Generator cutout: 1929 Hupmobile

[dalef62]

I am working on a 1929 Hupmobile and can't get the generator to charge.  I think it is the cutout, but I can't seem to find any testing data on it?    I have closed the relay and then the gauge shows that it is charging but I have to hold the relay down.  The car is 6 volts positive ground.   

Is there a way to test it to see if it is defective?  What makes the relay close?  What makes it open when the engine revs up?

Any help is appreciated,

Dale

Edited April 24, 2018 by dalef62 (see edit history)

[zeke01]

Can you post a picture of the cutout? Zeke

[huptoy]

 

In 1929 they used a cutout instead of a voltage regulator.

The relay is open until the generator is putting out about 8 volts.

It then closes to charge the battery.

At idle, the the relay is open.

 

Without a relay cutout, the generator will discharge the battery at idle.

 

Also the cutout could be bad.

 

Many cutouts have a connection on the bottom connecting to the generator & a 2nd connecting to the wiring harness.

 

 

Edited April 25, 2018 by huptoy (see edit history)

[Friartuck]

The cut out relay is used to make the connection between the generator and the storage battery. Without it, the battery would constantly try to spin the generator when the engine is off, thus draining the battery. There is no regulation with a cut out type system, just make or break the connection. When the generator spins fast enough (higher engine RPM) the generator's output reaches about 7-8 volts and is enough to pull the contacts closed. When the generator's RPM slows the spring tension of the cutout opens the contacts.

1. Check the spring tension on the cutout contacts, you might be able to bend the brass tab slightly to make it more sensitive. 
2. Its possible the generator's output has weakened over the years and will not generate enough to engage the cutout. There are many reasons for this including the generator's field coils are partially shorted. if you manually hold down the cutout contacts and the output is satisfactory (say 10-12 amps), then the generator is likely OK. If the output is low (say 3-4 amps), consider having the generator inspected by a shop.

[Curti]

I replace the points inside of the cutout with a heavy duty diode. The cutout looks completely original for judging  and reduces the chance of the points sticking  and running down the battery or worst case a fire. 

[dalef62]

Thanks for all the replies.

This cutout has two connections, one from the generator output and one from the wiring harness.  So, with the cutout off the car and base of the unit grounded, if I momentarily put 12 volts to the generator input side of the cutout it should close the points? 

[zeke01]

Try this: With the cut-out in place and wired correctly, run a jumper wire from one terminal of the cut-out to the other while the engine is running. Just a couple of seconds should be enough. Others more versed in electronics can explain the effect this has on the generator but it may fix your issue. Zeke 

[Spinneyhill]

Is it a 3rd brush generator? If so, are you sure the 3rd brush is adjusted properly?

[dalef62]

Yes it is a 3 brush generator.  All I know is it was working when the car was put away about 15 years ago.

 

[hwellens]

Here is some generic information on cutouts:

 

Cutouts.pdf

[MikeC5]

Keep in mind that if the coil has a broken wire somewhere, it will not pull the contacts closed.   I'm a fan of using a diode too for the fire prevention aspect.

[Akstraw]

I have a similar concern on my 1930 Franklin.  The diode solution is interesting.  A quick search and I found a heavy duty diode marketed for RV application.  So I just replace the entire cutout with the diode, and hide it under the original cutout housing?  Sounds like the thing to do.

[maok]

16 minutes ago, Akstraw said:

I have a similar concern on my 1930 Franklin.  The diode solution is interesting.  A quick search and I found a heavy duty diode marketed for RV application.  So I just replace the entire cutout with the diode, and hide it under the original cutout housing?  Sounds like the thing to do.

Any pics? What is the part number or specs of the diode?

[Spinneyhill]

13 minutes ago, maok said:

Any pics? What is the part number or specs of the diode?

See ply33.com. There is an article about it there.

Edited April 26, 2018 by Spinneyhill (see edit history)

[Bloo]

I'm not sure how this is fire prevention, as the most common failure mode of a silicon diode is a dead short.

 

I would want to troubleshoot. If the cutout relay is truly bad, a diode is a quick fix that should work. Do we know that the cutout relay is bad? There are plenty of good suggestions above about how to check the generator out. Has it even been polarized yet?

[JFranklin]

Model A and T suppliers sell kits with instructions for diode replacement.

[Curti]

This is how I do it. 

[alsancle]

Curt,  I like it.  But Big Al was sceptical when I ran the idea by him.  You would think as a radar tech in WII he would be better with electronics.

[Curti]

AJ, tell Big Al that every alternator made in the last 30 years has diodes.   The deal is , if the points stick closed and the car is shutoff,  the battery tries to motor the generator. It cannot because the belt stops it. The wire feeding the generator gets VERY hot.  Hence the need for a battery cut off switch, which is altogether another issue. 

[maok]

22 hours ago, Bloo said:

I'm not sure how this is fire prevention, as the most common failure mode of a silicon diode is a dead short.

 

I would want to troubleshoot. If the cutout relay is truly bad, a diode is a quick fix that should work. Do we know that the cutout relay is bad? There are plenty of good suggestions above about how to check the generator out. Has it even been polarized yet?

A fast blow 30amp inline fuse would solve the problem of the risk of a fire.

[robert b]

NEVER PUT A FUSE IN LINE FROM THE BATTERY TO GENERATOR , if this fuse blows the generator will make many hundreds of volts and do much more damage to the generator, and also the gauges ,lights and so on. The battery in this system is the voltage control and the third brush is the current control , generator protection is a fuse in the field wireing ,about 6 amp value , a fault in generator to battery will blow the field fuse an shut down the generator .

[maok]

1 hour ago, robert b said:

NEVER PUT A FUSE IN LINE FROM THE BATTERY TO GENERATOR , if this fuse blows the generator will make many hundreds of volts and do much more damage to the generator, and also the gauges ,lights and so on. The battery in this system is the voltage control and the third brush is the current control , generator protection is a fuse in the field wireing ,about 6 amp value , a fault in generator to battery will blow the field fuse an shut down the generator .

That's not a bad point you raise that I had over looked.

[Akstraw]

On ‎4‎/‎25‎/‎2018 at 10:19 PM, maok said:

Any pics? What is the part number or specs of the diode?

The diode I saw was called the "Roadmaster RM-790 HyPower" for under fifteen dollars.  It is rated for a maximum of 24 volts and 85 amps, so is probably overkill for a 6v system outputting less than 20 amps.  Snyder's Model A shop has part number A-10155-DIO for  $2.95 ea.  In further investigating this subject, I read that you could lose some voltage through the diode; 0.1 volts or so.  I am going to give it a try. 

[dalef62]

Just to finish off this thread:  I bought a replacement cutout and now the generator is charging as it should.  Now it is time for a test run out on the road for the first time in years and my first time driving it.

Thanks for all the help.

All is well in Hupp Land!!