The Stovebolt Site Forums The Shop Area The Electrical Bay Fixed 1/4 Ohm resistor

Gentlemen,

Planning to do some tinkering with my VR that is sending too many volts to the battery. The Delco Remy 1R-118 service bulletin for my VR recommends one method of a "Fixed 1/4 Ohm Resistance Method". What exactly is a 1/4 Ohm resister? Google has failed me.

Here is a copy of the bulletin:
http://www.harleykmodel.com/technical/regulators/dr-docs/1R-118.pdf

BTW, I am going to attempt the variable resistance method as I got a nice rheostat from an ebay tip from Jerry a year or so ago. Most likely will have questions on that in the near future.

Still having trouble grappling with the concept of electrons racing through pores in copper wire but getting there.

Thanks in advance for the help.

The 1/4 ohm resistor referenced in the article is a way of simulating a fully-charged battery so the final voltage regulator setting can be made without waiting for the battery to come to full charge specific gravity. The old Sun VAT-20 tester that was the industry standard back in the 50's and 60's has that resistor built into the unit. A quick work-around is to purchase four 1 ohm 250 watt resistors and assemble them in parallel with some #10 wire with alligator clips attached, and insert them in series between the BAT terminal and the output wire to the ammeter like the diagram shows. Then adjust the voltage regulator setting to the desired number (usually 14.5-14.7) Remember that the setting will decrease slightly when you install the cover- - - -steel conducts magnetism better than air. DO NOT try to use the field resistor I recommended for that procedure. It can't be adjusted low enough to get 1/4 ohm, and it might burn out due to insufficient current capacity. 1 ohm 250 watt resistors are available on Ebay, cheap!

That variable resistor is used between the field wire and ground to precisely control armature voltage while setting the cutout relay closing point, or any other time you need a specific voltage output for test purposes. It is not intended to carry full charge current.

The final check of the voltage setting is the water level in the battery. If the engine is starting reliably and the headlights are bright, and you don't have to add water to the battery frequently, you're good to go. If you're running some sort of sealed battery, adjust the regulator to the manufacturer's specifications, but be sure the battery is fully charged or use the 1/4 ohm resistor to simulate full charge before making the adjustment.
Jerry

Resistor values are rated in ohms. The power rating of a resistor is given in watts. The power rating is the amount of power the resistor can dissipate before failing. here is an example of a 1/4 ohm resistor. 1/4 ohm resistor

Just looked on Ebay- - - -the 250 watt resistors are outrageous- - - -100 watt will work, and the ones from Hong Kong, etc. are dirt cheap! Back in the days of vacuum tube circuits, high-wattage resistors were pretty common. Not so anymore, I guess!
Jerry

Thanks for the electrical lesson.

Since I didnt have the correct resistor, I made certain the battery was fully charged (12.7 volts)and made an attempt at adjusting the voltage setting. It was too cold/windy to dial in the correct voltage of 14.5 volts at VR temperature of 125 degrees Fahrenheit so I estimated the setting to 14.3 volts. Seems to have done the job as at least the generator is not overcharging, but would like to reset a little more precisely.

What exactly is the purpose of "cycling the generator", (page 6, section 4 in the bulletin)? Can I install the Clarostat 150 Ohm, 50 watt rheostat in the field circuit to lower the voltage to properly cycle the generator?

So many questions...

Cycling is easy- - - just push the voltage or current regulator points open for a second or so to drop the generator output to zero momentarily. The cutout relay will pop open and reclose as you do that. There's no danger of getting shocked by the low voltage present at the points.

Cycling the regulator assures that the adjustment you just made is accurate. Sometimes just making a change in the spring tension doesn't immediately affect the meter reading so turning the generator off and back on double-checks the new setting.
Jerry

Okay, so the rheostat is used to cycle the cut-out relay by reducing the voltage to below the cutout limit? Cycling of the generator sounds much like rebooting a computer. Thanks for the clarification as manuals often say to perform a procedure but they do not always explain "why".

I will keep an eye on the battery voltage for a while when the engine is running.

One more time- - - - -the rheostat is only used once- - - -to precisely control armature voltage while setting the cutout relay. Disconnect the Field wire from the regulator and connect the rheostat between the field wire and ground. The variable resistance allows you to sneak up on the closing voltage setting a fraction of a volt at a time while maintaining a constant armature speed. It's MUCH simpler to get an accurate closing voltage that way.

Closing voltage set? Good. NOW PUT THE RHEOSTAT BACK IN THE TOOL BOX! You won't need it again. Reconnect the field wire to the regulator. To cycle the generator during current or voltage regulator adjustment, to check the setting you just made, just push the points open with your finger and turn the generator off and back on. This procedure is really much simpler than it seems in print. Once you make a couple of hundred regulator adjustments, it will become second nature- - - -you'll just do it without thinking about it so much.

Have fun!
Jerry

This thread has been very enlightening to me. While it could come in very handy for me should I ever have a VR issue, the true value to me is that it removes all guilt from me for deciding to go completely away from these tedious electrical relics and go with an internal regulator alternator.
I do have a dream, one day, to do a complete as-built restoration, so I will save this info.
Carl

Those "tedious electrical relics", carburetors, and automatic transmissions were responsible for providing food, shelter and clothing for me and my siblings, thanks to a very talented and dedicated father who spent a large portion of his life running the best independent shop in Nashville Tennessee. He also passed on a lot of that knowledge to a couple of us, and we try to make sure it doesn't just go away. I've already got a son, a daughter, and a grandson who are all better than average wrench jockeys. Five generations so far!
Jerry

Thanks for the information Jerry...don't worry I have put the rheostat in the toolbox...just want to use all of this stuff you have coerced me to find.

I have always considered the voltage regulator sort of a "black box". Ironically it is a black colored box. Now I have a little more knowledge of the internal workings of this system. I wish the technical bulletin would state "open either the voltage or current points to cycle generator" versus the long winded method they provided. Thanks for the help.

Had some friends come around yesterday and they all needed to ride in the 42 truck. The VR/generator are working fine.

Gotta keep it real Carl.

Paul

It's good to hear somebody is willing to learn the skills to work on these older systems! It's fun to put an oscilloscope on a set of vibrating regulator points and actually watch what a complex waveform is being created to produce that supposedly "steady" voltage at the battery posts! That's why a digital meter sometimes reads random gibberish instead of a good readout. Now, if someone would just take the time to understand a Fairbanks-Morse magneto! Those things are really a can of worms!
Jerry