12v Generator test question

[rrlund]

Question then background. Where would I hook jumper wires to test a 12v tractor generator with a working gauge from a parts tractor? Worst part is, it's a British built David Brown disguised as an Oliver. The terminals on the generator are D and F. Dynamo and Field I assume instead of Generator and Field?

I was going to take the hood off and just jump to the back of the existing gauge, but when I gotit off, the gas tank is in the way. The gauge that's on the tractor now doesn't show charge or discharge, just battery condition with brown and green on the stripe across it with numbers from 8 to 14 or some such thing. Even after a full charge with the battery charger, it's sitting near the bottom at about 8.

The tractor sat all winter with a battery that was new a year ago. It started right up this spring. We took it to town for a show Memorial Weekend and it was fine. I went to start it Sunday and the battery was totally dead. I jumped it and when I took the cables off, it kept running, so I assume it was running off the generator. However, after charging the battery Sunday, it started right up Monday morning. I put the charger back on it just to be sure it was topped off. I loaded it on the trailer, took it to a parade and drove it for about two hours. When I got back to the trailer, I had left the ramps down, so I just backed it on and shut it off. When we got home, the battery was too weak to start it and we had to start it by rolling it down the ramps, leading me to believe the generator isn't working after all.

This morning, it rolled about like it did Monday on the trailer. I jumped it again, it ran fine, but when I shut it off in the shop, it was dead as a door nail. The regulator is up under the dash covered up by the gas tank too. I just don't want to pull that tank out without testing that generator first. I need to troubleshoot everything to find out of there's a short drawing the battery down, or if the regulator is sticking or just what's going on. I have a multi meter, but I have no idea on earth how to use it. Everything on there might as well be written in Arabic.

 

[JMOR]

(quoted from post at 11:15:48 07/06/22) Question then background. Where would I hook jumper wires to test a 12v tractor generator with a working gauge from a parts tractor? Worst part is, it's a British built David Brown disguised as an Oliver. The terminals on the generator are D and F. Dynamo and Field I assume instead of Generator and Field?

I was going to take the hood off and just jump to the back of the existing gauge, but when I gotit off, the gas tank is in the way. The gauge that's on the tractor now doesn't show charge or discharge, just battery condition with brown and green on the stripe across it with numbers from 8 to 14 or some such thing. Even after a full charge with the battery charger, it's sitting near the bottom at about 8.

The tractor sat all winter with a battery that was new a year ago. It started right up this spring. We took it to town for a show Memorial Weekend and it was fine. I went to start it Sunday and the battery was totally dead. I jumped it and when I took the cables off, it kept running, so I assume it was running off the generator. However, after charging the battery Sunday, it started right up Monday morning. I put the charger back on it just to be sure it was topped off. I loaded it on the trailer, took it to a parade and drove it for about two hours. When I got back to the trailer, I had left the ramps down, so I just backed it on and shut it off. When we got home, the battery was too weak to start it and we had to start it by rolling it down the ramps, leading me to believe the generator isn't working after all.

This morning, it rolled about like it did Monday on the trailer. I jumped it again, it ran fine, but when I shut it off in the shop, it was dead as a door nail. The regulator is up under the dash covered up by the gas tank too. I just don't want to pull that tank out without testing that generator first. I need to troubleshoot everything to find out of there's a short drawing the battery down, or if the regulator is sticking or just what's going on. I have a multi meter, but I have no idea on earth how to use it. Everything on there might as well be written in Arabic.

f I didn't know meters, and I had a generator on the bench, I would connect the D and F terminals together, then a battery to generator terminal D (armature) to see if it would 'motor' and if not, remove D to F connection & immediately connect F to ground to see if it would motor. If any good, it should motor with one field connection or the other, depending on whether it is a type A or type B generator.

Drain. High likelihood that regulator cut out contacts are stuck closed,thereby draining the battery thru generator when engine stalled. If so, the heat from such drain will warm up generator body...feel it after charged battery has been connected for several minutes.

 

[Janicholson]

Lucas generators (not alternators) are all B circuit type. The D terminal is connected to the load brush, and the other brush is grounded to the gen frame. The field is also internally grounded to the frame, and the F terminal connects to power the field. With these ideas in mind, a test can be made from the F terminal to ground with an ohm meter. it should show very low resistance, between one and 4 ohms. Ohm meters are often mediocre at low resistances, so it should show a connection to ground through the field windings. If it is open, or has high resistance above 10 ohms it has an issue of open field circuit.
To test the system for function after determining it has field continuity (as above) disconnect the F terminal start the tractor and jump the Hot battery post to the F terminal. Now measure the battery voltage across the posts. if it is above 12.6 volts, and more like 14+ volts the generator is good. If still battery volts, the brushes may be out of touch with the commutator. the Field circuit should draw about 3.5 to 5 amps through the jumper wire. Dont assume this is a fix, it only looks to the generator.

