nccamper
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Post by nccamper on Oct 7, 2015 5:33:36 GMT -8
How long can you run a small fridge off the grid before the battery is drained?
One person online says 6 hours, another says 12 hours, my neighbor says a week. A week seems hard to believe.
I searched old threads and couldn't find an answer.
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Post by vintagebruce on Oct 7, 2015 6:21:04 GMT -8
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bpmcgee
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Post by bpmcgee on Oct 7, 2015 6:47:25 GMT -8
NC,
I can offer you a specific example - I was trying to answer just this question with my new fridge on Monday.
I've got a Nova Kool R5810 (http://www.novakool.com/products/single_doors/rf5810.htm). It draws 4.4 amps at 12 volts.
So, if it's running 25% of the time, it will use 26.4 amps per day.
If I have two of these Trojan 6V batteries (http://www.trojanbattery.com/pdf/datasheets/6VGEL_Trojan_Data_Sheets.pdf) hooked in series to get 12v, they will be rated between 189 and 198 amp hours, but the manufacturer says never let them drop below 50% charge. So let's assume 95 amp hours usable.
So, under perfect conditions and without any parasitic losses, those two batteries could power my refrigerator for 3.6 days without damaging them.
Does this help?
Brian
P.S. One of the reasons I picked this refrigerator is that it's one of the most efficient I could find.
B
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nccamper
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Post by nccamper on Oct 7, 2015 8:38:22 GMT -8
Bpmcgee, so if it was a hot summer day and the fridge ran full time it might make it a little less than a day? Even that might work for us. Something like 6 hours would be useless. vintagebruce, great site. You're right, this fridge is you!  |
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bpmcgee
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Post by bpmcgee on Oct 7, 2015 8:58:30 GMT -8
nc,
The faster you draw down a battery the less you can draw from it -- notice the various amp hour ratings on the pdf. You can't work it quite as you'd hope, and there are lots of other inefficiencies. If I had to guess, I'd say those batteries would give me between 12 and 18 hours if the fridge was running full time.
B
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nccamper
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Post by nccamper on Oct 7, 2015 9:50:09 GMT -8
When hitched does the tow vehicle system keep the refrigerator running? So between sites with no power the battery charges and the food stays cold?
I have always used the ice box but as we talk about longer trips we need something better than melting ice. Have you ever tried to find ice in the Utah desert? We once drove 40 miles round trip for ice.
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bpmcgee
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Post by bpmcgee on Oct 8, 2015 5:12:17 GMT -8
NC,
If you're using a 7 pin trailer plug and the harness is wired correctly, AND the alternator in the car is up to the job it will.
Brian
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Post by vikx on Oct 8, 2015 22:33:37 GMT -8
I had a nasty surprise YEARS ago with a truck camper 3 way fridge. We were hauling horses to the PNW from Cali. Everything was fine until the lights started blinking on and off. Yeah the HEADLIGHTS. Seems older Ford trucks would do that as a warning.
The refer ran the truck battery completely down en route. Our alternator wasn't up to snuff.
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nccamper
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Post by nccamper on Oct 9, 2015 4:57:36 GMT -8
"Our alternator wasn't up to snuff."
Good to know. Hopefully our Tundra can handle the load.
I like the idea of a three way fridge but they're expensive. And the thought of a gas appliance always on in a tiny camper doesn't sit well with me.
I read that the 12 volt fridge keeps things cool but not cold. And based on what bpmcgee said above, just the battery will keep things cool for a couple of days.
I also read that the hot wire running through the hitch is such low voltage (in comparison to the main truck charging system) that it is more of a low voltage trickle than a full charge. I'd have to drive 12 hours to charge a camper battery. Do you think that's true?
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turbodaddy
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Post by turbodaddy on Oct 9, 2015 5:02:37 GMT -8
The Norcold in our camper does have terminals for 12V, but no one ever wired it. I'm guessing out of fear of discharging the TV battery. The Norcold manual clearly states that you should never try to do the initial cool down with 12V. You are supposed to do that either with LP or 110AC, then the 12V from TV is only to maintain the temp in the refer. Here is a link to the manuals www.rialtainfo.com/winnebago/refrigerator.htm#manuals |
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bpmcgee
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Post by bpmcgee on Oct 9, 2015 6:43:32 GMT -8
NC,
I think it's important to keep in mind that the 12v mode of a 3-way refrigerator is TOTALLY different than a 12v ONLY refrigerator.
A 3-way refrigerator uses the absorption cycle, which uses a heat source to pump the cooling fluid around. In 12v mode it uses a small heater coil as this source.
A 12v ONLY refrigerator like the nova kool is just like your home refrigerator, except that it uses a 12v pump.
B
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nccamper
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Post by nccamper on Oct 9, 2015 8:59:26 GMT -8
Bpmcgee,
Do you think the Nova kool keeps food cool or cold? Needs a long start up time? Works well off a converter if you're on the grid?
Thanks everyone for the well thought out answers. I've wired entire homes but the 12 volt experience is new to me. Right now I have one camper with a dorm fridge, one with an ice box and one with an old propane fridge that hasn't been started since 2004. I'm not brave enough to sleep with the propane on so I'm considering alternatives. And I've over the ice thing.
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bpmcgee
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Post by bpmcgee on Oct 9, 2015 9:05:26 GMT -8
I'll plug it in this weekend and let you know.
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Post by vikx on Oct 9, 2015 23:15:25 GMT -8
From what I've read, Nova Kools will not get 'cold'... They will only lower the ambient temperature 35* tops. So, 70 - 35= 35. Pretty good. 90 - 35 = 55, not so good.
There are efficient DC fridges (some made by Norcold) that do far better than Nova Kool. Spendy-around $500 for a little one...
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nccamper
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Post by nccamper on Oct 10, 2015 4:46:52 GMT -8
vikx, That's what I was wondering. I've heard that about other brands. Here in NC where the temp reaches 80+ for months at a time, that wouldn't work.
I'll check out Noracold and do more reading.
With that said, thanks for all the great info bpmcgee. I should have mentioned that I'm in the Heat Belt.
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