Protecting Fence Charger From Lightning

[Gregm]

I have been told that a fence charger can be damaged from lightening coming through the ground. I

have two questions: 1) Do others agree with this? 2) Is there a device that can be installed on the ground side of a fence charge to protect it from this?

Thanks in advance for any help on this.

 

[Harald Kapp]

1) In theory: yes. In practice such a device, exposed to harsh environment, should have built-in protection.

2) Maybe a varistor or a gas discharge tube, but probably unnecessary, see 1).

 

[duke37]

I have repaired a few electric fencers which have suffered from lightning. The fault can be one component or almost everything blown off the printed circuit board.

I doubt if the pulse comes from the ground, it is more likely to come from the fence which is in fact a very long aerial.

For fixed fencers it is a good idea to put an inductance in series with the fence wire. This should consist of several turns of wire, spaced about 25mm and of diameter 300mm. A simple wooden cross can be used to support the wire as long as it is kept dry.
A spark gap is sometimes provided in the fencer between the fence and ground terminals. One should be provided with a gap of about 5mm.

If you install some device between fencer and ground, then when there is a strike, the fencer will have a high voltage spike on it. This may not be good for any power supply.

 

[Arouse1973]

Their are a few of ways lightning can damage equipment.

Direct lightning stroke

1) cloud to ground or ground to cloud. Game over. Can be over 200,000 Amps.There is not much you can do about a direct lightning strike the cost would be prohibitive.

Indirect lightning stroke

1) Induction from the electromagnetic fields into the wires as mentioned by Duke37. Normally cloud to cloud.

2) Surge on the mains wiring coming into the feed for the equipment.

3) Ground lift as lightning hits the ground nearby. Made worse by dry rocky ground as in Finland.

The easiest one to fix is the surge into mains wiring. In the UK this is limited to 2000V but can supply 6000Amps. A 25,000 Amp GDT across Live and Neutral, then an inductor and then MOV across live and neutral after the inductor and protected with a fuse if the MOV goes into self destruct mode. Then MOV in series with GDT across Live and earth, the same across neutral and earth.

Do not put a GDT across any DC voltages not protected by a fuse. Use an MOV across the output and as Duke37 mentioned some series inductance to both wires is always a good idea to slow down di/dt rates.

Hope this helps
Adam

 

[(*steve*)]

as Duke37 mentioned some series inductance to both wires is always a good idea to slow down di/dt rates.

And possibly a spark gap on the fence side of this to try to shunt away larger energy pulses.

Probably nothing (rationally affordable) will protect from a direct strike on the fence. Strikes on the ground near the fence (near is a relative term) are probably the best you can hope to protect from.

Duke37 seems to pop up whenever there's an electric fence thread. He has a lot of experience. And when I read back, I note he has already suggested the spark gap, and has given enough details to allow you to constuct both it and the inductor.

 

[Gregm]

Thanks for the responses.

I have installed 3 lightening arrestors on the fence at various spots, a choke between the fence and the charger and a surge protector on the outlet the charger plugs into.

I just wanted to check and see, if something was needed on the ground side.

I have just fixed two chargers, by replacing the circuit boards and was trying to avoid having to fix them in future.