AC/DC Refrigerators

[Dave Walter]

I think that if I was to consider moving from 2 to 4 batteries, I would also try to fit the additional two batteries on the rear bumper. I really like the storage space in the front box, and to me, filling the box with batteries is a very poor use of space.

[float5]

Steve, I know you have 6Vs but could a 12V be used with the two 6Vs and put three batteries instead of four in the box, thereby still having some weight allowance for blocks and chocks?

[jamman]

Could - yes. Good idea - no.

They have different charging requirements and different discharge curves. You would need to install a (marine style) battery bank selection switch for using power. And a smart multi-bank converter/charger for recharging the batteries.

[float5]

jamman, there are people who have one 12V instead of the two 6Vs in their Escape. So I suppose someone could have two 12Vs.

But I have seen many claims that two 6Vs are better than one 12V for our purposes.
(Then there are are those who take issue with that.)

[cpaharley2008]

I have a single 12v group 29 battery and I'm thinking about adding another to double my capacity to about 100 useable amps (260 total) this may allow me to run my refer off 12v while towing with the smaller 95 watt ETI solar panel.

[rbryan4]

Originally Posted by Floating Cloud

jamman, there are people who have one 12V instead of the two 6Vs in their Escape. So I suppose someone could have two 12Vs.

But I have seen many claims that two 6Vs are better than one 12V for our purposes.
(Then there are are those who take issue with that.)

It's not just claims. The amp hours are higher with two 6v vs a single 12v. You can run stuff longer -- that's it.

There's always a trade-off, and here of course it's the space, weight and additional cost.

[rbryan4]

Originally Posted by cpaharley2008

I have a single 12v group 29 battery and I'm thinking about adding another to double my capacity to about 100 useable amps (260 total) this may allow me to run my refer off 12v while towing with the smaller 95 watt ETI solar panel.

Yeah, I don't think you'd have any trouble doing that with such a setup.

[Brian B-P]

Originally Posted by Floating Cloud

Steve, I know you have 6Vs but could a 12V be used with the two 6Vs and put three batteries instead of four in the box, thereby still having some weight allowance for blocks and chocks?

The mismatch would not be good, but three identical 12V batteries could be used. Having three would make the issues with getting the batteries to each do their share even worse, so two really big 12V or four smaller-than-usual 6V would be better.

Originally Posted by rbryan4

It's not just claims. The amp hours are higher with two 6v vs a single 12v.

Only because they're bigger in total. For the same total weight and bulk in the same range of batteries (same type and quality), it doesn't matter electrically whether they're split up in groups of three cells (6V) or of six cells (12V). You can use two 12V in parallel of the same size as two 6V in series, and have the same total capacity... but may have problems with keeping them balanced (sharing the charge and load equally). You can also buy one huge 12V battery which weighs twice as much as the typical "golf cart" 6V, and has the same amp-hour capacity as a pair of the 6V... but it's a problem to lift and get into place, and not common (and therefore not cheap).

The popularity of pairs of 6V batteries about the size of those used in Escapes and other RVs is mostly about being the largest manageable size for a person to lift, and being readily available. Both of those are important factors.

[rbryan4]

Well yeah, I'm talking about the common sizes that will easily fit into an Escape. (and easily power my DC fridge which I hope I hope to get ETI to install for me...lol)

[gbaglo]

Wouldn't a DC fridge running in extreme hot temps gobble a ton of battery?

[alanmalk]

Originally Posted by Brian B-P

You can also buy one huge 12V battery which weighs twice as much as the typical "golf cart" 6V, and has the same amp-hour capacity as a pair of the 6V... but it's a problem to lift and get into place, and not common (and therefore not cheap).

Back in my boating days I used one 8D 12v battery. That monster weighed about 170 pounds. Plenty of amps but I couldn't possibly lift it myself.

Originally Posted by Brian B-P

The popularity of pairs of 6V batteries about the size of those used in Escapes and other RVs is mostly about being the largest manageable size for a person to lift, and being readily available. Both of those are important factors.

Very practical advice. To carry it one step further, you could purchase 2v lead/acid cells from a solar supply store and make your own 12v battery. I think the smallest 2v cell weighs in at about 70 pounds. On a good day I might be able to lift one of those into place. On the other hand, do I really want to add 420 pounds to my trailer? Nope, rather carry fishing gear; so I'm still waiting for that fabled 30 pound, 250 amp-hour lithium battery for $125 US.

In the meanwhile I am seriously thinking about 2 Sears Platinum Marine group size 31 AGM 12v batteries in parallel, for a total weight of 150 pounds, and 200 amp-hours.

