Help! - 1955 Thunderbird 6V (ground-neg.) generator not charging
 

The generator on my 55 T-bird is not charging (6V ground-negative). If I disconnect the battery while the engine is running, the engine dies. My batt in the morning (fresh off of the charger) reads 6.6 volts. With the engine running, it reads 6.3-6.4 volts. I have polarized the generator properly, cleaned the voltage regulator contacts, and made sure all the connections are tight. Possible wire breaks (original wiring)? Bad generator (gen. was rebuilt only 3K miles ago)? Bad voltage regulator? Blown voltage regulator resistor (aren't they on the underside of the regulator)? What is the proper method for testing the generator (at the generator posts) with the engine running? Thanks.

Re: Help! - 1955 Thunderbird 6V (ground-neg.) generator not charging
 

I'd take the gen. to a shop that works on them and have them do a run test. Al

Re: Help! - 1955 Thunderbird 6V (ground-neg.) generator not charging
 

Your reading of battery voltage while running is low. could be th generator is not charging enough, or the voltage regulator is bad, or it might be that the regulator needs to be adjusted

Re: Help! - 1955 Thunderbird 6V (ground-neg.) generator not charging
 

do not overlook the battery have it load tested a volt meter will not show the true condition

Re: Help! - 1955 Thunderbird 6V (ground-neg.) generator not charging
 

Woohoo! I got it working! It was the voltage regulator -- the inner most and outer most coils needed adjusting. The outer coil was not closing at all and the inner most needed adjustment for greater output. Thanks for your help guys. And now a more specific question, What voltage do these things like to run at fully warmed up at idle at 75 degrees outside? I have it outputting right now at about 6.9-7.1 volts at idle. Needs a bit more juice? I just don't want to overdo it. The car actually runs much better now that it is producing enough spark on generator power instead of just batt. power.

Re: Help! - 1955 Thunderbird 6V (ground-neg.) generator not charging
 

I don't have a 6 volt car but 7 volts sounds good to me. Possibly up to 7.25 ???
You don't want the charging voltage too high or the battery will get too warm and tend to boil the water out of it a little faster.
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Re: Help! - 1955 Thunderbird 6V (ground-neg.) generator not charging
 

I think you have it about right.

Re: Help! - 1955 Thunderbird 6V (ground-neg.) generator not charging
 

All my 6 volts are Pos. Ground. Not Neg Ground

Re: Help! - 1955 Thunderbird 6V (ground-neg.) generator not charging
 

You'll know you've set it too high with the lights on (at night) and you go on the highway and the dash bulbs start glowing brighter and brighter as you approach 70 mph - its absolutely maddening! lol I think that's the biggest downside of a generator - faster you go, the more voltage it generates. The VR helps set the upper and lower bounds.

Took me awhile to hit that sweet spot. If memory serves I think I am somewhere in the 7-8 volt range. For 12 volt batteries I think you generally want to hit ~13.4 volts while charging so i applied that same thinking to my car and probably targeted ~7.4 volts.

Re: Help! - 1955 Thunderbird 6V (ground-neg.) generator not charging
 

Generators actually lose efficiency at higher rpm due to brush float. Most old DC automotive generators have a pulley diameter that will keep them within the sweet spot for daily operation but extremes will cause a loss of efficiency.

An electric light bulb that is designed for automotive use will sometimes dim at low rpms due to the lower output but will pick back up to normal as soon as the rpm gets back up to driving speeds. The generator control unit should keep the voltage the same at all rpms withing the normal range of operation. Lights should not get brighter at high rpm. If anything, they can start to dim with extreme rpm. A generator is not like an alternator in that respect. Voltage is usually from 7.0 to 7.4 volts in normal operation but can go as high as 7.6 after everything warms up. If it gets too high then the bulbs will burn out.

Most folks run the 6-volt systems with positive ground. Since this is the normal direction of current flow, it makes the system a tad bit more efficient. It will work on negative ground but it has to be re-polarized for that so that the residual magnetism in the generator will have the polar balance that it should have to generate a proper current flow. The caution of this is if a person has the old voltage step up vibrator replaced in the radio by a newer solid state unit. A change in polarity will kill a solid state unit. 6-volt systems use larger gauge wiring to keep the resistance in the system low. High resistance due to poor grounds or wiring will take its toll.

It's good to know what the three poles are for before adjusting things. The one marked "BAT" is the cutout relay. It's what brings the generator on line after the engine is started. If it sticks closed, it can burn the generator up after shut down due to it trying to reverse motor off the battery. The one marked ARM for armature is the current limiter. It has to be adjusted with an amp meter and an adjustable load so clean it but don't play with it too much unless you have the right equipment to check it. The one marked FLD or field is the voltage regulator. This can be adjusted with a volt meter but it has to be an accurate one. The range of voltage on a 6-volt system is narrow so take care with it. It basically buzzes all the time by rapidly opening and closing the points to maintain voltage. The points have to be clean and in good condition for steady voltage readings. It is sensitive so having the amp meter with the adjustable load and the accurate volt meter is a very good idea.