While going over the electrical system of the truck I noticed that at idle I am only producing 6.20 Volts, which seems very little. I imagined that at least I should be generating 7.2 or 7.5 volts to keep the battery up... With the parking lights on the value drops to 5.89 Volts or so, with the headlights on I don't register anything...;(
Now my truck does not have a voltage regulator which should not affect how much voltage the generator should produce to start with... My guess is that the brushes must be almost worn out and it is time to rebuild/clean... Any other thoughts? Another question, how tough is to add a voltage regulator to the system, and will I see a greater improvement in terms of battery charging and handling a load...
With no regulator, the only thing to control the voltage is the load. That would include the battery and lights, vs the rpm of the generator. It will never produce much at idle, nothing compared to an alternator with an electronic regulator.
The question would be how much voltage does it produce with the engine above 1500 rpm and at maximum cruise speed. These systems really dependent on the battery to moderate the system. The battery provides power at low engine speeds and absorbs the excess at high speeds to prevent over voltage. The gen is likely only rated for about 20 amps which will not hurt the battery as long as it is not at that level 24/7 like a battery charger might do.
If the gen puts out 7 to 7.5 at high speed, that's about all you can expect. An inspection of the brushes and commutator will tell you if any work is in order.
I don't know of any way to retrofit a regulator. You could replace the gen with a regulator controlled model but it will also not put out much at idle. Low speed output is built in, the regulator only stops over-voltage at high speed.
The physics of a generator or alternator depend on speed for output, an alternator runs at about 3 times engine speed (and can normally run safely at 10 to 12,000 rpm) as it does not have a commutator which can be destroyed by speed. Generators typically are belted for about 1 to 1.5 times engine speed on a slower engine.
Make sure your pulleys are not worn and the belt is in good condition.
Mac :{)
1962 K10 short step side, much modified for rally 1969 T50 fire truck, almost nos, needs a few things
My system has a cutout relay only... I need to find out the original GM number since I have an aftermarket unit and I don't know how good it is. If I am not mistaken, I believe that between the relay and the light switch the voltage is controlled... I have not tested the generator output at maximum cruise speed, which is 2,500 rpm for me (35 MPH)... I do know that the generator is a 23 amp unit. I popped the rear band off the other day and the brushes are about 50% and the armature was fairly clean... Truthfully, I just don't know enough about these systems without a voltage regulator to determine if it is in tip top shape...
The cutout disconnects the gen field winding from the battery when the voltage is too low to charge, mainly with the engine off. This prevents the gen from drawing current from the battery and running it down.
A voltage regulator normally has a cutout relay, a voltage regulator, and a current regulator in it, thus it has 3 "relays" if you pull the cover. The cutout does the same thing, the current regulator passes the entire output of the gen to the battery, if the current is too high, it opens its contacts and disconnects the battery. Of course at that point the current goes to zero so the contacts close again, resulting in buzzing of the contacts and limiting the current output to protect the gen. The voltage regulator senses the output voltage and buzzes when the voltage gets to high limiting the field current and thus the output voltage.
Dan
Mac :{)
1962 K10 short step side, much modified for rally 1969 T50 fire truck, almost nos, needs a few things
Does your generator have three brushes? A third brush generator was used by Delco Remy through 1938 or 1939 on Chevrolet cars but my books don't specify for trucks. The third brush was used to control current to the field windings and regulate current output at higher engine speeds. It took advantage of the inherent distortion of the magnetic field due to rotation. The maximum current level may be increased by moving the third brush in the direction the armature normally rotates. The faster the rotation, the more distortion so the brush was moved to a position to pick off higher current for the field windings at the RPM the generator usually turned. On a truck where the engine is running at higher RPM more of the time the third brush position would be critical to avoid overcharging the battery and shorten lightbulb life. Of course if it's set too far the other way the maximum current output might not keep up with the lights, heater, etc. Also setting it too high could overheat the generator to the point where the solder melts out of the commutator and the windings come undone. I had a Lucas generator on which this happened. Hope this helps.
Generator number Output @RPM Field Current @ 6V 1937-38=948-R * 20A 3400 2.3-2.6A 1938-39 = 1100004 28A 3600 2.3-2.6A 1940-48=1102667 35A 2400 1.75-1.9A *Third brush model All rotate clockwise All except third brush model voltage set to =7.4V Current and voltage regulator air gap =0.075" Cutout relay air gap= 0.020
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
No generator is designed to charge the battery at idle speed. Your 6-something volts at idle is perfectly normal and there's nothing you can do to improve it other than installing a very small pulley on the generator to spin it faster at idle. Then it will try to throw the windings out of the armature at highway speed due to overspeeding of the armature.
The third brush is only used to control the maximum charging voltage against a fully-charged battery. It has a sliding mounting point that allows the brush to be moved toward or away from one of the fixed brushes. This adjustment MUST be done when running at fast idle, and against a fully-charged battery. Most of the third-brush systems I've worked with had to be run at the maximum output to keep the battery charged properly. Some of the newer 3-brush systems have a circuit that puts the generator into maximum output when the headlights are turned on. Good luck!
