Inverter Power

The battery is small. Too small. I can’t get through the night with fridge and furnace. Getting up at 3am to silence the alarms and start the generator is a pain. Sooooo more power Captain. Whole house power. Every TV and outlet. And the fridge and maaaaayyyyyybe a few hours of AC….. The latter is something we need on the Eagle Cap Truck Camper. And, I also have a habit of messing with trailer tires in farm fields so I need a compressor etc. there…… Carrying a gas generator and fuel is a pain.

Yes, those are all three separate units. So a LOT of duplication. And that’s money. Wait, how about putting it all in the truck….. Feed the fiver, the TC and whatever power tools I want to throw at it……And, the ol’ Cummins can help keep the batteries topped off.

So then it became a matter of where in the truck can I hide LiFePO4 batteries, and inverter/charger, a DC to DC charger and assorted fuses, shutoffs and cabling…….

If you get under the RAM 3500 DRW with a creeper, you will find TONS of space in the fat bed and dually wheel wells. Tempting. One problem. LIP doesn’t charge below freezing. So they have to be enclosed and heated. Or get the heated batteries. But those don’t BlueTooth. More on that later. Then the lightbulb went off. It’s me and the wife and two puppies in 30″ travel crates. We don’t need to stinkin’ back seat. And out they came.

I promised myself not to butcher the truck in this project so using all existing holes from the seat mounts and threaded rods I installed some framing.

Further built up and a head board:

Some flooring:


Now the system…….

  • Batteries: as many Watts as I can stuff in there. (I’m starting with 6-100A, there’s room for two more which makes 8, the max the manufacturer says I should parallel.)
  • Inverter 3000W Pure Sine
  • AC Charger
  • DC to DC Charger

(Shutoff between truck battery and B2B charger not shown)

Lets start with the easy stuff: Charging while driving. 170A Alternator two batteries in the truck. Why two? Cold start of the Cummins diesel requires, of course, some form of pre heat. Some diesels use glow plugs, Cummins utilized a grid heater which preheats the intake air. It’s a power hog. Hence the second battery. You can watch the volt meter go like a windshield wiper when it’s cycling, which lasts as much as 5 minutes in serious cold conditions. So I decided to tie into the second battery, and install a cutoff switch so I could bring the charger on line after the heater was done.

Charger? Yes. The alternator and the circuitry, which is pretty sophisticated these days, look at the truck’s needs. They have no clue about a large LIP bank. It can mess up its brain, and it certainly won’t provide a proper, let alone efficient, charge profile for the “house bank”. So you use what’s called a DC to DC charger, 12VDC to 12VDC in this case. Other combinations are available as it is basically a transformer which sends voltage from one end to the other of the windings, passing on the current without physical contact. Magic. But, it nicely controls the output to form a proper profile for your (selectable) chemistry.

There’s a lot of them out there. I went with the Sterling, a tried and true performer. And, when you call the US number (they are made in the UK) a person answers the phone who knows his shit at loves yakking about it. My kind of company.


LiFePO4, no question. Less weight, a LOT more available power per volume, faster charge/discharge rates. But what about fire? These are NOT Lithium Ion…. there is a difference. LIPs are generally a LOT safer. If they have a decent Battery Management System…. the brain in every battery that wrangles the electrons. Watch Youtuber Will Prowse…. EXCELLENT videos on batteries, inverters, solar…. all that.

But which ones…. there is a SEA of cheapos…. 12V100A under $500….. Then there’s the other end…. Battleboro… $1000 plus. (But that’s down from $2,500 not THAT long ago……..) As stated, it all hinges around the quality of the components: BMS, bus ties, protection etc….

Long story short, I went with Renogy. They have a decent reputation and they are lower-mid cost. Will doesn’t hate them. I picked these, because I can talk to them via Bluetooth to ascertain state of charge (SOC) and which way it’s heading and how fast. I think they are a decent value.

Size wize…. I looked at the 200A versions and they would not puzzle nicely into the space. I also looked at 24V because it’s a lot easier on the wiring, but the reduction in available components resulted in less competition and thus higher prices.

Then it was a matter of fitting them into the space, tying them together and to the inverter/charger B2B charger. More on the fitting later.


Speaking of inverters, chargers and inverter/chargers……. I went with the combo. And the good one…. Victron. Yes they are expensive but they work VERY well. And with the money tied up in the batteries I wanted “very well”….. I’ve bought too many cheap(er) inverters that just didn’t perform. 120V, 3000W and 120A charging.

