Solar to run firdge etc

Hello Ed,

yes, you can use your car battery to power the fridge in connection with a solar panel.

A quick look at the anticipated fridge load requirement durig night time reveals that the car battery has to supply around 16 to 24Ah before the solar panel kicks in again. This is based on 1~1.5 amps average fridge current, and 16 hours of no or little sun.

This load requirement makes this a cyclic battery application.
Starter batteries aren't designed to supply hundreds or even thousand cycles like a VRLA AGM or gel, so expect a shortened life span, depending on how deeply and how often you discharge it.

The most important thing is that the battery voltage needs to be raised to the boost charging level (around 14.4V for flooded) for quick and thorough recharging before the panel runs out of puff again at the end of the day.

Most cheap solar regulators are set to regulate at the lower float voltage level of around 13.8V.
If you can get inside the regulator you might find some trim pots to adjust this up a bit.

The other option is to use no regulator at all, and keep an eye on the voltage levels during the day.
A 80W panel might just get you there by the end of a short day in winter.
But a 100 or 120W panel gives you the advantage of reaching the boost voltage level earlier in the day, followed by the much needed time to slowly absorb charge to the full capacity.
One way of stopping the voltage from climbing above boost level is to simply turn the solar panel away from the sun a bit after the voltage has reached 14.4V. Or, connect additional loads at this point in time.

Or, don't worry about this and bring along some demineralised water for frequent electrolyte top ups.
But regular overcharging leads to early deterioration of the positive grids due to increased corrosion.

Best regards, Peter

Ed,

Following on from Peter's comments, it makes good sense to have an auxiliary battery to power your fridge and leave the starting battery to run the vehicle.
In one form or another, that's what most of us do. It's called a dual battery system.

A very easy and successful method is to have a second battery (usually an AGM type deep cycle battery) mounted in the rear of the vehicle, close to where your fridge will be. AGM batteries are safe to charge while in the vehicle as they don't give off dangerous gases, unlike a standard wet cell battery. Also the AGM can be tipped over and it will not spill acid, unlike a wet cell battery.

The battery is usually contained in a battery case or box, and the better ones not only have the necessary 12 volt sockets to plug your fridge lead into, but incorporate an isolator to keep this battery separated from the starter battery.
This box is wired back to the starter battery with a heavy duty cable and receives a charging voltage while driving to maintain the auxiliary battery even while it is running the fridge. A solar panel can be plugged into the box to help maintain a charge, while stationary.

Derek Bester, from Sidewinder.com has an excellent battery housing with all wiring looms, etc. All you need in addition to this is a battery.

SO, although a sound solution is not as "simple" as your original perception allowed, it's also not that complicated either.

Another solution is a Thumper portable battery system from Blue apple which also comes with an in-car charging kit.

An AGM battery will cost around $340 or so.

Any of these options are very good solutions, depending on how much you are prepared to invest.

Bill.

Hi Ed,
I have the same Engel as yours and have it mounted in the Toyota. We have it connected to our second battery (a 120ah Full River agm deep cycle). We have a 80 watt solar panel mounted permanently on the roof of the car and this can be angled to face the sun. We find that this is an excellent setup and we use the Engel as a freezer for months at a time without any problems. The second battery also gets a boost every time you drive the car. I also have a 10 metre very heavy gauge lead made up so I can also use the solar panel to top up the camper batteries if we need to - with this setup we can keep the camper in the shade and still chargethe batteries! We can also connect the panel to the starting battery for emergency charging if we need to.
Hope this is helpful.
Cheers
Neil

Sd

You need, as others have said, an AGM Deep Cycle battery, about 120 plus ah, a quality solar panel, about 120 Watts (7 Amp) a decent solar regulator and some suitable cable.

The theory or fact is the battery supplies the power to run the fridge, so has to be able to do that with no hassle for about 2 days with no extra charge so it remains about 50 soc in 2 days.
The solar panel has to be able to replace in just 7 hours what the fridge uses in 24 hours.
This is where the mathematics get blurred to a degree so there ‘appears’ there is no perfect number, but very close numbers that will do just as well as some not so close.

(possible or maybe impossible example)
The fridge may use 50 ah per day, so you have to be able to have a solar panel that delivers at least those used 50 ah daily.
Mathematically a panel of 130 Watts will do the job.
But then some will say you need more Watts and some will say you can get away with less Watts, it depends on various factors and a quality solar regulator has to be included in the equation too, so it is not just the maths, you have to know how the current is treated by the regulator too so it starts to get complicated but not impossible.

Ask the question:
“who has your fridge model and what Battery and what solar panel and regulator do they use?”

“How long does the battery run the fridge with no sunshine?”

“are they happy to recommend there system for you ?”

( No, you don't need an Inverter, the inverter only changes 12v up to 240v )

I've a 200 Watt solar system, 200 ah AGM DC battery system with a quality regulator and it delivers 12 Amps (100% efficient) to the battery, as required, but I've a fridge that draws 10 Amps (2.8ah) so my system is much more than you will ever need, it's more than I've ever needed too :-)

Maîneÿ . . .