'31 Buick generator

[1wonton]

This Thermostat resistor unit is burned out; can I repair it or is there a source for a new one?  Can another resistor be used to replace it?    

 

 

ron

[Mark Shaw]

Photo please...?

[Old buicks 2]

1wonton,  send a picture to this forum thread,  I have several of them NOS.   Just need to know which one.

 

Tom

[1wonton]

Here's a photo of the tag.

[Old buicks 2]

Need a picture of the burned out resistor unit instead of the tag

[1wonton]

Sorry, I thought you meant you had several generators.  Here is a picture of the resistor.

 

 

ron

[Larry Schramm]

You should be able to buy nichrome wire and rewind it.  You will need to find the diameter of the original wire and buy the same diameter so the resistance would be the same. Also, wind it the same number of turns.

[1wonton]

4 hours ago, Larry Schramm said:

You should be able to buy nichrome wire and rewind it.  You will need to find the diameter of the original wire and buy the same diameter so the resistance would be the same. Also, wind it the same number of turns.

Thanks Larry, guess I can do that.  Would you know the resistance value for this resistor.  Couldn't the whole thing be replaced by a regular carbon resistor?

[Bloo]

Probably not a carbon one. I would expect that resistor to be less than an ohm. You might find a current sensing resistor made of metal oxide or something that could do it. I wouldn't rule that out, but I think it would be easier and less hassle to rewind the resistor. Someone probably ran the generator with no battery connected to load it. On a third brush generator that usually burns something up, it is just a question of what. That little resistor probably gave it's life to save the field coils.

[1wonton]

Thanks Bloo;  any idea as to the resistance value on this?  Do I really need the resistor, seems like the field coil just goes to ground unless the contacts are open.

[EmTee]

Just measure the diameter to identify the wire gauge size that you need.  Wind the new wire on the holder just like the old was.  It will work fine.

[Rock10]

Wouldn't that have to soak up a lot of power? I wonder how many watts?

[edinmass]

That’s a shunt………it’s a thermo control to drop the charge rate down when the temperature heats up. Since most of them from the 30’s used the same wire……only the number of turns/length seem different on the ones I have ever had my hands on, I would find a used one off a big car like a Packard or Pierce…….and cut the wire down to the same length as what you have in the car. It’s probably not that critical………and I’m not certain any modern wire would work as a replacement unless you can check it’s resistance hot and cold. Many generators have them bypassed and the charging rate is just set lower……..

 

https://en.wikipedia.org/wiki/Shunt_generator

 

 

 

Edited November 20, 2022 by edinmass (see edit history)

[Bloo]

11 hours ago, 1wonton said:

Do I really need the resistor, seems like the field coil just goes to ground unless the contacts are open.

It turns down the charge rate when the generator starts to get hot. As Ed says you would have to set the charging rate lower if you did that, and in those days the charging rate was either too high or too low all the time depending on what you were doing, because there was no voltage regulation. Then there is the fact that the resistor is burned out, and something in the car's history caused that. If the resistor had not been there, the field coils would have burned at that time. That is a separate issue from the resistor's main purpose of protecting the generator from overheating from overcurrent and throwing solder all over the place. Were it me, I would try to fix the resistor.

 

11 hours ago, 1wonton said:

Thanks Bloo;  any idea as to the resistance value on this? 

Nothing good enough to go with. That information must be in a book somewhere. 0.3 ohms sticks in my head from the last time this came up, but it might be wrong. If there is no spec for the resistor, there might be a spec for the current with the resistor kicked out? Pulling numbers out of the air, if there was nothing published to go on, I would expect the generator to cut back to about 2 amps of *charge current* with the points open, and that is what I would shoot for. @edinmass's idea of using period wire is the best, as it is difficult to measure resistance that is really low like that, and it changes anyway when the resistor gets hot. It never occurred to me that you might be able to get period wire, and If I was stuck using Chinese Nichrome wire from ebay (probably), I would get the same diameter and wind exactly the same length and number of turns like @EmTee suggested, and then test it. With everything set up as normal but the points blocked open with paper. In the absence of specs, If it was about 2 amps of charge current, I'd leave it alone and if not I might try a little more or less wire.

