Alternator / generator not charging

[Zogman]

So I'm digging in a bit deeper on My 78 B7100. looks like the battery is not being charged. I looked at the schematic and the 2 grey wires coming from the generator or alternator is putting out about 10 volts at idle. If I rev up the motor it goes down to 6V. I disconnected the output of the regulator and it has zero coming out of it. 11.6 if I connect it but that's the battery voltage.

How do I know if I have a genny or an alternator? My schematic says generator yet the repair manual say alternator.... and what it the best way to trouble shoot it? Thanks.

 

[85Hokie]

So I'm digging in a bit deeper on My 78 B7100. looks like the battery is not being charged. I looked at the schematic and the 2 grey wires coming from the generator or alternator is putting out about 10 volts at idle. If I rev up the motor it goes down to 6V. I disconnected the output of the regulator and it has zero coming out of it. 11.6 if I connect it but that's the battery voltage.

How do I know if I have a genny or an alternator? My schematic says generator yet the repair manual say alternator.... and what it the best way to trouble shoot it? Thanks.

This may not help you with your question, an ALTERNATOR is an AC device, produces AC and then is changed back to DC to charge the battery, A generator is a DC device that does not need to be changed to charge the batter, however BOTH need to increase voltage AT the battery, either or, the battery voltage should be about 12.7 ish volts fully charged, and a charging battery should get close to 14 volts. You say is gets lower as you run the rpms up ? that is strange, that tells me that the internals are messed up somehow, you can take the genny/alternator off and take it to your local parts store and they "might" be able to tell you if it is bad. If you have a picture that will help. Based on your RPM's it sounds like you have a generator.......

 

[Lil Foot]

On a B7100 that old it probably has a dynamo, & if I remember right, it puts out 48V AC… but some one at guru level will have to chime in from here….that's about the extant of my knowledge in this area.

 

[JoBo]

Technically it's an "Alternator". Alternators puts out AC current on the two gray wires.
"Dynamo" is a term mostly used by Europeans. (a translation thing from Japanese maybe)
Generators have brushes and were mostly gone in automobiles in the 1960's.

Two things come to mind.

Since the voltage on the gray wires is AC is your meter set to read AC voltage?

A slipping fan belt caused by it being loose or glazed might cause the voltage to go down as you rev the engine and there's more load put on it.

My alternator is currently on the garage floor along with a lot of other parts and when you turn it by hand you can feel the magnets repelling and attracting each other.

Hope some of this helps.
Joe

 

[kubotasam]

Kubota workshop manuals refer to it as an AC Dynamo. Jobo is correct make sure your meter is set to read ac voltage. To make the situation a little more complicated some early B7100 had 3 wire dynamos some had 2 wire dynamos. In your post you referenced 2 gray wires so I will assume you have the 2 wire version. With the wires disconnected and engine running a full throttle the work shop manual says you should read 43 VAC. I tested one of my tractors a few years ago and if memory serves me the voltage reading was closer to 30 VAC and mine charges just fine. Their is not much to go wrong on a B7100 dynamo. they use permanent magnets and have no brushes to wear out. About the only thing that could happen is the windings could short or open. I read one post where someone with low output had build up of dust inside and said blowing the dynamo out with an air hose corrected the problem.
Usually a tractor that does not charge the problem is the regulator/rectifier.

 

[Tx Jim]

Kubota workshop manuals refer to it as an AC Dynamo..

Is an AC dynamo an alternator or generator? Do any late model tractors come with a true generator?

PS: I think an ac dynamo is an alternator.

 

[kubotasam]

Is an AC dynamo an alternator or generator? Do any late model tractors come with a true generator?

PS: I think an ac dynamo is an alternator.

It does make alternating current so I suppose it is an alternator. The problem with the terminology comes from the fact that some B7100 were equipped with what Kubota refers to as a dynamo. Small permanent magnets device mounted where most people could mistake it for a water pump. Other B7100 tractors were sold with an alternator. Looks very much like what is on most cars or trucks that people would recognize as an alternator.

 

[Zogman]

Good info guys. Thanks. I'll retest with my meter in AC and go across both wires to see what the output is. I read elsewhere that output is supposed to be around 43V as Kubotasam mentions. In looking at the tight engine compartment, do I have to take the radiator out to get the Dynamo out? Thanks again.

 

[Dan_R_42]

Here are some photos of what a Dynamo from a B7100 from the late 70's early 80's should look like.

The first photo is looking at the engine with the radiator off. The 2nd and 4th photo are the Dynamo. Notice the upper radiator hose in the 2nd photo. This is why it is confused as a water pump. The old B7100D has no water pump.

