yes this is because internal resistance is going up faster @ a higher amp charge. basically you are not actually hitting 57.4 AT THE BATTERY. use the onboard volt meters on the battery and you will see this. you are probably managing to charge the actual battery to a higher voltage with a lower a charge, but on the charger side a higher imput amperage will result in a higher voltage reading. if you add up the 4 readings on the onboard digital display on the battery, you will get a more accurate( and probably lower) reading
New Battery on Amazon and Ebay - Global Power 12V100AH LIFEPO4 - $399! Has anybody actually bought one yet? Torn it down yet?
- Thread starter Indepthdude
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SolarRat
Solar Addict
I wonder what happens when a fully balanced battery reaches 3.45 per cell. I guess there must be a certain voltage differential between cells for it drain a cell...well, I'd hope! I wonder what that differential is? 100mV? Yikes.
Yes, I'm using a bench supply and feeding .25-.5a. It doesn't seem to matter, as these cells are practically already in the knees at 3.45v, so the voltage of the highest cell quickly (minutes) rises to the 3.65 cutoff anyway.. You'd think feeding .23a into what I measured as a .225a drain would slow it down, but nope.
I haven't seen more than two lights yet. It seems cells 1 and 4 might be paired somehow...same with 3-4.
I can’t actually see the volt meters on the batteries because of where they are installed but I can check each of the voltages with a voltmeter easy enough. I’ll try that when I get the time to do another cycle test. The batteries hold at 57.2 for a decent amount of time so I should be able to get a reading.
SolarRat
Solar Addict
Right, but that is what scares me. If ALL cells above 3.45 get shunted to ground then any charge above 13.8 is creating a tiny powerful heater inside the battery. If someone charges to 14.6v, that poor little balancer will cook away for weeks. There must be some parameters that must be met first...like a voltage differential
you might see a difference at the battery posts, but probably not much of one, the onboard meter is hooked in AFTER the bms, so it is reading the voltage at the cells, I just checked one I'm testing on my bench and even at very low charge rate, my multimeter and charger say 14.1-2 and the onboard says 13.9
SolarRat
Solar Addict
This is the main problem, and very damaging to the entire system. The battery is disconnecting from the charge source and the load. Neither like when that happens. Yet many here seem to think it is normal.
I'm balancing one with a real active balancer right now, you've got me curious, so once it fully balances I'll plug the passive board back in and see if it still bleeds them all down to 3.45.
SolarRat
Solar Addict
The onboard meter is very inaccurate. The battery posts are after the BMS also. If you disconnect the balance leads from the BMS, the battery output goes dead. Now, with this balancer board installed, instead of 1 connector there are 4. If any one fails the battery goes dead (my boat is stranded).
@5a it's probably not a big deal, @ 30a more so, and @the full 100a the bms probably wont survive very many times. it's just like throwing a breaker or disconnect, the higher the flow it have to stop the bigger the chance of letting out the magic smoke.
symantics here I mean 'upsteam' of the bms as in it's not reading the teminal voltage it's wired strait to the cell pack
SolarRat
Solar Addict
Exactly! But many people seem to not be aware that this is not normal, and the lifespan of their CC and load will probably suffer.
The onboard meter is wired straight to the pack? If so, it should read higher than my Flukes on the terminals, but it reads lower on both. Regardless, those meters shouldn't be trusted. I bought a 10 pack of them on amazon years ago for various projects, and they were all over the place. And any meter that only reads one digit past the decimal is pretty useless on a lithium battery anyway.
By the time I reach high voltage disconnect the charge rate has reduced to less than 5 amps. I assume the bms is doing that.
SolarRat
Solar Addict
Wild's explanation makes sense. Another reason might have to do with the way lithium cells behave when nearing full. On a lead battery, the higher its voltage goes the harder it is to increase it further. On a lithium cell, once it reaches a certain voltage it will quickly increase in voltage even at low charge levels. So it's possible your faster charge is moving the lower cells more before the inevitable cutoff from the highest cell?
I agree the meters are not accurate
SolarRat
Solar Addict
Are the batteries cutting off, or is the inverter cutting off? Either way, why run them that low?
SolarRat
Solar Addict
That is your charge controller switching from constant current to constant voltage, not the bms.
No usually just 2 or 3, and they're the ones that were on during charging.
as far as the low voltage disconnect goes,in all probability- either you have 1 weak or badly out of balance cell (which is technically 20 cells wired in parallel) it's hitting the 10v cutoff and shutting down the bms. As far as the charge voltage going way higher than the battery voltage at the top end @ higher amps,I can definitely confirm that. it had me screaming in frustration trying to program a growatt aio to behave properly. vis a vi charging profiles. getting the charger to cut out before the bms at both high amperage charge and low amperage charge rates proved challenging/impossible
The Dish Doc
Photon Pharmer
Edited
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I’m just testing to see if the batteries will reach the stated cutoff points. I’m close at high voltage cutoff but I miss low cutoff by 6 volts. 1.5 volts each battery.
