Batteries for electric fence

[McMurdo]

Here's a vintage fence energiser. Totally electromechanical, it uses a balance-wheel type mechanism that pulses the battery on and off the HT coil.

The problem is that the battery, originally a 6V dry battery, is only available on the continent and costs over £25 plus carriage plus tax to get here. They only last 'one grazing season'.

I've offered to convert it to some more modern battery, something more in keeping with life on the farm, i.e. frugal and rechargeable. The original one looks like it contained zinc-air cells as there is an air vent with 'remove to activate' covering it.

The problem is, I'm stumped as to what to use. The original battery is rated 90aH at 6v with a warning on the energiser 'do not use 7.2V batteries on this device to avoid contact burn-out'.

It works fine down to about 4V so I did think about a 5V powerbank, easily recharged, but i dont know how long it'd last. The current taken is around 200mA per pulse and nothing in between, each pulse occurs every 1 second or so and lasts for just a moment as the contacts briefly touch.

Here's a video of it working off my bench supply:
https://www.youtube.com/watch?v=5w_w7LkwtTc

Hope you like the frankenstein neck electrodes!!

[paulsherwin]

A USB powerbank is the obvious way to go. The big ones are just several 18650s with a charge controller and voltage changer. Some of them include a solar cell which may be useful in summer.

I suggest you hook the thing up to a cheap low capacity Poundland powerbank (say, 2Ah) and run it until it's exhausted. You can then scale up the run time to a much higher capacity unit.

[Refugee]

Those often had space for a 6V lead acid battery. The battery compartment was "D" shaped so that the round single use battery would also fit in many of those units.
A deep discharge SLA would be my go to solution. The internal resistance will be lower than with zinc air battery. If I remember rightly from the days when I helped with a "mini farm" the zinc air compatible ones had a capacitor after the power switch to squeeze as much as possible out of the disposable battery as the internal resistance increased.
Due to the lower internal resistance of an SLA it should be more efficient on power consumption.
The upper voltage limit is when the wheel goes right round and hits the wrong side of the contact.

[McMurdo]

I can#t find any power banks that come close to the original 90Ah battery. The biggest on Amazon in about 25Ah. There are some on ebay claiming 1000Ah which sounds vaguely ridiculous...

edit: a suitable 6V lead acid battery and charger is likely to cost more than a new energiser surely!

[paulsherwin]

I've certainly seen 40Ah ones, and there will be bigger ones in the non-domestic sector, designed for recharging multiple devices multiple times off grid. I'm no expert on this though.

You could always build your own with a couple of chips and a load of 18650s, or even build something based on a LiIon traction battery.

25Ah may actually be enough. How long is the 'grazing season'? Would the farmer be prepared to buy two units and swap them over every week or two? Presumably the cows aren't just left to fend for themselves for months on end.

[Refugee]

You can still buy disposable batteries for it.
They won't break the bank either.
https://www.moleonline.com/mole-elec...v-80ah-1177990
https://www.moleonline.com/hotline-p...ery-6v-1033084
https://www.moleonline.com/mvf-pp8-6...rgiser-1033088

[paulsherwin]

That is undeniably the simplest solution.

[McMurdo]

those wont fit, they're way too tall. The original battery is a circular thing and the big dome affair sits on top of it. Here's a pic of a 7.5V one that the label says is not suitable due to them burning the contacts. He did try one, it went flat very quickly and the contacts burned themselves open.

[Techman]

I'm wondering about one of those 6 volt lantern batteries available fairly cheap in such as Wilco etc.

[McMurdo]

I've just spoken to the farmer who says a 90Ah battery would normally last about 1 year in continual use!

[Lloyd 1985]

How about a smallish SLA battery and a small solar panel and charge controller?

That energiser looks a lot more robust than the piece of modern junk I had to try and repair! The horse kicked it and a transformer and a large capacitor came off the board, no matter what I did to try and get it going it always fried itself after a short period of seemingly working normally!

Regards
Lloyd

[emeritus]

I seem to recall that Alkaline D cells are around 20Ah capacity, longer at lighter drains. Can you get one or more 4 x D cell battery holders in the available space, possibly multiple holders connected in parallel for longer life?

[Robsradio]

It may be a cheaper option, (I don’t know how much they are), but Unipart Dorman sell an air depolarised 50Ah 6v lantern battery for road lamps. Two of these a year may be cost effective, don’t know but something to think about maybe? Great balance wheel action, very electro magnetic clock inspired!
Rob

[Electronpusher0]

A 6V lead acid Motor bike battery would do the job, these can often be picked up for practically nothing from bike repair shops, they are changed on bikes when they can no longer turn over the engine in winter, they would have enough oomph for a fencer.

Peter

[McMurdo]

I did look at a bike battery but they seem very low amp-hour, good short term current but not great stuck out in a field all year. (typically 5 to 20 Ah)

[GMB]

I have one of these and it had been converted by adding a series resistor for 12V operation using lead-acid - but external.

(I also have the next generation which needs repairs, using transistors and a valve!).

[paulsherwin]

Use the 7.5V one with a couple of 1N4001s to drop the voltage?

[GMB]

You really do not need to drop the voltage from 7.5V. These devices are really very crude!!

[McMurdo]

He used the 7.5v battery and it burned the contacts so it would not operate, I had to re-dress them.

[Trigon.]

The 6v round type is available in the UK, but is expensive.

https://www.tannertrading.co.uk/elec...nd-battery-6v/

Cheers