B7200 Dynamo question?

twomany

Active member

Equipment
B7200
Jul 10, 2017
793
138
43
Vermont
Inspired by another recent similar question........

At times, after starting the B7200e, the "charge light" on the dash remains illuminated. This might be the entire engine warm up time. call it 5 min.

Then, if the head lamps are turned on, or if the engine speed is alternately increased and decreased, the idiot light goes out.

What gives? balky contacts in a mechanical voltage regulator?

I'm pretty sure the electricals are all original. The Battery stays charged, and the engine always starts even in cold temps.

I;m used to seeing the charge lamp follow engine revs, but not used to seeing a sudden load or output change needed to "kick" the charge light out.

I have not evaluated the voltage present during the "lamp illuminated" periods. It hasn't caused any issues. But I am curious.

Ideas?
 

motorhead

Member

Equipment
2009 B3200, 2007 Dodge/Cummins powered Ram 2500 395hp
May 17, 2012
415
21
18
Atascadero
Do you have a mechanical contact type voltage regulator on this tractor? I had an old B5200D and it was a solid state regulator. There is NO wear parts in the dynamo other than the bearings failing. I would go through and clean all of the electrical connections on the tractor. Some voltage regulators require voltage from the ignition switch to work and some don't so check the wiring from your ignition switch too.
Best way to check is to hook a good volt meter across the battery and check to see if it is charging or not when the tractor is running and the charge light is on. Maybe a dumb question but is your V-belt tight?
 
Last edited:

Dave_eng

Well-known member
Lifetime Member

Equipment
M7040, Nuffield 465
Oct 6, 2012
5,107
926
113
Williamstown Ontario Canada
I looked at the wiring diagram in a B7200HST manual I found on Kubotabooks.com

It shows a two wire dynamo and then a regulator/rectifier.

The "no charge," light is controlled by the electronics in the regulator/rectifier.

It is not doing anything sophisticated in deciding to turn on or not. There would be a voltage sensing circuit and, from the sounds of it yours, is operating on the borderline.

It is not at the same technical level as the light in a modern car or truck.

The suggestion of measuring the voltage at the battery is the most practical one. The dynamo is so simple that failure is rare.

You could replace the regulator/rectifier if the battery voltage is good. A piece of black tape over the light might be a no cost solution.

You could add a voltage display like this one for around $9.00. Then you would know at all times the state of the charging system.

https://www.ebay.com/itm/DC-12V-24V...913a0a40f:m:mlzF0aRnQnAjzvy6ZI7SfEA:rk:3:pf:0



Dave