B7100 hst dynamo

BobInOK · Jun 7, 2019

Swapping a first generation motor into a 2nd generation tractor. Older motor has a 3 wire dyno existing motor has a 2 wire dyno. Thinking the regulator and wiring must go with the existing dyno right?

Managed to get the dyno off the existing motor using a gear wrench on that lower middle nut one click at a time. Can imagine what kind of chore it is going to be to get that nut back on. Any tricks?

Thanks, the saga continues...

D2Cat · Jun 7, 2019

Bob, before you get to taking the dynamos off and exchanging them, I think there is another wire on the regulator that is not used on the two wire dynamo. I believe is yellow is color and on the end opposite the black ground. You can use that yellow to connect the third dynamo wire.

Someone else will help to confirm or deny this!!!! Be patient.

Dave_eng · Jun 7, 2019

From memory, on early B5100, 6100 & 7100 the lighting system was not direct current but alternating current which is what the dynamo puts out. The third wire was paired with one other to feed the lights.

Owners of these early machines learned this when they installed LED lights which would either flicker or not work.

Kubota did this for electrical efficiency's sake as not rectifying all the dynamo output saved more energy for lighting. The downside was that the light's brightness varied with engine speed.

My suggestion is to tape off the third dynamo wire and try it in operation on your tractor with the 2 wire regulator. If you have acceptable charging voltage at the battery and your lights work, then you are all good.

The dynamo wont care is one wire is not used.

If you have no lights then we can work through a solution.

Dave

BobInOK · Jun 7, 2019

Thanks guys, I'm a little weird when it comes to stuff like this and will go to the trouble to change it even though the one on it will probably work just fine.

Guess the answer is either leave that bottom nut off or just deal with it. I'll probably deal with it and waste a couple hours of my life

North Idaho Wolfman · Jun 7, 2019

BobInOK said:
Thanks guys, I'm a little weird when it comes to stuff like this and will go to the trouble to change it even though the one on it will probably work just fine.

Guess the answer is either leave that bottom nut off or just deal with it. I'll probably deal with it and waste a couple hours of my life

Small steady hand and a lot of patience helps.
I use an old dipstick with a piece of tape doubled over to hold the nut to get it started.
A bad of grease on a screw driver works too.

Highpockets003 · Sep 12, 2019

Is there a means or way to test the B7100's regulator electrically to verify it's good? Couldn't find anything in a shop manual about testing it. I do have a dynamo putting out 11v but the battery isn't getting charged (probably bec of the dynamo). Wanna make sure the regulator is good before dropping $$$ into a dynamo.

Dave_eng · Sep 12, 2019

Highpockets003 said:
Is there a means or way to test the B7100's regulator electrically to verify it's good? Couldn't find anything in a shop manual about testing it. I do have a dynamo putting out 11v but the battery isn't getting charged (probably bec of the dynamo). Wanna make sure the regulator is good before dropping $$$ into a dynamo.

To start with you are likely not checking the dynamo properly.

You need to check it disconnected. You need to measure alternating current voltage between two wires or any two of the three if you have three. From memory around 30 volts +.

The dynamo rarely fails it is that simple.

Dave

Highpockets003 · Sep 14, 2019

Dave_eng said:
To start with you are likely not checking the dynamo properly.

You need to check it disconnected. You need to measure alternating current voltage between two wires or any two of the three if you have three. From memory around 30 volts +.

The dynamo rarely fails it is that simple.

Dave

Dave - I rechecked the AC voltage from the dynamo and measured 16.0 - 16.2 VAC, with engine at idle (measured with a Fluke DMM). Measuring one wire to ground gave 4.6 VAC, and the other wire to ground measured 0.4 VAC. Is that as expected?

And now, how do I verify if the regulator is good?

Dave_eng · Sep 14, 2019

Highpockets003 said:
Dave - I rechecked the AC voltage from the dynamo and measured 16.0 - 16.2 VAC, with engine at idle (measured with a Fluke DMM). Measuring one wire to ground gave 4.6 VAC, and the other wire to ground measured 0.4 VAC. Is that as expected?