In the 3rd photo, looking from the top, find the Dynamo sort of hidden under the upper radiator hose. As mentioned above you need to check the Dynamo output with your meter set on AC voltage.

 

[Dan_R_42]

Good info guys. Thanks. I'll retest with my meter in AC and go across both wires to see what the output is. I read elsewhere that output is supposed to be around 43V as Kubotasam mentions. In looking at the tight engine compartment, do I have to take the radiator out to get the Dynamo out? Thanks again.

I would pull the 2 hitch pins and remove the 2 pivot bolts that hold the hood on. That will give you much more room for testing. Blow some compressed air into the back of the Dynamo to clear out all the crud that builds up.

I would be very surprised if your issue was the Dynamo. Would be looking to the rectifiers/regulator before I pulled the radiator. Good luck on your testing. Keep us posted.

 

[Zogman]

Thanks for the pictures Dan. I put my meter in AC mode and measured 17 volts right before it gets into the regulator so the Dynamo is not putting out enough. I pulled the radiator out a couple inches and I see the 4 bolts that hold the fan on but I don't know how the dynamo comes out. Does the entire bracket behind the dynamo have to come out? You pic of the Dynamo shows a bolt coming out of the back of the Dynamo. I haven't blown air into the dynamo yet so it looks like that is by next step. Really don't care to start ripping this tractor apart this far yet.

 

[whitetiger]

Did you have the two wires coming from the dynamo unplugged from the harness and going directly to the meter with the engine speed up? I have never seen one that was putting out anything that low of AC voltage.

If you do have to remove the dynamo, set aside a lot of time. You have to remove the end plate from the front of the cylinder head to get to the bolt holding your dynamo on. The lower center nut is almost a "you can not get there from here". There are 6 studs in the front of the cylinder holding on the plate. Some people prefer to remove the head to R&R their dynamo.

 

[Zogman]

Thanks Tiger. That's exactly what I did. I disconnected the 2 grey wires at the regulator and measured there. I'm going to step back from the charging issue for a while. I'm not prepared to take the head off at this moment. Thanks for your help.

 

[North Idaho Wolfman]

I've swapped the Dynamo on my B7100 D750 without pulling the head, just get a cheap wrench 10mm and bend it to fit, takes a few min to get it off but it's doable.
And start that nut first before any others on reassembly.

 

[whitetiger]

I've swapped the Dynamo on my B7100 D750 without pulling the head, just get a cheap wrench 10mm and bend it to fit, takes a few min to get it off but it's doable.
And start that nut first before any others on reassembly.

I have two wrenches bent just for this operation as I have removed these covers 8-10 times when the head is on. It is doable for some, others are not going to be able to remove and replace that lock washer and nut. I have spent 20 minutes or more just breaking the nut loose. Some units have more open area under the dynamo in the little pocket where the nut is located. Unless you have very small fingers getting that nut restarted is worse than removing it.

 

[kubotasam]

Thanks for the pictures Dan. I put my meter in AC mode and measured 17 volts right before it gets into the regulator so the Dynamo is not putting out enough. I pulled the radiator out a couple inches and I see the 4 bolts that hold the fan on but I don't know how the dynamo comes out. Does the entire bracket behind the dynamo have to come out? You pic of the Dynamo shows a bolt coming out of the back of the Dynamo. I haven't blown air into the dynamo yet so it looks like that is by next step. Really don't care to start ripping this tractor apart this far yet.

When you measured 17 VAC did you have the engine running at full speed?

 

[Zogman]

17 VAC was at 3/4 throttle Sam. How about a pic of the shape of the wrench that y'all bent to make this work? Thanks

 

[kubotasam]

Test it again at full throttle. Also in reading one of your previous posts you said you checked the voltage near the regulator. There is a set of connectors about 5 or 6 inches from the dynamo. You should pull these apart and check the voltage at these connectors. If they are corroded or otherwise compromised they could be creating a voltage drop and your dynamo could be ok. If I get a chance tonight I will check one of my tractors at different rpms. If I remember correctly I had around 30 volts max at full throttle and my tractor charges fine.

 

[Zogman]

I will check at full throttle. I had to replace the connectors that connect the engine compartment harness and the dash harness. I went to unplug it and the plastic connectors crumpled in my hand. I cut the wires and re-crimped to new connectors and now the connection is good. I will test there again just in case though. Thanks Sam.

 

[Lil Foot]

How about a pic of the shape of the wrench that y'all bent to make this work? Thanks

I'll second that request….

If I remember correctly I had around 30 volts max at full throttle and my tractor charges fine.

Good to know, thanks!