12 vdc fridge

[grizz272]

2 friends of mine have purchased new campers that have 12dc only refrigerator in them. They both came with 50 watt solar panel on the roof. They are figuring on boondocking 4 or more days with only 2 batteries to keep the fridges running.
Is this possible?

[grizz272]

Sorry about now responding in such a long time. Both friends decided to get generators in the last second. After all they decided that air conditioning would also be needed.

[Skibane]

LittleBill wrote:
I have a arb cooler, which uses the danfoss compressor. this thing pulls 4.5 amps when running. in a car with a h7 battery it will be unable to start in about 2.5 days.

Group H7 isn't a particularly large battery size - only around 40-60 amp-hours.

Just one Group 31 deep-cycle battery will provide around twice as many amp-hours - and will increase your fridge's run-time accordingly.

[LittleBill]

I have a arb cooler, which uses the danfoss compressor. this thing pulls 4.5 amps when running. in a car with a h7 battery it will be unable to start in about 2.5 days.

[fj12ryder]

Maybe for 2 batteries, but seems like a lot for a trickle charger.

[bikendan]

grizz272 wrote:
The batteries are the cheap batteries the dealer puts in the camper when you pick it on delivery. One guy the dealer forgot to wire the second battery up. We will be camping on an island in the Mississippi river and there is always lots of son. From my past experience the batteries on my camper never last past midday Friday if we arrived Thursday morning. I never had solar panels before though.

Your friends solar panel of only 50 watts, is a trickle maintenence charge, for when the trailer is sitting unused and nothing on.

[Bobbo]

grizz272 wrote:
One guy the dealer forgot to wire the second battery up.

In 2017, when I bought my Airstream, I had the dealer add a 90 watt solar panel on the roof. For 4 years I could not tell that it was doing anything to keep my batteries charged, and I just figured I needed a second solar panel. Last year, I bought a second panel to add myself. I wanted to wire them in series, so I had to replace the PWM controller with an MPPT controller. When I opened up that compartment, I found that the dealer had miswired the controller. Both the positive AND the negative wire were hooked to the positive terminal of the battery. It didn't seem that I was getting any charge because I WASN'T getting any charge.

[valhalla360]

JimK-NY wrote:

valhalla360 wrote:
We have one in our current unit. Draws about 50w when operating, so worst case is 1200w-hr per day but assuming you don't camp in Arizona in the summer, 50% duty cycle would be more typical, so about 600w-hr/day......

With my unit, I don't have to be in Arizona heat to see a huge increase in energy consumption. At about 60 degrees, my unit runs less than 1/3 of the time. In the low 70s that increases to about 50%. In the mid 80 degree range, my units runs pretty much full time. I have camped in the low 90s and at that point the refrigerator cannot maintain proper temperature. I need to turn down the thermostat so it can try to get extra cool during the night and that helps it coast during the day. But by doing that I guarantee it will run constantly even at night. For me the numbers would be about 15-20 AH/day in cool weather, about 25 AH/day for medium temps and 55 AH/day in hot summer weather.

Again, my unit is small at about 4 cuft. Most RVs will have units about twice that size with twice the power consumption.

That's far worse than we have experienced and I think ours is around 6cft. It's the stock unit that came with the trailer.

Of course, 55amp-hr @ 12v is around 660w-hr, so I presume, your unit is only pulling about 25w when running and might explain why it struggles to keep the unit cool in warm weather.

[grizz272]

The batteries are the cheap batteries the dealer puts in the camper when you pick it on delivery. One guy the dealer forgot to wire the second battery up. We will be camping on an island in the Mississippi river and there is always lots of son. From my past experience the batteries on my camper never last past midday Friday if we arrived Thursday morning. I never had solar panels before though.

[pianotuna]

valhalla360,

Excellent post. ty.

[KD4UPL]

Even though no information on battery capacity or refrigerator draw has been given the answer is NO.
That's probably not enough solar/battery for most people to camp 4 days with an LP refrigerator. The lights, radio, pump, etc. will probably use up all the power without even taking the compressor fridge into account.

[JimK-NY]

valhalla360 wrote:
We have one in our current unit. Draws about 50w when operating, so worst case is 1200w-hr per day but assuming you don't camp in Arizona in the summer, 50% duty cycle would be more typical, so about 600w-hr/day......

With my unit, I don't have to be in Arizona heat to see a huge increase in energy consumption. At about 60 degrees, my unit runs less than 1/3 of the time. In the low 70s that increases to about 50%. In the mid 80 degree range, my units runs pretty much full time. I have camped in the low 90s and at that point the refrigerator cannot maintain proper temperature. I need to turn down the thermostat so it can try to get extra cool during the night and that helps it coast during the day. But by doing that I guarantee it will run constantly even at night. For me the numbers would be about 15-20 AH/day in cool weather, about 25 AH/day for medium temps and 55 AH/day in hot summer weather.

Again, my unit is small at about 4 cuft. Most RVs will have units about twice that size with twice the power consumption.

[valhalla360]

We have one in our current unit. Draws about 50w when operating, so worst case is 1200w-hr per day but assuming you don't camp in Arizona in the summer, 50% duty cycle would be more typical, so about 600w-hr/day.

A 50w solar panel will generate around 200-250w-hr/day.

So over 4 days,
- The solar panel would provide about 800-1000w-hr.
- The fridge would consume around 2400w-hr.

Therefore the battery bank would need around 1600w-hr of usable power or about 135amp-hr @ 12v. Of course, you can't use 100% of any battery bank, so:
- Lead Acid, you need about 270amp-hr (50% usable)
- Lithium, you need about 170amp-hr (80% usable)

I'm guessing from the description, he doesn't have a significantly upgraded battery bank, so unlikely he will be able to go 4 days without generator/shore power to supplement.

Bump up to 150-200w total of solar panels and it's probably viable but some of the above are estimates that will vary from day to day and how you use it (a teenage kid staring into the open fridge door regularly will up the usage)

PS: This ignores any other power draws. If you are running a lot of lights, an inverter or other items that consume a lot of w-hr, you will need additional upgrading to meet the loads.

[goducks10]

They won't make it 2 nights with just 2 batteries and 50W of solar. Sounds like they've been listening to their RV sales person too much. Just the angle of the sun and a few clouds or even an overcast day will make that 50W panel almost useless.
I'm sure their RV's have a Zamp solar side port since most all seem to these days. So I would advise them to get a 100W or higher portable solar panel and use that port.

[bikendan]

grizz272 wrote:
2 friends of mine have purchased new campers that have 12dc only refrigerator in them. They both came with 50 watt solar panel on the roof. They are figuring on boondocking 4 or more days with only 2 batteries to keep the fridges running.
Is this possible?

Not without upgrading the solar wattage and battery bank. 50 watts is insufficient and their two batteries are probably the typical cheap dual-purpose marine batteries.