electric fencing energiser / unit

[wildewood]

hi all

i have connected an electric fencing unit to the battery the wrong way round (in the dark) & now it won't work anymore - I can't believe that a reversed polarity has blown something - a torch doesn't break if the batteries are inserted upside down - does anyone know what it is that has blown?
cheers ~S

 

[sunnybob]

Youve blown the main fuse. I have seen a 30 amp fuse blow on electronics purely by reversing polarity.

 

[Brandlin]

Your comparison with a lightbulb suggests you think theres nothing in the control box any more complicated than an incandescent lightbulb?

I dont know the unit, but i'm willing to bet there are a number of circuits in there regarding protective cut outs, indicator lights and controls, safety switches, possibly even timers etc? control circuits like that would require the correct potential difference.

Having said that it would be a very poor design if it can be damaged by the user making such a simple mistake. If the polarity was critical, i'd expect the unit to have an internal fuse or a reset switch.

 

[Racers]

Electronics don't like reversed polarity, you might be lucky and have a diode across the battery terminals to protect it that might have gone short, CB radios used to have one and I fixed a lot that had been connected wrong.

Pete

 

[Woody2Shoes]

hi all

i have connected an electric fencing unit to the battery the wrong way round (in the dark) & now it won't work anymore - I can't believe that a reversed polarity has blown something - a torch doesn't break if the batteries are inserted upside down - does anyone know what it is that has blown?
cheers ~S

My very nice LED torch from Aldi blew up when I put the batteries in the wrong way round (which was very easy to do as the markings were pretty much non-existent).

Whether or not it's broken, and in what way, depends on the specific design of the circuits in your specific gadget - if you can post a circuit diagram someone may be able to suggest what's happened. It costs a penny or two to add circuitry to protect from reverse connections - but in a production run of thousands, someone will take a view on risk vs. reward - most cheap Chinese-made gear errs on the side of profit.

If you can find a competent electronics technician, they may well be able to mend it quite easily (and possibly add protection to prevent it happening again). Most people find it easier and cheaper to buy another gadget.

Cheers, W2S

PS I struggled for years with battery-powered energisers. Putting in a run of HT cable (inside a length of water pipe for added protection) from a new mains-powered energiser was a huge leap forward (no more dead batteries etc. etc.). e.g. https://www.electricfencing.co.uk/50m-h ... 2-5mm.html Maybe now's the time to make the change?

 

[Sheffield Tony]

My very nice LED torch from Aldi blew up when I put the batteries in the wrong way round (which was very easy to do as the markings were pretty much non-existent).

Whether or not it's broken, and in what way, depends on the specific design of the circuits in your specific gadget - if you can post a circuit diagram someone may be able to suggest what's happened. It costs a penny or two to add circuitry to protect from reverse connections - but in a production run of thousands, someone will take a view on risk vs. reward - most cheap Chinese-made gear errs on the side of profit.

It's not just cost. All the approaches have drawbacks. A series diode drops ~0.5v, which might matter when running off 1.5 or 3 volt battery. Might waste power and make heat in heavier applications. A shunt diode and a fuse - the diode almost always protects the fuse by blowing first !

Automotive electronics are the worst. Reverse polarity means what should be your ground is live, and the fuse is in the ground line. Any unanticipated connections to chassis ground mean your fuse is bypassed and the smoke escapes.