Excursion Auxiliary Power Set Up Help.

[hbabler]

Please help a novice plan this out.

I have a 7.3 Excursion that I am attempting to install a ARB element fridge in.

According to my figures I need at least 8AWG to the rear, but I am trying to leave some room for expansion as well. Eventually I would like an electric compressor among other things. I am planning on using the Blue Sea ST Blade 6 circuit.

Can I run the fridge off of my vehicle batteries for now?

Do I need to add a 3rd battery and or a roof top solar panel? If so whats the cheapest way to do that? Whats a reasonably priced controller to allow DC to DC charging?

If I don't add another battery will the voltage cut off on the fridge save my batteries?

Thanks for the help!

Hudson

 

[Rbertalotto]

You can certainly run it off your truck batteries. Most refrigerators offer a low voltage shut down so if the voltage gets too low it disconnects from the trucks batteries so you have enough left to start the truck.

I recently installed a RENOGY DC to DC converter. Offered in 20 and 40 amp rating. If you know the output of your alternator, a quick call to RENOGY will assist in what one to use. These units are amazing. With a good AGM or Li battery you can recharge from 75% to 100% in as little asa 30 minutes.

Do a search on youtube for Will Prowse....He does an indepth review of these Renogy DC to DC chargers.

As far as wire, don't use 8g to run from front to back. You will overload it in no time, trust me on this, I know! Use at least 4g wire and 2g would even be better. The 40a DC to DC charger requires at least 4g for a 20' (40' both ways +/-) Wire is cheap, use big is better! Don't forget a proper sized circuit breaker at the front battery.

Solar is great, but you need sun. Not always available. In my set up I have 120W portable solar panel that I deploy when stationary for any length of time. But for 90% of the time, the aux battery is being charged as I wander around in the vehicle. The refrigerator and the aux battery live in my tow vehicle at all times.....everything else in the overlanding trailer. The refrigerator is the only device that needs to be hooked up to 12V 100% of the time. And keeping it in an AirConditioned vehicle allows it to be more efficient during HOT season.

 

[hbabler]

Thanks for that info. I actually have a bunch of 2awg that I could use. Should I run both a ground and a power wire all the way to the back?

 

[WilloCo]

Yeah, big cabling is the way to go as it'll reduce the voltage drop. For big cables, I like to run them through some hose anywhere they can rub. (I do this on all my winch installs.)
Do yourself a favor and add a big breaker at the battery end. I like this style:

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Size it for your load. I'll pop if you short for some reason and protect your ride. It's also really convenient when you want to work on the wiring on the aux panel, just push the button to pop the breaker and you're safe. Edit: I use these on my solar system of my RV.

For your ground, You may want something like this anyway:

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Run your ground wire to that, then add a run down to the chassis from this as well. This is just insurance at this point but it won't hurt.

Keep in mind that fridge isn't really high load. The air compressor will be. (I have an ARB dual that has two 40 amp fuses, one for each motor.)

 

[luthj]

Its tempting to just ask for recommendations and anecdotes. However, the best option is to learn how to do the math. There are calculators to make it easier, like the one below. Figure out what your max load will be (including your future needs). Then calculate the round trip wiring length. Choose a 4% voltage drop for sensitive items (like fridges etc). If you have access to a good chassis ground, you can use that to reduce the total wiring length, and thus required gauge.

Circuit Wizard - Blue Sea Systems

With regards to running your fridge from your starter battery. What size is it? How old is it? How long do you need to run between longer drives? It depends on the fridge and ambient temps, but you may only get a day or two in some cases.

 

[Rbertalotto]

Using chassis for ground is usually frond upon. Somewhere in the chassis there might be a simple piece of wire grounding one part of the chassis to the other, this will be a weak point when using chassis for the return ground. If just a refrigerator, it most likely would be fine. But anything with a larger current demand could cause issues. An extra 15 to 20’ of wire is cheap insurance.

 

[rayra]

I've been planning all along to run a carrier-mounted winch from either front or rear hitches. So I ran some heavy cabling (1/0) to the rear cargo area of my vehicle and wound up using it as a power source for all sorts of power inverters and connections in the cargo area of the vehicle. I've also added rooftop solar and am backfeeding my under-hood Aux battery via that big cable.
I ran cables for both Pos and Neg, ran them in plastic armored flex conduit. Anchoring the conduit to the frame and body in a fairly sheltered location. Then up thru the cargo floor using bulkhead fittings. So the whole run is waterproofed and protected from abrasion. And I can basically run whatever I want from the rear.
THere's a bunch of details in several related topics.

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Designing a complicated power infrastructure, seeking inputs on my inputs and ouputs

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I've just done the front hitch and carrier fitting yesterday, and the next several weeks I'll be adding the extension cables and creating the front and rear bumper power plug connections.
The same general concepts apply to the OP's quest. It's a pretty straightforward solution to a power demand in the rear of the vehicle. Running a pair of heavier gauge wires, and doing so in some protective conduit is a pretty easy task. And there's a wealth of ways to terminate the lines or install bulkhead fittings or connections or an Aux fuse panel in the rear area to provide other charging ports, USB connections, etc etc. Once you lay the heavier wiring / cabling as a backbone all sorts of other options become possible.

 

[shade]

With a good AGM or Li battery you can recharge from 75% to 100% in as little asa 30 minutes.

What AGM battery will fully charge from 75% to 100% state of charge in 30 minutes?

 

[luthj]

What AGM battery will fully charge from 75% to 100% state of charge in 30 minutes?

One that was just fast discharged (C/2 rate or so). Even then you won't get above 95% in 30 minutes, even with a C/2 charger.

 

[shade]

One that was just fast discharged (C/2 rate or so). Even then you won't get above 95% in 30 minutes, even with a C/2 charger.

How many thousands of cycles would you expect from an AGM battery pushed that hard?

 

[luthj]

How many thousands of cycles would you expect from an AGM battery pushed that hard?

Hard to say. If the battery is always charged to 100% after each cycle? I would expect 500-1300 lab cycles. 300-800 real world cycles is more likely. High currents aren't as damaging as partial cycle abuse.

 

[67cj5]

I don't think you need to add all this stuff unless you are going to live in it full time,

I just spent 4 days using a single battery system and I run my fridge from a Dometic PLB 40 with it plugged in to the Cigar Socket, When I ran the fridge Only from the PLB 40 I used 14% of it's power after 27 hours and then I plugged the PLB 40 back in to the Cigar Socket and it only took 20/30 minutes to recharge it to 100% again,

The best part about it is does not need any fancy wiring or DC to DC Chargers or Charge Controllers or the need for heavy duty cables running from front to back, But best of all it's 100% portable.

 

[hbabler]

Okay thanks for all advice. I am in the process of building this set up out now.

I have done the circuit calculations and I am going to use the 2AWG that I have as it is actually the correct size for my numbers.

I will terminate it at the blue sea fuse panel and then wire the fridge off of that. Going ahead and sizing it correctly will allow me to add additional loads as needed.

I have two ideas for this set up long term. The first is just allowing the fridge to pull off of my truck batteries. I was toying with the idea of running a solar panel on the roof to keep the batteries topped off. If I did that will a normal charge controller like the renogy PWM wanderer work?

Later on I would like to add a house battery. If I did that then I would need a DC to DC charge in addition to the solar controller correct?

Thanks for all the help.

 

[hbabler]

Okay I’m getting close to building this setup. Here is a rough diagram, what do you guys think?

 

[hbabler]

Thanks Verkstad, drawing is not my forte and I couldn’t find a dang ruler when I threw it together this morning.