1925 Dodge starter generator fuse blowing

[Adolimpio]

The 10A fuse on the starter generator in my 1925 Dodge keeps blowing with the engine running. I even disconnected the wire to the starter switch after starting the engine, replaced the fuse and it still blows. Blowing with only the ground side connected suggests to me that the problem is internal to the generator.

 

Any thoughts?

 

 

[Oldtech]

Is this a North East 12 volt system? I don't think there should be a fuse anywhere on these. If this is just  in a charging line 10 amp isn't nearly big enough. Try 25 or 30.  Even an old S/g can put out 20 amps.

[Adolimpio]

It is a 12v, positive ground, but as I said in my post, the fuse blows even with the negative side disconnected so there cannot be any charging current. There certainly is a fuse in this system since it is built into the starter-generator, see below.

[TerryB]

A short somewhere in the field windings?

[Farmallregular]

According to my Dodge Brothers Mechanic's Instruction Manual, 10 amps is the correct fuse for a 12 volt starter generator.  Note that except on the very early cars, the reverse current cutout is in the starter switch on the floor, not in the starter-generator itself.  Here's a note from the mechanic's manual in the section discussing adjusting the cutout contacts  "sometimes too wide a gap between the carbon contacts will cause the starter-generator fuse to 'blow', high cut in voltage, or the commutator or brushes to burn"

 

The fuse is for the generator field winding, not the generator output.  Here's another quote from the manual "The fuse is placed in the generator field circuit to protect against possible open or high resistance circuits in the electrical system.  The fuse should be 10-amp capacity for the twelve volt system and 6-amp for the system volt system..."  

 

Note that because there is no voltage regulation other than that provided by the battery, the fuse is essentially an over-voltage trip to protect the rest of electrical components, hence the note about an open or high resistance circuit which would keep the battery from regulating the output voltage.  Also from the manual "if it ever becomes necessary to operate the car without the battery, be sure to first remove the fuse..."  Disconnecting the unit from the battery at the starter switch will cause the fuse to blow.

 

My copy of the Dodge Brothers manual is a reprint that I found new on e-bay some years ago, highly recommend one. 

 

Keith

 

Edited April 21, 2022 by Farmallregular
Additional info (see edit history)

[MikeC5]

Hi Adolimpio, welcome to the forum.

 

These cars have '3rd Brush' regulation (of current).  It can be adjusted but I suspect that isn't the problem.  Here is an excerpt from the Northeast

Equipment manual. The field fuse protects the system from over voltage in case of wiring faults. Should the Starter-Generator voltage ever rise too high as
a result of poor connections or broken wires, this fuse will blow and stop the machine from generating. If the Starter-Generator ever fails to charge

therefore, inspect the fuse to see if it is blown or loose in its clips.  In replacing a blown field fuse, never use anything but a standard 10 ampere fuse" 

Before a new fuse is put in, the entire car should be gone over carefully to locate and correct any loose connections or open circuits. The Battery should

also be inspected to see that it is properly filled and free from corrosion or other difficulties that might interfere with the operation of the Starter-Generator.

Always be sure the fuse flts snugly in the clips. Drain holes are provided at each end of the fuse cup to d.rain off any moisture that might collect. Do not

allow these holes to become clogged with dirt or grease.

 

I've also attached some other information that came out of a Dyke's manual (I think).  Does your car have original wiring?

[RAH]

Woah, I thought this had been covered in an earlier post. There is only ONE wire from the N/E model GA to the starter switch/cutout relay. The unit is self-grounding by virtue of the mounting hardware and a ground strap under the post closest to the engine. Check the fuse clips for contact to the fuse. I suspect the problem is NOT inside the unit rather in the foot switch.  Assuming that switch has NOT been upgraded or modified with a diode replacing the cutout relay. There needs to be a ground wire from the terminal marked 'Ground' on rear of that switch assy. back to the tranny where the battery ground (pos) wire is fastened. Actually the N/E unit could care less POS or NEG ground. It will repolarize the fields on next application of the starter switch. There is an adjustment for output via a screw on rear of unit. There are two 5/16" screws one marked lock and one marked adj. One should NEVER spin up that starter/generator without a battery (and associated connections) hooked up. That relay will cut in at appx. 10 MPH and spinning up to appx. 35 MPH or faster the unit will begin decreasing output. Good Luck and let us know your findings. Loose or intermittent connections are sometimes more trouble that potential shorts. However please double check those fiber insulators on each end of that armored power cable. If one or the other becomes faulty that external armor can contact to the connecting terminal causing arcing or short. 

[Adolimpio]

Thanks everyone, this is all very helpful.

 

As I understand it, the fuse will likely blow if the cable to the foot switch is not connected, so disconnecting it for troubleshooting purposes only made the problem worse. Now I know better! But the fuse did blow with the cable connected, and I'm sure the connection is good, with no shorts since it starts without a problem when pressing the foot switch.

 

The ground on the foot switch is properly connected, but it looks like it is only used to complete the circuit for the cutout coil, and although the fuse should blow if the cutout does not work properly, since it is blowing while idling and the cutout does not activate until about 10MPH, it does not seem like a cutout issue.

 

I was already planning to replace the cutout with a diode, so maybe that should be my next step.

 

Any thoughts?

 

Thanks again!

 

[Mark Gregush]

Just as a heads up, there is a Dodge Brothers section down the list of topics. Dodge & Dodge Brothers - Antique Automobile Club of America - Discussion Forums (aaca.org)

 

Re"One should NEVER spin up that starter/generator without a battery (and associated connections) hooked up." You can run the car with the fuse removed. Takes the generator out of the system. Same with blowing the fuse. When the fuse blows or is removed the generator is disabled. 

Edited April 22, 2022 by Mark Gregush (see edit history)

[Farmallregular]

"As I understand it, the fuse will likely blow if the cable to the foot switch is not connected, so disconnecting it for troubleshooting purposes only made the problem worse. Now I know better! But the fuse did blow with the cable connected, and I'm sure the connection is good, with no shorts since it starts without a problem when pressing the foot switch."

 

Keep in mind that once you take your foot off the starter switch, the battery is disconnected until the cutout relay closes when the generator output comes up to a specific level.  If the relay is not closing, or closing at too high a voltage as a result of the gap being too big, the generator output voltage will continue to rise until there's enough current through the generator shunt field winding to blow the fuse.

 

Keith