The regulator in this system puts battery/charging voltage into the F terminal. So with it running and connected as original you should see battery voltage at the F terminal. Jim

 

[used red MN]

I read your whole story not paying attention to the author. After that I went back to the top to see how many posts the author had made, much to my amazement Mr. Lund. I was then shocked by the last part and the comments about the multi-meter. Sounds to me like the tractor has a voltage meter by your description. If you are trying do a test on the tractor with an ammeter it is going to be a little tricky. You could disconnect the main power feed which is likely on the battery cable terminal at the starter. Then connect your ammeter in there and see what it shows. Should give you some idea of what is moving into the battery. Best thing you could do is take a lesson in Arabic and use your multimeter, see link. Select DC voltage in a range that will read 12 volts. Static charge of a good battery is 12.5 - 12.7 volts. With it running the charging system should get you something like 13.4 to 14 volts. Best of luck, lets see what JohnT says.
Meter decoder

 

[Janicholson]

I agree with the idea that the cutout contacts could be welded, but with low voltage shown on the meter (a Lucas volt meter good bad device) it could be a self discharging battery. Remove the D terminal connection at the gen. and keep it from touching ground. Charge the battery. Use a volt meter between the D terminal and the disconnected wire with the engine off. If voltage there, the regulator cutout is welded closed. Jim

 

[John T]

Yo Jim, Im glad you knew it was a Class B system, you are on top of this..

John T

 

[Janicholson]

Fixing a few hundred VW vans and Beetles helps.

 

[rrlund]

OK, here's what I did. I'd had the battery charger on it again since I put it in the shop. It was all the way up and the charger shut off. I got impatient when I didn't get an answer in ten minutes (LOL) and I took the wires off the F and D, then tried touching them to the posts one at a time and together with the engine off and with it running. I had no sparks anywhere no matter what I did. I took the generator off and took it apart. Everything looked brand new except that the armature was a little dirty and so were the end of the brushes. I cleaned the armature and contact portion of the brushes with some fine sand paper(not emery cloth) and put it back together. I got on an MG auto website to get the info on polarizing a 12v positive ground British generator. Tell me if I did this right. I clipped a wire to D on the generator and touched - on the battery. I started it and clipped the wire to ground and touched the F post. When I did, I got a spark. So does that mean it's charging now if I get a spark there with it running? That wonky fake amp gauge is still sitting pretty much at the bottom near 8 just like it was.

Pretty sure the contact isn't welded in the regulator. I remember regulators doing that over the years,and when they did, it resulted in smoke and melting wire coatings post haste.

I put the hood back on and put it back in the tool shed. I'll know tomorrow if the battery stays up, but there's a tractor drive coming up Saturday. I'd like to drive that one but don't have to, I have others, I just don't want to get out on the road for a few hours and have it die from a dead battery right there. Guys in the club have very little mercy on guys who have to be towed.

 

[rrlund]

Ya, I really need to learn how to use that thing. It's just that I so seldom work on electrical stuff that I forget what the symbols and terms on the face of it even mean. Pretty sure the mice ate the instructions.

 

[Janicholson]

If you have a volt meter (analog with a needle is best) charging voltage into a charged battery should be 14.2 to 14.6 volts. Running at 2/3 throttle. Your check for spark was a good one for testing stuck cutout points. Jim

 

[rrlund]

I'll have to figure out how to set that multi meter for volts. That'll be DC volts on the meter correct? Touch it across the battery posts, or one contact to F and the other to ground? What about one to the post from the battery on the starter button and one to ground?

See why I was asking about one of those magnetic amp gauges on tool talk a few weeks ago? Life was so simple with access to one of those. LOL

 

[rrlund]

When I was searching for answers, I came across a video that said to hook F to D, ground the case then hook a hot wire to D. Is it
really that complicated on those British generators? I've tested Delcos by just hooking one wire to A and one to F and they'll run.

 

[caterpillar guy]

Not libable to damage meter as long as you don't touch voltage with the meter on OHMs that is the little Q looking symbol with 2 tails one on each side. Voltage on DC is the one with a straight line over the dots. AC is the one with a squiggly line over the dots. Set you meter for slightly nore voltage than you will read.
mine has a 10 and fifty volt scales so I use the 50 with it only reading under the 20 volts amount like 13-15.

 

[MARK ROBKE]

To use your voltmeter, connect/touch the leads to the battery posts-pos to pos and neg to neg. I would check voltage before cranking, and after starting to see if voltage increases. Use DC volt scale. If I had any doubt about my wiring, I would also continuity test (ohm scale) my wiring with the battery unhooked. I would also check, with the battery hooked up, the volt reading at the gauge. Good luck, Mark.

 

[Bob N.Y.]

Have you disconnected the battery after charging it and let it sit for awhile? If a fully charged battery goes dead while disconnected, it is a bad battery.

 

[rrlund]

Not yet. I don't think now, that the generator was working. If the battery stays up, problem solved, if it goes dead sitting, I'll move on to the next step. I'm thinking now that just the distributor drawing the battery down while it ran so long was the issue since this morning it had about enough umpf to turn it over about half a turn, just like when I got it home Monday.