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  #21  
Old 09-27-2017, 11:19 PM
Normanby Normanby is offline
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GWIZ, I have probably not given clear information, so will try to fix that here. All previous measurements were with the paper under + (2) brush. However I have taken more measurements today from with each brush being insulated with paper one at a time, then the readings taken with one meter probe on that brush tail. I have copied your Rev 2 diagram and used a separate copy for each set of readings, scanned these so will now attach them to this post. I slightly rotated the generator (less than 5%) today before the readings so some readings have changed slightly. If this info is not clear please tell me along with any more suggestions. Thank you.
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  #22  
Old 09-28-2017, 03:07 PM
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GWIZ GWIZ is offline
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I should have had you first check for any resistance/shorts to ground.
Remove the paper from the brush.

make sure you get good contact with the probes, from your last post I think you are having issues making good probe contact.. and with all the oxidation you will.

===
one probe on the welders steel case exciter steel case or whatever.
The other probe try some of the points 1, 2, 5......

Most ground shorts if any are in the high resistance ranges so you need to set your meter higher.
Lets hope the readings are above 1 meg and that can be iffy.
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  #23  
Old 09-28-2017, 03:10 PM
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Quote:
Originally Posted by Normanby View Post
GWIZ, I have probably not given clear information, so will try to fix that here. All previous measurements were with the paper under + (2) brush. However I have taken more measurements today from with each brush being insulated with paper one at a time, then the readings taken with one meter probe on that brush tail. I have copied your Rev 2 diagram and used a separate copy for each set of readings, scanned these so will now attach them to this post. I slightly rotated the generator (less than 5%) today before the readings so some readings have changed slightly. If this info is not clear please tell me along with any more suggestions. Thank you.

If there is no Ground shorts then this all applies.

Your first picture from the post above (21)
All your readings are the same 39 ohms ( you did some thing wrong that is not possible in-less you fill the welder with water )

I was hoping we could skip the basics, maybe not.
The BIGGEST biggest issue that beginners have with making measurements is making sure that the probes contact a very clean surface.
If the contact surface is not shiny clean you have to double and triple check the contact connection
And
If a measurement does not make sense you need to go back, check the contact probe connection again and again

There is so much oxidation that at some time all the wire connections should be dissembled and cleaned.
==
When using the lower ohm scale clipping onto oxidized surfaces play hell in obtaining consistence reading

First check the probes.
on the lower ohm scale touch the two leads together you should get a consistence zero reading each time ( note some meters read 0.5 (point 5 )or abouts. point something but consistent)

In your case you clipped one meter lead onto the brush wire.
Note that wire is dirty (not shiny)
you have to check that connection (how good is it ? )
take the other probe and touch the next connecting surface "like the metal brush plate that the brush wire is tied to...
you should get a zero reading if not you need to clean the surfaces the probes touch.

=====

Looking at your second picture

the reading from 2 to 7
101 ohms
the drawing shows a straight wire from 2 to 7
your reading should be zero as if you connected the two probe leads together.

You need to trace the wire from brush 2 to point 7 and make sure where it connects.

===
Note when resistance's are measured in series the readings will increase each time you "ADD" more resistance.
Example
you measured 101 from 2 to 7
the next point is # 6 ( 64 ohm rheostat (wiper somewhere in the middle say half 30 ohms)

So 101 ohms in series with 30 ohms must = 101+30= 131 ohms total from points 2 to 6.

59 ohms is technically not possible with the drawing we are working with.

