DC to DC Chargers


Active member
This isn't really two inverters. It's one inverter that feeds the mains side of the house inverter, which is presumably really just a 120/240V powered battery charger/maintainer inside that happens to have another inverter connected to the battery.

Then it's the same as a DC-DC charger in the most basic form, converting from DC to AC and back to DC. You could also just use any battery charger designed to run from the mains in this case.

The overall losses are likely to be higher than a dedicated DC-DC charger mainly because the device won't benefit from being engineered to run all stages at best efficiencies per the task.

You can just check the datasheets.

For example a Samlex SA-1000K is full load efficient at 89% (for a 12V version) and 92% (24V). It'll be a little higher at partial load, sometimes as much as 5% at 1/2 rated load. Call it 90% on average.

Fed into a charger. This isn't necessarily a simple calculation, but it's possible to ball park. An Iota DLS is stated as >80% and a Noco or BatteryMINDr will probably just say it meets CA CEC rules. So that'll work out to about 89% or greater in plain numbers for active mode charging.

Compare this to a perhaps a Victron Orion, which are stated to be between 85% to 89% efficient depending on configuration.


So the difference isn't show stopping, maybe on the order of 5% or 10% worse losses using separate inverter and charger. In this case of a running engine alternator feeding the system the penalty isn't even really significant. It's not going to mean much difference in alternator temperature or engine load.

The trade-offs are convenience of an all-in-one solution verses multiple device and wiring. But then again having a separate inverter and charger gives you flexibility and would be easier to repair.

Where inverter efficiency is important is when the engine is not running. A few percentage points there might translate to significant changes in run times. Same with a charger to some extent. A higher efficiency charger that draws down your solar system less is important. But a few percent worse when skimmed from a 250A diesel engine-driven alternator might mean you go from 12.00 to 11.95 MPG on your trip.
You are inverting then converting and there are losses on both ends, which is not easy to calculate as you stated. I find it interesting that Victron are not stating the efficiencies of their combo-inverter chargers (who cares when plugged into shore power right).

But, if you look at their Phoenix Smart IP43 Charger dedicated charger converter it states efficiency at 94%.. Interesting topic for sure 😃


There are losses, no question. I believe my victron inverter that feeds the inverter/charger in the camper is around 92% efficient. I also have 24 volt house batteries. I think paid about $350 for the victron inverter installed in the truck cab. I the inverter/charger in the camper just thinks its on "shore power" so it charges the batteries at whatever level I set it to draw, which is 700 watts. Overall at least for my installation I found it much easier to do than going to orion B to B charger route.