Inverter Upgrade

EDIT: There is much more information on this subject in another (later) writeup HERE.

NOTE: There are, that I know of, two ways inverters are wired on the Berkshires. The first one I have seen on older coaches. There’s an AC supply to the inverter charger, and there are two circuits coming out of it, heading directly to the outlets that they power. They are either powered by passing through shore/generator power or by making 120VAC out of 12V. There are three breakers. A supply breaker and one for each circuit. I have seen 30A/15A/15A

In later coaches, and I don’t know the change year but this is how ours is wired, there’s an AC supply to the inverter charger and then ONE return to the breaker panel, a section of which serves as a sub panel for the circuits able to be powered by the inverter. A more detailed description of this is on my “AC Circuit Breaker Panel” writeup.

Depending on which setup you have you need to order a specific inverter charger.

On the MAGNUM ME2012 inverter/charger that came on our coach the inverter part is what is known as a “Modified Sine” inverter, versus a “Pure Sine” inverter. I’m not going to get deeper into the technical aspects of that but if you want to know more there’s a good explanation here.

To put it in easy terms…. modified sine is an almost-but-not-quite-somewhat-dirty version of AC current. It works on MOST devices and appliances. Sensitive electronics don’t always like it. The mid lav GFI didn’t like it and would trip while driving. Would not reset until I had “clean” shore or generator power on. Now, GFI’s can be finicky so I replaced it with another and that worked better. But still, it’s not good for your electronics, like the circuit board in the fridge which runs on inverter when driving. (Unless the generator is on to run the AC.) Motors running on modified sine AC run hotter. (Fans, vacuum cleaner)

Now it used to be that the pure sine inverters were a LOT more expensive than the modified sine. But like everything else electronic those prices have come down, and you can now buy a pure sine for a little more than a modified sine. Some Berks in the past came with, and now all come with pure sine inverters. In fact, the 2017 brochure specifies a pure sine for the Berkshire 38A. When I pointed that out to Forest River they said “No it doesn’t, and you got what you got”. Well it did, but they conveniently left out the “Second half 2017 models only”. Ours is the early 2017, before the change of a bunch of items. Not sure what I think about that attitude but let’s leave it at that.

Soooooo, I wanted to fix this. And I talked to the Magnum people, or more specifically a dude from Tekris Power Electronics who was on one of the Facebook pages. He told me that the Magnum MS2800 is a pure sine drop in replacement. And it’s 2800 Watts versus 2000. All for around $1500

I sat on that for about a year and called them back to go with it. Well, turns out they had a sale on the MSH3012M, which is a hybrid pure sine 3000W inverter. The hybrid part means that if wired correctly it will augment a generator or shore power with inverter power. I don’t need that,  and I didn’t wire it that way, but the thing was on sale for less than the MS2800 so in a box to me it went. Pure sine, and 3000W.

In fact, it has a 60A !!! input and max pass through. There are 2 60A breakers on the side. So I could replace the 30A breaker on my breaker panel with a 60A one to take advantage of the greater throughput of this thing, except, and aside from the fact that my supply is only 50A,…… I would have to upgrade the wiring too. Plus, I don’t have anything to add to the inverter to be powered. What is powered now is fine, all I wanted was the clean power. So….. 30A at the panel, and wiring the way it is. Yes, the thing is now oversized. No big deal. I’ll never have to run downstairs to reset the breaker on the box, that’s for sure. Which brings up the last question…. With the 3000W versus 2000W output is the wiring adequate? Yes.  The sheathing for the OUT is the same orange as the 30A IN……which makes it #10, which in residential code is rated to 30A. 3000/120 is 25A. We are good to go, and safely increased our output.

But there’s the 12V side of the equation…. what about fuse and wire size there? 3000W is 250A 12V versus the 2000W which is 166A 12V….. Well, a quick peek at the fuse and we see that it’s 300A. Cabling is short and 3/0 which is quite a bit fatter than the 2 gauge which 250 at 4-8 feet cable length calls for. Still good to go.

Except…….. we still have the same battery bank so USING more will SHORTEN the time. Load management is still the key……And, 250A from a 450Ah battery bank is going to do damage. Realistically speaking I am pulling a coffee maker OR a micro…. 1500 or so Watts for 3 miutes…….  We COULD get a bigger battery bank…… but that’s a story for another day.

The changeover itself was remarkably drama free.


Verify that the remote is blank/off and that the outlets normally powered by the inverter are also not powered.

LABEL the IN and OUT AC cables. You can see inside the inverter AC compartment which is which. Once you pull them out you won’t know. Unplug the Network, AGS and BMK RJ11 Cables and safely tuck aside. ( I took a picture before pulling them, but there are color coded labels. Thank you Magnum.) Remove 8-S2 bit screws holding the thing down. (The ones in the back are a little harder to get to, TIP: Put some electrical tape around the bit and extender so you don’t lose them back there). Pull the inverter out and place face down on a stool or the box the new one came in.



Now remove the 12V plus and minus cables. A few notes. There are multiple connections inside the 2012 AC side…. Hot1, in Hot1 out etc etc. These were all jumped so at the end it was 1 set in and 1 set out….. So I ignored all that and left the jumpers in place. Also, there is what looks like a thermal switch for a cooling fan (which I hear on occasion) on the left side of the inverter/charger. It is NOT connected to the inverter. So leave it alone.


And it’s FREE. Put it on the table next to the new one, and lo and behold all dimensions and connections are identical. Praise to MAGNUM for doing this and making this EASY. (Of course that also makes it easier for me to decide to spend the money to upgrade. Everyone wins).


Now reverse the process with the new inverter/charger. Yes they are heavy….. 50 odd pounds. But once in place and connected, reconnect the 12V supply (I got a spark here…. not sure why, but oh well) and turn on the breaker upstairs. And SEE the magic. Check your settings on the remote and adjust as needed. I THINK they saved, but I’m not 100% sure as I had things pretty much standard on there….


That’s it. 3000W of clean 120V inverter power. And, looking on eBay, the 2012’s sell for around $500 so, if I can get that for it the whole upgrade will have been about $1100. Well worth it if it extends the life of my electronics.

UPDATE! Turns out the 3000W is coming in handy for the “Running Roof AC without generator project“!