Inverter / Charger Install – MS2812









This post is technical in nature, for those not interested and/or unable to stomach the level of bore… Stop here!

When we bought the boat the inverter/charger had given up the ghost right before we purchased it. The seller agreed to take some money off the asking price so that we could get a new one. The boat was originally priced with an inverter/charger onboard. We did not get as much off the ask price for a new one as we had hoped for but at this point we were so tired of negotiations that we just went with what he would give us.

We needed both an inverter and a charger. The inverter for when we are away from a dock without shore power and a charger for when we are at the dock hooked up to shore power. The old broken one had been removed and a cheap portable West Marine charger was put in to top off the batteries while at the slip. I scoured through all the marine stores online for the best option. I wanted a combined inverter/charger unit. Tough choice I have to say. I ended up settling on the Magnum MS2812 Inverter/Charger combination unit. I also bought the remote control unit and battery monitor kit for the system. As always, one should shop around for the best price right? Everywhere I looked online the MS2812 was going for $1900+. Pretty pricey. I kept searching and stumbled on a website – They had the MS2812 listed at $1429! A really great price with free shipping to boot considering the unit weighed in at 60lbs! I called to make sure they had the unit I wanted in stock, they did. I immediately ordered it online and it showed up in a few days, shipped successfully to our marina. Here is a quick list of the stuff I bought for this install:

Magnum Energy MS2812 Inverter/Charger
Magnum Energy ME-ARC Advanced Remote Control
Magnum Energy ME-BMK Battery Monitor Kit
Class T Fuse Block w/400amp Class T Fuse
Perko Battery On/Off switch – To disconnect battery to Inverter on the positive cable
4/0 Electrical Cables for the DC Connection – Custom ordered to length
2×6 Board for supporting the shelf where the inverter is mounted
Stainless bolts and screws for mounting – Always go stainless :)
2amp inline fuse with wire for the Battery Monitor Kit

The hardest part, or should I say the most time consuming part of this whole install was finding everything I needed all the while making sure that I was following the manufacturers recommendations for the install. I was hoping to use the old 2/0 cable that was left in the engine room from the previous inverter/charger install. Nope (I actually ended up using one of the old 2/0 wires for the equipment ground.) The recommended wire size to the batteries was 4/0 (pronounced 4/aught) for a distance of 5ft or less. These wires are thick. You would think they would be hard to work with but they are stranded and bend relatively easy. I used a rope to figure out the exact cable lengths I needed. I just ran the rope where I was going to run the wires and then measured. This method worked perfectly as long as you take into account that the 4/0 cable will not have as tight a bending radius as the rope does. I found a place online – There was another place that provided custom terminated cable lengths but did not allow me to specify different terminal hole sizes for the SAME cable which I of course needed. The Genuinedealz place allowed me to have different sized terminals so I went with them. My install needed both 5/16 and 3/8 terminal hole sizes (battery posts and inverter were 5/16, the battery monitor shunt, fuse and Perko switch were 3/8.) Genuinedealz is out of Georgia and I received my custom 4/0 cables within a couple days. They were perfect.

The install itself ended up involving two back to back days. The first day (a few hours) was all about dry fitting everything. The second day was the actual install. After making sure we were done with the need for any electricity for the day (both AC and DC) we uncoupled the shore power lines and disconnected the battery bank. Now the clock was ticking, I was intent on having electricity later in the day for dinner and such so this job had to be completed. We then unmounted the shore power receptacle on the side of the boat, pulled it out and wired in the new AC wire to lead to the inverter/charger. Easy as pie. We strung up all the wires, positive side included Perko switch and Fuse block, negative side included the shunt for the battery monitor kit. We drilled the shelf to mount the inverter and installed the support board. Next we connected the wires to the battery bank and then to the inverter making sure the battery switch was in the off position. We installed the battery monitor kit and connected the wires to the shunt and then ran the cable for the remote control. All in all it took 6 hours. I did the work while Shawna handed me tools. Luckily our boat has an actual engine room. No standing room, but enough room to kneel. It was over 100 degrees in there and I sweated so much my clothes were soaked as if I had just went swimming. I was actually getting nervous about being so dripping wet around so much damn electrical potential! The whole thing was pretty grueling to say the least but in the end we were happy (and healthy.)

After all connections were verified and we made sure we had everything wrenched down snug we proceeded to start the system up. No shore power this time. Just testing the inverter. I flipped the battery switch on the positive side and the system came to life. The appropriate light sequence displayed on the inverter and our hard work was awarded with the fact that there was no smoke anywhere. We don’t like smoke! We tested the system with a small wattage light bulb to test the inverter output. It worked great. We ran a few more appliances to test the system. All was good! I could just start to imagine how Dr. Frankenstein must have felt.

We then connected the shore power line from the dock and flipped on the breaker. We now had live AC power going to the inverter (and still no smoke!) The inverter “saw” the AC electricity and automatically passed it on to the boat system at the same time switching off the inverter. These settings can be changed, but we have the inverter/charger currently set so that the change from shore power to inverter power is automatic. This seems to work for now.

I then set the charger to “Multi-Stage” where it charges in Bulk mode, then Absorption mode, and then into a final Float mode (the final stage is selectable.) There is also the option to equalize if needed. The charger worked great and the batteries are full as I write this. The remote control works great and lets me control the inverter or charger from the nav desk and also shows me any and all information I would ever want to know about the batteries. Definitely worth getting the battery monitor kit for the MS2812.

Done! This has been a big load on my mind for a while now. Now that this is complete I can get on with ordering solar panels and going through that installation. I think even Tesla himself would have been just a little bit proud.

The last picture is half of our engine room. Just a little bit overwhelming. I am happy to say that it is all starting to make sense to me. Someday I may actually know what everything does and where everything goes!

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6 thoughts on “Inverter / Charger Install – MS2812

  1. Mark Pitts

    Hi, Matt. I just purchased this setup for my Carver 504. I’m also thinking I’ll mount the unit in the engine room. How has the unit held up after a couple of years in the engine room environment?

    1. Matt Post author

      So far no issues at all in the engine room. Just make sure there is good airflow and it should be good. I do not have any extra fans on it, just the built in ones and no issues with overheating whatsoever and it is a pretty small engine room with really not a ton of ventilation. I mounted the remote outside of the engine room of course. I like the unit a lot. has never given me any issues. Good luck! I am sure you know to keep it as close to the batteries as possible. And don’t skimp on the recommended wire gauge. I should add that the people at Magnum support are great to work with. They answer the phone and their techs are very helpful if you have any questions.

  2. Heather

    Congrats Matt! That engine room does look a little daunting. But I have no doubt that you will learn it quickly.

  3. Bill and Beth Fehlmann

    Even non-electrical geeks can follow what you did. You write really clearly and well. And I’ve Got to tell you that engine room is probably the cleanest (including landlubber utility or laundry rooms and garage or basement work areas) I’ve ever seen.–bethmomnana


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