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Solar panel for leisure battery

Saldawop

Distinguished Member
My partner has a horse and runs the electric fencing using a leisure battery{85mah}.
She has a small solar panel (5w 12v)with controller(5a}, but doesn't seem to do anything .
We are assuming the solar panel /controller is too small?
Did anybody know which size she would need?
 

nheather

Distinguished Member
Are those numbers correct - 85mAh is a very small capacity.

Assume the battery is 12v.

If working at fully capacity, the solar panel can deliver around 400mA.

If the battery really is only 85mAh then the solar panel at full (bright sunlight) should charge the battery in about 15 minutes.

Cheers,

Nigel
 

nheather

Distinguished Member
That makes more sense - like a car battery.

The best the solar panel can do is 400mA and that will be in direct bright sunlight.

To charge a battery from flat would take around 200 hours.

But charging the battery is not what you are trying to achieve, it is to keep it topped up. Because electric fences are usually on all the time you really want a charging system that delivers more than is being taken out.

Or at least it is a good proportion of the drain so that it extends the time between battery charges.

So to choose a solar panel you really need to know what the electric fence is drawing rather than the capacity of the battery.

In a perfect world you would then choose a charging system that is higher than the drain.

Bear in mind that when the weather is overcast and at night the fence will still be draining the battery but the solar panel will not be topping it up. So a perfect system will need to compensate when the sun shines.

Cheers,

Nigel
 

Saldawop

Distinguished Member
Ok, energiser says input 2 joules, output 1 joules. If that means anything to you?
 

Saldawop

Distinguished Member
If we bought a 20w panel would that be enough?
 

RBZ5416

Distinguished Member
It would probably be simpler to just have a second battery on a proper charger & just rotate them. As above, you ideally need to know the draw of the fence so you can calculate how long each battery will last.

Edit
No expert but I believe lead-acid batteries use over-voltage to charge, hence the 14.4V a car alternator puts out. I think this applies even on trickle charge but at a lesser voltage (13.5V?), so a 12V solar panel is never going to do the job unless it's purpose designed for charging lead-acid batteries. I guess it depends on whether you panel is 12V or for 12V use?
 
Last edited:

nheather

Distinguished Member
A joule is a watt per second.

I'm out at the moment, when I get back I get a pencil, paper and calculator out to see if I can make any sense of it.

Cheers,

Nigel
 

noiseboy72

Distinguished Member
So assuming it's a continual power drain - charging up the fence energiser, firing and re-energising, that's 120W/hr. That is about 170mA continual drain.

Assuming the car battery is 85A/H, it should run the fence for about 500 hours theoretically, but as the battery cannot deliver its full capacity if discharged slowly, it's probably closer to 250 hours, so call it 10 days. Does that sound about right?

To top up the battery and run the charging electronics, I would estimate in a real world, you would need about 1Ah of charging, so about 12W. Assuming 30% efficiency and no more than 8 hours of daylight a day, 20-30W as a minimum I would suggest.
 

CooperUK

Well-known Member
If you do want to get a bigger solar panel, then Bimble solar in Brighton area are supposed to be good. A mate got a panel for the top of his campervan from them.
 

IronGiant

Moderator
I can't help but think, if James Joule and James Watt had got together to thrash this out we could have had a more easily understandable system of nomenclature :)
 

imightbewrong

Distinguished Member
Other way around.

A joule is a unit of energy, while a watt is a unit of energy consumption - 1 joule per second.
Yep was going to say the same. A Joule is an amount of energy - the same amount as the amount of energy needed to raise one gram of water by 1/4 degrees Celsius.
 

Aerojon

Active Member
a 20 watt panel will do what you require..personally I would put the batt on a mains charger for a 2-3hrs,just to charge it back up to strength..
 

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