Boosting a capacitor discharge electric fence charger with an air gap?

Thread Starter

FredFlintstone

Joined Apr 30, 2022
23
First of all, THANK YOU to everyone who contributed to my previous thread about building my own electric fence charger. I decided to buy this small, cheap commercial unit instead. It's mains-powered and advertised to charge a 2 mile / 8 acre fence via its 500mA input. It claims to output a pulse voltage of 4.2kV. It has a built-in pulse indicator light that flashes once per second, and it was on sale for $30 and came with a neon fence tester, so I thought I would give it a try based on the low cost for everything that's included.

I plugged it in and touched the terminals with my hand, and I certainly got a strong enough shock to NOT do that again! I think a raccoon would come to the same conclusion. However, when I tested the charge voltage with the included neon tester it indicates an output of only 2kV. This concerns me because the instructions provided by the seller say the fence charger should test at least 4000 volts -- so either the tester is incorrect, or the charger is not producing the advertised output.

I know I can exchange this unit for one that might actually indicate 4kV output, but I could also end up with another one that still indicates only 2kV. This made me wonder about something I read about once -- that creating an air gap between the charger and fence will increase the voltage pulse on the fence.

Is there any truth to this "air gap" theory, or is this fiction?

If true, this means I could install a spark plug between the charger and fence to create a stronger "zap" on the fence itself. It also suggests that this could be a solution to extending the life of a gradually weakening pulse fence charger as it ages.

???
 

Thread Starter

FredFlintstone

Joined Apr 30, 2022
23
Seems specious to me. There will be a voltage drop across the air gap
I don't know enough about this stuff to intelligently interpret what I've read about it, that's why I asked. Maybe the air gap issue relates to other kinds of electronics, but not to the charge imparted by an electric fence charger? Or maybe this works with some kinds of fence chargers but not others?
 

Ya’akov

Joined Jan 27, 2019
5,660
An air gap could be used as a spark gap to provide the voltage regulation of the pulse. If the air has to break down for the current to flow then the size of the gap would determine the discharge voltage.

The problem with this is the variability of the resistance of air based on humidity. It would have to be an enclosed device like a lightning arrester and I don‘t know why it would be better than other methods.
 

Ian0

Joined Aug 7, 2020
5,132
I wonder if adding the air gap increases the voltage measured at the output of the power supply, but not the voltage measured on the fence. That would make sense, and be the sort of thing a dubious supplier would attempt, to make the product look better.
 

crutschow

Joined Mar 14, 2008
29,792
All an air gap in series with the fence would do is absorb voltage across the gap, with less voltage on the fence.

I think 2kV is more than enough to give a racoon second thoughts about touching the fence again. :)
 

shortbus

Joined Sep 30, 2009
9,372
This made me wonder about something I read about once -- that creating an air gap between the charger and fence will increase the voltage pulse on the fence.

Is it possible what you read was talking about the gap in a flyback transformer core? They do use them in the newer high energy type E-core ignition coils to give a higher output, and I think a lot of people suggested to you to use an ignition coil in the other thread. So if you researched ignition coils you may have seen the gap mentioned there.

https://electronics.stackexchange.c...-is-flyback-air-gap-needed-for-energy-storage
 

Thread Starter

FredFlintstone

Joined Apr 30, 2022
23
What I'm wondering about is this Neon Tester. How does it test and indicate a voltage?
I don't know the details about how it works, but it looks the same as any other inexpensive neon fence tester. It has 6 neon bulbs labeled 1000v, 2000v, 4000v, 6000v, 8000v and 10000v. Only the first two light up when I use it to test the new charger. Naturally it could be the tester itself that's not indicating the actual output voltage. This is what I am hoping. But I cannot think of another way to test the charger at the moment.

The main reasons why I bought this particular charger are (1) it was on sale, (2) it came with the tester, and (3) it was sold by amazon.com so returns are virtually guaranteed. I wouldn't mind returning it to try and get one that actually tests at 4kV or higher, but given the fact that it's made in China I could easily be wasting my time expecting to receive one that is any different than the one I received. I think I should find another way to test the charger before I think about returning it. Any ideas?
 

Thread Starter

FredFlintstone

Joined Apr 30, 2022
23
All an air gap in series with the fence would do is absorb voltage across the gap, with less voltage on the fence.
That's what I was thinking too, but I am certainly no genius in this area.

