markuscis
New member
Hi all, Gas Engine, Dual Battery and alternators. I am certain that past and current diesel trucks have both batteries permanently connected due to the high compress starter requirements. I also do believe that the gasser with dual battery disconnects the accessory battery when the engine is off and connects it when the engine starts. I could be wrong on all this so please correct me if that is the case.
The problem: I use this truck exclusively for trailer hauling. My trailer has two LifePO4 460Ah batteries, 800watts of solar on the roof, and a DC-to-DC charger, multi-plus, Cerbo GX, etc. all Victron fully V-bus connected. This has worked for the last 1.5 years. I have not used the DC-to-DC charger too much but it has worked just fine even if I start the truck and turn on the high idle switch.
The accessory battery has connections to install a high powered winch, snow plow, etc but in this case it is a DC-to-DC charger configured to accept up to 50 amps from the accessory battery connection same as a winch or snow plow. The connections on top of the battery are already there it was very simple to add a fuse and 2 gauge cable along the rails to the back of the truck. Again all this worked before.
Today when I started out I needed to charge more so I hooked it up, Anderson Connectors. Turned it on and started driving. The victron app showed that the input to the DC charger started at 11 volts and pushed 40 amps then dropped to 9 volts which below 9 the DC charger turns off. It will take input voltage in the range of 9 to 14 and push whatever the current charge cycle is to the batteries.
Today it would drop to 9 volts turn off then back up to 10.4 volts then drop and cycle like this over just 5+/- seconds.
I stopped pulled out the trusty multi-meter, opened the hood and checked at the accessory battery and it is also cycling in sync with what the Victron app is showing at the DC charger. the main battery shows 12.8 volts while the accessory is different.
The question: When the gasser is running if the they are both connected either one should show the same or VERY similar voltage but this is not the case. I would think they are disconnected but why would it cycle from 10.4 down to 9 for 5 seconds and then back up again. That would imply the alternators are doing something but the batteries don't seem to be connected?
Another note: I keep the batteries on a dual tender/charger and the main was nominally at 12.3 volts while the accessory battery was at 12.8 volts.
One more piece of info: After all this I turned off the truck and an hour later the accessory battery is at 11 volts and the main is at 12.75 volts. The accessory is most likely bad now. But why wouldn't the alternators be trying to charge it, i.e. show 14 volts at the accessory while running?
Thoughts, ideas?
The problem: I use this truck exclusively for trailer hauling. My trailer has two LifePO4 460Ah batteries, 800watts of solar on the roof, and a DC-to-DC charger, multi-plus, Cerbo GX, etc. all Victron fully V-bus connected. This has worked for the last 1.5 years. I have not used the DC-to-DC charger too much but it has worked just fine even if I start the truck and turn on the high idle switch.
The accessory battery has connections to install a high powered winch, snow plow, etc but in this case it is a DC-to-DC charger configured to accept up to 50 amps from the accessory battery connection same as a winch or snow plow. The connections on top of the battery are already there it was very simple to add a fuse and 2 gauge cable along the rails to the back of the truck. Again all this worked before.
Today when I started out I needed to charge more so I hooked it up, Anderson Connectors. Turned it on and started driving. The victron app showed that the input to the DC charger started at 11 volts and pushed 40 amps then dropped to 9 volts which below 9 the DC charger turns off. It will take input voltage in the range of 9 to 14 and push whatever the current charge cycle is to the batteries.
Today it would drop to 9 volts turn off then back up to 10.4 volts then drop and cycle like this over just 5+/- seconds.
I stopped pulled out the trusty multi-meter, opened the hood and checked at the accessory battery and it is also cycling in sync with what the Victron app is showing at the DC charger. the main battery shows 12.8 volts while the accessory is different.
The question: When the gasser is running if the they are both connected either one should show the same or VERY similar voltage but this is not the case. I would think they are disconnected but why would it cycle from 10.4 down to 9 for 5 seconds and then back up again. That would imply the alternators are doing something but the batteries don't seem to be connected?
Another note: I keep the batteries on a dual tender/charger and the main was nominally at 12.3 volts while the accessory battery was at 12.8 volts.
One more piece of info: After all this I turned off the truck and an hour later the accessory battery is at 11 volts and the main is at 12.75 volts. The accessory is most likely bad now. But why wouldn't the alternators be trying to charge it, i.e. show 14 volts at the accessory while running?
Thoughts, ideas?
Last edited:
