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Rotating Diodes Checking


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  #21  
Old 11-10-2017, 04:16:53 PM
len k len k is offline
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Default Re: diodes checking (magniciter )

Even though my JB looks pretty rough/surface rusted the insulation type used in it looks to be still in pretty good shapel, both windings and wires. I think what people think of as bad on old motors and gens is the early 1900's stuff with cracking cloth and rubber insulation. The JBs era stuff uses insulation better than that.
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  #22  
Old 11-10-2017, 04:54:32 PM
Vanman Vanman is offline
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Default Re: Rotating Diodes Checking

Well, and about that older insulation- I collect Century repulsion start induction motors made in the teens and twenties. I have at least twenty in evidently original condition, and they ALL work. All I've ever had to do to any of them was commutator service.

The cloth covered rubber insulated wire just depends on the life it has lead. I have some that are all but bare and others that are in remarkable and perfectly serviceable condition.

Last edited by Vanman; 11-10-2017 at 07:14:08 PM.
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  #23  
Old 11-10-2017, 05:05:20 PM
zuhnc zuhnc is offline
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Default Re: Rotating Diodes Checking

Well, if it is "out with the old, and in with the new", when the old gets "out of fashion" or "worn around the edges", the most of us would have been pushing up daisy's long ago I prefer to work on the older stuff; mechanical or electrical. I am somewhat electronic literate in regards to IC's, LSI devices, etc, and how they work, but there is something to be said about working with and being able to hold in your hand discrete components. Besides, individual parts are easier to replace, for the most part. Way easier to see than those surface mount resistors and other components. How many of the current crop of "technicians" can tell you how precisely how an electronic voltage regulator operates. Or, for that matter, how the basic revolving field generator makes voltage. zuhnc
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  #24  
Old 11-10-2017, 07:24:35 PM
EnginePat EnginePat is offline
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Default Re: Rotating Diodes Checking

Well I got the difintive answer about this generator and it's still to much money, so I will pass on it. $600.00 Was the final word. As much as I would have liked to grab it. A water cooled generator is nice. I could have planted it by the sewage pump for those days when power is out.
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  #25  
Old 11-10-2017, 08:11:34 PM
Leon N. Leon N. is offline
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Default Re: Rotating Diodes Checking

My JB was built in 1966. It still runs and produces reliable power in accordance with the JB Magneciter performance specification.
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  #26  
Old 11-11-2017, 09:57:02 AM
Gunny Gunny is offline
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Default Re: Rotating Diodes Checking

Pretty easy to check/test a diode. All of them can be checked with an ohm meter. Should show open in one direction and some resistance, usually in the 400 ohm range in the other direction.

Diode needs to be out of the circuit to be checked, unless its obviously blown apart.

Diode can be forward or reverse polarity. There are (6) diodes in a rotating exciter (usually). 3 are forward and 3 are reverse.

A Magnecitoer has diodes and an SCR.

Then there are Zener diodes, LED (Light Emitting Diodes)...........
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Old 11-11-2017, 10:10:39 AM
pegasuspinto pegasuspinto is offline
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Default Re: Rotating Diodes Checking

It's better to use the 'diode check' if your meter has it. It actually puts a small amount of voltage on the diode. It should read open one way and it will show the forward voltage drop on the other...usually .3 to .6 volts.

You can sometimes do a quick check on a diode without taking it out of circuit. If it shows very low ohms/volt drop both directions, you'll have to take it out. BUT if it shows very high oms/volt drop or even reads open, it's bad and needs to be replaced. This of course only works if the circuit under test is completely depowered.
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Old 11-11-2017, 10:30:10 AM
Leon N. Leon N. is offline
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Default Re: Rotating Diodes Checking

Oops! There is no SCR in the Magneciter design? If so I would like to know where it is.
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  #29  
Old 11-11-2017, 07:08:05 PM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Rotating Diodes Checking

I'm a mechanic, not an electrician. I like to work on generators, got a 15KW Diesel Westerbeke marine generator, wasn't producing power. The manual had a good trouble tree, had to use an auto headlamp and a 12 volt battery to check the rotating diodes in place, they were OK. Is this a standard test?
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  #30  
Old 11-12-2017, 12:07:34 PM
Gunny Gunny is offline
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Default Re: Rotating Diodes Checking

Quote:
Originally Posted by Leon N. View Post
Oops! There is no SCR in the Magneciter design? If so I would like to know where it is.
Leon, running on memory here and you know how that works when we get a little age.

Though there was one in the circuit but I may be either confused with another design or mistaken. Have an Onan manual at work, will look tomorrow. If I can remember......
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  #31  
Old 11-12-2017, 02:03:58 PM
len k len k is offline
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Default Re: Rotating Diodes Checking

YD electronic reg has 2 SCR, magnaciter only diodes.

Only true way to test a diode is take it out of the circuit and test, can have a max of ONE circuit connection to it remaining. I like using an analog meter, once you test a good diode you'll see the pattern of a good one. The resistance while conducting all seem to fall in same meter deflection position. https://www.smokstak.com/forum/attac...4&d=1344478607

But may times in other electronics you can still see that it's acting as a diode even though it's still in the circuit. Guessing with windings resistance of winding is so low you'll have to take it out of the circuit to test it

Last edited by len k; 11-12-2017 at 02:16:40 PM.
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  #32  
Old 11-12-2017, 09:04:04 PM
armandh armandh is offline
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Default Re: Rotating Diodes Checking

old as time
replace vs repair

for a business
a known replace is easier to sell and do

for a hobby time is not that critical
and likely lower cost
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  #33  
Old 11-13-2017, 05:52:47 PM
Jim Marcozzi Jim Marcozzi is offline
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Default Re: Rotating Diodes Checking

Once I verify that the diodes are good with an analog ohm meter, I always load them with about half their rated amperage with a lamp in both directions.

I've found many diodes over the years that check good with a meter, but break down under load. With gen end diodes, I usually use a halogen headlight bulb. Under load, I like to see no less than .7-1.0V max drop when comparing the voltage at the load to the voltage at the source.
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