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Rewinding source coil

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Ryan Vanrooyen

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I’ve got an old bike that I am not able to obtain a new source coil for . I have tried to rewind with magnet wire of the original size but can’t seem to get any ohms when I’m done. I tried rewinding three times. First time worked for a second then failed and others haven’t done anything. I feel like for the amount of wire I’m putting on there should be a reading of something. This coil has one lead wire that grounds to core on the fastener and end wire goes to condenser and ignition coil. I’m just wondering if I have the wrong wire since I’m putting on close to what was there for wire or even a little more
 

dr pepper

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Are you talking about a magneto?
There should be a resistance, maybe a couple of k ohms, if you read open there theres no connection, the wire is either broken, or more likely where you soldered or crimped it there is a bad connection, did you scrape off the enamel before you made the connection?
Its better to err on the side of more turns rather than less.
 

Western

Member
if you read open there theres no connection, the wire is either broken, or more likely where you soldered or crimped it there is a bad connection, did you scrape off the enamel before you made the connection?
Definitely agree. Hopefully it's just a matter of re-doing the ground wire.

I would have thought at least hundreds of ohms, maybe not thousands ... but what sort of bike are we talking about?
 

Ryan Vanrooyen

New Member
It’s a 1980 yz50g, I found a replacement coil but at the tune of 200$. It is yes a magneto coil, right now the coil is rewound with 24g magnet wire , there is more than what was there originally and all I get is.003 ohms, I’ve checked another one I have that almost fits but not quite and I get .300 which is what I need , it even has less wire and some gauge, I really don’t get it . I unwound the coil from the first time and layed it out so I had both ends and nothing touching and still had no resistance, nothing broken just bare wire and 0 ohms. That was probly 100’ wire
 

dr pepper

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I searched for remington Pn155, I found remington's site but no reference to Pn155.
Are you sure the wire is enameled, ie insulated, one reason for you getting the resistance you mentioned is if the wire isnt insulated.
Most multimeters will not read as low as 0.003 ohms, or 3 milli ohms, are you sure the meter isnt reading 0.003 K ohms, which would be 3 ohms?
Try a couple of things, if you have a resistor say 1k does your meter read it correctly, you can pull one off a dead circuit board, and another trick you could try is place a small compass at the end of the coil, connect a 1.5v flashlight cell to the coild, its should influence the compass, if not its open or shorted.
If you have a soldering gun you might be able to get a spark by holding it up to the flywheel side of the coil, I must try that someday.
 

rjenkinsgb

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For info, 24AWG wire is specified as having a resistance of 0.0842 ohms per metre.

100' is 30.48 metres so should be around 2.57 ohms.

As Dr. P says, I suspect something is amiss with your meter readings if the laid-out hundred foot of wire did not give something near that.
 

alec_t

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just bare wire and 0 ohms. That was probly 100’ wire
If that's the true resistance I'll buy all you've got. Room temperature super-conducting wire would be handy to have :) .
 

Ryan Vanrooyen

New Member
Well regardless of my meter I’m still not able to generate voltage when this wire is wrapped around my source coil plates. I’ve wrapped three different coils with the same wire and no go, tried different tensions thinking that was it. Is it possible that if the condenser is drained it won’t build voltage when the magneto passes by the source coil . Or is it as long as the condenser is good it should still build and he source coil should put out something. Like I said I’ve installed three different coils I have wrapped, and quite nicely as well, and it generates zero volts. Also I’ve been using two different meters to make sure they are reading correct
 

Ryan Vanrooyen

New Member
So I got a different meter , looks like mine are both giving bad readings one for ohms and the other the voltage. The coil I wound is 3 ohms . I have installed it but am only getting .6 volts. The condenser is old , the points are filed nice. Before I filed them I had nothing 0 volts
 

alec_t

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this wire is wrapped around my source coil plates.
Did you first wrap some insulating film around the plates (laminations)? If not, a sharp edge on the plates could cut through the enamel on the magnet wire and short-circuit turns of the coil. A shorted turn would account for the very low voltage the coil is generating.
You could temporarily disconnect the capacitor (condenser) to see if that affects the coil voltage.
 

dr pepper

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A couple of things spring to mind.
Considering the trouble you've gone to change the condensor, if its shorted yes it could very much stop the spark, if open it will at least make a very weak spark and destroy the points contacts in time.
Dont try and measure the spark voltage, you'll kill your meter, the voltage will be several thousand volts, most likely a lot more than your meter can read, plus even if it could measure that kind of voltage you'd miss it as its only present for an instant.
Do you have one of these neon inline spark testers?, they usually light up with only a few hundred volts well before a spark is visible.
3 ohms is more like it for resistance.
Further to alecs comments you really should put an insulation layer between winding layers, and leave 1/2" each end so the ends of the coil wires dont flash to each other, so you wind one layer, put a wrap of insulation, then another layer, then another wrap of insulation and so on, plus the insulation should really be stuff made for the purpose ie have a high dielectric.
Dont try and start the engine without the plug connected, the resulting increase in spark voltage can flash over & damage the insulation.
This guy's done a write up, you dont need a lathe if your inventive:
http://www.brufnut.de/WORKSHOP/LUCAS/lucas.htm
 

dr pepper

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Quite.
The principles are pretty much the same, low and high voltage magneto's are still common in small engines.
 
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