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Raiders of the Lost Spark

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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 10:28
Coils often fail when hot, so testing cold is not always reliable. But with a multimeter set to resistance, you can easily check the primary resistance which should be around 4 ohms, maybe a bit less. Very high or low resistance would indicate a fault.
You can equally check the secondary coil which would normally have a resistance of 2 or 3k ohms from the ht connector to the case. Infinite resistance means a dud coil, and a very low resistance would mean a shorted coil.
 
You can also do a basic check on the condenser, but it's not that reliable. Connect the multimeter across the condenser and it will read high resistance, this reading will then drop. If it doesn't show this high resistance it might not work too well. (This test is best done with an analogue meter, a pointer and dial, as you can easily see the change). If it just shows a very low resistance then it is almost certainly dud.
But this test isn't perfect, you really need a specific test device for capacitors.
Brian.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ranton_rambler Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 12:53
Some multimeters have a capacitance setting, if you know what the correct value for the condenser is. But in the same way as coils they sometimes fail when hot so testing is not reliable.

I think an earlier post said "a condenser is a condenser" and I am indeed still running a Mini condenser on my loop rather than the proper one, but I think they are actually sized to suit the system. I'm not an electronics person (although I got an O-level in 1978) but I think they need to be matched to the coil inductance and frequency range. Probably not critical for a road bike though.

Ian
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iansoady Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 15:02
The best way I know of testing (although not infallible) is an old analogue multimeter. Set it on ohms and connect across the capacitor. The needle should twitch then fall back to infinity. Try again with the leads in the opposite direction and you should get the same.

Theoretically you shouldn't apply reverse voltage to an electrolytic capacitor but this doesn't seem to hurt them.

And of course it's not conclusive.
Ian
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Mike H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 18:00
Originally posted by ranton_rambler ranton_rambler wrote:

I'm not an electronics person (although I got an O-level in 1978) but I think they need to be matched to the coil inductance and frequency range.


They are all 0.22 µF (microfarads) as far as I know.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 18:16
It's not a tuned circuit, so frequency won't come into it.
 
Yes, I'm pretty sure they are all the same electrically. And no, they won't be electrolytic. All they do is damp the spark at the contact breaker.
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Mike H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 18:27
"All", but still quite critical, else all the energy is expended in making a spark across the points so there's none left for the spark plug.


Unfortunately most descriptions on the Internet about how contact breaker ignition works are b0ll0x Ouch


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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 21:30
It's slightly more detailed than that. An induction coil requires a steady current through the primary which is cut very sharply. If you get arcing across the points, that primary current reduces more slowly so the spark is less. It also stops pitting on the points due to arcing.
 
The other end of the scale, when the condenser gets leaky, it conducts the current so the points opening does nothing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mojoguzzi Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2017 at 10:58
Condenser? is that what they use to make condensed milk Big smile
2005 Breva1100 in Red with GPR can.
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