Re: Electric fencer woes

Yeah, you're right about the triac not firing if the transformer primary is "open".

I REALLY wouldn't expect the primary to be open (But to be fair WHO KNOWS if there was lightning involved!) I was thinking in terms of shorted turns or an open SECONDARY.

I HOPE you can find a 20uf cap of adequate voltage and give it a try!

The complete diagram does not always show in modern view. repost here

I have seen the input windings open a few times. I cut the transformers apart to see what happens. The ends of the winding are green with corrosion. I think maybe lightening flakes the varnish off and weakens the wire. Moisture and time finishes the job.

You got a pile of worthless info at that shop,C2 is 20mfd.400 mfd would cripple that circuit.Capacitors are NOT used as lightning arrestors.MOVs are used.A voltage above 130 makes them conduct.You can buy a fused plug for 5 bucks.Running with out fuses will cause trouble

hello 36 coupe
I just thought you might find this interesting:
I have an old capacitor discharge fencer that uses a 5U4 vacuum tube and relay. The rely winding is in series with the filament and one set of points. The filament after glow and warm up sets the discharge frequency. Surprisingly hot and works well except for contact point trouble.

Replace the TRIAC and go back to work. Remember it is a current operated device so the gate will only work with sufficient current if the TRIAC is OK.

(quoted from post at 13:58:33 12/25/09) Replace the TRIAC and go back to work. Remember it is a current operated device so the gate will only work with sufficient current if the TRIAC is OK.

Click to expand...

Its not a TRIAC, its an SCR. TRIACs are ac devices. They are both thyristors.
C2 was leaky.

Interesting discussion guys. I'm learning. I guess after a thread goes off page 7 of classic view it begins with new threads with an Re: in the front. I'm in modern now but looks like this is a second thread.

Anyway, if I can get out ot town tomorrow and anything is open, I'll get a 20 uf cap and I assume minimum voltage of 50 but I guess a higher voltage rating won't hurt as long as it is 20uf, probably more expensive the higher the voltage goes.

Bob with that 470 uf in there, the transformer was putting out only 200 volts per fire but it was hard to tell firing every 10 seconds. With the old 20 uf cap in there now, and when I rapidly fire the transformer by shorting across R4 it will bury the Zareba digital tester at 9900 volts. Shorting across it every few seconds only put out about 1900 volts. Seems like it puts out more volts the faster it fires as it warms up a little. I had checked the transformer before and it wasn't open.

Seems like with the charge cap, C1, rated at putting out 150vdc or as mine does 160vdc, then we know what the input range for the transformer. With all the input circuits for chargers being similar, then a lot of fence transformers should interchange with the variable being the output. Do we have any numbers off of any replacements?

Shorting across R4, the 680K ohm resistor, suggests to me that maybe down sizing to a 390K ohm (or one in between) may make it work as well but I will try a new cap first. What do the new models use for a fixed resistor and adjustable/potentiometer resistor? Time probably isn't a critical factor but you don't want a cow leaning on a fence wire too long before it gets zapped.

For the record, my R5 is a 39 ohm.

Still wonder about the necessity of the door knob output cap, C3?

I'm still thinking through the half wave versus full wave rectification with the addition of that D2 protection diode after the charge cap. It looks like we have AC to the charge cap and the D2 either brings full wave to the transformer or else justs stablizes the current to the transformer so the SCR fires it alone.

Thanks again. Merry Christmas to everyone.

I have interchanged the 70's- 80's vintage transformers where the resistance measures about the same. Seems to work ok. Can't interchange regular and low impedance transformers.

I think C2 is leaking the charge faster than R4 can supply the charge. This is the start of the failure of C2. You might be able to lower the resistance to make up for the leakage, but C2 won't be very reliable. It might leak enough to get hot, build up pressure and blow the end open. You could use a couple of 10 mfd caps in parallel if you can't get a 20 mfd..

The newer board I have has a 470k and 500 k varible ohm resistor in series to take the place of R4. I once mounted a big varible resistor with knob on the case so I could adjust it from the outside. I could turn up the speed to train cattle unfamiliar with electric fence. Worked good for awhile and then the varible resistor corroded and fencer stopped. I think a weather tight one would work better.

D1 is the half wave rectifier for the circuit. D2 is a protection diode for the SCR. When a high voltage is produced on the output winding, there is also a Kickback voltage thats much higher than 150 volts produced at the input winding. The kickback voltage would destroy the SCR. D2 is place across the SCR to quench the kickback voltage.

