"Simple but it works" 12v Power box writeup...

Martinjmpr

Wiffleball Batter
This is really a companion to my other thread where I installed a Renogy 20A DC-DC battery charger in my 2018 F-150.


That thread focused on the Renogy charger and how I got it installed and working, but I realized I kind of short-changed the description of what it was that the Renogy charger was actually powering. So I thought I'd do this writeup of my 12v "power box" for those who are thinking of coming up with something similar.

Background:

So the idea behind this was that I needed something that would take the place of the "house battery" that I had in my '04 Suburban. The Suburban had a dedicated spot for a 2nd battery and a relatively simple electrical system, so adding a 2nd battery to power the refrigerator (Indel-B TB-41 40 liter fridge/freezer) was a pretty straightforward process.

When I replaced the Suburban with a 2018 F-150 I had to reckon with two complications: First, there simply was no space to put a 2nd battery in the engine compartment without relocating other components, and Second that the modern F-150 with its battery management system and "smart alternator" might not work with a dual battery (or might not work correctly.) Given the complicated nature of modern electronics, I decided not to monkey with it and go with "plan B" which was to have a removable, rechargeable 12v power source for the fridge.

Construction:

I started with a Minn-Kota 12v Trolling Motor enclosure. This is basically a cheap battery box with a few modifications: It has a set of terminals that connect to the battery and go to terminal posts on the OUTSIDE of the box. These terminals in turn have wing nut cap screws to protect the terminals from grounding (they are also protected by a circuit breaker.) Additionally, it has a pair of 12v cigarette lighter type outlets (protected by a second, 10A circuit breaker) and a rudimentary "Red/Amber/Green" "battery life monitor" aka volt meter. Total cost was around $60 and available from Amazon (NOTE: I'll post the amazon links to all products at the end of this post.)

2019-09-23 20_55_17.jpg

The battery I chose was purchased at Costco, a simple Group 27 deep cycle Marine/RV FLA (wet) battery, 90AH. I may eventually upgrade to an AGM, or I may not. Biggest drawback is weight, probably 75lbs!

Although the battery box could have worked "as-is", I added a few things right off the bat. The first thing was a Battery Tender SAE connection for charging. I keep my motorcycles on a battery tender (trickle charger) at home and since I had just sold a motorcycle, I had an extra tender, so I put the lead on and hung it out one of the side cable slots on the battery box. This way I can keep the battery plugged into a trickle charger (.75a 120vAC) at home when not in use. The .75a charger will not over charge it and will make sure I always start off with a fully charged battery.

2019-09-23 20_56_42.jpg

The next thing I added was an LED Voltmeter and dual USB charging port. I actually had purchased this to put into the Suburban and never got around to it, so it was sitting on my bench. The Minn-Kota enclosure did not come with a USB port and I didn't like the "Red/Amber/Green" volt meter, I preferred an actual voltage reading, and this filled both requirements. It's wired directly to the battery with ring terminals.

2020-07-06 21.45.55.jpg

The next problem revealed itself the first time I tried to use it to run the refrigerator. Theoretically, the 12v "universal" power ports on the side of the Trolling Motor box should work for the 12v fridge right? Well, yes, "theoretically" they do - the problem is, they won't stay connected! The spring "plunger" in the middle of the fridge plug keeps pushing against the inside of the enclosure and disengaging it. I noticed this the first time on a camping trip where I couldn't figure out why my fridge was not being powered and I realized that if I wasn't actively pushing the plug in, it would not stay engaged.

Years ago I had purchased a simple 12v power plug that was attached to two alligator clips for direct attachment to a battery. I was relieved to find out that my 12v power plug WOULD stay plugged in to this socket. So I cut off the alligator clips and replaced them with ring terminals. Ring terminals then went onto the external power posts on the Minn-Kota box. Not pretty, but it works:

2020-07-06 21.45.43.jpg

Now at this point, someone is sure to say "why not just get rid of the crappy 12v cig lighter plug altogether and put the ring terminals on the fridge power cord?" Actually, I plan on doing that soon, although for right now this works (I do have a second power cord in case, for some reason, I need a 12v cig lighter plug for the fridge.)