The cutout relay interrupts the battery-to-armature circuit, not the fields. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Thank you for providing the part number for the breaker, I will see if I can find one at a reasonable price... As for the generator having 3 brushes, I have no idea... Will it be visible by removing the band? If I understand Jerry correctly, the Delco 948-R may or may not have a third brush? The only clear thing is that if it has a third brush, the adjustment must be done at fast idle with a fully charged battery..
It seems that whether at idle or 2000 rpm, I don't see more than 6.13 volts out of it... I just started the truck after 2 days and following a short drive the battery is at 6.13 volts at rest...A fully charged battery should probably be in the 6.30 to 6.50 volts I imagine?
Another curiosity is that the needle on the gauge never indicates a charge (or it is so slight it is not visible) but seems to indicate a discharge very well, especially with the headlights on... I wish I could adjust it to give at least 6.50 or 6.75 volts... The odd thing is that without using any lights the truck starts right up every time. With a system barely charging over 6 volts, it seems that it would be an issue over time... Only after a long run on the 4th of July parade (5 mph) while using the parking lights, I had a problem where the truck would not crank even after a 15 minute run at high speed (35 mph!)... Luckily, I had a slight slope and I was able to push the beast and get it started to get home. After that I charged the battery overnight and have not had any problems even using the headlights on two occasions at night for 15 minutes each time; yet I still have to adjust/resolve the charging system...It is clear that it is not where it should be, just barely functioning...
The 948-R generator does have a third brush, however, the 1937 shop manual states..."NOTE: DO NOT ADJUST THE THIRD BRUSH ON THIS TYPE GENERATOR" (This is about the only time I have seen capital letters in this manual). It goes on to say that the brush is set at the factory at the maximum safe output and this setting should never be disturbed. There are 3 resistance sizes available for the field resistor that goes on the back of the light switch. Normal is 1 ohm and you can use 3/4 ohm if the battery does not stay charged or the 1 1/2 ohm if the battery becomes overcharged.
Thank you very much for your help replying... Very important and useful information here! My next challenge would be to find a 3/4 ohm resistor for the light switch... Brillman carries one which must be the standard one...
Do you know by any chance the original Delco/GM part numbers for the other 2 options? I believe I only have the part number for the standard one on a different post...
You linked a 75.0 ohm resistor but they also have the proper 0.75 ohm resistor. One could solder the ends to ring connectors, and yes, even if you looked under the dash it would be hard to see tucked behind the rotary light switch. Kent
Last edited by Lightholder's Dad; 08/05/20198:14 PM.
I've always thought the three brush setup was a Rube Goldberg design and really had difficulty keeping the battery up in the winter time. I had a 39 Master 85. If you're not totally wedded to originality you could go to the 1940 setup that was used through 48, they look almost the same but you would have a regulator on the firewall unless you hid it somewhere else. The later design required less field current and by '49 output was up to 45 Amps at 2400RPM as compared to 20A at 3400RPM.
I used to pull a trailer with my 51 and had set the current limit up to keep up with the trailer lights. This was more than the Delco generator could handle and the solder melted out of the commutator. Close proximity to the hot exhaust manifold probably didn't help either on long pulls over the mountain passes. So I put on a 45A Autolite generator off some old Chrysler with the same Delco regulator. I only removed the Autolite generator when I converted to 12V and an alternator about 25 years later. The battery always stayed charged even with a larger pulley as the Chrysler generator output was rated at 1000 RPM instead of 2400.
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
Thank you very much for the part numbers, unfortunately I was not able to come up with anything even with a search through www.partsvoice.com. As for the other option for resistor (25J75RE - Through Hole Resistor, 75 ohm, 20 Series) I would certainly consider it regardless of originality if it did the job... Thank you for the lead.
Lastly, something else found through a Plymouth forum is a gentleman (James Peterson) that produces an electronic voltage regulator. Best part is that it does not alter the appearance of original unit...
As for the other option pointed out by 1 Ton Tommy, I am not against switching to a system that will incorporate an external voltage regulator since it will be period correct... The questions are:
1- Will I have to replace the headlamp switch 2- Can I go to a 35 or 45 amp system 3- Depending which way is best, I have to source out a generator and wire it to a truck that did not come with a voltage regulator, only a cutout relay... I also would not be able to use the mechanically driven tachometer currently installed (believe there since the 40's) unless the current backplate would ft the new generator... Ahhhh, it gets complicated!
Well, yes, the decimal point does matter, but like Lightholder's Dad pointed out, they have the correct one, as would many other suppliers. Thanks for getting that straightened out.
If you have the choice, the 5 watt will be better regarding the heat generated. It will be physically larger, will it fit? It's hard to say what the current through the resistor would be, that and the voltage drop multiplied would give you the minimum wattage needed to make the resistor survive.
Does the gen with the tach output have a special shaft too?
Mac :{)
1962 K10 short step side, much modified for rally 1969 T50 fire truck, almost nos, needs a few things
You can also use two 1.5 Ohm resistors connected in parallel to increase the wattage capacity while still maintaining the correct resistance value. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
The 948-R generator with a provision for a tachometer is cable driven and just has a different back plate for that purpose...The tachometer is a SW unit that I have never seen before... In spite of that I am still considering another generator that would have been an option for this year truck, or something similar easily accessible...
