I want to make an voltage tester for an electric fence, using 5 neon lights.
At a location where the fence voltage is maximum all 5 neons light. Fewer than that at lower voltage. I'd like a schematic for this, please, anyone. I know its just resistors that make up the circuit, but what values?.

 

I know its just resistors that make up the circuit...

How do you know that? Do you already have a circuit example?

Do you have any specifications for the bulbs you want to use?

 

I think we can assume the bulbs are NE-2.
Each level needs a voltage divider.
The part I don't know is the highest and lowest voltage that will have to be measured.
Then the idea that it is not practical to hold a current through a neon bulb and some mechanical shielding is necessary for the owner to see the bulbs during daylight hours...or only check his fence at night.

 

I had one of these testers before and I know it is only made up of 5 small neon indicator lamps with wire ends and a resistor divider circuit. It's the value of the resistors I need and their configuration in the circuit. I know some are in series and some in parallel. About 10 or so in total. The electric fence pulse voltage is 10Kv and more.

 

The tester resistors form a divider chain with some resistors in series and some in parallel. The fencer voltage pulse is 10Kv and more.
The neon lamps are just small wire-ended indicator neons. The pcb will be contained in a box shading the neons from daylight.

 

The fencer voltage pulse is 10Kv and more.

Certainly enough to blow the transistors in the input stage of a 'scope, as me and my buddy found out a few years back

 

True. This is not a scope problem. It's a simple voltage divider problem except the voltages are not exactly known and the resistors are expensive because they must survive in the 10,000 volt range.

I could guess at setting the neon's at 6,8,10,12, and 14 thousand volts, but it's only guessing, and the resistors are expensive. I'll go look some up.

HELP! ANYBODY have more information?

 

This pdf shows that 1 watt resistors in this style can survive 10,000 volts and they cost $5.34 each plus shipping. The parts to build this indicator, whether it be useful or a bad first try would cost over $60. This makes me think a retail version would be the better choice.

edit: That's a bad estimate. Most of the resistors won't have to be that quality.

 

This one says it goes from 1000V to 5000V, but the google search quotes 2000V to 10,000V:
http://www.ukcountrystore.co.uk/acatalog/Electric-Fence-Voltage-Tester.html

This one does 1000V to 10,000V:
http://shop.electricfencing.co.uk/index.php?m=shop&c=view&id=42:53:101:149


so #12 is probably right to assume that the device must be able to withstand 14kV.

EDIT!
This one from South Africa goes to 22kV!
http://shop.rabtron.co.za/catalog/portable-electric-fence-p-3232.html

 

When folks here ask how to build something that they can easily and cheaply go buy, I have to ask: Why?

If you specifically want a DIY project, that's fine, but tell us that. The design goals depend on the motivation. Is there something wrong with the commercially available device? Do you need customized features? Are you trying to save money? A designer needs to know the goals.

 

I'm seeing electric fence testers on eBay for $6 to $20
That's cheaper than the parts and a lot easier than me spending an hour or two calculating.

I've also seen elecrtic fence chargers from 1.2Kv to 25 KV. Incredible range to cover in a new design.

If you want the experience, Ohms law is E=IR
The right neon bulbs are www.mouser.com 606-C2A-T @ 50 cents each, 95 V breakover
The most likely input resistor is 71-TR20H1005F
That's 10 megs, 2 watts, 17.5 KV rated, 5% tolerance
If that isn't the resistance you need, follow the 71- prefix to find similar and better quality high voltage resistors.