AC Electric Fence Energizer

[talkinggoat]

I've got an AC powered electric fence energizer that's not working, anymore. It should pulse every 2-4 seconds, but now it doesn't do anything. There is an led that lights, when the pulse fires, that just dimly stays lit. I've checked the fuse, and it appears to be good. I was wondering if:

Anyone can look at the pictures below, and tell me what the components do.
If anyone can recommend what to replace to fix the problem.
How to increase the pulse rate to 2 per second and still maintain original line voltage.

If you need detailed photos of the components, I can take them.

Like I said, It's a very, very simple design, but I'm not an electronics person, although I want to learn more.

Circuit board's top:
**broken link removed**

Circuit board's bottom, flipped horizontally:
**broken link removed**

 

[vne147]

I don't know what advice I can offer you as far as trouble shooting aside from going through the components and testing them one by one. I drew up this schematic from the pictures you posted. I think it's correct but a good double check by someone would be a good idea. The only thing I wasn't sure about was the component marked SC1. I'm not sure what that is. Can you get a part number off of it or maybe post some additional pictures? Maybe someone else might know what it is.

 

[Hero999]

SC1 is an SCR, my guess is that as the LED is permanently on it's faulty and has gone permanently closed circuit which is a common failure mode.

You could look at the part number and buy an equivalent if you like but any SCR rated to 400V at a couple of Amps, in a package with the same pinout should do fine.

 

[gerty]

SC1 is probably an SCR, and in your drawing it looks like you have it bypassed with that connection to the right of RV2.




edit: Hero, you beat me by a minute

 

[schmitt trigger]

If indeed the TO220 device is an SCR, how come the gate and the cathode are tied together?

It would be good if you could take a picture of the front of the device, to see any markings and legends it may have.
That would help solve the puzzle.

 

[vne147]

SC1 is an SCR, my guess is that as the LED is permanently on it's faulty and has gone permanently closed circuit which is a common failure mode.

You could look at the part number and buy an equivalent if you like but any SCR rated to 400V at a couple of Amps, in a package with the same pinout should do fine.

I thought SC might have stood for SCR but that doesn't seem consistent with how it's used in the circuit. Why are 2of the 3 pins electrically connected?

SC1 is probably an SCR, and in your drawing it looks like you have it bypassed with that connection to the right of RV2.

I bypassed SC1 in my circuit on purpose to clearly show that 2 of the 3 pins were connected. I wasn't sure if it was an SCR or not because of how it's used.

If indeed the TO220 device is an SCR, how come the gate and the cathode are tied together?

Great question. Unfortunately, I don't know the answer.

 

[talkinggoat]

I've attached a couple images, but there doesn't appear to be anything written on it. Maybe there was at one time. I thought it might be the SC, too, because the caps don't show any damage and it's directly connected to the led. but what do I know? Shouldn't this be on some kind of heat sink?

I found this, of it would be equivalent?

Here are a couple shots of the SC. Sorry for the bad quality. It's a tiny part.

**broken link removed**

**broken link removed**

Thanks for the help, everyone!!!

 

[Hero999]

Maybe it's acting as a spark gap?

When the voltage across the SCR reaches its break-over voltage, it turns on and sends a high current pulse to the transformer.

 

[vne147]

Without a part number there is no way to tell if the part you have linked is equivalent. Are there any marking on the other side? It looks like both pictures are of the same side of the component?

 

[schmitt trigger]

You know, hero, you read my mind.
They may be charging the cap until the SCR goes in avalanche mode.

Very poor engineering practice, if you ask me.
The best would be to have a proper trigger device, (neon lamp, diac, etc) fed from a voltage divider, to properly trigger the SCR. Similar to the ciruits they use in auto-strobe lights

 

[Hero999]

I've attached a couple images, but there doesn't appear to be anything written on it. Maybe there was at one time. I thought it might be the SC, too, because the caps don't show any damage and it's directly connected to the led. but what do I know? Shouldn't this be on some kind of heat sink?

I found this, of it would be equivalent?

The part you've linked us to is a MOSFET which is almost certainly wrong.

 

[vne147]

I'm not sure how helpful this will be but it looks like the part in question might be in a TO-251 package.

TO-251

 

[talkinggoat]

I'm sure it's poor engineering. It's made to be as cheap as possible and break quickly.

Vne, the other side doesn't have anything on it, either.

Since you guys are educated about this, far more than me, what should I replace it with, without killing whatever touches the energized fence?

 

[vne147]

I'm sure it's poor engineering. It's made to be as cheap as possible and break quickly.

Vne, the other side doesn't have anything on it, either.

Since you guys are educated about this, far more than me, what should I replace it with, without killing whatever touches the energized fence?

I don't think you'll be able to get a very clear answer on that from anyone. I certainly wouldn't want to hazard a guess as to what exacty that part is let alone what you can replace it with so it doesn't kill anything.

You're not totally finished yet though. You don't even know for sure if that part is your problem until you've checked all the other components. Maybe you'll luck out and it will be something else.

 

[talkinggoat]

I don't even know how to go about checking the other parts. Do I need to take them off the board, or can I test them in place?

 

[Hero999]

It's actually pretty well build compared to lots of rubbish I've seen.

If you want to gamble, try an SCR but don't be surprised if it doesn't work.

 

[Boncuk]

Hi,

I reverse engineered the circuit and came up with the same schematic as vne147 did. I did something extra to see if schematic and PCB are consistent compared with the original PCB layout.

As much as SC1 is concerned my guess is that it acts as rectifier when RV2 voltage gets high enough to fire the thyristor.

Boncuk

 

[meatpie]

I think the blk and wht wires are the primary side and the 2 large posts off the transformer go to the fence.

 

[vne147]

Boncuk,

Thanks for double checking me but I think there might be an error with your schematic. In the pictures posted by the OP, there are 2 pins on the SCR that are connected together which then connect to the anode of the LED. However your schematic has the single pin from the SCR connecting to the LED. I think you can fix this easily in your schematic by flipping around the SCR so that the anode is on the bottom. Am I mistaken?

Also, does anyone want to take a stab at simulating this circuit?

 

[mneary]

RV1 is in parallel with the 'SCR',, not in series.