Thats an SCR

The 5u4 draws a lot of heater current.Used to find many with the heater out.The solder gave out from too much heat.I have a crimping tool that crimped the pins,used it on many pix tubes.Some chargers used a clock motor for timing,The Parmak balance wheel worked well if you knew how to adjust it.Some posts have got me laughing pretty hard.The two guys in the electronics shop are full of misinformation.Or BS

This basic circuit was used by all fence charger mfg.It was very easy to service at low cost to the customer.The out put capacitor c3 was not used in most chargers.International transformers came with a capacitor.I cant remember finding a bad one.It was a doorknob type that early tvs used.I have a two qt jar full of them under the bench some where.NTE parts cost too much,I dont use them.

D2 has a lot of failure from lightning strikes.D2 is a 6A at 1kv in later chargers.

BC,You wont make a fence charger tech.You assume too much and dont understand the circuit.Plus you seem to ignore good advice from fellows who repair chargers.Those 2 birds in the electronics store didnt know nuthin, they didnt even suspect nuthin.A friend said that half the info on the net is wrong.

BC is the only person I know of that is trying to learn and is learning something about fencer repair. Who else is trying? He did ignore the early hints about C2 being bad and replaced other parts, but he will remember that next time he has a fencer opened up. He learned to hand trigger the SCR though the diac on his own. Not many would have learned that. (I don't see why he then wanted to replace the SCR,diac and transformer). I could have pushed harder for C2 replacement but I think he learned more the way things went. Its a shame he's not a 17 year old kid.
Do you have a youngster working with you so you can pass your knowledge on? Most of the youngster nowadays only want to repair computers. I don't consider computer repair as real electronic repair. Its just straightening up the software and changing cards.
I decided to talk about repairing fencers so there is a record of it on the web. As far as I know, this is a first for the web.
I talked to a tech at Zabera a few years ago and he knew very little electronics. I think he just swapped boards.

Fence charger design is changing for the worse.Only board changers will be needed.Im 72 and getting tired of my shop.I close it in winter months now.You can lose money fixing chargers now.Just order too many circuit boards for the spring rush.If the repair work doesnt come in you lose money.Suppers ready Im gone.

I was out of town on the weekend and finally got to it tonight. Ended up getting 2 10uf & 50vdc caps at radidio shack. Put them in in parallel and it started firing like normal. Guess I replaced the other stuff for nothing. Don't know how much voltage but it sparks good and the zaps are loud.

My zareba tester was shocking me through the case before it quit and Zareba give me a return number so I can send it back.

I'll post back on the other threads for archive purposes.

Thanks for your help. I'd still like to find a comparable transformer. Anyway, I'll hook up this international fencer and pull the Zareba 100 miler down and tinker with it a little. I'll put together a parts list and we can see what is available.

20 mfd is a common size for that capacitor.Anyone with experience would have known that 400 mfd was wrong.I hope you have learned to beware of imformation you get from clerks at electronics stores.You did tend to ignore the fact that you had only 27 volts where you should have seen 32.Zareba will supply few parts.You will end up changing the entire circuit board along with with the glued on trans former.A woman brought in her sisters fence charger.It had been checked out at a big farm store.They told her there was nothing wrong with the charger.She took it home and hooked it up to her fence.Her horse got out the highway and got hit by a truck.Sister paid big vet bills plus damages to the truck.I plugged the charger in,The timing was very erratic.I turned the circuit board over and unsoldered the 20 mfd capacitor.It was all green with corrosion underneath.A new 20 mfd capacitor brought the timing back.I let the charger run for 15 minutes, closed it up and gave the customer a bill for 5.75.The maker of that charger will only supply the circuit board for 39 bucks.

I use my mental AND metal work benches all the time! Often much more time on the mental one before using the metal one.

Both fencers are the same animal.The old one is better.Low impedence is a cute name.

I have found these with shorted lightning arrestors that had been soldered on connecting the ac line to the charger case.The plastic and brass arrestor was shorted out by overheating.Found later models that used mov arrestors that do it yerselfers soldered the mov leads together after lightning had blown the mov to small pieces.This connected the ac line to the case.When the owners use a 30 amp fuse in the charger fuse holder you have a deadly charger that can kill people and livestock.If you have burned wires other parts will have to be replaced.The Agway A50 is an old charger that has some parts gone obsolete.Have it fixed by someone who knows what they are doing.