Trimpots not adjusting voltage on charger

[veloman]

I have one of those BMS battery style 400watt EMC chargers. It was set to 58v, then I lowered it to the minimum which I found to be 50.7v. Now I am trying to bring it back to 57v, but I am unable to get the voltage output to change. I've tried all 3 trimpots. I can't remember which one is voltage.
Any idea what is going on here?

 

[dnmun]

there should be two trimpots next to the current sensing shunt. one is directly connected to one leg of the shunt and that is the one for maximum current. there is the other one next to it that sets the current level where the charger goes into the CV mode.

the third one will be close to the IC current controller chip and that is the one that controls the output voltage.

 

[veloman]

Thanks for the info.

 

[dnmun]

set the trimpots to the middle of their range and see if it will work. then adjust the voltage to your needed final voltage. then put it on the battery which should discharged enuff to allow full current charging. then while charging, well below the final voltage, adjust the max current trimpot while observing the output current on the watt meter. don't try to push max current too far ahead of the power rating on the charger or it will overheat the transformer.

when you get close to the final voltage and you can observe the current dropping on the meter as the pack fills up, adjust the other trimpot so the fan turns off and the light goes green as your current drops to 1/10 of the Ah rating of the battery pack.

 

[dogman dan]

Taking the voltage trimpot all the way to the stop broke it?

Could be stuck at 50v now. I mean it ran the adjuster off the threads of the screw.

 

[dnmun]

you can verify that the wiper still moves with a DVM.

use the ohmeter and put one probe on the wiper and the other probe on the terminal and it should change value as you rotate the screw.

 

[veloman]

I thought clockwise would raise the voltage. Then I decided to try CCW and it works. Back to 57v now.
I'll check the current while charging. I'm sure that is off now after having messed with it.

The board says VR3 at the trimpot closest to the shunt. The other trimpot is next to it and says VR1. I'm guessing the one closest to the shunt if for adjusting max current.

 

[dnmun]

yes. there should be a quad op amp next to the other one. divide the rated power by your output voltage to come up with the max charge rate.

your pack needs to be balanced to adjust the setpoint for the CC/CV transition on that final trimpot. it may take several iterations as you get the pack closely balanced to finally set the correct current level. 1/10 of the Ah is the general number but you can go to 5% if you wanna try that. so you need a wattmeter to follow the current.

you want the charger to operate so that the pack will go right up to full charge at max current and then switch over to the balancing current with very little charge left to push into the pack.

i always set my chargers to voltage just a little above the final balance voltage and let it go into the balancing current when the entire pack has reached full charge. hope that makes sense. usually about .1-.2V above the 16Sx3.60V level, 57.7, 57.8V.

 

[veloman]

The current trimpot was not the closest to the shunt, I found.

I don't need to worry about when it goes to CV mode since there is no BMS on this pack. I am charging at 5amps and the cells are 45ah. I set the charger voltage to 4.07v per cell. They are Chevy Volt cells, and are staying perfectly balanced since I got them in the spring. I occasionally check them. But at 4.07v/cell there is a large safety margin.