Outer Limits 4x4 Board

Any one have a idea of how many watt solar panel will run my engle 39l fridge. i think it uses max of 7amp hrs

Cheers Rhett

Rhett wrote:Any one have a idea of how many watt solar panel will run my engle 39l fridge. i think it uses max of 7amp hrs

Cheers Rhett

I trust you understand that you can't run a fridge directly off a solar panel, but you can use a panel to charge the battery which runs your fridge.

Amp-hours is more a measure of average energy consumption than current. 7Ah doesn't sound right for a 39l Engel.

Over a 24hour period, I would expect your fridge to be consuming 20-30Ah, depending on use and ambient conditions. The "7" might be max current draw? Which I would expect to be a transient "start surge" measurement, rather than steady-state draw. But I could be wrong, and I'm drifting off-topic.

Allow 30Ah per day, at 12V, equals 360 Watt-hours per day. What size solar panel?

Solar panel power ratings are based on ideal conditions, and don't represent what can be pushed into a battery. Under real world conditions, peak output (which can be pushed into a battery) is likely to be 50-65% of nominal. One "rule of thumb" is to budget on 5 (effective) hours of output.

So, 360 Watt-hours in 5 hours requires 72 W of "real" output, which would require a panel nominally rated at about 120W. That's a big, expensive panel.

An 80W panel may produce about 50W in the real world, or around 250W-hours per day, which would be OK if your fridge consumes around 20Ah per day. If anybody tries to tell you a panel under 80W will run your fridge, they're kidding themselves.

An 80W panel could extend your battery from 1-2 days, out to 5 or 6 days - if you're lucky. Would you camp for 5 or 6 days without running your engine?

Note: All of the above is based on guesses, assumptions and half-remembered facts. It's worth about as much as you've paid me for it.

I have an 80 watt solar panel hooked to a deep cycle battery. When in full sun the panel puts out 4 amps, when the fridge (39l engle) runs it draws 4 amps. So if the fridge is not running the battery charges at 4 amps, if the fridge is running it sits at no charge no drain and if the sun is not shining the fridge pulls 4 amps from the battery. I have used this setup on many camping trips with great success. But you still need a decent battery for backup.

-Scott- wrote:

Rhett wrote:Any one have a idea of how many watt solar panel will run my engle 39l fridge. i think it uses max of 7amp hrs

Cheers Rhett

I trust you understand that you can't run a fridge directly off a solar panel, but you can use a panel to charge the battery which runs your fridge.

Amp-hours is more a measure of average energy consumption than current. 7Ah doesn't sound right for a 39l Engel.

Over a 24hour period, I would expect your fridge to be consuming 20-30Ah, depending on use and ambient conditions. The "7" might be max current draw? Which I would expect to be a transient "start surge"
measurement, rather than steady-state draw. But I could be wrong, and I'm drifting off-topic.

Allow 30Ah per day, at 12V, equals 360 Watt-hours per day. What size solar panel?

Solar panel power ratings are based on ideal conditions, and don't represent what can be pushed into a battery. Under real world conditions, peak output (which can be pushed into a battery) is likely to be 50-65% of nominal. One "rule of thumb" is to budget on 5 (effective) hours of output.

So, 360 Watt-hours in 5 hours requires 72 W of "real" output, which would require a panel nominally rated at about 120W. That's a big, expensive panel.

An 80W panel may produce about 50W in the real world, or around 250W-hours per day, which would be OK if your fridge consumes around 20Ah per day. If anybody tries to tell you a panel under 80W will run your fridge, they're kidding themselves.

An 80W panel could extend your battery from 1-2 days, out to 5 or 6 days - if you're lucky. Would you camp for 5 or 6 days without running your engine?

Note: All of the above is based on guesses, assumptions and half-remembered facts. It's worth about as much as you've paid me for it.

All pretty good advice. Whatever your fridge draws while it is in (I assume around 4.5A), count on it being on for around 25minutes per hour. The best way to prove this is to fill it up with food, get it all up to operating temperature, get a pad and pencil and sit next to it withe a stop watch for at least 30 minutes and write down the exact times it is cycling on and off. Once you have that info and you have physically measured the current draw (don't assume it's 4.5 A, cos it may be more or less), then you can accurately calculate a 24 hr battery draw. In practise, in the hot sun, in the back of a hot car and with you opening the lid every 15 mins for a beer, it will be a little more, but for now this way of calculating will be reasonably accurate.

As far as the solar panel is concerned, the output will depend very much on cloud cover and angle of the panel to the sun. Make sure you set it up so that you gain the absolute maximum time per day that the panel will output at or near it's maximum performance. 5 hrs per day is fairly typical, but you should be able to stretch it out longer if you are prepared to shift it as the sun moves across the sky. When I lived on my yacht years ago, I had 4 x 42 W Solarex panels, 2 of which I could angle to the sun. I fitted amp meters to each panel so I could monitor each individually and from memory they put out around 3 amps each while in full sunlight. I had a danfoss fridge (which drew 4A when on and was on for 21 minutes per hour), TV, stereo and 12v lighting and 2 x 100AH deep cycle batteries. I never had to charge the batteries other than by solar in the 7 years I lived aboard, but that equated to 120W of panels and very little shading from the rigging of the yacht.

When you go camping, it's always nice to camp under trees, so you will have to rethink your camping strategies with solar panels. In your situation, I would be going for at least 80W of panels and 200 AH of batteries, because that should stretch your fridge out to 3 or 4 days. Any longer than that and you will have to think about more panels and/or more batteries.
Ric

i have never seen my engel use more than 2A
they claim 2.5A max but i have never seen use that much.
how are you guys drawing 7A