Alternator question.

[Dave W]

Got a tiny little kubota 2 cylinder engine with this alternator on it and a separate voltage regulator.
Question is should it charge at the nominal 14.5v like a regular alternator?
I'm only getting max 12.5v with no load on the system (Engine would run without battery connected)

 

[Pheasant Surprise]

Think I’ve got the same on my lawn mower with a D782 triple in it. Can put a meter across it later on...

 

[Netherfield]

Is this voltage across the battery terminals you're talking about?

 

[Dave W]

Is this voltage across the battery terminals you're talking about?

Yes. Where you'd expect to find about 14.5v on a regular setup. This only 12.5

 

[Pheasant Surprise]

It’s also a dynamo + regulator setup, rather than alternator...

 

[Netherfield]

Where's @Mursal .

I think I would expect to find around 14v on a good battery

 

[Pheasant Surprise]

Where's @Mursal .

I think I would expect to find around 14v on a good battery

12.6v across the terminals for a fully charged battery at standstill and anywhere from 13.8 to 14.2v when running (charge being delivered). Typically.

But check the Kubota specs above - this is from my lawnmowers WSM, but Daves will be about the same.

I’ll check the dynamo, regulator output / battery terminal voltage on my Kubota ride on a bit later on and see how they stack up.

 

[Sharpy]

Probably not charging, but put a load on it like a worklight and see what happens to the voltage.

 

[multi power]

An alternate won't change without the battery connected

 

[Pheasant Surprise]

Got a tiny little kubota 2 cylinder engine with this alternator on it and a separate voltage regulator.
Question is should it charge at the nominal 14.5v like a regular alternator?
I'm only getting max 12.5v with no load on the system (Engine would run without battery connected)

Kubota workshop manual spec above suggests you should be seeing 14 to 15v from the regulator....

Check the dynamo AC output voltage is @ > 20v too

 

[Pheasant Surprise]

An alternate won't change without the battery connected

It’s a dynamo + reg setup, so doesn’t need juice from the battery to kick things along (excite the stator)

 

[Dave W]

Kubota workshop manual spec above suggests you should be seeing 14 to 15v from the regulator....

Check the dynamo AC output voltage is @ > 20v too

Thanks. That's answered what I needed to know.
I was half hoping it was only a trickle charge type thing and only put out 12v but looks like somethings fooked.


So will it be dynamo or regulator?
One thing I noticed was the dynamo wasn't free spinning. There were magnets that held it in certain positions. Is that how they are? Definitely not bearings tight

 

[Pheasant Surprise]

So will it be dynamo or regulator?
One thing I noticed was the dynamo wasn't free spinning. There were magnets that held it in certain positions. Is that how they are? Definitely not bearings tight

Yes a dynamo has permanent magnets on the stator. So as it rotates it will ‘stick’ as the rotor and stator magnets align. An alternator uses a series of windings to create the magnetic field in the stator, so it’s comparatively smooth to turn by hand.

Check the dynamo AC output - reg can only work if it’s getting sufficient voltage.

 

[Pheasant Surprise]

Thanks. That's answered what I needed to know.
I was half hoping it was only a trickle charge type thing and only put out 12v but looks like somethings fooked.


So will it be dynamo or regulator?
One thing I noticed was the dynamo wasn't free spinning. There were magnets that held it in certain positions. Is that how they are? Definitely not bearings tight

So to compare with approx same setup here:

A steady 14.6v out of the regulator / across the battery with engine running - no change to output voltage with revs. Same reading from idle to full revs.

Dynamo/generator output varies from 14 VAC (idle) to 37 VAC (full revs)

 

[Dave W]

So to compare with approx same setup here:

A steady 14.6v out of the regulator / across the battery with engine running - no change to output voltage with revs. Same reading from idle to full revs.

Dynamo/generator output varies from 14 VAC (idle) to 37 VAC (full revs)

Excellent as ever
I'll get some readings taken thank you.

 

[Pheasant Surprise]

Just found my tacho, with leaky AAA batteries in it ...

Revs on dynamo pulley at engine idle (1250 rpm) is approx. 2040 rpm.

At full engine revs. (3280 rpm) approx. 5280 rpm on the pulley.

 

[Mursal]

As above and also worth checking fuse 5 and 7 on the above diagram from @Pheasant Surprise.
Earth point 3 would be next and 6 on the same diagram.

Can be extremely difficult to pin point a fault when the regulator is external from the alternator.

 

[Pheasant Surprise]

As above and also worth checking fuse 5 and 7 on the above diagram from @Pheasant Surprise.
Earth point 3 would be next and 6 on the same diagram.

Can be extremely difficult to pin point a fault when the regulator is external from the alternator.

Yeah definitely. If the main slow blow fuse (5) is gone then there will be nothing delivered from the regulator / charging system. So with engine running, the only voltage across the battery terminals would be from the (resting) battery itself, nothing from charge system.

Also if the dynamo is completely disconnected, the regulator should put on the charge lamp (or there should be 12v present across the lamp holder) while the engine is running.

 

[Dave W]

As above and also worth checking fuse 5 and 7 on the above diagram from @Pheasant Surprise.
Earth point 3 would be next and 6 on the same diagram.

Can be extremely difficult to pin point a fault when the regulator is external from the alternator.

Yeah definitely. If the main slow blow fuse (5) is gone then there will be nothing delivered from the regulator / charging system. So with engine running, the only voltage across the battery terminals would be from the (resting) battery itself, nothing from charge system.

Also if the dynamo is completely disconnected, the regulator should put on the charge lamp (or there should be 12v present across the lamp holder) while the engine is running.

Unfortunately its on a roller from local cricket club. Wiring diagram above won't apply sadly. The basic principles in the workshop manual should sort it though

 

[Mursal]

If you have AC voltage coming out of the alternator (measured across the two wires), put a DC voltmeter across the +BAT pin and earth on the regulator and you should have charging voltage (above 13Volts, varying with revs).
If you have AC and no DC suspect wiring or regulator.

Hope this helps a bit .........