Generator bench tests OK but does not work in car... what am I missing?

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Model T Ford Forum: Forum 2011: Generator bench tests OK but does not work in car... what am I missing?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Bamford, Edmonton AB on Friday, August 26, 2011 - 12:42 pm:

I am befuddled by the generator in my '24 Speedster and hope someone smarter than me can help. For years it was a useless ridealong, running unconnected and featuring a spun solder commutator. I have since carefully re-soldered and undercut the commutator, replaced some poor inside pigtails, then gave it a good cleaning, new gear, sealed bearings and fresh paint. It benched-tested OK per the MTFCA Electrical Book, motoring smoothly with a 5-6 amp draw.

I drove the car for a while with no VR or cutout, but always with the generator output pigtailed to a good ground. My ammeter appears to work properly, showing a slight discharge when running on coils and about 10A discharge with lights on.

Yesterday I installed a 6-volt negative-ground VR from Fun Projects. Following FP's instructions I set the 3rd brush to minimum charge and attached the battery wire. There was a tiny spark when the wire was attached (FP said this is OK) but no movement/discharge on the ammeter. So far, so good.

Started the engine, ammeter didn't budge irrespective of engine speed. Advanced the third brush position, still no apparent charge. Voltmeter show 6 volts at the VR battery terminal but 0 volts at the generator terminal.

Took off the generator, nothing apparently amiss, bench-tested it again, still motors at 5-6 Amps. Followed the car wiring and it seems OK: VR wire to GEN terminal, GEN terminal to horn and ammeter then on to key switch. Other side of ammeter to BAT terminal and so on.

Re-installed it this AM with the other, brand new, FP VR I have here for use on my '26 Touring. Again... no charge indicated at the ammeter, 6 volts showing at the VR battery terminal, 0 volts at the generator output.

Clearly I missing something here. Any suggestions?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Patrick on Friday, August 26, 2011 - 01:46 pm:

If the engine and chassis and generator casing has been thoroughly primed and painted it is possible that it is not getting a good ground to the battery. Run a temporary ground wire from the negative battery terminal directly to the generator casing and see if it works. Jim Patrick


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Friday, August 26, 2011 - 02:18 pm:

Chris
Just because a generator will "motor" on the bench does not mean it will produce a charge. I suspect the brushplate lead is not set correctly. I know your thinking "I did it just like the book stated", but that adjustment can be very tricky to get exactly right so the generator will start up on it own. I rebuild generators every week and even I sometimes I have trouble with this adjustment.
Try this:
If the generator is in good shape and charging excessively or not at all with the third brush fully retarded it is caused the brushplate “neutral” not being set correctly. This is a common problem with newly rebuilt/repaired generators. Setting the brushplate “neutral” can be very tricky. You can follow the standard procedure, but getting it in just the correct spot for proper generator operation is sometimes very elusive.
I have used this procedure for years to correct the brush plate not being in the correct "neutral" position on running Model T’s. You will need a helper to watch the ammeter.
Install a known good relay type cutout (not a VR) on the generator. Remove the generator cover band. Adjust the third brush to the fully
retarded position (all the way CCW when viewed from the gear end of the generator). Start the engine and run at a speed where the generator should be charging.
Loosen the four #6-32 screws on the brushplate end cap 1-1 1/2 (only) turns. With your fingers reach inside the generator case and rotate the entire brushplate to a point where the ammeter is reading 1-2 amps charge. Tighten the four #6-32 screws. Now reset the third brush to the desired charging rate. Given the way Model T’s are driven today this should normally be no more than 5-6 amps. This is also very easy on the poor generator and it will thank you for it.
If everything else is working correctly, this procedure will set the brushplate "neutral" to the proper position.

Report back with results.
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Bamford, Edmonton AB on Friday, August 26, 2011 - 06:36 pm:

Hi Jim — while I was pretty sure the three mounting bolts c/w lock washers would provide ground continuity, your suggestion was an easy one to try. Alas, a jumper from the generator casing to a known good ground resulted in no improvement.

Thanks, Ron for your detailed reply. I used the non-VR cutout from my '26 Touring (assumed good) and followed your suggested procedure. Surprisingly, there was still no hint of charge at the ammeter with the brush plate in any possible position.

I then looked through the MTFCA manual again and followed the written procedure for setting the brush plate. It was very difficult to find that neutral point where the generator was not trying to motor one way or the other. I thought I maybe had it set right, but the generator, when re-installed, still showed no charge at amy position of the third brush.

Is there any other condition that would result in the generator motoring OK but not charging, or should I go through these exercises again hoping for improvment?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Friday, August 26, 2011 - 07:12 pm:

Chris
There is some other problem inside the generator.
Set the third brush midway in its travel. With the generator null point reset using the relay style cutout start the engine and rev it up. Short between the two cutout terminals and see if it starts charging?.
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By steamboat on Friday, August 26, 2011 - 07:19 pm:

Chris,

Disconnect the field winding leads from the brush holders. With an ohmmeter check the resistance to ground. Do the same for the hot brush and the third brush, lifting the brushes away from the commutator. The resistances should be at least in the thousands of ohms or higher. If they get too low the generator will motor OK but will not be able to get a charge going. While you are at it do the same for the armature, after lifting the ground brush.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Friday, August 26, 2011 - 07:27 pm:

Chris
What direction did the generator motor as viewed from the gear end?
Did you cross the field leads before connecting them to the brushholders?
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By steamboat on Friday, August 26, 2011 - 07:29 pm:

Chris,

One other thing. When it is motoring, does it rotate in the correct dirrection?


