Generator? Dynamo? Not Charging B7800 Battery

[charlessenf]

Boosted the battery and jump started the tractor ran it for an hour or so dragging large logs from the bottom to higher ground where I turn them into firewood.

Put the tractor away and went out today to start it and it would not start.

Before I run out and buy a battery, I'd like to know how to test the charging system on the B7800 tractor.

I don't know what I am looking for or where whatever it is might be mounted (well somewhere near the fan belt ... perhaps). I've read something about dynamo instead of Alternator or Generator back when.

Anyone know how to check if a B7800 Kubota tractor is (trying) charging the battery?

 

[Ed ke6bnl]

No sure of all the wiring BUT the first thing to do is to check battery voltage with engine running. Need to see somewhere around 13.4volts. Then i would head over to fuse box and a/c volts off the dynamo. Maybe 40 volt with engine on fast idle. I am ooen for corrections

 

[JWR]

First, get your battery tested. Many auto parts stores do it and for free. Of course clean the cable ends and connections (both ends) retighten cable bolts, etc. You will NOT find 40 volts anywhere on the tractor (unless maybe internal to the alternator diode bridge doing the conversion from AC to DC which is probably not accessible and is of no interest to you anyway in the context of this discussion.). The battery standing alone with no load and no alternator doing charging should read right at 12v. Charging voltage should be around 13.8v at the battery terminals (whether from the alternator while running or from a battery charger.) Forget the charging system until you see if the battery is good and will hold a charge.

 

[charlessenf]

I found a wiring diagram and it refers to a dynamo' not an alternator.
A member volunteered:
"The B7800 comes standard with the dynamo with a 13-14 amp output.
"An alternator kit is/was available for about $200.
"I believe the dynamo produces AC voltage.
"Trouble shooting procedures should exist in TBN somewhere."
number two Veteran Member
Northern Lower Michigan
Tractor Kubota B3030HSDC Kubota L2501HST

All I know for sure is that his last sentence is spot on!

 

[number two]

The dynamo has two leads of the same color.
Voltmeter on AC current,test leads on each wire.
Doesn't matter which as you are measuring AC current.
Voltage increases with RPM.
To 30-40 volts???
Dynamo very reliable-only really hear of bearing failure on rather older models.
Good Luck!

 

[CalG]

I just replaced the dynamo with an alternator on my B2601.

At low idle, the dynamo did not put out enough juice to detect a charge voltage to the battery. that is, DC volts at the battery were at the 12.5 volts typical of a good charged wet cell battery.

At high idle, the measured value got up to just over 13 Volts.

With the alternator, the voltage at the battery is 13.5 at low idle.

I didn't investigate further.

I have the take off dynamo and it's rectifier/ regulator in a box.
It's the same unit as fitted to my B7200, so might come in handy "someday".

Dynamos , as fitted to these Kubota tractors, are PERMANENT MAGNET, devices (AC generators).
Not electrically excited,Three phase alternators we might be more familiar with.

Certainly 14 amps will keep a wet cell charged, but ..

More is better at low revs, depending on operational envelope.

 

[charlessenf]

The dynamo has two leads of the same color.
Voltmeter on AC current,test leads on each wire.
Doesn't matter which as you are measuring AC current.
Voltage increases with RPM.
To 30-40 volts???
Dynamo very reliable-only really hear of bearing failure on rather older models.
Good Luck!

B7800HSD (SUPPLEMENT), WSM WIRING DIAGRAM

The generator Dynamo is directly connected to the IC REGULATOR I have not been able to find the location of this part on the other parts diagrams found so far. Nor can I find a KUBOTA Test Procedure for the Dynamo. I find the idea that a generator Dynamo to support a 12VDC electrical system is putting out forty volts.
If, as you suggest, I should measure the amperage at the dynamo generator - how many amps should I find?

 

[CalG]

The rectifier/regulator module is in the dash.

 

[5030]

Many decades ago I owned a smaller Kubota with a dynamo. In reality, if my amperage requirements weren't that great (my Kubota's have 50 amp and 70 amp alternators on them respectively, I prefer the dynamo. Nothing to wear out, no rectifier bridge to fail and no brushes to fail either, Problem is, the output is too limited for my uses.

 

[CalG]

B7800HSD (SUPPLEMENT), WSM WIRING DIAGRAM
View attachment 1057435
The generator Dynamo is directly connected to the IC REGULATOR I have not been able to find the location of this part on the other parts diagrams found so far. Nor can I find a KUBOTA Test Procedure for the Dynamo. I find the idea that a generator Dynamo to support a 12VDC electrical system is putting out forty volts.
If, as you suggest, I should measure the amperage at the dynamo generator - how many amps should I find?

The maximum continuous output amperage is limited by wire size and heat.
The minimum output is limited by resistance.

A "test" procedure for a bare dynamo would need to specify the load in Ohms, and to account for the magnetic field strength .

Are those Orsteads? or a Gausse, or a Tesla? Hmmmm

Magnets are so confusing.....