6V generator performance

I suspect it is fast approaching time for a generator rebuild on my WD45. I was trying to check output yesterday with my voltmeter. Whether I had the tractor running or not, the max I got on the voltmeter was right at 6 volts. Checking both at the battery and generator cutout -/+ terminals with the tractor NOT running gave me 6 volts. That made sense to me. However, I was expecting slightly more than 6 volts at the generator cutout -/+ terminals with the engine running. Even tried all positions with the 3 position switch and nothing changed volt reading. New ammeter in tractor dash does register about 5 amp draw with headlights on. Am I checking this right and need to consider generator rebuild soon? What is the best way to check generator output and make sure that I'm not just reading battery voltage in the system at that time? Thanks.

Checking your ammeter via headlight draw was good first step. Next check battery voltage with engine stopped, then running. With switch on high charge it should be significantly higher no matter the state of charge. Cant remember the exact voltage but you should be reading on the order of 7.5 -8 volts on high charge with a battery in decent shape and state of charge. Next step is to loosen the generator belt and get a helper to watch the ammeter. Then remove the cover from the cut out relay. With the engine stopped momentarily close the contacts with your finger. Dont hold the points closed!  tap them and release. Three things going on with this test. A- the ammeter should show a large discharge. B- The generator should turn or "motor" C- the generator is now polarized. If all this checks out start engine and check voltage once more and report your findings. Gets pretty long winded to explain the entire process out front


Edited by Butch(OH) - 16 Sep 2016 at 6:37am

7.1 volts is the full charge voltage for a 3 cell battery. The three brush generator with just a cutout can push the voltage higher and remove water from the electrolyte.

Grounding the F terminal will check the generator, but that should be done by the light switch if its good and wired right. A separate check with a wire will help check the switch. The switches fail often enough that a couple vendors on this site stock or rebuild them. If the voltage doesn't go up at the generator A terminal with the field terminal grounded, then the generator needs work. If the A terminal voltage goes up more without the battery voltage rising, the cutout needs to be replaced.

The generator voltage will be higher at load speed than at idle, the generator tends to not charge at slow idle engine speed.

Gerald J.

[QUOTE=Hubert (Ga)engine7]First off - polarize the generator then check it. 

I also have other related questions that I just now thought of. OK, the 3 position switch should be 1)off; 2)low charge; 3)high charge with lights-correct?? OR is it 1)low charge; 2)high charge; 3)lights only?? Should I be seeing a low charge above 6 volts(say 7??) with the switch at #2 position and then higher(say 8??) with the switch at #3 position?? I'll have to check again since the tests I did before were at idle.

Yesterday my CA wasn't charging so ran a wire from screw that attaches light switch in box to the ground terminal (+) on battery, cured problem.

Couple of things...at idle the tests wont work. Wont charge at that speed. Also the switch positions are low , high with lights on, high with lights off. With lights on shouldnt be any discharge at least. High output should run the lights at least.

The three position switch needs to be grounded, so where it attaches in the instrument box it should be clean and free of rust. I always suggest to our customer's to run an auxilary ground wire from the mounting screw that holds the switch in the panel to the Pos ground post of the Battery or where the ground goes to the chassis. This ensures a good ground for the 3 pos. switch. The three position switch works as follows:
All the way in- charging will run through the resistor at around 3 amps to the Battery
Second Position-  Lights, resistor by-pass full field from Gennie to Battery 5-8 amps
Third Position- NO Lights-  still a full field charge to the Battery.
Remember-  depending on the position of the 3rd brush in the Gennie will actually determine the amount of amperage the output would be at the Battery.  A nice and simple upgrade to the 6V system would be to disconnect the 3 pos. switch and add a Voltage Regulator. Just use the Headlight/Charging switch for Headlights only. Your choice there.....   HTH
Steve@B&B

Adding a voltage regulator is definitely a step forward for the electrical system, and will significantly increase battery life by controlling the charging voltage so the battery is fully charged but never overcharged.

Gerald J.

Yes there have been 6 volt regulators since the 40s at least. The light switch can be simplified or left as is. Either will work. For ignition I prefer the simplicity of the points and condenser compared to the dozens of parts in the electronic ignition, though some users of electronic ignition find it works better. I haven't a tractor with electronic ignition though I guess my last 4 or 5 vehicles came from the factory with it.

Gerald J.

Gary Burnett wrote: I'll be the Heretic here and ask why does anyone mess around with a 6 Volt system especially on a WD45 anymore when you can solve all your charging problems with a $60 one wire 12V alternator? I was raised on a WD45 with 6V was always a pain in the rear.

