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Solar electric fence

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hi,
Using 10mA at 1 sec rate, what do you expect the energy in Joules to be.???
As I said in an earlier post you need at least 1.5 Joules to zap a sheep.
The 555 timer in my circuit is on for 10% , the current then is 100mA which is 10mA average. With 6V battery it is 600mW = about 2.5 Joules. Am I right?
I only want to keep the the sheep inside not to Bar B Q them.:)
 
The voltage doesn't really matter - it's how much current it can feed in to the battery - a battery is very much like a zener diode, and will regulate the voltage fed to it..
Yes, but if the open circuit voltage of the solar cell is too high, the battery will try to charge beyond the recommended max voltage of the battery. I would not want to charge an SLA battery beyond 14.5 V, or so. A 50 V open circuit panel would keep sending current into the battery beyond the safe max voltage limit. But a proper open circuit voltage (lets say 17-18V) would be fine.

For this particular application, where it's a fairly light (and constant) load on the battery, a correctly sized panel would easily do the job with no regulation needed
Yes, that is exactly the point of my contribution to the thread.
 
steveB
What is the size of your solar panel?
It's about 18V open circuit and measures 12 x 30 cm for the area.

I'm unhappy to hear that you have solar electric fence, I thought mine is the first in the world.
Sorry to burst your bubble, but they are very common to buy and commonly used. I thought you were doing it to save money, cause they are a little expensive to buy.

You write in your page that you are happily married,
Frenchmen say that when a man say that he is happily married he is telling a lie.
Yes, it's just a lie to keep all the girls from chasing me. :)
 
I agree mr gibbs, if its run 7 years then its reliable.

Are you using a baked bean can style lucas coil?, they are pretty hardy, later ones esp marrelli which are designed for constant energy ignition are not so forgiving, even fiat say in their blurb you can kill the coil in seconds with no plug connected.

Lead acids self discharge, and there is a max safe trickle charge rate, your fence is a constant load, if your solar cell doesn not generate more current than the max trickle charge plus the drain from the fence then you dont need a controller.
There is a possibility if you had a huge cell and a small battery you could boil it dry, I dont think you'll need a big cell at all from what you've been saying the discharge rate is, however bear in mind batteries degrade so get more capacity than you need, by 2 or 3x.
 
Yes, but if the open circuit voltage of the solar cell is too high, the battery will try to charge beyond the recommended max voltage of the battery. I would not want to charge an SLA battery beyond 14.5 V, or so. A 50 V open circuit panel would keep sending current into the battery beyond the safe max voltage limit.

Only assuming it's a high current panel, but you wouldn't use a high voltage panel to charge a 12V battery anyway, as it would be far too inefficient.

But assuming it's a 50W panel then the most it could feed in to a battery (12V or overwise) is 1A - an 18V panel only 18W would give exactly the same performance, a complete waste of most of the 50V panels capability. Assuming the battery is perfectly happy trickle charging at 1A (pretty common for a lead acid battery) then it would never damage the battery.

VERY rough figures of course.
 
Only assuming it's a high current panel, but you wouldn't use a high voltage panel to charge a 12V battery anyway, as it would be far too inefficient.

But assuming it's a 50W panel then the most it could feed in to a battery (12V or overwise) is 1A - an 18V panel only 18W would give exactly the same performance, a complete waste of most of the 50V panels capability. Assuming the battery is perfectly happy trickle charging at 1A (pretty common for a lead acid battery) then it would never damage the battery.

VERY rough figures of course.
OK, but a point is that you can (at least in principle) oversize the solar cell to the point of damaging the battery. A 10000 W, 250 V panel would do it I'm sure.

What I was trying to say, for the OP's benefit, is that a simple panel, SLA battery and diode will work, if the correct panel is chosen. I know that because the ones you buy work that way. I know that, because I took mine apart and that's what I found.

Damage aside, there is just the issue of trying to optimize the performance too. I would expect the people that sell these electric fence systems put some time into figuring out a good choice for the panel.
 
It's about 18V open circuit and measures 12 x 30 cm for the area.
Finally an answer to my question, thank you. I saw a panel that it is for boosting car battery. I will use a transistor and a zener to limit the output voltage to 6.4V
I hope you are successful keeping the girls away.:)
 
All of us - it makes you VERY careful :D

It was bad enough with people blasting guns off all round (and over) you :D

It's a very strange feeling hearing lead shot falling all around you!.
Is Derbyshire still a war zone?
You have to check that your solar panels give little current because they were shot.:)
 
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OK, but a point is that you can (at least in principle) oversize the solar cell to the point of damaging the battery.

Obviously - if you buy a 10 ton truck and then load it with 500 tonnes of stone you're have a problem as well :D

But it's only common sense to have at least some vague kind of design when building a system, and sensible sizing of the panel is the major part of that (bearing in mind that a large range of panels would work without regulation for this particular scenario).
 
Here's a couple of pictures of some panels at work - now these DO need controllers (we have those as well).
 

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I'm not arguing at all. I'm trying to say basic things. My feeling is that there is an optimization that can be done with solar cell power and voltage, and I expect that manufacturers choose the cell ratings wisely. In extreme cases there can be damage. Nigel says that it would be very extreme cases that are so obvious they aren't likely to happen. I wont argue with that because I don't do these designs.

Clearly you don't want the cell open circuit voltage to be below the battery voltage, so it must be higher. How much higher is the question. The power and voltage rating of the cell will determine the trickle current that will flow when the battery is charged. I would expect you want that value to be somewhere around the self-discharge current of the battery (for SLA batteries). Nigel says higher voltages can be used no problem. I cant argue with that because (again) I don't do these designs. Still, my gut feeling is that there is an optimization to be done. If the voltage is too low or too high, there is the potential to either over-current the battery when fully charged, or to not be at an efficient power point on the cell during the charging phase.

I think it is only common sense that there is an optimization to be done. I don't think we should expect a "top-hat" design curve where we go from a region where solar cells cause damage to a region where any voltage/wattage is all the same.
 
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Nigel says higher voltages can be used no problem. I cant argue with that because (again) I don't do these designs. Still, my gut feeling is that there is an optimization to be done.

There's a BIG difference between 'can' and 'should' :D

As I made clear previously, while using small low current panels at too high a voltage can't damage a battery, it's poor design and VERY wasteful.

Optimization is important to get the best performance at the lowest cost.

My point all along, is that unless your panels are particularly large, and your battery particularly small, then you don't need a regulator - and shouldn't have one (it's just wasting money and energy for no positive result).
 
When I look at the pictures I understand why you don't want to say how much you get on a cloudy day, it will be bad for your business.:)

The panels are nothing to do with our business - they belong to the bosses son - he wants them to provide lighting on some horse shelters in distant fields.
 
There's a BIG difference between 'can' and 'should' :D

As I made clear previously, while using small low current panels at too high a voltage can't damage a battery, it's poor design and VERY wasteful.

Optimization is important to get the best performance at the lowest cost.

My point all along, is that unless your panels are particularly large, and your battery particularly small, then you don't need a regulator - and shouldn't have one (it's just wasting money and energy for no positive result).

OK, so it seems we pretty much agree on everything.
 
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