11 hours ago, Rock10 said:

Wouldn't that have to soak up a lot of power? I wonder how many watts?

I don't know, but not as much as you would think. It is in series with the field, and thats just a control circuit that off the top of my head probably draws about 2 amps of *field* (control) current with the generator running full bore, only held back by the third brush regulaton. Ignoring a bunch of important details for a wild guess, that's about 1.2 watts.

 

Edited November 20, 2022 by Bloo (see edit history)

[edinmass]

In most early 1930’s car, the shunt cuts back the amperage by 50-60 percent AT FULL OPERATING TEMPERATURE. Today there are many other issues to consider……..mainly battery technology and charging rates of glass mat units. They like lower amperage charging rates. Fact is 98 percent of collector cars don’t get enough driving to keep the battery properly maintained. And associated issues of both over and under charging come into play. Toss in electric fuel pumps, driving at night with lights on(both very high load issues), and you need the system to charge at least one or two amps when hot under max load………and then there are the same shunts/resistors in the voltage cut outs/regulators. Makes for interesting problems. When on tour, I carry spare charging systems IN THE CAR. Yup, I have a generator and cut out as well as a battery! Even with very well sorted cars, charging issues are a top three problem on long tours. In the last five years, the only issue that left me on the side of the road in tens of thousands of pre war driving miles……..it was a charging system that stopped my car. Fortunately with the entire spare system on hand, a roadside repair was accomplished in under thirty minutes……….but it still caused us to go off schedule and miss a significant portion of the daily tour.

Edited November 20, 2022 by edinmass (see edit history)

[EmTee]

The thing to note with that resistor is like @Bloo stated, the resistance changes with temperature (like an incandescent light bulb filament).  As demand increases and the generator works harder, the resistor heats up, increasing its resistance and thereby reducing the field current (and hence the generator output).  I guess if you're concerned about winding a new resistor correctly you could always add one or two turns and then test the output.  If the charge current is too low you can shorten the wire until it meets specification.

 

Edited November 20, 2022 by EmTee (see edit history)

[drovak]

Isn't there a bimetallic strip involved in the '31 generator?

 

If you were near me, I'd offer to put a constant current through a length of the remaining nichrome, and knowing the voltage drop across the nichrome itself, calculating the resistance is as easy as dividing. Save for that, I second (third?) the suggestion of measuring the diameter of the nichrome and simply winding it back over the existing form. 

[Bloo]

The bimetallic strip has points attached that short out the resistor.

 

The generator is a third brush design, with only current regulation. It is set up as any other third brush generator, and inherits the typical overcharging/undercharging issues, such as the inability to properly compensate for the load of headlights. When the generator gets HOT, the bimetallic strip opens some points and then the resistor is suddenly in series with the field coils. This lowers the charge rate when the generator is hot. It allows a higher charge rate setting on the third brush than would otherwise be practical.

[edinmass]

Isnt it amazing what was done 100 years ago, without solid state parts?  Give me analog any day!

[1wonton]

4 hours ago, drovak said:

Isn't there a bimetallic strip involved in the '31 generator?

 

If you were near me, I'd offer to put a constant current through a length of the remaining nichrome, and knowing the voltage drop across the nichrome itself, calculating the resistance is as easy as dividing. Save for that, I second (third?) the suggestion of measuring the diameter of the nichrome and simply winding it back over the existing form. 

I took a 1 1/2" piece of the remaining wire and checked the resistance.  I found it had about one-half the resistance of a piece of new Nichrome 26 ga.  I guessed and wrapped 5 turns around the mica insulator; Who knows?  I'll start the engine tomorrow and see what happens.  Probably have to fool around a few times to get an acceptable charging rate.  Seems like the easiest thing to do if you're doing a lot of driving would be to just raise the hood and move the third brush to fit your charging need.