I can only assume you had a bad connection at # 2 probe clip point and 101 ohms changed in the middle of your check (lower).
===
I have been trying to verify the wiring drawing with you pictures I'm thinking that something maybe wrong from points 2 - 7
trace your wires 2-7 and tell me if it is the same as the drawing.
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Last edited by GWIZ; 09-28-2017 at 03:26 PM.
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  #24  
Old 09-29-2017, 06:41 PM
Normanby Normanby is offline
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Hi GWIZ, At the start I checked the probe contact by touching them together with a reading of 0.6 Ohms and they were the same yesterday. Before these to ground readings I cleaned all the contact points I could get to and also an area on each side of the frame as well as the earth point on the front of the machine, between each of these it was 0.6 Ohms to show they were good earths.
Then I did the following readings to earth: Point 1 = 9.8 Ohms, Point 2 = 21.0 Ohms, Point 5 = 77.2 Ohms, Point 6 = 77.4 Ohms, Point 7 = 78.1 Ohms. At a point between the shunts = 36.3 Ohms. All these readings with nothing disconnected, ie the generator in running condition as when the problem occurred. I did check the different range settings on the meter and they were in agreement with just a change in the decimal point as appropriate.
Have not done any more readings so will wait until you reply. I know I am taking up some of your time so if you decide you don't wan't to continue let me know and I will leave it go.
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  #25  
Old 09-30-2017, 05:58 AM
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Will keep going, these threads can get pretty long.

Before I get back to your last post lets check the exciter voltage.

The reason I started with resistance checking it is safer.

===
no paper under the brushes

Set your meter for DC I guess the 200 volt range. (from other manuals the exciter voltage is around 125 volts DC)

Connect your probes, one on each brush of the exciter (points 1,2).

set the rheostat in the middle of its range.

Start up the welder and see what you get. you may have to run up the RPM to get up to 125 volts.

*** if you get a reading also take note which polarity is point 1 and 2
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  #26  
Old 09-30-2017, 10:01 AM
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Lets try run the welder at rated speed and read the exciter voltage safer that way .
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  #27  
Old 09-30-2017, 06:27 PM
Normanby Normanby is offline
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Ok, I have done the voltage tests as GWIZ requested. The Vdc are only 10.4V, which I checked with two different meters and both agreed. The positive is point 2 so agrees with your sketches. Also checked the voltage to earth at each of the Rheostat terminals, both 10.4V. The voltage at the exciter was with the rheostat in the middle of adjustment, moving the rheostat adjuster around to each end made no change to exciter voltage.
The engine is running at rated speed of 1800rpm (checked with a tacho.) There is no speed adjustment for the engine as the governor is set for 1800rpm, no way to throttle down to idle before shutting down. The Lincoln operating manual specs are: Speed-No load 1800, Full load 1650.
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  #28  
Old 09-30-2017, 07:00 PM
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Lets try to find out why you are getting readings to ground, that is usually very bad. the drawing does not show any connections to ground.


Going back to resistance measurement do not start the welder.

as a double check lets check from ground to points 1 and 2 again.

if the ground short is still there.

Lets isolate the armature as a source by placing paper under both brushes and check from ground to points 1,2

from your other post 9.8 ohms (point1 lowest ohms) indicated the short is on that side, maybe where the two exciter coils connect to each other.
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  #29  
Old 09-30-2017, 08:14 PM
Normanby Normanby is offline
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Here are the measurements: Not running, Pt 2 + = 65 Ohms; Pt1 - = 31 Ohms.
Both brushes isolated with paper: Pt 2 + = 1.2 M Ohms; Pt 1 - = 31.9 Ohms. So a big difference, as you say above is there a short to earth from Pt1. To get a good look at the end of the exciter I will remove a plate with 4 bolts which sits under the instrument panel. What should I look for?
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  #30  
Old 09-30-2017, 09:00 PM
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Quote:
Originally Posted by Normanby View Post
Here are the measurements: Not running, Pt 2 + = 65 Ohms; Pt1 - = 31 Ohms.
Both brushes isolated with paper: Pt 2 + = 1.2 M Ohms; Pt 1 - = 31.9 Ohms. So a big difference, as you say above is there a short to earth from Pt1. To get a good look at the end of the exciter I will remove a plate with 4 bolts which sits under the instrument panel. What should I look for?
With those readings there is more than one issue.

Pt2 at 1.2 meg reads as an open.
if you total all the resistances in a series line pt2 should be less than 500 ohms and maybe below 200....
==
pt1 should have stayed at 9.8 ohms.

lets see if the armature is also grounded.
with paper under both brushes check the armature's copper commutator bars to ground. if shorted that would account for the increase (more than one ground short)


pt1 at 31 ohms that "may" may move the short closer to pt8
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