Electric fence monitor

Hello, I have looked through many forums, with no real answer. So I am making my own.

I have an solar powered DC electric fence (~15 miles) that outputs around 15,000 V every second if everything is hunky dory. When plants get in the way, the voltage can drop to around 10,000V. When there is a short, it will go <7,000V. No I don’t want to measure it at the battery, because there are multiple fields far away that I want on or off etc.

I want to measure this fence voltage, and eventually insert a HV relay and zigbee to send back to the house. I will worry about the relay and zigbee later.

Problem: I don’t know which path to choose.

Using an EMF detector on Arduino

Using resistors

Basic optoisolator discussion

The EMF detector doesn’t seem accurate enough for my application as I want to know the voltage within around 1,000V.

The resistors I have read are just an all around bad idea unless I get a very good zener diode and corona dope etc. It will pretty much short circuit.

Finally, what seems like the win here is the optoisolator. Sparkfun makes one, but it is not rated to the voltage I have.

I know people have made these before, but I would like to know if anybody has any ideas or tips to proceed?

Thank you!

How did you get those voltage values?

It may be easier to measure the current instead of the voltage. This can be done at the battery (low voltage) side. But you should have a scope for watching the current shape with various loads (fence length, plants...), because the pulse duration may vary more than the pulse amplitude.

Your post caught my attention as I have an electric fence around my 6+ acres of land and the deer are always getting into it. No way to tell till I go look at the charger or see deer in the yard!

I tried a solar charged battery operated fence charger years ago and it only provided a few thousand volts and battery would not be charged during the short daylight times during the winter. My AC powered charger provides about 3,000 volts to the entire perimeter fence due to loss in insulators, etc. A short fence allows up to about 9,000 volts.

As I can hear the pulse in my ham radio receiver on almost any frequency, I think a radiated EMF detector, not the voltmeter you linked to. A wire parallel to a portion of the fence, one end connected to ground, the other to a rectifier/capacitor to give a DC voltage and then monitor that with the Arduino would work. The capacitor charge would have to be bled off with a high value resistor.

The Arduino program would monitor the peak voltage over several minutes and compare to a standard voltage relating to a perfect fence voltage. If the value goes some way below the perfect, then alarm.

By the way, evening dew will reduce the peak voltage quite a bit.

Paul

We used to use an old sparkplug as an indicator.

Thanks,

I got the voltage from a handheld monitor like These.

I think the EMF would be great and cheap, but not very accurate. It might just take a lot of trial and error. I would love to be able to use the optoisolator safely with an UNO.

stevenette:
Thanks,

I got the voltage from a handheld monitor like These.

I think the EMF would be great and cheap, but not very accurate. It might just take a lot of trial and error. I would love to be able to use the optoisolator safely with an UNO.

An optoisolator would be able to just give an off/on indication. I thought you wanted more.

Paul

Paul_KD7HB:
An optoisolator would be able to just give an off/on indication. I thought you wanted more.

Paul

Shoot, really? Yes, I was hoping for a varied response from the fence. Not just on or off.

Would a bunch of HV resistors work instead, or is that idea dead?

Some ideas

Ya, That was the 3rd link I posted. Read through it, but no good conclusions. Or at least none that I took away.

Back to the trial and error method I guess? I'll try to report back if I get anything useful.

first off, you most certainly use resistors. the problem is that you cannot use just one. you would multiple in series. take a simple Yago, wants to have a working voltage of 200 volts.
so, you put 100, end to end and you have 200 volts across each one, when you have 10,000 volts.

now, with 100 in series, you have a lot of places to choose where to connect.
and you can add something larger so that you have a 5v drop across that one resistor to measure the voltage.

your fence will have a capacitive component to it
when you charge it, immediately read the voltage to watch the decay.

dave-in-nj:
first off, you most certainly use resistors.

mmmkay, that is what I was thinking would be the simplest way. The only issue I could see is that I have tried to squeeze between this fence and a wooden pole and been thrown on the ground even though I was a few inches from the fence. I could potentially see an arc jumping a couple of inches too. I wonder how I could place them in a chain so that they don't all arc over each other and eventually destroy a fragile little arduino.

I do have a ton of Uno's to spare at the moment, so I'll get some HV resistors and give it a go!

Buy one of these, take it apart, and see if you can duplicate it for the desired voltage:Fence Volt Indicator | Gallagher United States And use phototransistors (connected to the Arduino) at each light, for isolation.

That is a good idea. I'll see if I can get my hands on one as they are much cheaper than the digital ones I have used. Although I never had to ground it to the actual ground.

I'll bet a short on the output changes the supply current to the inverter. You could measure that.

stevenette:
That is a good idea. I'll see if I can get my hands on one as they are much cheaper than the digital ones I have used. Although I never had to ground it to the actual ground.

You have probably done this a couple of months ago but in case you haven't gotten round to it then I grabbed a couple of photos of these as I was thinking on the same lines as you. It's really just a series of resistors and neon bulbs.

Btw. The digital ones are connected to ground really. It's just that you are the path to ground.

JonGretar:
You have probably done this a couple of months ago but in case you haven't gotten round to it then I grabbed a couple of photos of these as I was thinking on the same lines as you. It's really just a series of resistors and neon bulbs.

Btw. The digital ones are connected to ground really. It's just that you are the path to ground.

The NE2 neon bulbs need about 60 volts to fire if exposed to light. Light keeps a few of the neon atoms ionized all the time. So the resistor chain needs to be able to allow at least 60 volts across the resistors in parallel with the lights.

Paul

Just for fun I made a simulation of a a voltage divider based system.
Added a resettable peak detector so that the you could sample the voltage outside the incoming pulses.
With good components this could be very accurate.

Of course you would need add a bunch of protections. There are many things that could go wrong with this.

JonGretar:
Just for fun I made a simulation of a a voltage divider based system.
Added a resettable peak detector so that the you could sample the voltage outside the incoming pulses.
With good components this could be very accurate.

EveryCircuit - Electric Fence Voltage Monitor

Of course you would need add a bunch of protections. There are many things that could go wrong with this.

JonGretar
Looks good would be interested in making this up to test. Did you happen to have a components list?