solar to battery to fridge

Submitted: Saturday, Jan 29, 2011 at 16:48

ThreadID: 83980 Views:3454 Replies:5 FollowUps:2

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Solar Power

This article covers every aspect of solar and its design and installation in RVs (camper trailers, caravans and motor homes). It shows how much power solar panels really produce,

christo2510

Do I need a regulator of some sort if running my fridge from the deep cycle battery at the same time 8o watt solar pannel is connected? I have an AGM 120amp deep cycle battery which will be a stand alone and only changed from the solar pannel.

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Reply By: Sand Man (SA) - Saturday, Jan 29, 2011 at 17:59

Saturday, Jan 29, 2011 at 17:59

Yes, you definitely need a regulator.

Solar regulators protect the battery from overcharging.
Without one you run the risk of over voltage also and this will also have an adverse effect on your battery.

Bill.

Bill

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AnswerID: 443457

Reply By: farouk - Saturday, Jan 29, 2011 at 18:45

Saturday, Jan 29, 2011 at 18:45

christo2510

I remember nearly 20 years ago when I first installed solar I accidentally shorted the regulator and I had to send it back to the dealer in Perth and I was worried about the battery overcharging and their answer was " do not worry about it as with the fridge continually running even on the thermostat and then using battery at night will stop battery from overcharging"

Just keep your eye on the voltage and you will find with a 80 watt panel it will certainly not get to the stage of boiling
Farouk

AnswerID: 443463

Reply By: Mandrake's Solar Power- Saturday, Jan 29, 2011 at 19:17

Saturday, Jan 29, 2011 at 19:17

An AGM battery will not like 24 Volts being poured into it !!!

Please use a small regulator or have deep pockets for your next battery ..

Cheers

Steve

AnswerID: 443471

Follow Up By: Lex M (Brisbane) - Saturday, Jan 29, 2011 at 22:02

Saturday, Jan 29, 2011 at 22:02

There is no way that an 80 watt solar panel will put 24 Volts into a 120 Ah AGM battery.

Without knowing what type of fridge it's impossible to even guess at the answer to the question.

The safest way is to get a solar regulator.

FollowupID: 715540

Follow Up By: farouk - Sunday, Jan 30, 2011 at 09:03

Sunday, Jan 30, 2011 at 09:03

Mandrake

Being no expert I was always under the impression the solar panel voltage of 18 t0 21v was only achieved under OCV and as soon as you connected it to a battery it would drop to the voltage of the battery.

AGM batteries do have to have a different charging limit to lead acid but that upper limit would not be achieved from 1 x 80 W panel being used to power a car fridge and the requirements of the van as well ie you would only get about 30 amps on a good day out of a 80 watt panel, IF it was a good day, and the fridge would draw if the temp was only about 30 degrees a minumum of 48 amps plus the other requirements so the chances of overcharging of the battery or even getting it up to float is highly unlikely.

All things being equal I would say fit a regulator if the application is permanent but for a trip away I would certainly not bother, I would just ensure that I monitored the battery .
I will insert here a post which virtually agrees with my theory

"PV panels are "current (amp) devices", so if you connect a 30V panel to a 12V battery, the voltage instantly (and harmlessly) falls to the battery voltage, and you are just pumping amps into the battery. Since 12v is way below the peak power curve of a 30V panel, you will not get full power, but more like the short circuit amps listed on the nameplate.
With an 80W panel, 120AH battery, heavy nighttime loads, and 1 week camping connected only, no controller needed."
farouk

FollowupID: 715568

Reply By: Member - Robert R1 (SA) - Sunday, Jan 30, 2011 at 00:35

Sunday, Jan 30, 2011 at 00:35

Christo,

Many years ago I built a battery charger using an old tv transformer which I rewound and wired through a bridge rectifier. It put out about 21v which is roughly what an 80w panel will put out. Across a 12v battery the charge current was about 6 amps which dropped very quickly to about 3 amps as the battery voltage started rising under charge. (Close to what your panel will do).

Based on that you could get away without a regulator but I wouldn't recommend it. Regulators are pretty cheap these days so you might as well get one and possibly save yourself the drama of an over-cooked battery at an inconvenient time.

Regards,
Bob

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AnswerID: 443495

Reply By: Mandrake's Solar Power- Sunday, Jan 30, 2011 at 09:56

Sunday, Jan 30, 2011 at 09:56

Considering his battery is an AGM 120 aH - It probably cost around $300 to 400 ???

Are you guys really willing to advise him NOT to use a voltage controlling device .

For a small investment of $30 a small 8 amp controller will save a lot of later grief .

It also means he can walk away from his campsite without the need to MONITOR the battery ....

I would never recommend NOT using a controller on any panel above 40 Watts...

My 80 Watt panels will reach a short-circuit output of around 24 Volts at times of bright direct sunlight .. even though they are rated at 18 V with a manufacturers short-circuit voltage of 21 Volts ...

Cheers

Steve

AnswerID: 443516