Negative amps

[Doods]

Hello! I am working to upgrade our ATC Bobcat. I recently pulled our AGM house battery and replace with a Battleborn Smart 100Ah LiFePO4. I disconnected from the battery isolator/alt charging. I was noticing the battery was showing negative amps with no accessories on while our 150W was in full sun. I even pushed the main power switch. Our solar charger is a Renogy PWM Wanderer and is set for Lithium. Any ideas of what is causing the negative amps? I do have a Victron 100/30 mppt already on the way since I want to add a second panel. Thanks.

 

[rubberlegs]

For our camper, the 110V charging system goes through the kill switch, so it can be turned off. But the solar is always connected to the battery.

 

[Vic Harder]

Where are you seeing these "negative amps"? Do you have a Victron or other shunt based SOC meter? On the Victron BMW 712 or Smart Shunt, one can "zero" the current reading if you are sure there is no draw or charge.

Are you sure the truck/alternator is disconnected? Current will flow from a fully charged LiFePo4 battery towards the AGM/FLA battery in the truck.

 

[PaulT]

As Vic indicates, the camper solar system is charging the truck battery. Power flows from high voltage to low voltage. With LiFePO4 camper batteries at 13.4+ voltage, (maybe 14+v), and truck engine off, the truck lead acid battery is likely lower than 13 volts after sitting a while as the various computers in the truck are consuming power all the time. I found my Battery Monitor indicated 2 amps or more flowing to the truck from the camper to keep the truck battery fully charged.

Drove me nuts for a while until I figured it out. I could never keep the camper batteries fully charged. This is not necessarily a bad thing as your truck will always start when camping.

I disconnected the truck to camper charging system under the hood and use solar only unless I am plugged in to campsite or home AC shore power.

If you replace the battery isolator charging circuit with DC-DC charging circuit, that camper negative flow will end. Or just disconnect the two systems and be responsible for charging the camper batteries by using shore power periodically. We find it useful to skip boondocking and stay at a commercial campground occasionally to take showers, fill our water tank, empty our porta-potti, buy supplies, eat at a restaurant, etc.

 

[Doods]

Thanks for all the quick replies. The Battleborn Smart battery has the shunt/monitor built in. I am starting to think the smart battery may not be all that smart. We don't have a shore power option. The truck is disconnected (unless I am missing something). The plug is disconnected and I have removed the wires to the camper battery. I was still seeing negative draw so I popped on the power switch and started turning on accessories. The charge reversed in the app. That doesn't explain why I was seeing negative at night with everything off. Am I still missing anything here?

I am going to send off an email to Battleborn tech support to get their take too.

Thanks for all the comments so far.

 

[Jon R]

The camper may have a carbon monoxide and/or gas detector powered by the 12 volt system. If you have a Maxxair fan the fan controller draws several milliamps. Those together draw a small fraction of an amp. They turn off if you push in the FWC silver battery switch.

If your Battleborn battery’s built-in battery monitor is reading current with the battery terminals disconnected, there is either something wrong or the battery has an internal heater that is operating.