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Can someone identify this component?

joe82

Oct 4, 2018
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I'm just trying to reverse engineer this circut. it is an electric fence charger. the component there has 6 pins. 4 on one side and 2 on the other with a visible coil on top. I'm guessing it's some type of relay?
 

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¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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That is a transformer.
 

joe82

Oct 4, 2018
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the one I labeled m is the transformer I'm trying to figure out. if you can make any sense of this
 

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Ylli

Jun 19, 2018
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Give us an in-focus picture of the entire board, both top and bottom.
 

joe82

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¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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ok, I kinda thought that at first sight but then I thought it might be something to do with timing. so would it be 2 secondary windings?

It could be 2 secondaries, or it could be 2 primary windings.
 

duke37

Jan 9, 2011
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It would be nice to know what the power supply is.
A common fencer charges up a capacitor (C8) and then discharges it through a transformer to produce the high voltage. One of the transformers will be used to charge the capacitor and one will be connected to the output.
There seems to be a SCR or similar next to C8 to do the output switching.
The rating of C8 will give some idea of the power of the fencer.
 

joe82

Oct 4, 2018
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It would be nice to know what the power supply is.
A common fencer charges up a capacitor (C8) and then discharges it through a transformer to produce the high voltage. One of the transformers will be used to charge the capacitor and one will be connected to the output.
There seems to be a SCR or similar next to C8 to do the output switching.
The rating of C8 will give some idea of the power of the fencer.
it is powered by a 6v la battery with a solar panel to charge it. I think the cap is a 10uf 300v. I guess what's throwing me off is that I was under the impression that you needed a timer circut to pulse the dc to a transformer. I guess the only way I can think of that they are achieving that is charging a cap through a resistor slow enough and then opening a transistor momentarily? will a cap act as a switch until it has enough charge?
 

duke37

Jan 9, 2011
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If the capacitor is charged to 250V, then it will hold 0.3J which is significant for a battery driven fencer. Mains driven fencers can go up to 10J and will supply miles of wire but I would not go near them.:)

A common way of triggering the switch (SCR?) is using a diac which triggers at about 20V so will need a sepatate capacitor for timing. I have used a neon bulb which triggers at about 90V in a very old fencer which ran on a 120V high tension (B+) radio battery.
The triggering is done by turning the switch on for a short time. The advantage of a SCR is that only a very short trigger pulse is needed as the device will stay on until the load current stops.

One of your transformers will be used in an oscillator to generate about 250V and the other (1:20) will step up this voltage to 5kV or so for output.

What is wrong with the fencer? I see no lightning damage. Does the oscillator charge the 300V capacitor? The 300V capacitor is likely to be an electrolytic at that size, they are not recommended for pulse work. Some of the film capacitors for pulse work are horrendously expensive. I would look at a motor run capacitor but this may be impossible to fit within the case.
 

joe82

Oct 4, 2018
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If the capacitor is charged to 250V, then it will hold 0.3J which is significant for a battery driven fencer. Mains driven fencers can go up to 10J and will supply miles of wire but I would not go near them.:)

A common way of triggering the switch (SCR?) is using a diac which triggers at about 20V so will need a sepatate capacitor for timing. I have used a neon bulb which triggers at about 90V in a very old fencer which ran on a 120V high tension (B+) radio battery.
The triggering is done by turning the switch on for a short time. The advantage of a SCR is that only a very short trigger pulse is needed as the device will stay on until the load current stops.

One of your transformers will be used in an oscillator to generate about 250V and the other (1:20) will step up this voltage to 5kV or so for output.

What is wrong with the fencer? I see no lightning damage. Does the oscillator charge the 300V capacitor? The 300V capacitor is likely to be an electrolytic at that size, they are not recommended for pulse work. Some of the film capacitors for pulse work are horrendously expensive. I would look at a motor run capacitor but this may be impossible to fit within the case.
thanks for your time, this one actually works fine. I was just tinkering and trying to understand how it operates. it seems that every manufacturer has a different way of achieving the same thing. a neighbor with a fence company said he'd pay if i could fix some of his inoperable ones. i also was going to try to make one with a 555 timer so i decided to look at this one and was surprised not to find a timer or logic of any type in there. it actually doesn't stay charged like I wish it would. I thought I could use a 555 circut to pulse a transistor to hit the low side of a transformer but now I'm thinking it would have to be more elaborate to charge the capacitor. i guess I'll have to do more research and see how the ones with a single transformer work.
so is farad x voltage relative like volts x amps? like does a 100uf cap store the same power at 12v as a 10uf at 120v? now I'm thinking of having the discharge cap on a separate circut but I'm now wondering if the transistors I have could take the power of a cap discharging through it.
 

duke37

Jan 9, 2011
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Capacitors do not store power, they store energy. This energy can be used at high power for a short time or lower power for a longer time.

The energy stored is C*V*V/2 so if you have 10 times the voltage, you need 100 times the capacity to store the same energy. The choice of capacitor and voltage will depend on the dielectric available and the convenience of switching the output. Polypropylene capacitors at 600V or so are often used.

SCRs are often used as switches since they can block a high voltage and pass a high current for a short time. They just need a pulse to start them off and will turn off when the current drops to zero, ready for the capacitor to be charged again.

Fencers can fail due to lightning, corrosion improper supply etc. One fencer I looked at had plug in boards which arced at the plugs, producing ozone which rotted the works.
 

joe82

Oct 4, 2018
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Capacitors do not store power, they store energy. This energy can be used at high power for a short time or lower power for a longer time.

The energy stored is C*V*V/2 so if you have 10 times the voltage, you need 100 times the capacity to store the same energy. The choice of capacitor and voltage will depend on the dielectric available and the convenience of switching the output. Polypropylene capacitors at 600V or so are often used.

SCRs are often used as switches since they can block a high voltage and pass a high current for a short time. They just need a pulse to start them off and will turn off when the current drops to zero, ready for the capacitor to be charged again.

Fencers can fail due to lightning, corrosion improper supply etc. One fencer I looked at had plug in boards which arced at the plugs, producing ozone which rotted the works.
thanks Duke, you've given me some very helpful info
 

hevans1944

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Jun 21, 2012
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... it actually doesn't stay charged like I wish it would.
What?! You want high voltage to be present on the fence ALL the time rather than pulsed on and off? That's a recipe for disaster and perhaps death by electrocution. Don't even think about modifying a commercial fencer to make it "stay charged" all the time. Also, don't tug on Superman's cape, never spit into the wind, don't f*ck with the Lone Ranger's mask, and never, ever, pee on an electric fence. Oh, and BTW, never mess around with anyone named Jim... or Slim.
 

duke37

Jan 9, 2011
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What?! You want high voltage to be present on the fence ALL the time rather than pulsed on and off? That's a recipe for disaster and perhaps death by electrocution. Don't even think about modifying a commercial fencer to make it "stay charged" all the time. Also, don't tug on Superman's cape, never spit into the wind, don't f*ck with the Lone Ranger's mask, and never, ever, pee on an electric fence. Oh, and BTW, never mess around with anyone named Jim... or Slim.
I was given one fencer to repair where the output pulse had been rectified with a long string of high voltage diodes. These had all been blown apart by lightning. Replacing these cured the problem.
I do not understand the advantage of this, I doubt if the fence is sufficiently insulated to hold the charge between one pulse and the next.
 
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