Linus Tremaine

Generator voltage output

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All,

I have a 1930 car with a starter/generator and it keeps popping all the light bulbs. I replaced them all and they lasted about an hour.  The unit was putting out about 20 amps and has an adjustment for amp output. I moved it down to around 10-12 which is about where the manual suggests I put it. I am still making 8.8 volts. What determines the output voltage of a generator and can I adjust it?

Thanks.

Edited by Linus Tremaine (see edit history)

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As far as I know there is no way of adjusting the Voltage this is set by the builder of the gen starter. Only suggestion I can add,  do you use a Gel battery or the old lead/acid one.

Should you use a gel one try the old one The post of the third brush gen addresses this as well. 

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I did this too while rewiring the car ! I had left a wire disconnected coming from the battery. Look for an open connection between the cutout and the battery. The generator thinks the battery is dead and the generator is pumping all it can to charge it. It blows all the lamps when you switch them on. I wondered what that flash was, so I tried the other switch positions. That blew out ALL the lamps. 

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I do have an optima red top in the car but my friend runs the same cars with optimas and has no trouble. I may just be unlucky. I have a lead acid battery, I will switch it out.   I doubt that I have any wires burned that are disconnected as its an original car and I have not messed with it, this problem just sort of started suddenly. Ill look though.

 

 

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Linus, I cannot be sure but I have  two cars of about the same age, one runs excellent without trouble and the other burns coils like second to none with the optima battery. No trouble any more after the battery switch on the coil burning car. The other one still uses the optima without issues of any kind. Perhaps the generator winding or the field have tolerances that causes these differences,  I do not know. It's worth a try

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You said that you are getting 8.8 volts on the generator output.   You need to dial down the voltage to about 7.4 volts max output.  The high voltage is why you are burning out the bulbs.   Current is what the bulb (device) uses to operate

Has the car ever had a higher voltage system installed?  If so you might need to go back to the correct VOLTAGE REGULATOR to keep from burning out the bulbs.  Also, if you put in a 6 volt battery and charge it at 8.8 volts you will overcharge the battery. 

My gut feeling is that you probably have a bad voltage regulator.

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16 minutes ago, Larry Schramm said:

You said that you are getting 8.8 volts on the generator output.   You need to dial down the voltage to about 7.4 volts max output.  The high voltage is why you are burning out the bulbs.   Current is what the bulb (device) uses to operate

Has the car ever had a higher voltage system installed?  If so you might need to go back to the correct VOLTAGE REGULATOR to keep from burning out the bulbs.  Also, if you put in a 6 volt battery and charge it at 8.8 volts you will overcharge the battery. 

My gut feeling is that you probably have a bad voltage regulator.

 His car does not use a regulator. Regulators were not invented yet. :)

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In most early systems, the battery itself is the voltage regulator. I know my '29 Cadillac once had one of the battery cables come loose and the voltage spiked and blew the brake lights instantly. Double check the voltage on your battery and perhaps try a different battery. I've never seen a 6V battery put out 8.8V, but that doesn't mean it can't happen or somehow you got an 8V battery or a defective 12V battery from China or something.

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Hey neighbor. I wonder if the generator was rewound for 12V operation at some point in its past. If so, it might not be possible to adjust the charge rate low enough. I'd try to set it up such that the ammeter reads just above zero while driving with the headlights on.

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14 hours ago, Linus Tremaine said:

All,

I have a 1930 car with a starter/generator and it keeps popping all the light bulbs. I replaced them all and they lasted about an hour.  The unit was putting out about 20 amps and has an adjustment for amp output. I moved it down to around 10-12 which is about where the manual suggests I put it. I am still making 8.8 volts. What determines the output voltage of a generator and can I adjust it?

Thanks.

The regulator action caused by the vibrating contacts is the magic of the mechanical starter generator regulator and because brushes rub against things that spin these things get dirty, so cleaning and inspecting for wear after 80+ years might not be too bad an idea. Can't tell you what exactly to look for, or if voltage is internally adjustable, never been inside one that's older than I am. Can tell you that a couple good raps with a rubber mallett can free up a stuck switch and that might just be all you need.

A simple explanation of how this works is after the engine is started and the voltage from the battery/switch/solenoid is removed from the terminal that feeds the drive winding the field winding is grounded by the internal mechanical / centrifugal / rotary switch which is the voltage regulator. As the armature turns, current in this spinning coil creates the magnetic field in the generate pole piece. When the output reaches design voltage the regulator connects the armature to the battery and the current flows to the battery charging it. When the voltage gets to about a volt above design voltage the magnetic / mechanical / centrifugal / rotary switch regulator starts vibrating breaking the ground on the field coil which controls the amount of voltage induced in the armature.

