Author Topic: 12Vdc Electric fencer for garden, zapped?  (Read 821 times)

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Offline aweman

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12Vdc Electric fencer for garden, zapped?
« on: May 31, 2016, 11:12:06 AM »
Hello every one, this is my first post here so I hope I am in the right place.
I have been lurking here for a while now, nice site with so much info..
I haven't needed to register, just read.
I was hoping that someone might be able to help me with a old fencer.
this fencer has been working great for many years, it's from the mid 1980's
It quit working after a lighting storm passed by the other day, maybe just timing
I have it apart on my work bench, there are no signs of burnt components
The transformer for output doesn't show open on my tester
all components test good on my tester , that I can test
just been trying to track down all the parts, and found one I can't Identify
I removed the heat shield from the part I can't identify (transistor)? X44C776
have any of you ever worked on one of these or know what that component is?


thanks and take care
Cam


 

Offline oztules

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Re: 12Vdc Electric fencer for garden, zapped?
« Reply #1 on: May 31, 2016, 05:30:59 PM »
yes, a 800v or thereabouts scr or triac will replace it.

If you look at where it goes it interfaces the cap and the transformer.... so it is your hv dump to tranny switch ( small inductor in series too)

The other TO220 will be your oscillator for your small ferrite transformer to make the 500v or so  to store in your big capacitor.

The small TO92 will likely be a UJT to time the pulse to turn on the scr.

The big diode on the board across the tranny leads will be back emf thing, and could be short too.

Other big diode may be used in the quench in the oscillator.

Replacing the silicon bits blind should make the unit run again.. if lightning was the cause. It usually takes everything out.

Check the resistors, the inverter transformer windings, main and it should work again.

I saw one once that had a strike..... even killed the main transformer (big one too with 1.5mm wire). and every component inside it was toast... blew the case apart from the instant vaporising of the copper tracks... truly amazing ...

Neat little unit it is too.


............oztules
Flinders Island...... Australia

Offline aweman

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Re: 12Vdc Electric fencer for garden, zapped?
« Reply #2 on: May 31, 2016, 07:19:53 PM »
Thanks for your help oztules , wish I had a schematic with component values.
my original plan was to just replace any bad parts to keep this thing running.
I could get info on 2 of the 3 transistors, just the last one with the heat shield.
the price of new components can't be that much vs buying a new fencer.
I am not sure we are talking about the same component.
I am having trouble with X44C776, it seems to be connected 12v B-, ferrite coil, thru a resistor to the hi-low switch
the two other transistors are
2n6027  ujt the smaller one
2n6404 Thiristor this seems to be directly connected to 12v B- and thru the output transformer primary to the large cap + terminal
large cap seems to be about 10 uF
output transformer primary 0.1 ohm
secondary RED output  3.0 ohm
the smaller round ferrite transformer seems two have 3 coils inside of
.8 ohm, .2 ohm and 52 ohm
all components were tested with one side out of the circuit or just removed
I have not tested the 3 transistors yet
not sure if the ferrite or transformer values are correct, but not open is good I hope
I have never worked on this fencer or any fencer before, so it's quite new to me
thanks for any help
take care
Cam




Offline oztules

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Re: 12Vdc Electric fencer for garden, zapped?
« Reply #3 on: May 31, 2016, 11:16:11 PM »
AhHa....  I see you removed the heat sink, took the photo, and then took photo's with the heat sink back on.....
ie

In picture at top #5233 the transistor three legs seen on the RIGHT hand side underside is attached to the output tranny, thats the scr

Next pic 5234, that same TO220 is center top of the board, without heat sink.. thats the scr i reckon.

Pic#5 ( last one) shows the TO220 that you are questioning... which I wrongly assumed was the same as the top center one.. ie no heat sink.... I was fooled.

It will be a NPN standard transistor eg 2sc4242 or mje13007 etc. It needs a heat sink, the scr does not.


maybe I got the right one this time.

Is is totally dead, or is there a squeal... if it has a squeal, then likely the scr ... no squeal, likely the npn at least. The flyback diodes are also at risk.

Small ferrite sounds like it should work with those values.. two low ( or split ) impedance ones on the primary, and a hv winding 52r secondary. Two primary ones cause the oscillator to oscillate using the 2sc4242 etc. If  you use a tip35 etc, the oscillator will work too well.. the 4242 should be about right for that one. They will be found in many many computer power supplies, or MJE13007 etc

Dead UJT.... unit charges but won't fire, or unit behaving like scr is on all the time.

Dead SCR will be short....will hear the oscillator, but no voltage coming out of the tranny to the cap.

Short flyback... will cycle, but no voltage output.


New fencers are expensive compared to a few dollars worth of parts.

................oztules
Flinders Island...... Australia

Offline aweman

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Re: 12Vdc Electric fencer for garden, zapped?
« Reply #4 on: June 01, 2016, 04:25:36 PM »
thank you so much for you help oztules!
zap zap it's working again..
following what you said, it was dead nothing..
so I dug thru my stockpile of dead electronics and found a 13005a
installed it first try, buzzzz ting, buzzz ting  it's alive
the original npn has continuity across two pins forwards and backwards and pin3 open, so it was zapped
now I have to check the differences between the 13005a and the 13007
but it's working, so next time I order components I will add a 13007 to the order
safe veggies again from ground pests..
just need a zapper for the gd Starlings...
thanks again
take care and be safe
Cam

Offline oztules

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Re: 12Vdc Electric fencer for garden, zapped?
« Reply #5 on: June 01, 2016, 05:13:47 PM »
13005 will be fine I expect. Just check the temp after 10 mins, if ok, then good for a long time yet.

..........oztules
Flinders Island...... Australia