View Full Version : Dedicated Fridge Battery

April 8th, 2010, 21:13
What's the easiest and cheapest way to do this? This may be temporary, I'll probably upgrade after an upcoming trip for more power/options.

I'm looking to add an Optima Red Top i have as a dedicated batt for my Fridge, and have it charge when the Jeep is running.

Being able to jump myself would be cool as well.

Again, i'm electrically challenged so help me out here.

April 8th, 2010, 22:10
First off, I wouldn't do a red top if you are planning on running it down once in awhile. Do a Yellow top. They are designed to be flat lined now and then.

April 8th, 2010, 23:06
I already have the Red Top, if i were buying another i'd have opted for the Yellow or Blue.

I read numerous times at EXPO that guys state they can go 3 days on their fridge with a Red as their starting batt. Figure the Jeep will run just about everyday to recharge and should get me through the trip.

Or am i misinformed?

April 9th, 2010, 07:15
If you already have the battery than I would use it.

The best way to hook up a dual battery system to use things like a fridge, winch and accessory lights is to run it through an isolator.


What this does is basically isolate the two batteries from each other. The charging system charges both at the same time. You keep the normal one under your hood running just like it is but hook all your accessories through the second one. This way if your fridge kills your battery...or winch, or offroad lights...or or or..... You can still start your jeep.

My plans in the very near future are to get rid of the factory air box and put a second battery plate there. Then I will run all of my gadgets off of that. I plan to even wire the factory 12v lighter plugs off of that battery. Then, unless the main battery dies I can still start the Jeep. Somewhere I remember seeing an isolator switch that would let you via an inboard switch, switch between the two so if the main battery died you can switch the the aux battery to start the vehicle without a set of jumper cables.

edit...found one with a good explanation of how they work.

April 9th, 2010, 09:22
OMG so yesterday i stopped at this place that does solar and wind power and talked to the guy for a few minutes .. when i left there my head was spinning... told em i wanted a system for my trailer completly self reliant .. what i wanted to power and so on.. basicaly i want a couple led lights and to run a fridge.. and a kegerator.. no problem , bout a thousand bucks he says.. i dont think sooo.. i can buy a lot of flashlights and ice for that price.. but he was talkin bout batteries and the differances he was explaining that the solar batteries are kinda inbetween a regular battery and a deep cycle.. way expensive ... good luck overland and let me know what you figure out

April 9th, 2010, 10:42
Thanks Doc, i'll read up. The isolater switch you mention.. could the same thing be accomplished by adding a Marine switch? I just want to get something up and running for this trip.. then really think about what i need for the next rig/trailer.

Did you see that ebay link posted over EXPO about the Nat'l Luna copy?

I'll have to do some reading...

Swampy... you could get a Honda EU1000? genny for half that.

April 9th, 2010, 14:19
You'll want the secondary battery (and related accessories) on an isolator, so you don't drain your starting battery when the vehicle is OFF. There are two ways to do this - you can use a solenoid isolator (/not/ the Ford starter motor solenoid, but a decent quality 100% duty cycle piece. It's going to cost more, but it's also going to last a good deal longer) or you can use a solid-state isolator (which is essentially a network of high-current diodes.)

The solenoid:
Advantages -
- May be wired with "bypass switches" in various configurations
- Physically smaller (about the size of your fist)
- Available in much higher current ratings
- Less operating heat
- Some are sealed against immersion, most can handle being splashed.

Disadvantages -
- Not always easy to locate
- Requires finding and wiring in a "trigger" lead for automatic operation

The solid-state pack:
Advantages -
- Automatic. No switches
- No user intervention required past installation, in fact.
- No need for a "trigger" lead generally, either.

Disadvantages -
- Greater operating heat - the case is a heat sink. Make sure it can get a useful amount of airflow.
- Limited current capacity.
- Expensive - and not a linear relationship between current capacity and price
- Not always waterproof or weathertight.

Which one would I use personally? It really depends on the application, although I have more experience using solenoid isolators than solid-state packs. A proper bypass switch would allow you to "self-jump" without even getting out of the driver's seat, in fact - and getting a solenoid that has an ampacity of two to four times that of the typical solid-state pack is easy.

However, if I'm designing a system to run on minimal to no user intervention whatever, I'm probably going to go with the diode array. Most people who need the "user friendly" setup aren't going to be the sort of people who are going to remember what to do with which switches, so I'll simplify their system as much as possible.

