It is common for a camper to have different house battery charging sources:

• solar
• alternator
• shore power
• generator
• etc

Some solar installs will even have separate charge controllers running their own panel[s].

So what happens when multiple chargers are running at the same time? Nothing dramatic, as it turns out.

In general, the charging source with the highest voltage will win.

Most charging involves holding¹⁾ If a charging sources sees the bank voltage is above its own setpoint it thinks the job is done.

Example. Pretend you have a bank in a van with alternator charging and a large and small solar panel on the roof. Each panel has a dedicated charge controller because the panels are of wildly different specs. This gives us three charging sources if you are driving down the road at dawn.

The alternator is just a plain alternator and puts out 14.0v all the time. The Morningstar charge controller is factory set to start Absorption at 14.4v.²⁾ The Xantrex charge controller has been configured by you to start Absorption at 14.7v.³⁾

Let's charge that battery. Here is the battery voltage along the way:

• 12.2v at daybreak, approximately 50% Depth of Discharge. Charging is in the Bulk stage and all three sources are charging; the battery bank voltage is lower than what they all want to provide. The alternator is contributing the most because it can produce the most current.
• 13.9v a few miles down the road. Voltage is climbing but all three sources are still charging.
• 14.1v by the you get to a neighboring town. Alternator charging ceased at 14.0v; it has plenty of current but no voltage “pressure” to force that current into the battery. Your battery bank is now being charging only by solar.
• 14.6v in the parking lot as you stop at an Oasis water kiosk. The Morningstar stopped contributing at 14.4v⁴⁾ so we are down to just the Xantrex.
• 14.7v on your way back to camp. This is Absorption setpoint (Vabs) of the Xantrex, the highest setpoint of all three. Only it wants to hold voltage this high so only it is charging. The Xantrex will continue the Absorption stage until it is complete, then drop back to Float voltage (Vfloat).