So, time to do some dry fitting. First some wood to screw in to and hold it all in place. The genuine plastic wood veneer piece in the middle will be accessible from above. I need the rear registers to have some place to put their air/heat. Inverter is heavy. I wanted it flat on the floor.

The B2B charger is the only thing that you may want to look at when in the driver’s seat, to see whether it is doing its job. Yes there is a remote, but that’s another thing to figure out where to put. Where it is here I can actually see the LED’s…… (On edit: It was moved up one step, to make room for two batteries)


Now to cable.

The B2B 60A over 10 or so feet requires a 4 gauge cable…. or fatter. Happened to have a brand new 1 gauge 24′ jumper cable……perfect for all my connections! Proper lugs and a proper crimping tool and viola, cables. Add a shutoff (with key to avoid accidental activation) and an 80A fuse, connect the charger and temp sensor to the batteries, select the proper chemistry and we have “driving charging”.

Running said cable up there was another thing. This is the hot side of the engine and there was really no elegant way down. Eventually I settled on running on the inside of the plastic inner fender. Soft, dry and not too hot. Some lugs, heat shrink tube and the battery end was connected. I put in an 80A fuse, per the installation instructions, and it just sits there nicely on top of the felt like stuff on top of the battery. I wanted the fuse as close to the source as possible to protect the wire. And, to have a way to disconnect the whole show from the outside.

The keen observer will notice cables coming up through the platforms. (The cable to the truck battery still to go) In my quest to molest the truck as little as possible I decided to bring the cables in through the plastic tubs that form the storage compartments under the rear mat. I wouldn’t have access to them anyways, and…. it is a double layer. An outer tub which is bolted to the truck, and an inner tub that comes out. I can repair a hole in the outer tub without anyone ever finding it. To get in and out of the bed I found two holes with slitted grommets already in there. More on the bed-end of it later.

Inner tub pulls right out. Remove the four torx and the lid comes off. Didn’t want it sitting there to get beat up by the wood. So then drill some holes and we have cable from bed to energy center.

Meanwhile…… the batteries arrived. Four on their sides, two on the floor. Note the B2B up one floor.

Pulled and secured the rest of the outside cabling. Some paint and some more trim pieces, then tied all the pieces together. Secured Batts #1 and #2 (behind passenger seat. Put two shutoffs on the trim pieces. One is truck battery cable before the B2B, the other will be in the 12VDC supply from the LIPs to the Inverter/Charger. I can reach both of them from the driver’s seat. And they are the key type. This will avoid accidental activation and it allows me to shut both off positively, even in the dark, or a smoke filled cabin.

Yes, the B2B is “front of house”. It’s the only thing I need to see underway. (An LED telling me all is OK). There is a remote for it, and I may break down and get it. It’s yet another piece. I did spring for the Bluetooth for the Victron. It will allow me to control the thing from my bed 6 feet above…..

All that was left was to: Tie it all together with cabling, program the B2B and the Victron, and trim/upholster. I’m considering adding a small 12V fan front and center to boost the AC/Heating registers….


To finish the trim I put a fiddle all around the platform, a “headboard” in the back, a nice carpet remnant on top and some decorative lattice on the side……

A little bit of trimming and some stain on the visible frame pieces to go……. (All wood was finished using a wipe of stain and then boiled linseed oil)


Back to the battery cabling. 2AWG is good to 250A at 4 feet…… No cable is longer than that, aside from the cables coming from the truck battery and those are 1G and will carry no more than 60A. An AC and a fridge are less than 2000W, that’s 167A….. Lugs and a proper crimping tool and it was all connected.

Word is to keep the cables between batteries, the paralleling cables, all the same length on each side….. The longest stretch was 20″, both the + and -, so that’s what I did for all of them. Leftovers from each of the two 15 foot coils were less than 6″. I’ll take that.

On to programming. Victron first…… hah. As I become more familiar with the Victron eco system I am learning that it is amazingly capable, especially in high power systems. The boxes do amazing things, and the operation and monitoring once installed is awesome, to the point where you can monitor and control the system from anywhere (almost) in the world. But the installation….. I am now aware of FOUR com systems. There’s CAN, USB, WIFI, some form of LAN/Ethernet, VE.Bus, VRM, VE.Direct although there probably is overlap in that list. Newer boxes come with Bluetooth. You can get a dongle for the older ones. Which I did. And it didn’t work. Wouldn’t even light up, and there was power to it. Finally figured it out. Some cheese head had put the sticker upside down on the plug……. B+ and B- were not lining up. I took the plug off, attached the wires per the sticker and plugged it into the dongle without even looking. Eventually I figured it out.

