Which solar panel + fridge qn??

Hi All, I have 2 qns that I am hoping someone can offer some advice on.
I have an Engel 40lt fridge running off a dual battery set up. I will be doing some off roading and believe I need to supplement the power supply to keep it going when I am not driving/charging. I will be doing this in Northern Oz so while being on the warmer side, should have reliable sunlight.

1. would a 120w solar panel be suffice??
2. Can I split the dual battery output plug, plugging in the fridge to one and the solar panel into the other--effectively that would mean I would be drawing energy while also for a good part of the day, feeding in energy?? Is it this straight forward??

Many thanks in advance for responses.

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Reply By: Mick O - Tuesday, Feb 05, 2013 at 21:44

Tuesday, Feb 05, 2013 at 21:44

have a read of this;Electricity for Camping

It will give you a lot of info that should make things clearer about what is needed or possible with DC power/solar etc.

Cheers Mick

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trip would doubtless be attended with much hardship.''
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Reply By: Member - Barry H (WA) - Tuesday, Feb 05, 2013 at 21:52

Tuesday, Feb 05, 2013 at 21:52
Hi Jason G,

I am no expert on this matter but, this is the system I run, which is similar to what you are proposing.

I run a 50ltr Waeco fridge (as a fridge) and a 35ltr Waeco (as a freezer)
They both run off a 100ah AGM battery (dual battery set up) without any energy supplement I would get about two days use from them.

I have a 190w Solar Panel set up, which delivers (given the right amount of sunshine each day) about 35 - 45ah per day, that gives me almost parity with what I am using each day.

The panels are connected to a regulator, via an Anderson plug, the battery is housed in a battery box with 2 merit plug outlets, which power both units, so the solar panels put energy in, during the daytime, whilst I run the two units.

Because you are only going to use one unit, you should be able to power one unit, and replenish the energy at the same time.

As I said I am no expert, but this works for me for almost two years now.


Barry H
AnswerID: 504162

Reply By: Danna - Tuesday, Feb 05, 2013 at 22:10

Tuesday, Feb 05, 2013 at 22:10
Hi Jason,
I know which solar panels NOT to buy ....... from these people: m2cptyltd on Ebay.
See thread ID: 100337 from 03 Feb 2013 10:43
Ciao Dana
AnswerID: 504165

Reply By: Sand Man (SA) - Wednesday, Feb 06, 2013 at 07:26

Wednesday, Feb 06, 2013 at 07:26

Although it is possible to do what you propose, it is not really recommended, as the output to your fridge would not be protected from shorts, etc.

The solar panel circuit should be connected directly to the auxiliary battery terminals, as should the input from the alternator. Pretty straight forward.

Another circuit from the auxiliary battery terminals would supply power to your fridge, etc. via an inline fuse on the positive wire and terminating in a good quality socket such as a merit style socket, or an Engel one.
I prefer the merit type for standardisation with other 12 volt equipment such as a fluro light, as the plugs are much cheaper and just as robust.

I know the Engel patch lead contains its own fuse but what if you are running something else off the circuit.

It is also a good idea to include a low voltage cutout device between the battery output and the fridge to stop any possibility of the battery being overly discharged.
They are only about $25. I replaced the ciggy socket and plug on the leads with a merit plug and socket. (refer standardisation above)

As far as the solar panels are concerned, 100w is good enough to support the Engel, but if you can go the extra 20w then the panels would not be much bigger in size.

I actually get by with an 80w bi-fold panel, but 100w bi-folds are more common now and the cost has come down since I purchased mine some years ago.

Ensure you the panels include a solar regulator, or add one between the output of the panels and the input to the battery.


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Reply By: Member - Frank P (NSW) - Wednesday, Feb 06, 2013 at 12:01

Wednesday, Feb 06, 2013 at 12:01

I presume your dual battery setup is conventional, with an isolator.

I think 120 watts of solar will be adequate for what you want to do.