 

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I have not run into an over voltage problem. What may not known by many is the difficulty to yank the starter-generator out of a model L Lincoln. If it was easy you would have done it. So lets see if we can diagnose this with the unit still in the car.

  1. Have you done the obvious like check the brushes and that and that the brush holders are moving freely and allowing the brush to apply constant pressure to the armature? Especially the ground brush.

  2. Have you cleaned the armature copper segments with a brake clean? Use a tooth pick to clean between the segments Small amounts of dirt getting between the contact (segments) can cause problems.

  3. As you may know there is no regulator, just the circuit breaker box on the inside of the firewall.  

  4. As far as I know there is no adjustment to adjust specificly the voltage output, just the current by moving the 3rd brush. The voltage is a fixed value based on the number of windings, how many turns are on each number in the field coils, and magnets.

  5. Check the 3rd brush carefully and the fine wire on it that acts like a thermal circuit breaker. Maybe something unexpected happened to that assembly.

  6. Is the armature surface smooth? Maybe the brushes are bouncing up and down on the armature and the short time the brush is off the armature may cause voltage spikes. You measured 8.8 volts, but I suspect that is an average value and does not tell us if small 12-15 volt spikes are present.

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There is merit in every suggestion and no question is foolish. If I knew I would not ask. I learned something from every post. When I bought my 1928 Dodge Senior and got it started I was elated. The ammeter showed a constant 20 amps . The manual says 15 amps. I ran the engine a couple of times and the generator went dead. A new fuse did not help. On dismantling the generator I discovered the output brush. was grounding at the place of anchor by a small screw. The insulating washer had deteriorated causing the generator to overcharge, burning the armature and field coil to a crisp . The battery was good and was 8 volts., could not take more volts. Advance Electric Rebuilders did a good job. Now the amperage is 15 , right where  it should be. Bench testing a generator or alternator ? Just ground the field and the amp will shoot right up. Do it for prolong periods and you may fry the field.

 

SO FELLOW MEMBERS, DO NOT CRUCIFY ME, BECAUSE I AM SUBJECT TO CORRETION. I AM ONLY STATING MY EXPERIENCE.

Cheers and have a nice day.     

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Thanks all. Its true, I do not have a voltage regulator. As Matt suggests, the battery is in some capacity the "regulator" in this circuit. I went out and bought a lead acid 6 volt battery and shoot dang the thing is now putting out 7.6 volts. As some of you also suggested, I did take the cover off and clean the brushes and commutator.  I drove the car around for an hour with the lights on and they are all still working. I turned the amp output adjustment back up a little. The factory manual suggests 10-14. I think I have it set so that it peaks at 15 amps. So, more field tests (running modern cars off the road) are required. 

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Sounds like you're on the right track. I wouldn't adjust the amperage output too high, because it will put that out pretty much constantly. I have my '29 Cadillac adjusted to the point where the headlights and the generator pretty much fight to a standstill, which is about 10-12 amps. Remember that too much amperage will boil the battery, which is why, on longer drives, I will turn on the headlights for a while to remove the load on the battery. If you don't do any night driving, you could turn it down even more to help. But it sounds like the battery was your problem, because 7.6 volts is about right for a 6 volt system when the engine is running.

 

Good news!

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Glad you tried it and it solved your problem as suggested. The way the optima gel is build, tends to invite  the high voltage, my reading turned out to be 11.5 to 12 V on the coil with the optima.

it took me a lot longer to find out, because after restoration i had the lead acid battery in the car and measured an set the gen reading with this battery. without a second thought I changed it with an optima gel.

Took me  awhile to solve the several problems that surfaced, running bad revving the engine , running bad with the lights on , not willing to go above 45 mile and so on. It ís a most unknown problem,

most due to the fact I assume, most cars have a regulator run fine with the gel and not all that don't have one run bad with an optima. At least we came out more knowledgeable then we went in this question 

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8 hours ago, Matt Harwood said:

Sounds like you're on the right track. I wouldn't adjust the amperage output too high, because it will put that out pretty much constantly. I have my '29 Cadillac adjusted to the point where the headlights and the generator pretty much fight to a standstill, which is about 10-12 amps. Remember that too much amperage will boil the battery, which is why, on longer drives, I will turn on the headlights for a while to remove the load on the battery. If you don't do any night driving, you could turn it down even more to help. But it sounds like the battery was your problem, because 7.6 volts is about right for a 6 volt system when the engine is running.