Feel free to hit me backchannel if you want to start designing a setup. The good news? Most multi-battery isolated setup really don't care what battery is on each side of the isolator - so when you finally kill off your existing Red Top that you're going to use, you can replace it with a Blue Top without making any changes at all to the system (solid-state or solenoid-based!) The only time battery type and age becomes a problem is when you have a "bank" of batteries - if you've got, say, four batteries in parallel and one goes out on you, you'll be replacing all four batteries in the bank. The starting battery, on the other side of the isolator, can be replaced on its own.

Yes, this also applies with "off-grid" storage arrays fed by solar, wind power, or small hydroelectric setups.

April 9th, 2010, 21:20
Did you see that ebay link posted over EXPO about the Nat'l Luna copy?

No...do you have a link? I have $500 bucks sitting aside waiting for the Edgestars to go back on sale. Soon as they came back down I was going to buy one.

April 10th, 2010, 08:31
Jon, as always thanks for the detailed info. I'll read it again and ask questions if i need to.. sure i will.

Ryan.. the Nat'l Luna copy i referred to was a batt mgt system. Stump runs the NL setup. I'll get you the link.

I hear those Edgestars are nice.. but i'm glad i got a deal on an Engel. Keep your eyes open.. they pop up often.

April 10th, 2010, 14:06
Jon, as always thanks for the detailed info. I'll read it again and ask questions if i need to.. sure i will.

Ryan.. the Nat'l Luna copy i referred to was a batt mgt system. Stump runs the NL setup. I'll get you the link.

I hear those Edgestars are nice.. but i'm glad i got a deal on an Engel. Keep your eyes open.. they pop up often.

No worries - you know how to find me!

April 11th, 2010, 13:25
Jon, stopped at a buds and did some work on the wifes ZJ while we were BS'n on his dual batt setup.

He recommended the Sure power 120amp part#12023a. He said this will do exactly what i want at minimul cost. ~100 for the isolator and wiring kit.

I didnt think to ask about the 120amp rating.. is this amp requirement dependant up on the alt's max output? So a 90amp alt would have a safety margin with the 120 amp isolator?

Now, swapping this isolator in to the ZJ later with a 136amp alt would it then be insufficient? Would a 140 amp isolator have enough of a safety margin?

Or am i still clueless to this point?! :D

April 11th, 2010, 14:59
The current rating of a given isolator is the max current you can push through the thing consistently. It isn't strictly dependent on the alternator's output current peak, since you're running your engine management off of your alternator as well (for a modern FI engine, you're looking at 30A or so to keep it running, sometimes more. Subtract that from your alternator's max output.

(Also note that actual max has a tolerance of -5%/+10% from rated max output. So, you're 90A unit would have a theoretical max from 85.5A-99A)

If you want to ensure that you don't kill your isolator - since I'm assuming it's a solid-state pack and tends to cost more than a solenoid - you can put in a fuse or a circuit breaker between primary distribution and the isolator proper - so, if you try to shove too much through it, you'll blow a ten-dollar fuse instead of a hundred-dollar isolator. Guess which one I'd rather blow out!

Given that he's talking about the 120A unit he's using, that should cover you handily up through a 136A upgrade without adding a fuse (theoretically.) If you to past that, I'd definitely want to put a fuse inline.

Granted, I'm more into simplicity and overkill - which is why I'd use a 200A constant-duty solenoid switch. But, that's just me (and I've plenty of experience in dealing ith solenoids anyhow.)

April 11th, 2010, 16:23
I use the Xantrex Pathmaker 100 set-up, and love it. I got it from Will at Sierra Ex. Just got back from a 3 day trip to the mountains camping, and my aux battery (deep cycle die hard...) went from 12.7 when we got there down to 12.1V when we left (3 full days, with no charging), and was stil pulling everything I had running with no problem. I run a big Norcold fridge and the same inverter you have John. I think the Red top will be just fine for an overnighter or two on your trip. Once you get going again, it'll top off just fine.

~ James

April 13th, 2010, 12:43
Looks like everything is getting covered, BUT - just a thought - depending on where you put the battery, you'll want a battery box in the cargo area.

I gotta admit that I like my NL setup, but it was expensive for the portability; however, I can take it all out of the car and go exploring for the day if I'm in a remote location without fear of getting it all stolen.