After that it did connect. But, surprise…… You can see some parameters and change Cº to Fº or adjust the max available AC amperage IN (or less if you’re not in a hurry as it extends battery life) but that’s it. You can not get to the programming part. (As in tell the darn thing the battery chemistry.) Old way was another dongle, hard wired to the Com port inside the I/C to a PC. And you need a password. New way is via another com protocol, on line via the VRM com system. Requires Cerbo GX box and an account….. All I want to do is tell the thing what kind of batteries I have!

And then the kicker…..

Victron (the manufacturer) does NOT provide support to end users, period. Videos, FAQ’s, manuals yes, but if you call they tell you to call your dealer/installer. My what? Dealer/Installer. Product comes into the US to distributors, who sell to trained installers, or in the case of my Amazon dealer: Brand Centric E-commerce. Like all dealers/distributors they get paid to support the product. Took me a while to figure out who my seller was. A piece of paper explaining the process and giving contact info inside the box would have made this a lot easier. The sales director North America who emailed me after I called and sent a rather terse email to Holland said that should have happened. It didn’t. Big fail on Victron’s part. It should be EASY to get help.

In fact if I had known this all up front I would have gone Magnum (again). It is not nearly as capable as Victron in larger more complex installations, but it is decent, there is excellent customer support, and it would have worked nicely in my situation. 95% of all motorhomes use it, I am well versed in it.

Fortunately there is also the internet…… Youtube and FB. Especially the latter has some reasonably versed people on it, and if you’re careful not to ask questions that can be answered with the book (RTFM) you can get some help. So with a LOT of time, effort and setbacks I slowly got my head around enough of it to do what I needed to do……. Which was first order the MK-3 USB interface.



Finally, the outside part. Lots of ways to do it, but again I didn’t want to drill a bunch of (large) holes for connectors etc. So, again, routed out the plastic outer storage tubs in the floor, into the bed through a hole with a nice rubber grommet in there. Used the female end of a 30A RV extension cord on one side so I have a nice sealed plug, and the same with a male end for a 12/3 extension cord, good for 15A. For storage, and to protect against the elements I put them in little plastic water tight cases, except for the holes I made in the bottom, and I hung the cases on the truck bed wall with aluminum brackets. (Love the flat beak vice grips/hand break)

Note 30A RV to three 20A Edison dog bone. Bring on the tools! And the other side the shore power cord:


Last but not least…… testing.

First problem I found was that the cutoff switch in the cable between the batteries and the I/C was getting hot. And that was at 80A charging. One of those key models says they are good for 200A. Right. So replaced that with a proper 400A battery switch. Got a little fancy there too. ON/OFF switch for the Victron Bluetooth as well as an orange LED with ON/OFF switch to provide some light under there…… falling phones and all that.

Batteries were talking nicely. Only gripe there is that EVERY time you leave the app, I didn’t say close, I mean going to another page like the Victron, you have to wait for the batteries to reload. But, the info is there. VERY cool.

Then I had a flashing absorb/float LED on the unit itself. This is a “temperature sense” error, as confirmed by the app. It’s seeing temp, (68ºF) apparently, and the probe is hooked up. More on this to come when I figure it out…… which is not easy as we learned above.

The next issue was this thing. 250A….. right. Got up to 130ºF at 90A charging and popped after inverting for five minutes at 125A/140ºF. Apparently these are junk. Returned and replaced with a Blue Sea straight MEGA/AMG fuse, 200A. This also allows me to adjust the value if I need to. I’ll just have to carry a spare or two, then again…. these should NOT be blowing. (pic of new setup forthcoming)

And, I was having second thoughts about cable sizing. Cables were not getting warm, but there was some voltage drop along the way. Under 3% total, but I wanted to see if I could reduce that. Because when the I/C says 14.6 and you get 14.2 at the last battery…..The longest run was from the I/C to the other side of the cab and the negative terminal of battery 1. I decided to upgrade this to “0” gauge. And kits with two colors are cheaper, and while I was at it, I decided to upgrade the positive to the first battery as well, while I was replacing the fuse…..

Here is the data….

From the I/C positive side to the first terminal on battery 6: 0.22VDC loss. Through 6 batteries to number 1 another 0.08VDC for a total of about 0.3VDC That’s just over 2%. Less than the 3% mentioned on a lot of websites as “good”. Question was: Would fatter cable help?


Nicely: 90A on my 15A garage circuit.


Also nicely. Plugged the camper into the 30A plug and fired up an air conditioner. 1200W. Until the 250A fuse blew. (See above)