I was thinking it might be a balance issue. I’m hoping the balance boards will help with that. I will run another discharge and charge cycle to see what low cutoff is and to see if my ah is going up or down. Then I think I will set my charge profile a bit conservative but still in the range of keeping the balance boards running and my inverter low voltage shutdown above whatever my low voltage cutoff is now and see what happens.
The Dish Doc
Photon Pharmer
Then you'd be "Up LifePooh creek without a paddle"
SolarRat
Solar Addict
Has anyone got these boards to do a damn thing? I wasted enough time with these crap batteries. I just deleted a long rant post, but I gotta tell ya, I'm pissed.
I attempted to do a final amp hour test but I wasn’t able to be very accurate because I had a setting incorrect on the charger and it stopped charging before the batteries were full But I’m very close to 100ah. I think the balance boards have helped but they have such a short range that they balance in and such a small amperage that they balance at it’s going to take a lot of cycles to make any difference. I set my charger at 56.8 volts for the top and inverter for cutoff at 47 volts. I’m going to let it operate for a few months and see what happens.
SolarRat
Solar Addict
An amp hour test won't really tell us much, because we still don't know how many amps the cylindrical cells are. For all we know they could be grade B 6amp cells * 20 = 120ah, but with such poor balancing they sell as a 100ah battery (lifespan will be very short if this is the case). Some of my cells never reach 3.4v, while others are killing themselves at 3.65+.
I've been cycling for three days straight with these balancers, at least 5 cycles a day. And I've bled the high cells lower than the low cells 3 times now. If anything, the balance got worse. BMS still disconnects around 13.7v. Here is the better of the two batteries:
Day 1 start Day 4 start
3.427 3.428
3.340 3.340
3.340 3.340
3.406 3.410
Cells 2-3 never go above 3.37 when charging, then settle back to 3.34.
I'm charging that battery with a bench supply at very low amps (under 1).
The other battery I'm just charging with a 10 amp charge controller till cutoff, then draining with a 10 amp load, then charging again. CC is set to 13.8v. I think the BMS is starting to fail as I now have to disconnect the sense wires all the time to restore power to the terminals.
Anyone got a link to a decent, cheap BMS, in the US?
I've been cycling for three days straight with these balancers, at least 5 cycles a day. And I've bled the high cells lower than the low cells 3 times now. If anything, the balance got worse. BMS still disconnects around 13.7v. Here is the better of the two batteries:
Day 1 start Day 4 start
3.427 3.428
3.340 3.340
3.340 3.340
3.406 3.410
Cells 2-3 never go above 3.37 when charging, then settle back to 3.34.
I'm charging that battery with a bench supply at very low amps (under 1).
The other battery I'm just charging with a 10 amp charge controller till cutoff, then draining with a 10 amp load, then charging again. CC is set to 13.8v. I think the BMS is starting to fail as I now have to disconnect the sense wires all the time to restore power to the terminals.
Anyone got a link to a decent, cheap BMS, in the US?
Are you disconnecting the charger after the bms trips or leaving it hooked up? I would leave it hooked up at >1a and walk away. The balance board will bleed the high cells until the bms turns on then the whole bank will charge... rinse repeat until balanced. I started a new one balancing last night, this morning 3 cells are above 3.45, I'll update when all 4 are. Imo these don't work nearly as well as active balancers, but they do work. Remind me what voltage you are running and I'll try to find a good replacement bms if you want to go that route, but if I where you and these don't/ won't work to spec, I'd just return them for a full refund.
SolarRat
Solar Addict
Leaving them on, shutting them off, and a combination of the two. On one battery, I tried the bench power supply I from 200ma to 3 amps . On the other battery I just let the 10amp charge controller do its thing. After a while with 10amps the bms would just trip and stay tripped. Unplugging the balance connector on the bms itself usually resets it. The last time it took a while for it to reset. I don't think the bms's can handle cycling like that.
But, I haven't tried leaving them overnight banging the bms limit. It can't be good for the high cell, bms, or the charger/PS. But at this point, why not. I'll go set the PS at 1.5a and walk away. I've kept it going for a few hours <1a at least once, but with no change on the low cells measured on the Fluke I called it quits. I had to keep a fan on the balance board...it is working overtime, but all it seems to be doing (using clamp meter) is shunting the high cells to ground at 225ma.
I did order the 5a active balancer a couple months ago, but before installing I came back to this thread for updates and saw that there was a plug and play solution (and my JST cables haven't gotten here from china yet). Maybe I'll rig it up when the connectors come.
Originally, I ordered 1 of these batteries to see if they were good enough to buy more for my 36/48v golf cart and boat. The first wasn't working right so he sent another which did the same. I kept them both at a discount figuring I'll just top balance them and all would be well. LOL. So now I have two, and I'd really like to be able to buy one or two more for a matching set...but at this point it seems I'd be better off starting over and building one...but now is not the time to be ordering from China, so I keep trying to get these workable...