[1wonton]

Got the generator back in the car but still no current.  Took it back out, pulled off the back cover, checked the field coils, brushes, armature; everything seemed ok.  Put it back in, timed the distributor, started to connect the generator and battery wires and then noticed the little letters on one of the cutout terminals; GEN.............................  As a brilliant car mechanic and electrician, I thought to myself "hmmm, maybe that means GENERATOR....".  I learned from this exercise that a cutout relay will not work when installed backward.  Live and Learn, I guess; problem is remembering what you learn..............

[edinmass]

I see said the blind man picking up his hammer and saw, you do said the deaf mute, while the man with no Iegs got up and walked away.

Edited November 23, 2022 by edinmass (see edit history)

[edinmass]

Available new........93.00 

I have no association with the seller.

 

If you want purchase info, PM me. Best, Ed

Edited December 6, 2022 by edinmass (see edit history)

[Str8-8-Dave]

On 11/19/2022 at 2:13 PM, Larry Schramm said:

You should be able to buy nichrome wire and rewind it.  You will need to find the diameter of the original wire and buy the same diameter so the resistance would be the same. Also, wind it the same number of turns.

Right on.  Larry is right.  You could even re-connect the original wire on the bench and measure the resistance with a good volt ohmmeter as a sanity check for your new resistor winding's resistance.  If for some reason you couldn't buy the same diameter nichrome wire, if you knew the resistance of the original wire you could simply find the length of new wire that duplicates the resistance value of the original wire.

 

I would be considering what might have burned the resistor out in the first place.  Something likely overloaded it.  

[Bloo]

You're not wrong but, but I think bench testing the generator with the points blocked open (and a battery or other load) is essential. That resistor is probably a fraction of an ohm, and getting a useful reading with an ohmmeter could be difficult. Not impossible, just difficult.

 

For me, it's an easy guess how it got burned out in the first place. I think someone ran it with no battery attached. On a third brush generator there is nothing but the load of the battery to control voltage. The main brushes are directly across from each other. One is at 0 volts (ground) and the other is at 6, 7 or 8 volts, whatever charging voltage is at that moment. The third brush powers the field coils (electromagnet), and it is located at some fraction of the distance between the two other brushes. The field coil runs on what? 2/3? 3/4? 7/8? 9/10? of the charging voltage? Who knows? The third brush is usually adjustable. Running with no battery, the charging voltage raises uncontrollably, and the field coil's fraction of the charging voltage raises uncontrollably right along with it, usually burning the field coil out. I think that probably happened and the resistor burned out instead.

 

In 90+ years, the odds are just about any car will encounter an owner who doesn't know that you can't safely operate a third brush generator with no load.

 

Edited December 6, 2022 by Bloo (see edit history)

[Str8-8-Dave]

Yeah- it's a wonder the generator in my 31 Buick 60 series car didn't have a problem with no-load damage.  When I got the car it had just enough jury-rigged wiring to allow it to start and run on the battery, the generator wasn't even hooked up.  I re-wired the car with a repro harness and wound up adjusting the 3rd brush to reduce generator output, it would peg the ammeter at about 1500 rpm.  I moved the 3rd brush and got the output down to about 15 amps.

 

The ignition circuit, as received from previous owner.  Note the high-quality speaker wire used...

 

More speaker wire along with very creative throttle linkage to go with the then contemporary wooden gas pedal.

 

Poor Mr. generator, all dressed up and no place to go with the output...  No wire connection to the cutout relay!

 

After installation of the repro wire harness, ignition switch now properly wired.

 

No more speaker wire and correct carburetor/heat riser/accelerator pedal linkage.  Oh- and by this time I painted the firewall black.

 

Repro wire harness connection to the cutout relay.

Edited December 6, 2022 by Str8-8-Dave (see edit history)

[Bloo]

Nice Buick!