How long off grid

[Milarepa]

I have the standard Dometic CRX50 fridge with two 60W solar panels.
i am planning to be off grid parked under trees. How long should my batteries be ok for if running the fridge and just led lighting, with no charging of gadgets?

I kept the fridge on parked on the driveway and was surprised that the batteries were showing in the high 11’s although this was over some time. But it had been sunny.

 

[Deaky]

I have the standard Dometic CRX50 fridge with two 60W solar panels.
i am planning to be off grid parked under trees. How long should my batteries be ok for if running the fridge and just led lighting, with no charging of gadgets?

I kept the fridge on parked on the driveway and was surprised that the batteries were showing in the high 11’s although this was over some time. But it had been sunny.

That all depends how big your batteries are

 

[Alanmh]

How long is a piece of string?
Firstly though, how big is your leisure battery?

 

[Milarepa]

I have no idea really I’ve tried to look it up and can’t find out what battery it is. But it is a standard leisure battery that came with a conversion from Venture Caravans.

 

[Pete C]

If Venture Caravans did the conversion, them I would start with them, and ask what capacity the battery is.
If they sold it to you pre-converted, then I doubt they will know.

Pete

 

[Phil_G]

I would guess its an 85, so maybe 40Ah usable. If your fridge uses an average over time of (say) 2 amps, it will last 40/2 = 20 hours without solar.
Pro-rata if the fridge current is different. However, even under shade, 120w panels might give 2 amps anyway, in which case - as long as you like!
Its impossible to predict accurately, too many variables

 

[AussieMick]

If parked under trees ,so shade or partial shade, solar will be adding very little back to your battery, if your battery is about 100ah then you should get from 1 to 2 days provided your battery was fully charged before hand.ie by a smart battery charger. Your alternator will not charge your leisure battery to 100percent. So get as much sun on your panels when you can.
Also ambient temperature will affect your fridge operation, the hotter it is and the more times you open the door will bring the compressor on more often drawing more power from your battery.

 

[Milarepa]

That’s great. Thanks for the replies

 

[Stay Frosty]

@Milarepa Looks like a 100aH battery and that's what was in my Redline camper from Venture.

The Waeco crx50 draws an average of 40 watts which at 12 volts is just over 3 amps so 100 amps divided by 3 amps is in the 30 hours area, factoring in water pump for the sink, any lights, USB skt use etc and that could easily be down to one day parked under a tree this time of year.


Being nosey now but did you install the solar panels as solar wasn't an option on my camper and the electrics are a Sargent ec160 and smart relay from the engine battery so not ideal for charging the leisure battery from the vehicle battery.

Out of interest my leisure battery (brand new) will drop from 13.2v charged to 12.4v in a week when left on the drive, this is with everything supposedly turned off on the Sargent unit.

 

[Milarepa]

Solar panels were an option when I bought the prebuilt van. I forget how much they were. We also had an awning and towbar fitted then they gave us some discount.
I don’t need to hook up when I’m on the driveway and never do but then again I normally turn the fridge off

 

[Alanmh]

Dont forget that you can only run a normal (non lithium) battery to 50%, so you only get 50Amp hours out of a 100Amp Hour battery.
Also, to maximise your off grid time, make sure your fridge is on for at least 12 - 24 hours before you go and the battery is fully charged on hookup.

Keep monitoring the voltage and if it goes below 11V, start the engine to get some juice in and prevent it ruining your leisure battery.

Hope that helps and have a great trip.

 

[Milarepa]

That’s great thanks for the advice. I was also thinking that if the worst came to the worst I could leave some ice blocks in there and turn the thing off if I got worried.
what does 50% represent with those numbers is it below 11?

 

[AussieMick]

No, a 12volt agm battery is fully charged at 12.8v to 13v. You can run it down to 50% without damaging it .This is about 12.05v or so. Dont run it below this too often or you will shorten its life. 11v is too low. Batteries like to be kept fully charged as much as possible to last the longest.
This means if you have a 100ah battery you really can only use 50ah before recharging or damage will start to accumulate.
Here is a chart that Dellmassive has posted before but is quite relevant to battery charge.

.

 

[JasonW]

I put a couple of ice blocks in anyway before setting off so the fridge doesn't have to work so hard off the leisure batteries to maintain the low temperature...

 

[Alanmh]

That’s great thanks for the advice. I was also thinking that if the worst came to the worst I could leave some ice blocks in there and turn the thing off if I got worried.
what does 50% represent with those numbers is it below 11?

Oops. Sorry, that 11v should have been 12volts. That chart is very useful.
When our solar panel failed while away in a campsite with no hookup last year, I swapped ice packs and ran the engine with the fridge for 30 minutes twice a day, then turned the fridge off again.
Some people advocate turning the fridge off overnight anyway when off grid. Not a bad idea.

 

[Milarepa]

That’s very useful. Thanks

 

[Blitz]

As mentioned shade is going to be your problem over the panels rather than a cloudy day with the panels in the open. I guess there is a scientific equation some where but shading parts of a panel reduces the efficiency overall much more than the actual percentage of the panel shaded. .
Plus 120 watt isn't that much especially at this time if year.

 

[Phil_G]

I have the standard Dometic CRX50 fridge with two 60W solar panels.

Hopefully they're wired in parallel - if they're in series, a shadow across one panel affects the whole array.

 

[T6Jay]

Here's some real world figures:

I have a 50L Vitrifrigo fridge, 160W (Renogy) panel and 95AH (C100) battery. The only other loads are a few LED lights and phone charging.

On a September UK night the battery goes from 100% to 90%, so about 10Ah used, the thermostat is set at about 25% (near the 'warm' end)
On a sunny morning it's back up to 100% by 10:30am ish.
On a rainy day it can take all day to get back up to 100%.
Outside our house the sun doesn't hit the panel until 12ish, if it's sunny day it still charges up before that time.
So, shade/indirect sun on a bright day seems a lot better than overhead sun through any clouds.

For us, we reckon we can last indefinitely, as half an hour driving will give us a big charge if the skies are gray.

Hope that helps

 

[Milarepa]

Thanks. I plan to be parked up under trees in November for five nights. Running just a fridge and one LED light occasionally.
and I won’t be able to move the van once I’m parked to charge the battery.
sounds a very specific scenario, I know!