Welcome to Manins' truck camper project

Alternator Control

The vehicle alternator is rated at 180 A and charges the starter battery, and through a BEP digital voltage sensitive relay (DVSR), the camper battery also.

When the two OEM 120 Ah AGM batteries were in place I observer a charge rate of 122 A, far in excess of their design maximum charge rate of 24 A each ( Fullriver HGL120). My replacement 360 Ah LiFe battery can easily accept the full output from the alternator — 156 A is possible (see below).

BEP Cluster


A cluster of BEP switches behind and below the passenger seat manages the loads on the start battery and camper battery.

The cluster is wired per the BEP recommendation, with starter battery isolation, camper battery isolation, emergency parallel isolation, and DVSR to charge the camper battery once the starter battery voltage rises to 13.4 V.

The yellow Emergency Parallel Isolation switch can be set ON when the winch is used extensively. The winch is powered from the camper LiFe battery. Then with the engine running, the alternator can boost the camper battery.




Three issues arise with a LiFe battery installed:

  1. The continuous alternator charge rate to the battery must not exceed 125 A, the maximum for the DVSR. Relevant when low State of Charge of the LiFe battery.
  2. The alternator charge needs to be stopped if the cell voltages or pack voltage exceed specified limits.
  3. When the engine stops the DVSR will stay on so long as the start battery or the camper battery is above 13.4 V. This is very likely for the LiFe camper battery so it would then discharge into the start battery, an unnecessary and unwanted occurrence.


Wiring for the relay control of DVSR. Control is NC.

The DVSR has an optional setup that provides ignition control — the DVSR is ON only if the engine / alternator is running, i.e., if there is a +12 V signal on the Red wire at the (Ignition control/Storage mode) pad. This is what is neeed here.

I cut the red looped wire from the Start Batt positive stud at the back of the DVSR and connected it via a relay to Pin 8, the "alternator operation" pin, on the 20-pin Body Builders Plug using one of the "SP" spare wires put in by Travel Trucks. The relay is wired so that Pin 8 is normally connected to the DVSR (NC), i.e. normally the alternator charges the LiFe battery, but of course only when the engine is running.


The relay coil has a suppression diode across it, one end is grounded locally, and the other is joined to "SP1 to Camper" and so is available behind the touch screen. To stop the charging of the camper battery this wire can be connected to +12 V to activate the relay. See how this is done in practice using a battery management circuit and an override manual switch.

While amongst the wiring, I connected the orange wire (joined to the orange sticker on the back of the DVSR) to a remote LED next to the relay to show DVSR in operation. The LED receives power from a spare fuse, Fuse F3 (3 Amp), behind the passenger seat.


Charging the Camper Battery when Low SoC

When the LiFe battery charge is low, below about 1/3 SoC (120 Ah), the 125 A continuous rating for the BEP DVSR is a problem. The solution is as follows:

  • I turn ON the yellow Emergency Parallel Isolator in the BEP cluster before starting the engine.
  • Most of the alternator output to the Camper LiFe battery goes via this circuit, not via the DVSR. I have observed up to 156 A charge rate on the BEP monitor in the camper.
  • When the engine is next turned off, I also then turn off the BEP Emergency Parallel Isolator Switch. The charge rate to the Camper battery is by then most likely well below the safe maximum for the DVSR and it will then take on the task of supplying current when the engine is next started.