From the Road: Does an Inverter/Charger Need a Separate Converter?

Hello there! In my Questions From the Road column, I take a crack at answering real questions from real RVers, just like you. You might find your question here! If not, please send me an email!

Does a diesel pusher have a converter for DC versus running directly off the batteries? The onboard inverter is a Magnum ME2012. Is it also a charger or does it have converter capabilities?

A deckmount RV inverter from Magnum Energy

Lot to work through here, Bill!

What’s a Converter? What’s a Charger?

1) I don’t quite agree with the assumption behind the first question. An RV converter, technically, transforms 120-volt AC electricity into 12-volt DC electricity. Actually, the converter’s output voltage is variable, but it’s normally 13.2-13.6 volts.

Now, RV users look at a “converter” a little differently, because many RVs are built with an all-in-one RV converter + AC/DC power distribution panel (WFCO is a major manufacturer). Some RV manufacturers prefer a separate deck-mount converter plus a separate AC panelboard and DC fuse panel, but many combine the two out of cost and efficiency. See example below:

RV Converter Power Center Installed in Wall
A combination AC panel board, DC fuse panel, and built-in converter/charger.

So technically, a “converter” doesn’t have anything to do with 12V DC electricity from the battery. The battery already provides DC electricity; it doesn’t need to be converted! It goes straight to the loads, unfiltered.

Now, most 12V circuits are wired “to the converter,” but what we’re really saying is that the 12V circuits are wired to a fused DC distribution panel, which is powered by ALL 12-volt power sources. The 12V circuits don’t go through any fancy gadgetry like a DC-to-DC converter. If you strip away all the excess, they’re still just simple fused circuits.

Now, are the 12V circuits powered by the converter, or by the house battery? Answer: Yes! At the risk of oversimplifying the answer:

  • If you’re plugged into shore power, the converter/charger will directly power your 12V circuits AND charge your battery. (A battery cannot be charged and discharged at the same time.)
  • If you’re NOT plugged into shore power, the 12V circuits operate directly off your battery, and the converter/charger doesn’t really do anything.

What’s an Inverter/Charger?

2) The Magnum ME2012 is an inverter/charger, which basically means it can invert DC to AC electricity and convert AC to DC electricity. So it goes both ways. Pretty cool, huh? Here’s the schematic showing how it works:

Here’s some information directly from the ME2012 manual:

An inverter takes direct current (DC) from your batteries and turns it into alternating current (AC). It also takes alternating current (when connected to an onboard generator or to shore power) and transforms it into direct current to charge your batteries. These two modes of operation associatedwith this inverter/charger are referred to in this document as:

•Inverter Mode: When the inverter is properly connected to batteries and turned on, the direct current(DC) from the batteries is transformed into a modified sine wave alternating current (AC). This AC is similar to the voltage provided by a utility for your home, and is used to power the electrical appliances (i.e., AC loads) connected to the inverter’s output.

•Standby Mode: When an external source of AC power (e.g., shore power or onboard generator) is connected and qualified on the inverter’s AC input, it operates in the Standby Mode. In the Standby Mode, the unit operates as a Battery Charger to convert the incoming AC power into DC power to recharge the batteries; and at the same time, automatically closes an internal AC Transfer Relay to pass the incoming AC power directly to the inverter’s output to continue powering the connected electrical appliances

-Magnum ME2012 Manual

Don’t get too confused by the converter vs. charger lingo. A charger is a converter, but a converter isn’t necessarily a charger. It’s kind of a semantic thing. Basically, people use the term “charger” to refer to a microprocessor-controlled electrical device (usually an AC-to-DC converter) designed specifically to charge batteries. The ME2012, for instance, has a robust 3-stage charging algorithm to recharge your RV house batteries. 

So yes, your Magnum inverter is also a charger. All RVs are wired a little differently, but I’d guess that you probably don’t have a separate converter. The ME2012 can handle both jobs.

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