Solar Panels Help

[cass_cass94]

Hi,

I have a 2011 GU patrol with dual batteries and a redarc SBI12 isolator.
I got a Waeco CF40 as a xmas pressie and want to use it while im away at a music festival in early january. The car will be stationary for about 3 to 4 days tho without starting it. So i believe i will need some solar panels to charge the battery to keep the fridge going.
So my question is, how do i work out what size of solar panel i need to use, and what do i need to connect them up (like do i need some sort of regulator between the panels and the battery to make sure it doesnt overcharge). Also if im just connecting the panels up with aligator clips straight to the battery do i connect it to my aux battery or to the main.

Cheers
Liam

[the evil twin]

What sort of isolation ro battery manager, if any, do you have between the cranker and Aux?
I would prob recommend clipping the panel to the Aux depending on the above

For the CF40 about 60 watts of Solar panel will be oodles.

Yes, you will need a Regulator (anything above 20 watts into a Car battery will, below 20 doesn't) but they are a cheap as chips

[threedogs]

I made up a lead from my AUX battery to the Bullbar especially for solar panels.
IMO an 80 or 100 watt panel will do what you need, dont forget to chase the sun
to get the full benefit from them[panels].
Bigger is not always better and consider as well the extra weight , a killer for any 4x4

EDIT ::::: I only went the bigger panels , if you wanted to run lights or some other 12v gizmo's

[cass_cass94]

I've got the redarc sbi12 isolator so it should keep my starter battery all good. So if I get a 100 watt panel and a regulator between that and my aux battery it should keep it charged enough to run the fridge. Cheers for the help guys

[threedogs]

Yeah try to run all accessories from your AUX deep cycle battery
after all thats the reason why you fitted it in the first place isnt it. lol

[the evil twin]

I've got the redarc sbi12 isolator so it should keep my starter battery all good. So if I get a 100 watt panel and a regulator between that and my aux battery it should keep it charged enough to run the fridge. Cheers for the help guys

If you have an SBI12 then I would def connect to the Aux when camped up.
Be aware that if the Alt has been running and the SBI12 is energised when you connect the Panel then the Panel will usually hold the Isolater energised.
No biggee it just means both batteries will be getting current flow so the Aux won't get all the juice.
They should both be in a high state of charge anyway.
Once the SBI12 deenergises it won't switch back in until you have Alternator or Panel Voltage on the Cranker so the Aux gets all the juice from that point on.

A 100 watts (most get 2 x 50's that fold) setup correctly will be heaps more than you need for your Waeco
Depending on the quality of the Reg the ideal setup is to run the Waeco off the 'load' terminals.
Again, not a biggee, just means the fridge compressor cycling doesn't confuse the Reg.

Those little power meters like TD posted are very handy and cheap at around 15 bucks on Ebay

'Normal' Panels give me the shits, big heavy mongrels of things so I use these.
Expensive but if you shop around or wait for a deal they are def better for storage etc
http://www.ebay.com.au/itm/100W-Fold...MAAOxykmZTMh~D

[FNQGU]

Hi Liam,

The 'bible' that I generally refer back to called 'Solar that Really Works' and is written by Collyn Rivers and he says the following:

"A correctly installed electric compressor fridge of 30-80litres is likely to draw about 0.7 Ah/day for each litre of its internal capacity, but more in warmer places." This is based on fridge makers specs of 4*C thermostat temp and an external ambient temp of 25*C. For each degree celsius colder that the thermostat is set to, the energy draw increases by about 5%.

Your fridge will either be on or off as it cycles during the day. So if for example your fridge draws 2.5 amps for 12hrs each day (on average) then it adds up to 30Ah/day right?

From your avatar you are in Perth, and as it is end of December/early January, the Peak Sun Hour contour tables say that you should be getting around 7.5 peak sun hours each day in good sunny weather, and this is 'chasing the sun' (or regularly moving your panels to face the sun) as mentioned by TD.

So, you then multiply the peak sun hours (7.5) by the real output of your solar regulator and divide that by 12 V, you will get the number of Ah/day you are going to likely put back into the battery to manage your fridge. As long as you are getting 30Ah/day or more, then you will be fine for as long as you have beer to keep cold.

Your regulators output is a big factor in how cold your beer will stay, and in this regard you get what you pay for, and there is plenty written elsewhere on this topic.

If it is cloudy or raining, then expect to only get around half of the real output of your panels, or about 3 to 3.5 peak sun hours.

The golden rule, according to Collyn, is to have at least 120-150W of solar for every 100Ah or battery capacity if you want to be sustainable. Now given that you only want to be running the fridge for 3-4 days, you can probably just do as advised by TD and ET and use minimal solar capacity to keep putting something back, as the fridge slowly runs the battery down.

If you are also running a few camping lights then it might run down slightly quicker, depending on the type of lights.

Worst case - start your engine and run it for an hour or so on your second and third days!

[GeeYou8]

Use a maximum power point tracking (MPPT) regulator/charger for more efficiency, it will get the most out of your panels.

[the evil twin]

Use a maximum power point tracking (MPPT) regulator/charger for more efficiency, it will get the most out of your panels.

Agree... with a few ifs and buts...

If you are regularly adjusting the panels, (MPPT needs the max point on power curve so needs to be close to optimum angle)
If the array is big enough to warrant MPPT (gains below about 120ish watts array power are in the milliamps),
If the panels are cool (the hotter the Panels get the closer the performance from a PV reg will get to an MPPT anyway)
and if the Reg is a genuine MPPT device it is darn expensive by comparison.

For anything under 120 watts or so in the Aussie Summer months MPPT isn't worth the $ for a casual user.
The gain is around 0 to 5% or so at best for a 'plug it an leave it' scenario.
Efficiency wise you are usually better off spending the $100 (or more) for an MPPT reg on upsizing your array.
IE a 100 watt MPPT Reg array will not outperform a 120 watt PV Reg array and the 120 system will be cheaper

MPPT comes into its own on big arrays in cooler conditions preferably with tracking (or regularly adjusted) panels.

I have both types of Reg but only really bother with MPPT on my Van when I may have 200 watts or more of array.

[threedogs]

A good idea is to limit the amount of time the fridge is open,,,,, opening and closing it say for one can at a time
will test your battery.
I use my Engel for food only and when I load it some food is
frozen others are just chilled, this limits the amount of times the fridge cycles.
You might want to consider an Esky for your cold drinks if you have ice nearby,
and the cold water is great to refresh yourself in the morning and doing the dishes