Beginner would like to build Sandbanks PI Metal Detector

Aliman I take it that you have tried leaving it on for a few minutes with no coil connected to see if the TIP32A still gets hot? It could be that you are having an insulation breakdown in the coil remember that you have 20vac going in but at the collapsing of the magnetic field the voltage can go up to 500v now I don?t know what the voltage is but you should consider the possibility. The pulse is simply consisting of IC1,Tr1,Tr2 and the coil five resistors and three caps so the fault must be in that vicinity it does look like the coil though try a bigger coil just to see if you still have the same problem. Then change Tr2 Are you using new or old magnet wire? If old then it could be the wire.

Regards Xavier


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Xavier

Aliman as far as I?m concerned it is not normal but that is a question to ask Cornelius he will be able to give you all the nitty gritty about that. If the wire that was on that old transformer of yours got hot then cold then hot and so on the insulation that is on it gets hard and brittle( even just with age )so when you peel of the wire small hair line cracks appear in the insulation but of course you cant see them and if the wire was hard to get off the coil then there are chances that it came off in places it's always better to use new wire if you can afford to I don?t for two rezones 1) I?m tight on cash at the moment and 2) it?s very hard to get new wire where I stay so I always look out for old TV?s as there is about 140m of wire on the deflection coil of course it depends on the size of the TV how ever that would not help you as the wire is far to thin but for my VLF coils it?s just right. I think that you must have about 45 to 47 turns on your coil so you could go to a motor re-winder get 50m of wire and you?ll have some left over and it will cost you a lot less than getting a complete bobbin of the stuff. Just have a look if D2 and D3 are still ok don?t bother with D1 as it?s not used at the moment you will have to take them out though. Set your multi meter on diode the black line on the diode is where you will place the negative lead of your tester and of course pos goes on the other side now you should have a reading turn the diode around so that pos goes to neg of the diode you must have no reading if you do have a reading the diode is dead and you will have to replace it and if you don?t get any reading then it?s dead too check on other diode?s to make sure that your measurement is good .

Best regards
Xavier


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Xavier

Ali .  Never use old wire for building your coil .  The enamel will most likely have come off . Especially if resin was used on the outside of the coil that you are taking apart . If you connect a coil which is shortcircuited it is the same as connecting the coil contacts with a single wire . The current going through your  Tip 31 is going to be so high that it will heat up . Try to get good materials when you build a detector . If not you will be sorry later on .  Cornelius

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Ali . Go with  the wire stipulated in the documentation . If you only can get thicker wire give it a few more windings  .  Cornelius

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I would like to know about this detector. I am always looking for something to build. I suggest the wire out of a tv yoke . There is lots of wire in the 22-26 range in the coils. Also the degaussing coil on the picture tube. I have oodles of transistors etc if anyone is interested. Have oodles of resistors , capacitors and ic's. i bought out a tv shop awhile back. I'm not selling the stuff but am willing to barter.

My email is on my profile.

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