Solar panels

[Output Flange]

Could someone confirm something for me please?

I have an electric coolbox with this stat:

Wattage is 42W. Draw in amps is approximately 3.5A from a 12V supply

I'm looking at getting a set of folding solar panels to take camping, rated at 100W. I'll also have a 115Ah leisure battery.

I'd like to run the coolbox for 4-5 days.

Is this the right setup to do it? I notice that the solar charge controller has a 12v load side - is it able to draw power from the battery to supply that, so if I connect the coolbox to the load side of the controller it'll use solar or battery power automatically as required?

TIA

[JimbobVFR]

I'd suggest the coolbox will be the problem here, ideally you want a proper compressor type coolbox. IMO the best ones are Waeco but they ain't cheap.

[Jakg]

Output Flange said:

Is this the right setup to do it? I notice that the solar charge controller has a 12v load side - is it able to draw power from the battery to supply that, so if I connect the coolbox to the load side of the controller it'll use solar or battery power automatically as required?

The load side is typically to power lights etc when it's dark - I'm not sure what current it's rated for - but I would imagine it's wired internally to the battery but with a relay to turn it on / off.

Even if the power came straight from the panel I wouldn't see the point - you wouldn't run anything in a car directly from the alternator, you'd run it from the battery.

Remember that a 100w panel produces 100w in optimum conditions - right angle, lots of sun, right inclination. Any of the above missing (inc clouds) and you'll be looking at less power.

[chopper602]

It's not going to work. You'd need a gas powered fridge really. We have a three way in the motorhome, 240v when on hook-up, gas for when no hook-up and 12v WITH engine running to power it. Fridges take a lot of juice.

[Output Flange]

OK, so I need to bin the crocodile clips off the panel -> battery connector and wire it into some proper post terminals, and then connect the 12v socket to the battery too and plug the cool box into that?

[bristolracer]

http://www.campingandcaravanningclub.co.uk/helpand...

My 120w panel runs our 42w fridge fine. It is a compressor type though so will use less than an electric coolbox type.

[Output Flange]

bristolracer said:

http://www.campingandcaravanningclub.co.uk/helpand...

My 120w panel runs our 42w fridge fine. It is a compressor type though so will use less than an electric coolbox type.

Thanks.

I took a 110Ah standard car battery last year, and that ran the cool box for 2.5 days with no solar assistance. Despite the helpful guesses above, I suspect that with solar panels it should top it up enough to get another couple of days out of it.

I'm surprised no-one has direct experience of it TBH.

[donaircooleone]

chopper602 said:

It's not going to work. You'd need a gas powered fridge really. We have a three way in the motorhome, 240v when on hook-up, gas for when no hook-up and 12v WITH engine running to power it. Fridges take a lot of juice.

Absorption fridges hammer the 12V side as depending on size it will want between 70W to 130W on electric (mains or 12v).

Compressor fridges need much less and will cut in and out depending on temperature its maintaining.

We need to know how much power it will need to run each day really (in Ah, Amp Hours), to give you an example a 100W panel will typically give you approx 45Ah per day assuming you have largely clear skies in June at a similar latitude to Exeter.

[Output Flange]

According to the email I just received, the solar panels should be waiting for me at home later today. Need to swing by and collect a leisure battery, then I shall rig it all up and do some testing. My aim is to have the cool box running from the solar panels during the day (and also them charging the battery) and then run it off the battery overnight, assuming the ambient temp is warm enough to need it.

I shall report back in due course...

[Chicken Chaser]

If you can afford to change coolboxes, may I suggest a Mobicool FR35? Its a compressor fridge, so its not running all the time but keeps stuff cold down to -10 if needed, has plenty of room and runs off 240v or 12v but obviously lasts longer than the Thermostatic fridges which are constantly running (and are noisier). Its made by Waeco but for some reason its cheaper than their own range. It also has a setting for auto cut-off to prevent the battery from going flat. I bought one a few weeks back and its been used a few times already and has been excellent. I no longer have to worry about getting coolpacks cold or trying to maintain temperature.

[Output Flange]

Thanks for the advice, but at the moment I don't really want to spend that much on a cool box / fridge, for two reasons: firstly, the one I have does a perfectly good job, I just need to finesse the power situation. I'll have a generator as backup this year in case the leisure battery / solar panels aren't the answer, but I'm hoping they are. Secondly, I'm still plotting a better, more permanent solution to camping so until that's sorted I don't want to commit money to something that may not be transferrable.

Panels were here when I got home and look decent enough. Will update once I've done some proper testing.

[Mark Benson]

Output Flange said:

bristolracer said:

http://www.campingandcaravanningclub.co.uk/helpand...

My 120w panel runs our 42w fridge fine. It is a compressor type though so will use less than an electric coolbox type.

Thanks.

I took a 110Ah standard car battery last year, and that ran the cool box for 2.5 days with no solar assistance. Despite the helpful guesses above, I suspect that with solar panels it should top it up enough to get another couple of days out of it.

I'm surprised no-one has direct experience of it TBH.

Not direct experience, but we put a 220w panel on the roof of our camper (it was cheap, but massively over-specced - see my profile for a build thread) and we run a Waeco compressor fridge plus lights and charging for phones/tablets/rechargeable camping equipment for all our friends.
In the summer, the indicator tells us the panel has the 110Ah battery fully recharged by the time we're eating breakfast.
The docs with the fridge say it pulls 'up to 4A' in unfavourable conditions (ie. hot interior of van, not much in the fridge) but in reality it'll be nowhere near that.

However, even with your 3.5A coolbox, running the panel for 12 hours of decent daylight should keep the battery topped up indefinitely as the coolbox will use (at a guess) no more than 35Ah (3.5A x 10 hours of darkness) overnight then the panel will begin recharging. A 100W panel will produce 8.3A (A=W/V) in optimum conditions, but lets say over the course of a day it averages only 5A due to cloud cover etc (which is very pessimistic), the panel would need 7 hours of running to completely replace the 35Ah.

Even given losses for wiring etc. it's unlikely you'd need more than 100w.

[Output Flange]

Thanks Mark. It transpires that the controller on the panels is duff, so will need to be replaced.

O/T - random one - were you in the Boxster at Silverstone a couple of weekends ago? I was with the white E36 M3 parked behind you if you were!