Famtraveler24
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If the voltage is adjusted after charging begins, what is the impact? In my 8s 280ah pack that I am top balancing, I am routinely checking the voltage of each cell. Thx!
Top balance mistakes could use some help
- Thread starter Carpslinger
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RCinFLA
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You need to attempt to get them up in voltage with low charge current rate. Electrolyte breaks down below 0.2v so the longer you leave them the worse it will get. Also metal dendrites can grow creating cell shorts.
Start out pushing about an amp into cell. When it rises to 2.0v work on another cell, and so on, so you get them all up to at least 2.0v. If any cells will not rise with 1 amp it is likely bad. If cell get warm in process it is likely bad. I would not try to do them all in parallel at the same time. Do each cell individually so you can tell if one is abnormal in its reaction.
Once you get them all up to 2.0v let them sit for a day to see if they stay up. If so you can do normal recharge after that.
Start out pushing about an amp into cell. When it rises to 2.0v work on another cell, and so on, so you get them all up to at least 2.0v. If any cells will not rise with 1 amp it is likely bad. If cell get warm in process it is likely bad. I would not try to do them all in parallel at the same time. Do each cell individually so you can tell if one is abnormal in its reaction.
Once you get them all up to 2.0v let them sit for a day to see if they stay up. If so you can do normal recharge after that.
RCinFLA
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When power supply is in current limit you will not see any rise in power supply voltage when you adjust it. If the knob is cranked up to an unloaded power supply voltage of greater then 3.65v you will not know until cells approach full charge where their current drops off, power supply current limit is not in control, turning over voltage limit control at the higher voltage setting.
With too small wire gauge used for power supply leads there will be voltage drop at the current limit of power supply. Rising power supply voltage to compensate for wire drop is dangerous as when cells approach full charge the current drops, voltage drop on wire drops, and cells will then be subjected to the elevated supply voltage limit setting. Use #10 or #8 wires.
Don' think you can catch it before this happens. Cell voltage rises and charge current drops off quickly above 3.4v and it will get away from you resulting in cell overcharging and possible cell bloating damage.
mikefitz
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you may damage the cells. The power supply should be set to the magic voltage you intend using before connecting to anything and keeping at that setting until the process is completed.
As you may guess I am not a fan of parallel cell balancing.
Mike
Famtraveler24
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Do you recommend turning off the ps, and resetting?
Turn off the supply. disconnect from the cells. Then adjust the supply to the set voltage and reconnect. Maybe change your leads as well if you're using some included crocodile clip ones. Proper gauge wire with ring terminals are recommended.
Famtraveler24
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Thx. Using 10 AWG with ring terminals. Gator clips were not sufficient.
One problem with adjustable power supplies is that most are NOT designed to be battery chargers!
When the supply sees the low IR of a battery bank, it can be mis-detected as a short, and the power-supply CROWBAR circuit kicks in. The "crowbar" circuit is so-called because it acts like placing a direct short on the output in order to force the supply to shut down internally and not provide any current. In many cases, the crowbar just fries. It's a simplistic protection, but the secondary effect of a fried crowbar or other circuitry is not kind to batteries who now see a failed power supply as a load!
en.wikipedia.org
So the one "trick" to prevent this from happening was when first setting up your lab-supply, make sure you turn up the current a little bit, and then adjust your voltage with a reliable meter. THEN make your connection to the battery and NEVER adjust the voltage again during charge. If your current pot isn't turned up a little bit, it may not be enough to FOOL the crowbar circuit that there isn't a short masquerading as a discharged battery on the other end.
Turning the current pot up a bit PRIOR to attaching to the battery, can sometimes help prevent the crowbar from kicking in. But of course be careful!
Some adjustable lab-supplies will actually state that they are suitable for charging, but of course they cost more.
Ie, if you can initially adjust your lab supply voltage, but your current pot is at the dead end of rotation, nudge it just a little to get it off the stop and cross fingers that this will be enough to fool the crowbar.
When the supply sees the low IR of a battery bank, it can be mis-detected as a short, and the power-supply CROWBAR circuit kicks in. The "crowbar" circuit is so-called because it acts like placing a direct short on the output in order to force the supply to shut down internally and not provide any current. In many cases, the crowbar just fries. It's a simplistic protection, but the secondary effect of a fried crowbar or other circuitry is not kind to batteries who now see a failed power supply as a load!
Crowbar (circuit) - Wikipedia
So the one "trick" to prevent this from happening was when first setting up your lab-supply, make sure you turn up the current a little bit, and then adjust your voltage with a reliable meter. THEN make your connection to the battery and NEVER adjust the voltage again during charge. If your current pot isn't turned up a little bit, it may not be enough to FOOL the crowbar circuit that there isn't a short masquerading as a discharged battery on the other end.
Turning the current pot up a bit PRIOR to attaching to the battery, can sometimes help prevent the crowbar from kicking in. But of course be careful!
Some adjustable lab-supplies will actually state that they are suitable for charging, but of course they cost more.
Ie, if you can initially adjust your lab supply voltage, but your current pot is at the dead end of rotation, nudge it just a little to get it off the stop and cross fingers that this will be enough to fool the crowbar.
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