Top of pagePrevious messageNext messageBottom of page Link to this message  By steamboat on Friday, August 26, 2011 - 07:31 pm:

I guess Ron and I were typing side by side.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Bamford, Edmonton AB on Friday, August 26, 2011 - 07:38 pm:

Thank you Ron and Steamboat for your suggestions. A family event prevents me from getting back at the job until late tonight, but I will report back ASAP.

One thing, Ron... not at all sure I can re-set the generator null point using the relay style cutout, as last time I tried there was no response, at all, from the ammeter no matter the brush plate position.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Friday, August 26, 2011 - 08:04 pm:

Reset the null point on the bench with a battery. Install the relay style cutout after installing the generator on the car.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Friday, August 26, 2011 - 08:39 pm:

Chris:

Let me chime in here and say that under NO circumstances do you want to install either of your VR's on this generator to see if that might "fix it" since they will then likely need to be repaired. Installing a good VR onto a questionable generator results in a questionable VR. My advice is to pick one guy here and work OFFLINE since we all mean well but too many cooks can get you trying all sorts of things and not get you closer since you may be adding problems as fast as you are looking for them. A scientific analysis step by step is best and results in the minimum repair bills for things not destroyed along the diagnosis trail.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Bamford, Edmonton AB on Friday, August 26, 2011 - 11:15 pm:

John, your advice to not install my two new VRs on this questionable generator is as wise as it is late. I believe it was reasonable to install the one initially, as the generator motored fine and I had no particular reason to suspect any problem. Subsequently trying the second VR was clearly a reckless, and very possibly costly, move.

Ron — I am not confident the null point was accurately set on the bench, however, when installed on the engine with a relay cutout, shorting between the two cutout terminals did not result in charging. Rather, it resulted in a heavy discharge.

When motoring on the bench, the rotation was CCW viewed from the gear end.

I believe the field leads are crossed correctly. Photo attached.

Steamboat — Field leads to ground (yoke) very high resistance, ohmmeter does not budge. Field lead to field lead approx 2.5 ohms. Hot brush to ground, third brush to ground and armature to ground all very high resistance, ohmmeter does not budge.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Friday, August 26, 2011 - 11:36 pm:

Is the battery polarization and the generator polarization the same? Have you tried re-polarizing the generator in the car?


Top of pagePrevious messageNext messageBottom of page Link to this message  By steamboat on Saturday, August 27, 2011 - 12:34 pm:

Looking at the gear end the rotation should be clockwise, same as the engine when it is running. Reverse the field connections and the rotation should be clockwise.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Saturday, August 27, 2011 - 02:14 pm:

No, don't reverse the field connections--Leave them crossed! Adjust the null brush position.
This is done with the third brush off the commutator. The generator should NOT motor in this configuration when the brush plate is adjusted correctly.

But this is a mute point. It sounds like the field coils are shorted internally. As I recall, the field coils are about 1.1 ohms each or about 4.5 ohms lead-to-lead.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Saturday, August 27, 2011 - 02:22 pm:

Ken
I worked with Chris this morning.
The minute I saw it would only motor CCW I immediately knew the trouble. He had one of those field windings that was formed backward. As soon as he reversed (uncrossed) the field leads, re polarized the pole shoes, set the null point it took right off.
Chris has installed his VR, it is showing a charge and he is out driving the car recharging the battery and making sure that when it is charged the ammeter falls back to zero charge. .
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthonie Boer on Saturday, August 27, 2011 - 02:23 pm:

One time I had an generator where the field connectios are NOT crossed !!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Bamford, Edmonton AB on Saturday, August 27, 2011 - 02:24 pm:

Bingo!

I have benefited greatly from the advice of people much more experienced than me. As John Reagan suggested, I have been working with someone on this problem off-forum. Ron Patterson was most helpful.

As Steamboat posted, the field coil leads had to be reversed so they are NOT crossed. Late last night I was reading past posts about similar problems and learned there were field coils manufactured some time ago that were constructed such that the leads were NOT to be reversed. That quick change, resetting the null point, and a re-polarizing of the generator were all that it took. The generator is now charging merrily away at a maximum 5-6 amps.

I am now reminded of the day last spring when I disassembled the generator for cleaning and new bearings. I generally make good observations of how things come apart so I can get them together again properly. I recall, now, some confusion around the field coil leads — I thought they were not crossed upon dissasembly but when putting the rascal back together all the reference material said the leads should be crossed so that's what I did. Oops.

Whether I have toasted my two new VRs by all this monkeying around remains to be seen. After getting the generator charging OK I replaced the old relay-style cutout with a VR and the ammeter still shows the same charge rate, so there is hope. We are going on a 100 mile shakedown run this afternoon, which ought to be enough to fill the battery and cause the VR to bring down the charge rate to near-zero. We'll see.

One other important fact learned through this process — bench-testing and setting a generator should be done with a 6-volt battery, not a battery charger, as the charger does not give a pure DC current.

Many thanks to all involved, especially Ron Patterson, for your comments and suggestions. This forum is a wonderful place.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Chris Bamford, Edmonton AB on Saturday, August 27, 2011 - 10:39 pm:

Just to finish this off...

We went on a 120 mile shakedown cruise today and the battery achieved full charge roughly half way. From there on the ammeter needle hovered on the positive side of zero. Looks like I got lucky and didn't fry my VR after all.

BTW, we got 29 mpg Cdn/24.5 mpg US over 120 miles (mostly at the 47 mph sweet spot). Its a fairly light speedster carrying two fairly heavy guys, with Z-head, Simmons SP carb, static balanced, larger valves & intake manifold, two outside oilers, coils & mag, 3:1 rear gears.

Thanks again everyone for your help.


Top of pagePrevious messageNext messageBottom of page Link to this message  By steamboat on Saturday, August 27, 2011 - 11:18 pm:

Congratulations! It is great when the efforts to solve problems work.


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