B7100 dynamo and regulator

[Patrick524]

Hey folks, I have a b7100 I use to push up feed to my heifers. The tractor has to be jumped every day to start so I started checking my wiring (I rewired this thing a while back, got rid of lights, horns etc....). Long story short the dynamo puts out 27.5v ac at full throttle and I'm only getting 11.3v dc out of the regulator... I have two more of these tractors laying around for parts so it wouldn't be hard to try another regulator but I don't have a lot of time to pull parts off so I'd thought I'd start here. So would the regulator be bad? Any help would be much appreciated.

 

[Tooljunkie]

I believe thats what you want to do,as long as other wires on regulator are doing their job.not having a wiring diagram handy i cannot advise you in which steps to take. Regulator swap would be an easy test.

 

[100 td]

Regulator swap would be an easy test.

X2

If that doesn't do you and good, (before you change the dynamo) does this tractor have a 3 wire dynamo? If it does, it's possible you may have mixed up some wiring when removing light switches which are part of a 3 wire dynamo circuit, and you may have the incorrect legs of the dynamo hooked up.

In any case, ensure you fully charge your battery with a charger before doing any voltage tests, and make sure the battery is holding voltage overnight. This then eliminates low voltage from a poor battery and the low output dynamo not being able to keep up with the drain on it.

 

[85Hokie]

100 gave you great advice, follow that!

THe fact that the regulator is putting out something close to right is a good sign I would think.

If two wire dyno - it will not matter since AC is being produced - but the 3 wire could be hooked up wrong. Testing without a "good" battery can give you funny results too. What RPM you running to test?

On my B7100 - something around idle = 12.4 ish.......once I get a little RPM (guessing 1200-1500) I get 12.8-13 ish......and when up there close to WOT I get 14.4 ish

And as TJ said - a swap will be quick and easy!

 

[torch]

the dynamo puts out 27.5v ac at full throttle and I'm only getting 11.3v dc out of the regulator...

Sounds like a diode is shorted in the rectifier/regulator unit. The WSM does not give any details about the internals, but from the looks of the tractor wiring diagram it's probably a simple 4 diode bridge rectifier with a 14v zener or similar clamping the output to ground. Google can produce hundreds of results to the query "how to test a bridge rectifier" but the simplest is certainly to swap in a known-good spare.

 

[Patrick524]

Ok thanks for all the input.
-The test i did was done at full rpm.
-There are only two wires coming from the dynamo.
I'm going to charge the battery overnight and check the load in the morning. If the battery is good I'll change regulators.

 

[100 td]

You can also unplug and check for AC volts on dynamo wires before changing regulator.