The final modification was getting power TO the box to keep it charged. I used a HYCLAT Anderson-type connector with some 10g wire I had laying around to connect the DC-DC charger to the battery box. 10AWG should be more than adequate to get the power from the Renogy charger to the battery box (roughly 2.5'/30" max.) Wired to ring terminals on the battery through the cable tunnel on the opposite side of the SAE connector:

2020-07-06 21.45.59.jpg

Results:

After almost a year and 6 camping trips with this system, I have to say it has met or exceeded all of my expectations. Never has the battery voltage dropped low enough to cause the fridge to shut off. The Renogy charger seems to keep the battery well charged and with 90AH on board, I don't need to worry about running it down.

Most recent camping trip was 4 days. We actually had an electrical hookup at this campground and normally when we have electrical hookups, I just run an extension cord to the fridge to run it on 120vAC while we are parked. But in this case, I really wanted to see how well the battery box and DC-DC charger would work and it worked very well. Even though it was hot (over 85 degrees every day) and I normally kept the windows on the truck rolled up (I'd estimate daytime high temps inside the truck were over 100) the fridge stayed cold and battery voltage never dropped below 12.3. I did a little driving each day - maybe an hour the first day and a half hour the second day - but that seemed to be more than enough to keep the battery "topped off."

My guess is that without running the truck, I can power the fridge just from the power box for at least 2 full days depending on outside temperature. If I drive the truck at least an hour each day, there is no practical limit as to how long it will run (or as I like to say it "I'll run out of food to keep cold before I run out of power for the fridge.")

Would I do it again? To be honest, I'm not sure. By the time you add up all the components I bought (including the DC-DC charger and all the wiring necessary for that) I'm in for about $450, and that does NOT include my time (most difficult step was figuring out how to get power to the DC-DC charger. I eventually settled for running a pair of 8g wires directly to the battery through a hole in the floor of the cab, which I had hoped I wouldn't have to do.)

Nowadays, for $450 you can get a Lithium-Ion "power pack" that will charge off of either 120vAC or a 12v DC cig lighter, and even includes an inverter (which mine does not.) Would that be a "better" solution? Only time will tell. Certainly it would be a LIGHTER solution than my ~80lb monstrosity (though in all fairness, I could lighten mine up considerably with a Lithium battery, too.)

Those who are very particular about safety may also note that I did not put a fuse in-line between the Anderson connector and the battery. Should I have done so? Probably, but this entire run of cable from the battery to the DC-DC charger is only about 2 1/2 feet long, on double insulated wire (i.e. insulated and then surrounded by wire loom) and stays inside the truck at all times. I suppose if I wanted to be "Mr. Safety" I could splice a 30A fuse in between the Anderson connector and the battery but I don't really think it's necessary.

Anyway, that's my writeup. Hit me with any questions you have.

For those interested, here are the links:

Minn-Kota trolling motor enclosure:
https://www.amazon.com/MinnKota-Trolling-Motor-Power-Center/dp/B001PTHKMG/ref=sr_1_5?dchild=1&keywords=minn-kota+trolling+motor+battery&qid=1595271028&sr=8-5

Battery tender SAE harness:

12v dual USB port and volt meter universal cig lighter socket:

12v Universal Power Outlet with Alligator clips:

HYCLAT 6 -10 gauge Anderson type connector:
 
Last edited:

Martinjmpr

Wiffleball Batter
Forgot to add this but the main advantage of this system over a dual battery system is that this is fully removable and can be used on multiple vehicles if necessary (as long as there is some way to keep it charged.)

