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diy solar

Help balancing

mystic pizza

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Jun 20, 2021
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Help please.

I just connected my 4 cells in series with bms until cut out of one cell hit 3. 6v (14.4 total)

I then disconnected and charged one bank of cells in parallel at 3. 6V on power supply.

The voltage at the dvm connected to the psu is steadily decreasing. Was initially 3.463,now 3.446 @0.5A.

What am I doing wrong. Isn't it supposed to increase?
 
If the power source is disconnected, the voltage will drop. It will settle some where around 3.4.
 
Most likely there was at least one low cell that is now dragging the others down as they charge it .... just be patient and keep the PSU set right .... with no load .... and it will work out.
 
Most likely there was at least one low cell that is now dragging the others down as they charge it .... just be patient and keep the PSU set right .... with no load .... and it will work out.
Thanks. Do I need to sit and watch it, or can I leave it too it? It's getting late
 
You should be getting more than .5 amps on 4 cells at 3.45 volts. The current dial should be cranked full out and the voltage set. If the current is limiting the output then the voltage will start to drop to keep the current down.
 
You should be getting more than .5 amps on 4 cells at 3.45 volts. The current dial should be cranked full out and the voltage set. If the current is limiting the output then the voltage will start to drop to keep the current down.
OK. Maxed out current on psu. Still only 0.5A going into 7 cells, not 4
 
What are your connections like? are you using the alligator clips?

What are you reading the voltage from? from a digital multi meter or from the power source?
 
As long as the voltage is 3.6 maximum, should be fine to just let it run.

Does seem odd that 0.5 amp would pull the voltage down at the PSU. I would expect at least 8 amps if the voltage at the PSU was folding down.
Or is that battery voltage?
 
What are your connections like? are you using the alligator clips?

What are you reading the voltage from? from a digital multi meter or from the power source?
Bus bars are clean. Alligator clips, I know it's not ideal. Digital voltmeter on output terminals of PSU
 
Thanks. Do I need to sit and watch it, or can I leave it too it? It's getting late
You don't need to sit and watch it if you set the PSU properly.

Put the DVM on the leads and set it for 3.65 without the cells connected .... then connect it to the cells.

I agree with the others that the crappy leads that come with those power supplies can be problematic. Best to replace them with 10-12 gauge wire and ring terminals on each end.
 
As long as the voltage is 3.6 maximum, should be fine to just let it run.

Does seem odd that 0.5 amp would pull the voltage down at the PSU. I would expect at least 8 amps if the voltage at the PSU was folding down.
Or is that battery voltage?
I did charge them as a 12v bank initially, and the current as measured by the BMS app was 2 A. Initially 10A earlier in the day, so 0.5 seems to reflect they are nearly there, but the voltage is still dropping at the DVM
 
You don't need to sit and watch it if you set the PSU properly.

Put the DVM on the leads and set it for 3.65 without the cells connected .... then connect it to the cells.

I agree with the others that the crappy leads that come with those power supplies can be problematic. Best to replace them with 10-12 gauge wire and ring terminals on each end.
I was aiming for 3.6V. The psu won't take rings easily, as the plugs don't unscrew. Happy to make up some better cables, but not sure how to connect them
 
I was aiming for 3.6V. The psu won't take rings easily, as the plugs don't unscrew. Happy to make up some better cables, but not sure how to connect them
Hmmm .... mine unscrew. You would probably get some gain just by replacing the alligator clips.
 
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