Something is Charging my battery bank?

[Streff]

I have 3 battery banks. All 3 banks are isolated & independent.

A Lithium bank attached to an Inverter charger. That bank powers 120v outlets and devices (fridge, dishwasher, MW, TV, Starlink, etc).

One AGM bank for Bow & Stern thrusters. Has its own dedicated hardwired charger.

Third bank (AGM) is for starting engines, genset, all powering DC loads (water pump, lights, windlass, electronics, etc). It has its own chargers that needs to be physically plugged in an outlet. This bank is also charged from Alternators. The mystery is with this bank.

Recently, I started noticing a peculiar situation. At anchor with engines off and the third bank chargers are Not plugged in, when the generator is running, the Victron shunt for third bank shows a 6-7amp charge going into the bank. I do not understand how this could be happening. It seems that the bank is being charged from somewhere or maybe the shunt is defective? The shunt behaves perfectly otherwise.

This does not happen when connected to shorepower. Only when running the generator.

I checked all cables, connections and wires.. nothing seems unusual.

Any comments would be appreciated.

Thanks

Streff

 

[Delta Riverat]

Does the generator have it's own alternator?

 

[Streff]

Hello,

Great observation. Yes, the gen has an alternator but I did not see wires from the alternator going to the battery bank. But possibly wires going from the alternator to the genset startor which is connected to the starting batteries.

Thank you

Streff

 

[Bacchus]

Hello,

Great observation. Yes, the gen has an alternator but I did not see wires from the alternator going to the battery bank. But possibly wires going from the alternator to the genset startor which is connected to the starting batteries.

Thank you

Streff

Thats likely and the usual scheme with main eng starter & alt.
No need to duplicate heavy Ga cable from start battys to starter so using it to charge the battys using the alt only requires a short jumper from Alt + to start +

 

[tiltrider1]

Most boats have a switch that allows you to combine banks in an emergency. Either the switch is in the all position or has been wired incorrectly.

It is also possible that a battery combiner is wired into the system.

You either need to trace all the wires attached to the batteries or higher some one to map out your electrical system.

 

[Streff]

Thank you tiltrider,

The battery combiner came to mind right away but since this only occurs when running the genset, I did not pursue it any further.

Today, I ran the gen and watched the battery monitor. It seems that the genset alternator charges at a higher rate (6.5A) when no load is put on it. When I had a load it only charged at 3.5A.

I dig deeper in the genset manual and it mentions alternator (20amp at 12VDC). I never paid it much attention and I did not see it until I installed a battery monitor.

I appreciate everyone’s comments and ideas. Great forum.

Streff