The main drawback is weight. As I said I would estimate close to 80lbs. Don't let that flimsy plastic handle on top of the box fool you, you will NOT be lifting this up with that handle! Two hands on the side of the box and a hernia-inducing walk to get it from the garage to the truck. After that is stays in the truck and does NOT move until we get home.
 

tsherrygeo

New member
Looks good! I've been checking out the Ice Fishing battery packs and was thinking of wiring up a small portable one using a spare ammo can.
 

Recommended books for Overlanding

We Will Be Free: Overlanding In Africa and Around South A...
by Mr Graeme Robert Bell
From $20
Jupiters Travels: Four Years Around the World on a Triumph
by Ted Simon
From $21.83
The Longest Line on the Map: The United States, the Pan-A...
by Eric Rutkow
From $13.96
Road Fever (Vintage Departures)
by Tim Cahill
From $7.49

john61ct

Adventurer
For less manly users, can get portability by breaking it up into modules with Anderson connectors in between.

30lbs of LFP delivers a fair bit of energy, and there is no need for it to be in the same box as the SC, inverter etc.

Even 600Ah can be made portable in that sense, silly to have separate banks for your camper vs trailer vs boat vs off-grid shack
 

Martinjmpr

Wiffleball Batter
For less manly users, can get portability by breaking it up into modules with Anderson connectors in between.

30lbs of LFP delivers a fair bit of energy, and there is no need for it to be in the same box as the SC, inverter etc.

Even 600Ah can be made portable in that sense, silly to have separate banks for your camper vs trailer vs boat vs off-grid shack
Yeah, but 600ah of LFP, you're talking big $$ there.

My setup is heavy but it's also cheap.
 

john61ct

Adventurer
Yes absolutely.

In fact lighter lead batteries have a much shorter lifespan.

In that case I'd probably leave the lead in each vehicle / location, and just have the output bits and electronics as one or more separate modules.
 

obchristo

New member
Funny I have the same box and battery. Ran into the same issue with those crappy 12v cig lighter plugs, so I replaced them with a similar dual usb / voltmeter on oneside and a Powerwerx Panel Mount Housing for Two Anderson Powerpole Connectors with a Weather Resistant Cover (with a 30 amp fuse) on the other. I replaced my fridges cig lighter plug with an Anderson Powerpole connector. Similar charging setup except it attaches via ring terminals. I also made a Anderson Powerpole connector to cig lighter cord so I can hook either an air pump or 6 usb Outlet that I use to charge multiple devices.
 
I went the very similar route with a 50 Ah LiFePO4 in a Milwaukee packout box. Was able to get a steel mounting plate so that it sits secure above my storage drawers in the trunk. John's point about disaggregating stuff is quite valid. I'm not short on space but if I ever get to that, I would consider just a small enclosure for the battery with everything else external and mounted around the vehicle and paired with quick disconnects. All in I'm sitting at just a tad over 26 lbs total ( though my DC-DC is mounted in the vehicle). It's just light enough to quickly remove from the vehicle and has all the usb, usb type-c, QC 3.0 and other charging sources for when we are outside the vehicle.

I have the same dc-dc charger and have mixed feelings about it. I picked it up for under $100 so was super cheap, but it is quite large (in comparison to other options) and loud when charging. I like the fact that I can just wire an ignition wire and not worry about smart alternator charge detection (I charge my starter at times via the OBD port so wouldn't have to worry about the DC-DC picking up the higher voltage and draining my starter). I also like how easy it is to set up the DIP switches for the exact lithium profile for the battleborn LiFePO4 (or any other chemistry).

I could fit an 18 or 30 Amp Victron dc-dc charger in my box so that may option exists as well in case I want a box mounted dc-dc so that I can take the unit from one vehicle to the other more easily.
 

Attachments

Last edited:

Martinjmpr

Wiffleball Batter
A month or so after I posted this I went ahead and deleted the 12v cig lighter plug for the fridge. I cut the 12v plug off of the fridge power cord and put a couple of ring connectors on there - now the fridge gets hooked directly to the two terminals via the ring connectors, so I don't have to worry about it getting disconnected.
 
Top