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1925 Buick starter generator coil


KEK
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Hi everyone -

 

Does anyone know how to test the coil in the starter generator?  I have the SG on the bench and trying to get it to motor. Everything else checks out okay. I have a growler and tested the armature and its good. My brushes are used but they fit the armature and I replace all the wires. The coil is the only component that I don’t know if its okay.

 

Thanks,

Ken

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Use an ohm meter. Primary winding will have some ohms I dunno how many, like 30 or 100 but if it's dead it will have ∞ ohms. Secondary winding has thousands of ohms. Maybe 2000 or 3000, dunno. If dead, it will have ∞ ohms.

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Morgan -

 

i tested the coil from the 1925 standard SG and I also have a spare coil from a 1925 Master that I tested. Results for both coils are very similar. The Ohms between the field wires are 4.0 and 3.7, respectively. The Ohms across the brass tabs are both 1.1. 

 

Based on these results do you think both coils are dead?

 

Thanks, Ken

 

 

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I don't know what you mean by "brass tabs." I measured the primary at two steel terminals, one for the wire from the ignition switch and one for the wire to the points. The secondary was between the steel terminal to the points and the (brass?) tab that goes to the coil wire and spark plugs.

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Posted (edited)

We are talking about the coil in the starter generator. There are 2 field wires.An upper and and a lower. I measured 4 ohms across these wires with nothing else connected to them. The coil also has two brass connectors. One of these brass connectors is where the large lug that the positive wire from the battery connects. I measured 1.1 ohms across these 2 brass connectors with nothing connected to them. See the attached photo. The field wires are on the left.

 

Thanks 

Ken

2D5297E4-7AE4-47D8-B48A-37BAD3288A7D.jpeg

Edited by KEK
Typo (see edit history)
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The fact that you have resistance means the wires are still connected and not burned out. Sorry I don't know what the reading should be. But since both coils tested the same I would think you are OK. Is the SG not working?

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No it doesn’t motor. Everything checks out. The armature is good. Brushes are used but conform to the curve on the armature. New wires. Morgan got 21000 ohms and my coils measured 1.1 ohms. Something is not right...

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I would think your readings are ok. 21k ohms is an open for anything on a starter.   How stiff is the armature to turn? is there a way to hook it up and see if it's trying. Check for hot spots.

I'm not conversant with the 25 , more the older ones.

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I have a new sealed bearing on the armature and it turns easy by hand. My field coil doesn’t measure 21k ohms. It measures 1.1 and 4 ohms.

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Posted (edited)
1 hour ago, KEK said:

I have a new sealed bearing on the armature and it turns easy by hand. My field coil doesn’t measure 21k ohms. It measures 1.1 and 4 ohms.

I'm saying it shouldn't read 21K. your readings sound good.  I'm suggesting looking around for other possibilities.   There are experts on here for the25 type S/G. They may chime in.

Edited by Oldtech (see edit history)
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3 hours ago, KEK said:

I have a new sealed bearing on the armature and it turns easy by hand. My field coil doesn’t measure 21k ohms. It measures 1.1 and 4 ohms.

 

I got 2100 not 21000 and it was the coil. The coil which sits on the starter generator. I never heard of anybody refer to anything as a coil except the coil.

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OK, @Morgan Wrightis measuring the spark coil which is mounted on the starter generator. @KEKis refering to the internal coils of wire that form the fields of the starter generator. The two have NO interaction. As the OP is asking about the starter generator coils and help making the starter generator operate, lets just drop the spark coil out of the discussion.

I have no hands on experience with this starter generator, but the ohm readings make sense in general. I see nothing that screams shorted or open in the readings. If it does not motor, I would really look closely at the brushes and brush springs. If possible, measure the resistance through the brushes and armature. If you do this, make sure you do not press on the brushes and alter their contact with the commutator.  Something simple is wrong. It will just take a systematic approach to finding the problem.

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The discussion is about the " Field Coil", not the "Ignition coil".   

Ken,

Did you paint the SG housing or the lower brush housing?  The lower brushes ground to the SG housing and there can be no paint or corrosion on the mating surface.  Same goes with the back side of the SG housing mounting bracket.  No paint.  

 

Hugh

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Hi Hugh -

 

i didn’t paint the areas that you indicated not to paint in your procedure. I tested the SG on the bench and verified I have ground. 

 

When I first tested it to see if it motors, when I touched the positive battery to the terminal, it sparked a little bit. I tried it a few other times but it didn't ever spark again. I don’t think I shorted out anything because I didn’t hold the positive battery on the terminal but for a brief second.

 

I cleaned the brushes and made sure they contact the armature. There is continuity with the brushes and armature. I tested the armature with my growler and its good.

 

The only component I didn’t tested was the field coil. But from what Oldtech is saying it sounds like my field coil is good.  Do you know what the ohms reading are on your 25 standard field coils?

 

Thanks, 

Ken

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@KEK, I just looked at the wiring diagrams Hugh supplied and now have a really silly question....  Are you trying to motor the starter configuration or the generator configuration or both?  As I see in the diagram, to motor the starter you need to hook up ground and battery positive, THEN press the starter pedal section to engage the starter brush. Are you engaging the starter brush?

 

Yep, silly question, but I was taught that the only dumb question was the one not asked.....

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Not a silly question Roadmaster. I am testing the SG on the bench and not in the car so the procedure is different.

