looks also like you have some minor connection problems from the readings on the resistance of your BMS wiring.
Despite what Andy says, an active balancer is not needed for anyone who fully charges on a regular basis. I use one to help with the initial top balance and then take it off.
No need to let cells rest for more than a few hours when top balancing, letting them sit at 100% is one of the worst things you can do for longevity and causes degradation quickly.
I'll have to check to be sure, I can remove it but it was a recommendation on here and given the the need for a washer between the bus bar and the balance lead (due to holes size on the buss bar) it seemed like a good idea.Labeling isn't a bad thing.
It is possible you have some oxidation of the aluminium cell terminals causing you some issues. Does your copper grease have antioxidant properties?
There might be more too it as the problem continues. Last night under a 2.7kw load I had cell 12 dipping noticeably so went down with the Fluke 325 and checked that cell and confirmed it was genuinly a solid .1 .2 v below the other cells under load 3-3.1v vs 3.2-3.3v in adjacent cells. So either the balance is WELL out or I do have some actual cell issues, the thing that gets me is if it was a cell problem why does the problem cell move around so much.
I am going to have to pull the pack and top balance it to be sure, at which point I'll remove the Heltec and leave the JK doing it;s thing above 3.4v.
The thing with the Heltec, and I've tested this it moves barely any current unless there's an actual cell difference. The 325 has a clamp meter so I've measured this. I've never seen anything more than 3 being shuffled into cell 12 and when there's no load on the pack it's doing basically nothing, .1a etc
Re connections, I noted the balance wire leads are not a perfect fit for the studs, so I was considering re terminating each wire with a new terminal that exactly fits the stud. Of course this also means biting the bullet and labelling all of the individual balance leads first so I know where they go back :'(
No, you should not have a washer between the bus bar and the balance lead ring terminal. Use a better ring terminal on the balance lead.
Depending on how long you had the Heltec connected, they could be extremely out of balance, yes.
How to top balance (3 Pre-charging the cells to get them ‘mostly’ charged.):
Top Balancing LiFePo4 Cells using a low cost benchtop power supply.
To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...diysolarforum.com
Excellent resource, I highly recommend the pre-charge process to help speed things up (i.e. using a BMS to charge until a cell hits HVD, keep the HVD set at 3.65v please, don't try and set it higher).
Explanation of why you want to top balance (sounds like you already know why):
https://diysolarforum.com/resources/explanation-for-beginners-of-top-and-bottom-balance.127/
A little bit of current adds up when done 24 hours a day, 7 days a week.
If you are in the USA, 1/4 inch will work fine, much easier to find than 6 mm ring terminals.
Judging by some of the readings you have shown, cutting off your existing connections and putting on new ones would help. It certainly wouldn't hurt as long as you verify they are good. A decent meter is your friend in this case to measure the resistance of each connection.
These are what I've been using for balance connections, although if memory serves me correctly, the JK uses larger wires than most due to having an active balancer.
26-24 Ga. Heat-Shrink Ring Terminals, 1/4" Stud
26-24 Ga. Heat-Shrink Ring Terminals, 1/4" Stud For use in harsh environments, these terminals feature a heat shrink connection that also has an internal sealant. After crimping the terminal onto the wire, simply apply heat. Keeps moisture out while ensurcrimpsupply.com
I'm thinking almost certainly on cell 12 so I'll remove those studs and chase the thread to clean it out.Do you have grease hydrolicly compressed in the bottom of the terminal preventing the stud from bottoming out?
I'm starting to wonder if the carbon grease is allowing these connections to back off/move with hot/cold cycles.
Re the terminal posts, they are only M4 studs and the busbar holes are actually slots to allow for sideways movement meaning the balance need connections, when tightened down can deform into the slot a little which is why the washers were there.
I considered putting the balance leads underneath but then you have busbar making contact with the post of the terminal only and not the rest of the cell terminal surface area.