BMS not showing charge from Renogy DC-DC charger

[v0rt3x]

Hey,

I'm wiring up my van's electrics (VW T4 so an old dumb alternator), have 4S 100Ah lifepo with a BMS (Daly knockoff it seems), Renogy 20A MPPT and 20A DC-DC charger.

I've connected everything but don't get any charge current when the van is running and the DC-DC charger is on. Green LED is on and there is voltage on the output terminals. But even when it says 0A on the BT app I can see the voltage slowly rising, so would suspect it's charging? (pack is now at 3.1-3.2V per cell) I've only tested it with the van idling. Could it be that's it's charging under 1A and the BMS doesn't register it? (but the battery isn't full yet) I have the jumpers set at 14.4V.

The BMS is active as I do see charge current via MPPT or if I connect a battery charger directly to the BMS/battery.

DC-DC input + is on battery, - is on chassis ground, output + to battery and - to BMS -. I've also tried wiring the DC input - directly to battery - but no change.

 

[Tomthumb62]

Hey,

I'm wiring up my van's electrics (VW T4 so an old dumb alternator), have 4S 100Ah lifepo with a BMS (Daly knockoff it seems), Renogy 20A MPPT and 20A DC-DC charger.

I've connected everything but don't get any charge current when the van is running and the DC-DC charger is on. Green LED is on and there is voltage on the output terminals. But even when it says 0A on the BT app I can see the voltage slowly rising, so would suspect it's charging? (pack is now at 3.1-3.2V per cell) I've only tested it with the van idling. Could it be that's it's charging under 1A and the BMS doesn't register it? (but the battery isn't full yet) I have the jumpers set at 14.4V.

The BMS is active as I do see charge current via MPPT or if I connect a battery charger directly to the BMS/battery.

DC-DC input + is on battery, - is on chassis ground, output + to battery and - to BMS -. I've also tried wiring the DC input - directly to battery - but no change.

Is your battery already fully charged? Or near so? If yes, then you’re not going to see 20A going through the BMS. The current may be too low for the BMS to detect. Try putting a load on the battery and see if that helps.

 

[v0rt3x]

Maybe, this was the last status:

But the MPPT was still charging it.

 

[Tomthumb62]

I’m not an expert on battery balancing, but it looks like your cells are possibly out of balance enough to affect or slow down a full charge. There are ways to fix this, the short version is to completely discharge the battery until the BMS cuts out, then charge to full.

Edit to say, what you’re seeing might be the BMS limiting the charge in order to balance the cells. You might also just wait a good long while to see what happens. Could be hours or days before it finally achieves balance. Someone once told me it could take months. The balance sequence usually takes place as the battery nears full charge.

 

[v0rt3x]

Could be, I'm going camping over the weekend so will drain the battery some and then see if it raises the current.

Will also top balance the cells individually since I haven't done that yet.

 

[mikefitz]

Comments,
Renogy DC to DC needs a D+ signal to function, 12v on terminal 5.
House battery negative connects to to output and to van metal or starter negative.