I think 2kV is more than enough to give a racoon second thoughts about touching the fence again.
I would have to agree with you. It certainly got my attention when I touched it!

After that first shock I was absolutely NOT willing to touch it again. And given the fact that a raccoon is much smaller than me, and will likely touch it with his nose -- or his front hands/paws which are very sensitive -- I'm pretty sure this charger already produces enough zap to drive away any raccoon, even if its actual voltage is below spec.

For all I know, the written info about this charger is incorrect. Maybe they all produce only 2kV? This would not be the first time the written info regarding a China-made product is inconsistent or just plain wrong, either due to laziness or intention. In fact, the amazon description says 6 months warranty yet the printed info on the box clearly says 12 months. Go figure.
 

crutschow

Joined Mar 14, 2008
29,792
One important parameter, not given in the specification for that charger, is the energy of the spark (stated in Joules).
That, along with the voltage, is what determines the intensity and shocking ability of the spark.

The powerful ones have a 0.5J or more output energy, but they tend to be expensive.
 

Thread Starter

FredFlintstone

Joined Apr 30, 2022
23
Is it possible what you read was talking about the gap in a flyback transformer core?
Yes, this is possible, and I should have bookmarked the page to refer to later, but I didn't -- probably because I didn't understand how it would work.
 

Thread Starter

FredFlintstone

Joined Apr 30, 2022
23
One important parameter, not given in the specification for that charger, is the energy of the spark (stated in Joules).
That, along with the voltage, is what determines the intensity and shocking ability of the spark.
All the other chargers that advertise the same 2 miles / 8 acres capacity say they put out 0.1 Joules, so I am assuming that this one produces the same 0.1 Joules. The reason I make this assumption is because I also assume that the internal electronics in this unit are likely made in the same Chinese factory as all the others. Here are a few that advertise essentially the same specs:

https://www.amazon.com/Energizer-Ortis-Controller-Livestock-Squirrels/dp/B0972F5QW6
https://www.ebay.com/itm/234538897728
https://www.ebay.com/itm/194990482308
https://www.ebay.com/itm/334350915673

The powerful ones have a 0.5J or more output energy, but they tend to be expensive.
Yes, those are quite a bit more expensive than the one I bought. Not only that, but since I have no idea how many Joules I might need, I decided to go with one of the smallest cheapest chargers I could find. Even this small unit claims a 2 mile capacity which is 50 times longer than the fence wire I will be charging ... so theoretically it should be enough for my needs, assuming the intensity of the shock is strong enough.

I have yet to learn how to interpret the importance of "Joules" when it comes to all the things related to electric fencing, such as insulation, energized wire length, moisture/humidity, contact with weeds, etc. It is easy enough for almost anyone to understand that "more Joules = stronger shock", but how many Joules I actually need is another question.

Is it possible to have a fence charger that produces "too many" Joules?
 
Last edited:

DickCappels

Joined Aug 21, 2008
8,708
The voltage reading appearing to be low may be because the voltage indicator is not working correctly. If the charger did not come with a voltage checker you would probably be overjoyed with the shock you received.

The meaningful test will be on an actual electric fence, which might load down the output.
 

Thread Starter

FredFlintstone

Joined Apr 30, 2022
23
The voltage reading appearing to be low may be because the voltage indicator is not working correctly. If the charger did not come with a voltage checker you would probably be overjoyed with the shock you received.
I don't know about "overjoyed" but I would certainly be satisfied with it. Tonight's the big test. I will hook it up to a metal trash can that stores cat food. The raccoons have learned how to open it, so tonight they may learn something new when they touch it ... :)
 

MisterBill2

Joined Jan 23, 2018
11,880
First, the 4 KV output is under some very specific set of conditions, and ONLY under that specific set of conditions. That may include no load and perfectly dry air. So you need to duplicate the conditions to have any chance at getting the same voltage.

What will a series spark gap get you??
A series gap will provide a much faster rise time on the pulse. That can be useful if there is a bit of leakage resistance to ground, but it also means that you are not delivering as much energy to charge the fence wire, since the pulse voltage does not start charging the fence wire until the spark gap conducts.. So probably you get no benefit from a series spark gap.

To check the voltage measuring device, you need a known voltage source, such as a neon sign transformer. But be careful because that high voltage is steady, it does not pulse.
 
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