Everyone has their preferences. The 6V system is about as simple as the Tractor, and is reliable providing the system is looked after frequently. But, it does have its limits with additional accessories, and that's where the line is drawn. I've found two work lamps along with all the other regular stuff that's on a mid 40's Tractor ie-headlights, taillight Battery Ignition, etc. is about all you want to put on that 6V system when everything is on. The two most important items that need to be in tip top shape is the Starter motor, and the Gennie. A tired Starter will definitely drag on 6V's big time, and in most cases is the starting issue. Some throw an 8V Battery at it as a bandaide, and it may work for a while, but still hasn't fixed the problem which is the dragging starter motor. Basically, you just gave yourself another problem on how to charge up the 8V Battery if you don't have a charger with the 8V mode. Once rebuilt the proper way, the Starter issues are pretty much eliminated. An excellent way to keep those 6V Batteries in good shape is to invest in a Battery Tender to keep the electrolyte active in the Battery for top performance when the Tractor is not in use. On the charging end of the 6V system, the addition of a Voltage Regulator is a great upgrade which also helps in keeping Battery life while the Tractor is in use. One gauge or larger cables are the norm for the 6V system, and again, as long as some maintenance is done keeping them clean will result in good operation. Tractors that live outside, have to put up with Mother Nature's torture all year round. That actually initiates the problems with humidity, rain, etc. even if the Tractor is tarped. I can attest to that being my Model B is 6V and sits outside tarped. She kicks right over though when I need her to do some tasks but not without some maintenance on occasions.

The 12V system is a great advantage when you need those extra lights and accessories, especially if you still farm and need that extra lighting working into the evening hours. And yes, there are advantages when jump starting is needed, or having more reserve in the Battery just in case a charging issue occurs to get the Tractor back to the barn if its equipped with a Battery ignition. With todays solid state Alternators, they can get the job done quite quickly supplying power where its needed on the Tractor. Its really tough to beat one of those over the old "DN" series external regulated units of the past. With all the cool stuff out there on the market, its pretty easy to make a very reliable 12V Tractor providing you don't have a problem with upgrades that aren't OEM. I'd say our customer's started out to be around 50/50 with the 6V crowd and 12V crowd when we first started offering wiring systems for the AC Tractors. But, after 16 years of building these systems, its shifted more toward 70/30 in favor of the 12V version. As I've always said, its up to the individual what they decide they want to do, and whether they want to stay OEM or move on. It looks like a lot are moving on....
Steve@B&B

Many a 6 volt system was designed for working the tractor all day on one start and so the generator power was low allowing it to take nearly all day to charge from that one start. Also JD 12 and 24 volt systems into the early 70s. Taking low shaft horsepower at the generator improved tractor performance and fuel economy, especially with a low horsepower tractor.

Before about 1955 the SAE standard for vehicular and farm tractor electric systems allowed 6, 12, or 24 volts with either polarity. Long about 1955 the standard was changed to take out 6 volts. 12 volts takes less than half the copper in the wiring for the same power to a load which is a manufacturing cost saving, and also is lighter weight slightly improving the road economy of cars and trucks. The lower the voltage the more critical is voltage drop, and wire selection is more based on tolerable voltage drop than in wire heating, and voltage drop for a given current in a wire is a bigger portion of the supply voltage at 6 volts than at 12 volts.

Long about 1960 the standard was revised to make 24 volts very limited and to prohibit positive ground. Tractor and vehicle makers didn't necessarily change their designs the years the standard changed.

In my experience  the battery posts and connectors on a 6 volt system need to be cleaned twice a year whether used occasionally or daily. The fumes from the battery leaking around the posts corrodes the connections. 12 volt systems seem to need that battery post cleaning every couple years unless the battery posts are sealed better than they used to be. With the low demand for 6 volt batteries, few stores carry them and fewer have fresh batteries or keep them charged so often a "new" 6 volt battery is a bad buy from sitting on a shelf for too long. Then that need for post cleaning is because there is little tolerance for voltage drop in connections and wiring at 6 volts.

However with a good 6 volt battery and a good starter 6 volt systems have run for half a century or longer. 12 volts just is not original on vintage tractors but is less confusing for the electrical illiterate that might try to jump a 6 volt system with 12 volts and the wrong polarity. That can cause serious damage and injuries when the abused batteries explode spraying parts and battery acid.

The 10SI and more modern alternators with internal regulator hold the voltage more precisely than external magnetic regulators and so treat the battery better. There is no fundamental reason they couldn't be built for 6 volts positive ground but even 12 volts positive ground is uncommon, though mentioned in the Delco alternator book. I doubt any common auto parts store can find one for positive ground or 6 volts. I have a large Leece-Neville that was built for either polarity. Early Leece-Nevile used an external rectifier so were easily connected for positive ground.

When I had a 6 volt starter rebuilt about 40 years ago I had to insist the shop put in new bushings because I thought it was dragging but they didn't commonly worry about them. With a cleaned up commutator, new bushings, and a new brushes it did crank that engine good.

Gerald J.