And now, how do I verify if the regulator is good?

Please do the AC voltage check at full speed.

The voltage should be greater than 20 volts AC at full speed

Voltage to ground is meaningless. The dynamo has two wire coils that do not connect to ground. Permanent magnets provide the rotating magnetic field.

The regulator condition is determined by default. If the dynamo is good and there is low DC voltage at the battery, then the regulator is bad.

Dave

twomany · Sep 14, 2019

For some time, I've wondered if these small A-C dynamos could be "hot rodded" by proper location of additional high performance magnets.

There are some REALLY GOOD Magnets available for small money these days.

The difficult part is getting anything added close enough to the armature to make a difference.

I need to get my hands on one of those dynamos, but I'm not taking my B7200 out of operation so I can play around in the lab on a cold winter's day. ;-)

Dave_eng · Sep 14, 2019

twomany said:
For some time, I've wondered if these small A-C dynamos could be "hot rodded" by proper location of additional high performance magnets.

There are some REALLY GOOD Magnets available for small money these days.

The difficult part is getting anything added close enough to the armature to make a difference.

I need to get my hands on one of those dynamos, but I'm not taking my B7200 out of operation so I can play around in the lab on a cold winter's day. ;-)

Easier to switch to a John Deere dynamo. 35 amps with three output leads. You would need to use a JD regulator.

Even a two wire JD is rated for 20 amps. Much more than Kubota's.

The B7100 is more complicated because of where its dynamo is located within the fan assembly.

Dave

Highpockets003 · Sep 19, 2019

Dave-

Checked the dynamo's AC output on its 2 wires. Running the engine from idle to full throttle, the AC output ranged from 13ish-VAC to 35VAC, so am concluding the dynamo is good, and the regulator is bad as there's no additional VDC at the battery, aside from 12.5. VDC.

Thanks for the help.

twomany · Sep 19, 2019

Dave_eng said:
Easier to switch to a John Deere dynamo. 35 amps with three output leads. You would need to use a JD regulator.

Even a two wire JD is rated for 20 amps. Much more than Kubota's.

The B7100 is more complicated because of where its dynamo is located within the fan assembly.

Dave

easier,

just bring $144. Plus the regulator cost
Easier yet is to just trade the old tractor in for a new one with a higher output electrical system.

I was thinking of things one can do for themselves.

Easier isn't always the most pleasurable.

Dave_eng · Sep 19, 2019

Highpockets003 said:
Dave-

Checked the dynamo's AC output on its 2 wires. Running the engine from idle to full throttle, the AC output ranged from 13ish-VAC to 35VAC, so am concluding the dynamo is good, and the regulator is bad as there's no additional VDC at the battery, aside from 12.5. VDC.

Thanks for the help.

I agree with your conclusions.
Please let us know the outcome of a new regulator.
A B7100 is a great machine.

Dave

lugbolt · Sep 19, 2019

I would've expected to see more ac voltage than that but I'm not that familar with the B7100 dynamo. Most of what I see is zero turn diesels; most of those will make 30-90v AC depending on the speed of the engine.

Highpockets003 · Sep 20, 2019

Dave, et al,

After checking the regulator's price local in ABQ, NM, they want $164.68 (+SH). Coleman's list it for $128; so there is a disparity. ABQ probably has the mark-up above retail, which Coleman's is charging.

Before spending that retirement account, think I'm gonna buy the Beijing special on evilBay for $30 and verify the charging system works.

flynavy · Oct 27, 2019

I bent a 7/16 craftsmen ignition wrench ( about 10" long) , bent it 90 deg approx 1 1/2" from the end. Then filed out so that it was 10mm size. Then used duct seal to hold the nut in place over the stud then very carefully got the 1st 2 threads to hold removed the wrench, tightened with fingers until it was snug, then again used the wrench to finish it off
It took me 1/2 hr to get it off and 3 hrs to put it back on, Saying tough is an understatement!

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