dynodave
Saw Builder
equal opportunity GEARHEAD
Posts: 246
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Post by dynodave on Apr 1, 2014 14:58:35 GMT -5
Just for grins I thought I'd check the condensers(capacitor)in the 2 707D's. Since I work occasionally with british motorcycle magnetos and they almost never have good caps. Of course the magnetos stopped production in about 1963. Well guess what...both caps were very leaky. One was 5ma@400v and the other was 10ma@400v. How bad is that??? well 5ua (micro amps) is not good! The thing is, the saw may fire up, but you will have to pull very hard and fast.
FWIW NOS caps from 20 years ago may not be any better.
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dynodave
Saw Builder
equal opportunity GEARHEAD
Posts: 246
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Post by dynodave on Apr 16, 2014 7:09:04 GMT -5
Condenser/capacitor update. I bought off ebay a NOS cap "genuine Homelite 59862 condenser ignition Phelon REPCO XL500 XL12, XL660 saw nos" I was shocked it was almost as good as a new cap with only 1 microamp of leakage @400vdc This cap is the same form as what we need on the EZ- 775 series saw except it is mounted on a different mount. I will unsolder the XL-12 mount and replace with the 707 bracket. Then a NOS 55987 from Dwayne yeilded 240 microamps of leakage @400vdc. Way better than what I had in my saws but technically no good. Nothing bad against Dwayne, since testing them requires more sophisticated equipment than a volt/ohm meter. A VOM CAN find a bad cap...but a VOM CAN NOT verify a good cap. Many VOM use a 9v battery. If you have leakage with 9v, then you have NO hope with 400-600VDC. I almost 100% find caps to be ZERO leakage@ 400VDC for new caps. Actually a 600VDC test is more common and 400VDC is being a bit soft on the test.
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Post by sweepleader on Apr 16, 2014 10:06:44 GMT -5
This is some good stuff Dave, but how is an ordinary mortal to know which cap is good and which is bad? I use a Fluke digital multimeter and watch the analog meter display, if it charges slowly, I figure it is good. That would be at 9 volts, not saying much for leakage, eh? Can you come up with a method I could use with my Fluke meter? Would setting it to amps and applying a higher DC voltage do the same thing as "more sophisticated equipment"? Of course I could kill myself doing that I suppose.
Thanks for bringing this up. Dan
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dynodave
Saw Builder
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Posts: 246
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Post by dynodave on Apr 16, 2014 11:00:50 GMT -5
It's super simple. Get a 400v power supply and hook your fluke in series with the cap and power supply and take the current measurement. That is exactly what I have except I built it all into a single piece of test equipment. Only difference is I have 3 switchable scales, 5MA, 500Ua, and 50Ua. I start with 5 MA and if it doesn't peg out the meter over 10%, then I go to the next scale. If I can get to the 50 Ua (micro amps) scale then I look for ZERO. but 5 to 10Ua is not to bad. Any thing other than real electronics or physics is of little interest to me. I worked 42 years in radar, HV electronics, and industrial instrumentation (and now "retired", I still occasionally do consulting and a bit of High Voltage testing to 20KV) These magnetos are toys to me. Also raced/built sports cars and motorcycles since 1970. Won a few local championships too...back in the 70's. atlanticgreen.com/
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Post by sweepleader on Apr 16, 2014 12:12:53 GMT -5
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dynodave
Saw Builder
equal opportunity GEARHEAD
Posts: 246
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Post by dynodave on Apr 16, 2014 20:34:09 GMT -5
I thought about it for a while after reading a few threads. I think of this as wave shapes resulting from the electromagnetic coil and flywheel and then possible controlling electronics schemes. One consideration is that some of these devices call for a "polarity". With the magnet wizzing by the coil you will get a AC voltage pulse/sine wave. Then if the points were closed it would allow current. Since the module takes over that job...what happens if the module is reversed and how will it react to the wrong polarity coming first.... no conduction....high impedance reflection then smaller pulse on the rebound...now it fires but at a lower power level. Plus it had to fend off a highish reverse polarity pulse rather than a correct first pulse.
A bit like the CDI SCR but with entirely different power levels. 40-75 volts rather than 400v for the CDI.
I don't have a final theory on these devices. But any electronics are entirely heat sensitive, especially pulse systems. A good design can run at rated power indefinitely. Once/if it gets damaged by possibly being hit with a reverse voltage pulse continuously it might start a melt down and the control device fails.
Just an initial guess.
A points type replacement system has to run lower voltages and much higher currents than a CDI. Also I've seen posted that some points saws when upgraded by factory EI system require up dated flywheel also such as reversed magnetic polarity like on my cast iron Briggs & Stratton engines using their magnetron module.
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Post by sweepleader on Apr 17, 2014 7:20:58 GMT -5
I have seen "watch spark, swap leads on chip, hook it up permanently with the connection that gives the bigger spark" somewhere in discussions of the chips. Perhaps that is evidence of what you are referring to. Do I have your thoughts correct, that reversing the leads on the chip would give bigger spark and protect the chip? Weak spark corrected by a chip connected this way may be a clue that the condenser was bad to begin with and the strong spark could have been accomplished with a good condenser... Hmm, Maybe you already said that... Dan
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Post by sawnami on Apr 19, 2014 5:53:17 GMT -5
Used to run into something similar to that back in the GM HEI distributor days. If you put an Oldsmobile pickup coil in a Chevy distributor or vice versa, it wouldn't fire the coil. The only way to tell the difference was the the color of the two wires coming out of the pickup coil. Other than that, they were identical. The distributors turned in opposite directions.
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Post by sweepleader on Apr 19, 2014 10:21:48 GMT -5
I never had that problem with one, never saw a bad pickup. I did get lucky putting an HEI in a Continental engine that powered a 1957 Clark Equipment tug we used for pushing dead cars. It would only start in the winter with a huge engine heater and a battery charger. I fiddled with the voltage regulator to charge a 12 volt battery and put in an HEI with guts and cap from a 6 cylinder GM engine in a Vega 4 cylinder body. I cut off the long shaft and pinned on the drive tang from the original Prestolite distributor. It had spark and cranking rpm (6 volt starter!) to beat the band. Started with no trouble after that, even when it sat outside at 20 below.
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