--
Alan

[rbryan4]

Originally Posted by gbaglo

Wouldn't a DC fridge running in extreme hot temps gobble a ton of battery?

The one I want draws 2.3 Ah/h at 25C/77F ambient temperature, 2.6 Ah/h at 32C/90F ambient temperature, while maintaining an interior temperature of 5C/40F. The duty cycle at 25C/77F is about 40%, and at 32C/90F the duty cycle increases to 55%. Totally doable with the amount of solar and batteries I will have. The fridge is popular in the Australian outback, but it IS sold also in the US - The Dometic/Waeco Coolmatic CR-140. And yes, it fits through the door, and the coutout for the current Dometic Absorption fridge ETI installs is almost the same.

The trick is getting the fridge, and having it installed.

ETI might be able to get it from their Dometic rep directly, but here is another US source I found:

http://www.justkampers.com/waeco-coolmatic-cr-140.html

[float5]

Originally Posted by alanmalk

In the meanwhile I am seriously thinking about 2 Sears Platinum Marine group size 31 AGM 12v batteries in parallel, for a total weight of 150 pounds, and 200 amp-hours.
--Alan

If that is the case, then two such 12Vs are equal to four 6Vs for amp-hours for hardly more weight. Don't see how that means 6Vs are better.

[rbryan4]

Originally Posted by Floating Cloud

If that is the case, then two such 12Vs are equal to four 6Vs for amp-hours for hardly more weight. Don't see how that means 6Vs are better.

4 of the 6V batteries ETI uses would be 464 Amp hours (232 x 2). More than double the two 12V mentioned. Of course, the weight would go up to 240 lbs, and only about half of those amp hours are useable.

[NJ Joe]

Based on the installation manual for the CR-140, it looks like there is a current draw of 5.9A @ 12 V and 3A at 24 V. This current draw seems to be the same for all CR models. The manual also lists the average power consumption for the CR-140 at 70W. This average power consumption decreases for the smaller models (CR-110 50W, CR-80 48W). This would imply the same compressor for all models with a reduced duty cycle for the smaller ones.

[Brian B-P]

Originally Posted by rbryan4

4 of the 6V batteries ETI uses would be 464 Amp hours (232 x 2)...

... or 2 of the 6V batteries ETI uses would have similar capacity to 2 of the 12V Group 31 batteries of similar weight. Again, 6V or 12V doesn't matter to total capacity.
It's just a matter of how much lead you want to carry.

[float5]

Don't think ours are 232. Will have to look next time. It's on top I guess.

[rbryan4]

Originally Posted by Brian B-P

... or 2 of the 6V batteries ETI uses would have similar capacity to 2 of the 12V Group 31 batteries of similar weight. Again, 6V or 12V doesn't matter to total capacity.
It's just a matter of how much lead you want to carry.

Well, there's alot of debate on the topic, but remember, it isn't just weight that is the deciding factor. Durability is important too. A 12 Volt deep cycle battery has six cells that each output approximately 2.12-2.15 Volts. Generally, the the larger/heavier the lead plates in the cells are, the longer they will last, and the more deep cycle discharges/recharges they will take. The 6 Volt batteries have 3 cells instead of 6, even though their outer dimensions are roughly the same. Most 6 volts batteries therefore can use larger plates, and will last longer in a deep discharge/recharge situation - like an RV.

PS - it's also one of the reasons the 6 volt batteries are widely used in applications other than an RV where deep discharge and recharge occurs frequently - like a golf cart.

[WestEnder]

Originally Posted by alanmalk

I'm still waiting for that fabled 30 pound, 250 amp-hour lithium battery for $125 US.

--
Alan

That's coming. I think lithium batteries are the missing piece of the puzzle that will make compressor fridges more common. The fridge technology is there now, solar has become much more efficient and cheaper, storing enough power within the size and weight constraints of a trailer is the problem.

I'm not sure I'd put lithium in just now unless you have the early adopter mindset and enjoy tinkering with it. The costs are already pretty good if you take projected lifespans into consideration and are willing to DIY on the system. I'm not going to put lithium in now but will make sure the wiring will accommodate it in the future. Maybe, by the time I'm ready for my second or third set of batteries, lithium will be the best replacement.

[grc]

Lithium batteries are already standard in a top of the line trailer made in Australia. The Kimberley Kruiser T3 caravan comes with either 520watts solar or 720watts solar and a total of 480 ah of lithium batteries depending on your choice of air conditioner. They even sell the lithium batteries or an e-book, "Amazing Lithium Battery and Charging Guide"

Kimberleykruiser - T3 Off Road Caravan - the lightest full size in Australia