Renogy Battery Monitor Connections

[WalterM6]

I have a problem with my battery monitor. The specs for my battery claim it's a 15A charger. The best my BT App ever showed was 11.5 amps. When connecting the Renogy to the battery I understand that all negative connections to the battery should be connected to P- instead of B-. While trying to come up with a solution to why my charging current reads low I noticed that I didn't connect the black wire from the BMS to P-, it's still connected directly to the battery B-. Before I change it I thought I'd ask if changing the black wire connected to the P- side of the shunt is going to affect the voltage that the BMS is reading because I'm adding resistance in the line. And will I be better off leaving it connected to B- ?

[Pat911]

Hi Walter,

Leave the black wire, which is the pack 0v reference that the BMS reads, connected to the negative of the first cell. The Renogy shunt is seperate, and secondary to the BMS. Nothing should interfere with the BMS connections. All the thin sense wires, which the black wire is one, should be connected directly to the cells. The BMS forms part of the battery. You don’t have a lithium battery without a BMS. The Renogy shunt meter is a device that connects externally to the battery to measure the energy in and out of that battery. The power drawn by the BMS is negligible and probably wouldn’t be seen by the shunt anyhow. And yes, if you move that black wire the BMS will see incorrect voltage readings, especially under higher currents.

The low charge current that you see could just be due to an overly optimistic rated charger. Have you measured the current with a multimeter?

Cheers
Pat.

[WalterM6]

Thanks, Pat911 for your answer. I'm just going to let that black wire where it is. I did try measuring the charger current with a clamp-on ammeter. It is giving some strange reading for which I have no electronic explanation. If I measure the positive wire current I measure 15A. When I switch to the negative wire I measure 9A and on the Renogy and BT, I measure 11.5A. With that being a series circuit I would think they would be the same. Do you have any ideas?

[Pat911]

Could be that current is being shared by multiple ground wires. Where are you clamping? Does the negative you’re clamping to go directly from the charger to the Renogy shunt, with no other negative wires connected to the charger/charger plug (if you have one) or anywhere else that may allow charge current to flow.

It would be helpful if you could post a clear picture.