 

Good news!

I agree on what you advise on lower settings, and also how you run with lights on very long trips.  With an unregulated system set to owners manual amps output, the car that never is driven with lights, is cooking the battery.  Many people claim 6 v batteries don't have a long life even with a true voltage regulator on a newer car, so going to minimal amps is very good advice.

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Many years ago before owning any old cars, my dad told me about the need to run with the headlights on to keep the old unregulated generators from boiling the water out of the  battery.

Also about 3rd brush generator balancing output to draw.

That served me well when i did get into the hobby years later.

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Matt basically hit the nail on the head with his comment. This is the fine line that I am riding now - undercharging with the lights on or over charging with the lights off. I tend to run with the lights on usually because it keeps the amp output on the gauge down in the 10-12 area. I have two of these same cars and that has been my habit on both. But, there is nothing worse than driving for two hours with your lights on only to find that the battery has been discharging the whole time and that it wont start again.

 

So, usually I drive with the lights on quite a bit, but not all the time- unless its dark! Also, sometimes I run the car in the driveway with the lights off before parking it to just top up the battery if is is low. 

 

 

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On ‎3‎/‎22‎/‎2016 at 7:46 AM, Friartuck said:

I have not run into an over voltage problem. What may not known by many is the difficulty to yank the starter-generator out of a model L Lincoln. If it was easy you would have done it. So lets see if we can diagnose this with the unit still in the car.

 

In 1971 Ford decided to celebrate the Lincoln 50th anniversary and my dad covered the show floor with every old Lincoln book and picture he could find from 1921 on up. When the year was over my brothers and I got to divvy up the stuff.  I didn’t have anything for the 1930 L body, but the 1929 motor and chasse drawings gave me a good idea of what kind of a job it would be to pull this thing and the 1927 instructions for turning the lights on and off gave me a pretty good chuckle.

After reading how installing a lead acid battery corrected this problem and having taught Electrical Engineering Technology, I was curious and set myself to work investigating this phenomenon.  After hours of study I have determined that the gel type battery will not work with these three brush generators and yet, by reports of others, sometimes they do.

In the 30’s a scientist named Antoine Magnan, mathematically proved that the bumble bee was aerodynamically incapable of flight, but that didn’t stop the bumble bee from flying and I am dumbfounded by the apparent battery related voltage regulation of this starter generator. It works because it works.

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I believe Linus said in another post he drives his car a lot. Could this be a case where the gel battery got over charged? Perhaps the battery in this case failed somehow.

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My 1970 Yamaha 90cc enduro bike will also over voltage when the battery is disconnected.  It's a 6v system too.

 

Terry

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Didn’t give any thought to the 1970 Yamaha voltage spike, but I was absolutely dumbfounded to explain why a gel optima will work in one of these 1930 cars and not in another, when by all rights it should fry in all of them.

A gel battery requires regulated voltage.  A gel battery does not work like a lead acid battery. A lead acid battery is not a capacitor but it does have a capacitive affect on a circuit, it’s also not a resistor, but it does add resistance to a circuit. This is a car that came from the factory with a light switch on the dash and instructions to adjust the third brush every time you used the switch to make the system work.  I shook my head at the incongruity of this until I realized when this car was built that elevators had operators and not even automatic washing machines were fully automatic.  The overlooked human factor was the mathematical impossibility of this voltage regulation operation and constant operator interaction, mechanical condition and how the car is driven is the best explanation for why a gel battery will work in one of these cars and fry in another.  

Edited by Digger914 (see edit history)

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I run an Optima in my 1929 Cadillac with no problems, except for the aforementioned time when the cable slipped off (but that was on a lead acid battery anyway). I've been running it for nearly 5 years without issues. No burned-out bulbs, some nighttime driving, always enough juice to start. I'm a fan of Optimas but had no idea that they wouldn't/shouldn't work in a system without a voltage regulator. I do not mess with the third brush, just have it set to about 10 amps which, as I said, allows me to run the headlights at night and have about a 0 charge. I will note that the overdrive solenoid will not fire with the headlights on; I need to turn off the headlights, activate the overdrive, then turn the lights back on. But that's a current issue, not a voltage issue.

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