Refrigerator conversion

[MCDenny]

Originally Posted by Timber Wolf

This is very interesting and I am glad somebody with actual experience with this set-up posted. I am curious about two things: 1) Why did use two group 31 batteries over two 6V batteries? I have my own theory why the two 31s may be preferred but would like to hear your reason. And 2), there are several people posting to this thread saying that 2-3 days of partial Sun makes a 12V refrigerator or Solar system impractical for them. You seem to state the opposite (based on your actual experience) that your system can run 2-3 without ANY Sun. This seems to dispute their position. Would you agree?

We also have a 12v compressor fridge, a TruckFridge 4.2 cu ft model. It uses about 380 watt hours (31 ah at 12v) per day. Two batteries, whether 12v or 6v, give about 200 ah capacity. 3 days takes about 50%. Obviously one battery gives half as much.

We also have a 100w solar panel but have not used it in any shady areas. In the desert the batteries are fully charged by noon.

More than you probably wanted to know on this subject at the "refrigeration" post on our blog.

I use two 6v is series to insure they both see the same charging current. Two 12v in parallel would work fine too but keeping the batteries equally charged is trickier. A 12v battery is six 2v cells connected in series. So is two 6v batteries.


Denny Wolfe
Wanderingourway.wordpress.com

[Carol H]

Originally Posted by Nut501

Per,
Where can you buy Novacool equipment in America?
thanks,
Carl

I believe its actually Nova Kool and their website Novakool.com has a list of distributers you could contact for a seller near you.

[Steve Hammel]

Good used ones can be found. I'd start with wrecking yards that dismantle semi trucks. 12v fridges are what they use in the sleepers on these rigs. I have bought several from wrecking yards, off of craigslist and off of ebay. 12v fridges with solar are FAR superior to propane. Don't let people who have never used one talk you out of it.

[Timber Wolf]

Originally Posted by Byron Kinnaman

NOTE---- Scamp wiring is designed for 20 amp maximum. A larger converter with a big load like you're talking about requires rewiring Scamp with bigger wire.

That's a good point and yes, I was planning on rewiring the 12V side of the Scamp. I am using 12 guage wire for all new 12V circuits and adding a new 12V fuse and distribution box along with the new converter/smart charger. Just bringing the old Scamp into the current Century.

[Nut501]

Originally Posted by Carol H

I believe its actually Nova Kool and their website Novakool.com has a list of distributers you could contact for a seller near you.

Carol,
Thanks! I should have thought to just Google Novakool in the first place!!!
You have been very helpful!!!!!

Carl

[Per Walthinsen]

The reason for using two Group 31 batteries is a bit embarrassing: I decided 14 years ago during my first intro to trailer ownership to move the batteries inside into vented boxes, one on each side of the trailer. Custom built the boxes, ran the wiring and switching. Seemed to work OK, so I kept it, despite some evidence that two 6-volt units would be better. (Group 31s are easy to find, so that was a factor, and switching from one or the other if necessary is also easy, so out of laziness I kept it).
I have yet to go below 50% charge (in order to protect the batteries), so if we camp under the tree canopy things get iffy on the third day if we use heat during the nights. If we go down the road a spell for another camping spot, the car could theoretically charge the batteries up, but generally the solar panel is enough. My current tow vehicle has a hefty alternator, but so far I haven't tried to use it to charge.
One factor is the MPPT type solar controller (Blue Sky) which is able to start charging with minimal light available while being fed by a solar panel which puts out more than 20v when going full bore. The MPPT does not waste the excess electricity but converts it to the appropriate voltage and has several charging stages to protect the batteries.
Another factor is that I changed the charge wiring from the car to 6 gauge should I need to use it. Otherwise slight voltage drops to the batteries can inhibit effective charging.
Here on the left coast I found the NovaKool at Boat Electric in Seattle. If you want a frig which uses as little power as possible look for a brand with a Danfoss compressor or the equivalent. We no longer turn on the frig two days ahead of going camping any more, since it cools down in a big hurry.

[Timber Wolf]

Thanks for the reply Per. I would like to love two 32s just because it makes sense to me that if one goes down you still have 12 volts, but one battery is probably not going to die all at once. The other advantage to two 31s is I could buy just one now to get going and add one more later. But then I would have batteries of different ages and conditions and that is not good. There does seem to be a small advantage size wise to mounting two 6V batteries, they are shorter but taller. I am just going to have to bite the bullet and pony up for two sixes it looks like.

I am glad to hear about your positive experience with the MPPT controller. I just bought a system with one and it was significantly more expensive than a PWM unit. I figured it was worth it and also got a little bit larger controller so I could "grow" (add panels) with it.