 

To test the motoring on the bench you insert a wooden dowel in the opening where the pointed operating rod goes then lift the brushes off the armature and apply voltage. It should motor. Mine does not.

 

To test the starter you remove the wooden dowel and this simulates when you step on the starter pedal then apply voltage and the starter should run. Mine does not.

 

Ground appears to be good, my armature tests okay, and there is continuity between the brushes and armature. The only thing missing is power... Doesn’t this seem to indicate a problem with the field coil?. 

 

Ken

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@KEK,  I am retired out of the electronics industry so my approach to any electrical issue is to start at the beginning and work through the system in an orderly manner. Never skip a step no matter how obvious it is. The fact that neither the starter nor the generator motor as expected brings us to a common problem. What is common to both? The only thing I see from the diagram is the grounds. Remember, I am not hands on with this unit so those that are, are much better sources of good information. Looking at just the starter section, it is a very simple series motor. It should be easy to follow the voltage through the circuit starting at the battery positive and going point to point with a voltmeter. If you get to the grounded brush and still have voltage you then know the brush ground is not grounded. This is just one example. Keep us posted!!!

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Roadmaster -

 

I don’t have a spare 6V battery so I have been bench testing with short touches of the positive end of a 12V battery using jumper cables.  I hate to leave a 12v source on the positive lug to do the tests you recommend. Do you think if I hooked up a 6V battery charger on the positive lug it would be enough power to do the ground checks?  - Ken

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Posted (edited)

Ken, 

    I checked the field coil from the 1925-25 SG that you got all the other parts out of.  The shunt side is 5.1 ohms, and yours read 4.0 and 3.7 .   On the series side, I read .4 ohms, and you had 1.1    Not sure why we are getting different readings.  Maybe just the meters.  I get no reading between the coils, so they are not shorted to each other.  Since they do not read 0, they are not open.  No opens, no shorts, I say all 3 are good coils.  

 

Using a 12 volt battery for the tests is not going to hurt anything.  There is no load since you are bench testing.  A 15 second motoring test or Starter test is a non issue.  A 6 volt battery charger is not what you want.  

 

You wrote the following, but this is not correct.   I am adding in CAPS regarding what is left out.

To test the motoring on the bench you insert a wooden dowel in the opening where the pointed operating rod goes then lift the brushes off the armature and apply voltage. It should motor. Mine does not.  THE WOODEN STICK NEEDS TO HOLD UP THE STARTER BRUSHES AND ALLOW THE GENERATOR BRUSHES TO REST ON THE ARMATURE.  DON'T LET THE STICK TOUCH ANY ROTATING PARTS.  YOU ALSO HAVE TO APPLY VOLTAGE TO BOTH TERMINALS A AND F.   See the attached wiring diagram.  The ignition switch is a spider.  When it rotates into position, it connects wires on numbers 1, 2, and 3.  This is easiest done with a couple wires with alligator clips on the ends.  Hook up all the positive wires.  When you are ready to bench test, connect the ground lead to the battery.      

 

MOTORING TEST. (from my procedure you may only need the A terminal for motoring)

Ground the SG frame to the battery.  Use a round wooden stick to lift the starter brush thru the hole in the front of the unit.  Touch the A terminal with positive voltage.   This should “motor” the armature at a different speed than the starting speed.

 

To test the starter you remove the wooden dowel and this simulates when you step on the starter pedal then apply voltage and the starter should run. Mine does not.  

THIS IS MY NOTE FOR THE STARTER TEST.

STARTER Test. – Lay the SG Unit on it’s back.  Using Jumper Cables, Connect the black wire to the SG base, and to the Neg battery terminal.  Connect the red to Battery Plus.  You will want to use a jumper wire from the + battery cable to the F terminal.  Touch the F terminal with + voltage at the same time that you touch the Battery connection on the SG.  This will make the Starter spin.

 

Sorry that I cannot verify all of this procedure, but my car is on a jack and in gear, and I have a wheel being respoked.      Hugh 

    

 

1338216437_Wiring-1924-1925Buick-bestdiagram.jpg.20b3229706eb8d2c95605a186f163a7c.jpg867469746_StarterGeneratortestphoto.JPG.ee35b60f4a0044baf72ad9e8ab0c3863.JPG

Edited by Hubert_25-25 (see edit history)
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@KEK, Follow the above instructions from Hugh. Everything he has said makes sense to me.  I am still coming back to brush issues because the resistance measurements you posted of the field coils seem well within what I would expect. As said above a 12 volt  battery will not hurt the SG unit in short bursts. I think the 15 seconds mentioned is a good number. The most important thing is heat! If anything begins to get hot disconnect the battery immediately!!  The 6 volt charger is to light to motor the unit, but if it does not overload and shut down it could be used to do the voltage tracing I mentioned. One good thing with the charger is that if you manage to cause the unit to try to motor, it will not have enough power to jump out of your hands or hurt you 😀.

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Roadmaster -

 

I actually followed Hugh’s directions when I did my motoring and starter tests. My description of the process was to simplified and not clear.  I am going to put everything back together and repeat the tests using a 12V battery. If I don’t get it it motor then I will do the voltage testing as you suggested. I think the consensus is my coil is good so looking for a ground issue is probably the best place to start.

 

Thanks everyone,

Ken

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