I would set it up this way:

1 If your panels come with a regulator stuck to the back look for a LOAD output. If there is no load output, get yourself a stand alone 10 amp regulator with a LOAD output.

2 If the reg on the back of the panels has a LOAD output, connect the reg to the battery and your fridge to the LOAD terminals on the reg. Job done.

3 If the reg has no LOAD output, bypass it and wire the panels to the SOLAR IN of the new reg via an Anderson, Merrit or other suitable plug.

4 Connect the reg to your second battery.

5 Connect the fridge to the LOAD terminals of the reg. (Anderson or Merritt?)

The advantage of a reg with a LOAD output is that the reg will run the fridge directly (but at the right voltage) from the panels when there is enough sun. Any output more than what the fridge needs goes to charging the battery. If there is no sun the fridge is automatically powered from the battery. In partial sun the panels may contribute to running the fridge and the remainder will be drawn from the battery. If the fridge is cycled off, then obviously all the output from the panels goes to the battery.

A couple of things to note:

If your reg is not hard-wired in place then the order of connection should be
1 connect the reg to the battery
2 connect the load to the reg
3 Connect the panels to the reg.

Disconnect in the reverse order.

The cable from the reg to the battery should be as short as possible and/or reasonably heavy gauge - say 6mm. If unavoidably long, then larger cable is desirable to avoid voltage drop.

The cable from the panels to the reg can be smaller gauge, but if you choose long cables so you can move the panels around to avoid shade, then consider thicker cable. For 10m panel cables I use 6mm sheathed twin-core.


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Follow Up By: Member - Frank P (NSW) - Wednesday, Feb 06, 2013 at 12:24

Wednesday, Feb 06, 2013 at 12:24
Sorry, I didn't include a fuse. There should be one in the +ve between the battery and the reg, as close to the battery as possible, sized to suit the reg.

You could up the reg to 15 amp so it's not working so hard so much of the time.

Also, a half decent, but not necessarily expensive, reg will have an internal low voltage disconnect facility, often programmable. Your fridge probably has an internal one of its own anyway, but having one in the reg or a separate one as Sand Man suggested protects the battery if you are running other stuff.

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Follow Up By: Member - John and Val - Thursday, Feb 07, 2013 at 08:26

Thursday, Feb 07, 2013 at 08:26
Frank - While I agree with much of what you say, may I correct your reference to the LOAD terminals on a regulator.

Different regulators work in different ways, but generally speaking the BATTERY terminals are to connect to the battery (obviously!). The loading (fridge etc) current is drawn from the battery. It can be drawn directly, but if the load is connected to the LOAD terminals the current passes through, and is monitored by, the controller. The controller can disconnect the load if the current is excessive, or the battery voltage drops down too far. That is the purpose of those load terminals.

If the controller is an MPPT type, it will deliver a voltage suitable for charging the the battery, which will also be suitable to power a fridge, BUT in the absence of a battery to inform the controller of its voltage requirements I wouldn't trust the controller to run anything!

If the controller is NOT an MPPT type, it will not provide any voltage conversion at all, and in the absence of a battery to manage voltages, a solar panel may deliver much higher voltages than a 12V fridge will tolerate.


J and V
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Follow Up By: Member - Frank P (NSW) - Thursday, Feb 07, 2013 at 14:49

Thursday, Feb 07, 2013 at 14:49
Hi John,

Thanks for your follow-up.

I assumed that when in use the controller would always be connected to a battery. I did not intend to suggest (and I don't think I did :-) ) that Jason should use the LOAD terminals on a controller not connected to a battery.

Having said that there ARE controllers which can power a load without being connected to a battery. I have this one. It is MPPT and is very good. (No affiliation, etc.) From the manual:
"Note: This unit can be used to directly power (without a battery) a 12VDC motor or pump of up to 150W."

Nevertheless I agree with you John, as a general rule you should use the load terminals on your reg only if it is connected to a battery.


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