Is this totally stupid - charging car battery for an electric fence?

Eriskayowner

Eriskayowner

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To use the battery that's in my car as the second battery, and just keep swapping them over?

Obviously I won't let the one on the fence run down completely, but the alternator in the car should then be able to charge the car battery up, and I can swap it back?

Does that make sense, or have I missed something?
 
Bad idea. The thing that knackers a battery faster than anything is a rapid charge. Your semi flat fencer battery will have the full power of the car alternator thrown at it and it will cook it. Even your regular car battery will rapidly fail if you repeatedly run it low,a loose alternator belt ,lights on and heater will drain a lot out ,when it charges back up it will be subjected to more than is desirable and rapidly shorten the life. Swopping batterys about damages them because they tend to get banged about and this damages the plates. In addition most modern cars have engine management systems which are easily damaged when changing a battery(very expensive). So this is a definate NO.Find yourself a couple of cheap batterys and change them regularly,long before they have gone so flat they wont run a fence unit,and ONLY trickle charge them.
 
Your best bet is a leisure battery (I think they are called). Used for example in boats. They are designed to charge down, as opposed to a car battery which is always kept charged and used regularly.

You will definitely shorten the length of your car battery significantly doing it this way, and as Mike says chopping and changing your battery is not the best plan. Not to mention you will have to reset the clock, the radio code, etc etc :rolleyes:
 
Agreed, they are expensive. Luckily for me my Dad is a mechanic so I got mine at trade - a significant discount!

The other thing we've done is buy a cheap solar charger from Maplin. Saves lugging the battery about. The only problem is it got wet, so no need to figure out how to make it waterproof :rolleyes:
 
We bought a £12 maplin job and it definitely worked. Oh just looked and they are on sale! It came in plastic packaging and we left it in there and it seemed to stay dry. However we should have taped it up as one day it got windy and the top part blew off - then it got wet and now it's knackered.

However at a tenner, I may just be about to order a new one :)

http://www.maplin.co.uk/solar-powered-12v-1.5w-battery-trickle-charger-98358
 
Mike007 said:
Bad idea. The thing that knackers a battery faster than anything is a rapid charge. Your semi flat fencer battery will have the full power of the car alternator thrown at it and it will cook it. Even your regular car battery will rapidly fail if you repeatedly run it low,a loose alternator belt ,lights on and heater will drain a lot out ,when it charges back up it will be subjected to more than is desirable and rapidly shorten the life. Swopping batterys about damages them because they tend to get banged about and this damages the plates. In addition most modern cars have engine management systems which are easily damaged when changing a battery(very expensive). So this is a definate NO.Find yourself a couple of cheap batterys and change them regularly,long before they have gone so flat they wont run a fence unit,and ONLY trickle charge them.
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Your car's regulator/rectifier will protect the battery, so it won't be subjected to more then desirable charging. So charging with the alternator won't damage the battery.
However all the hassle of resetting the clock and the radio and alarm/immobiliser would be a pain in the proverbial. Off to the 'scrappy' I think. I've got an 'Optimate' Battery charger and conditioner. I leave it plugged in when a battery isn't being used.
 
lazybee said:
Your car's regulator/rectifier will protect the battery, so it won't be subjected to more then desirable charging. So charging with the alternator won't damage the battery.
However all the hassle of resetting the clock and the radio and alarm/immobiliser would be a pain in the proverbial. Off to the 'scrappy' I think. I've got an 'Optimate' Battery charger and conditioner. I leave it plugged in when a battery isn't being used.
Click to expand...

Wrong!,your regulator on the alternator senses the battery voltage and initialy will charge at about 60 amps.In an ideal world, your battery on your car is fully charged and your car starts easily.Little current is used from the battery sothe voltage doesnt drop much .The alternator therefore doesnt need to chuck 60 amps at the battery so it doesnt (or at least only for a second or two.Put a semi flat battery on and it will get the full output for far too long and cook.
 
Mike007 said:
Wrong!,your regulator on the alternator senses the battery voltage and initialy will charge at about 60 amps.In an ideal world, your battery on your car is fully charged and your car starts easily.Little current is used from the battery sothe voltage doesnt drop much .The alternator therefore doesnt need to chuck 60 amps at the battery so it doesnt (or at least only for a second or two.Put a semi flat battery on and it will get the full output for far too long and cook.
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Hang on, not wrong.
I've only ever seen a duff battery causing an alternator reg/rec to fail as it has to run flat out at 60 to 100 amps as it tries to maintain a healthy battery state. Not the other way round as you suggest ? This is regularly seen on Honda motorbikes.
 
The plates on a lead /acid battery start to disintegrate under a prolonged high charge rate. Incidentaly we have a lot of equipment with these batterys and record when they are fitted. The thing that stands out a mile is that the batterys on the ones that have old fashioned dynamos ,(15 amp max charge rate)will last maybe 8 or 10 years but you can destroy a battery on one with an alternator in a matter of weeks if you run it low and let it recharge off the alternator.A proper leisure battery is no different from a conventional one except that the plates in the battery are stronger and designed to not buckle under a high charge rate.
 
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