How to bench test a Permanent-Magnet alternator?

[steinmann]

Hello, I'm a new member, glad to be here.
I am actually not a farmer any more, but was until military service. I drove MF 35's, MF 135's, all kind of John Deere's, David Brown, Eicher, petrol McCormick, Caterpillar, Fiat, International, Porsche tractor and Holder's. But now, now I own a vintage BSA M20 motorcycle, and I'm fed up with all the trouble I get from its charging system (6 volts).
I intend to upgrade to 12 volts by changing the original Lucas dyno to a Kubota Permanent-Magnet alternator, which I recently bought via ebay.
According to the seller, it will supply 14 Amps. at 12 volts at about 500 rpm's already.
Before I go into the process of building and constructing a new bracket etc., I ran this PM alternator on my lathe, and was disappointed to see only poor 6,5 AC volts on my volt-meter.

The way I measured it:
I run the unit on the lathe, while holding it in the jaws of the chuck, on 1000 rpm, and measure between the 2 wires getting out of it.
Resistant checked between them and found ok with 0,4 ohms.
What next?
As the unit is brand new, the seller is reliable and I am a lousy electrician, I tend to believe that I'm doing something wrong.
I measure it between the 2 wires coming out of the unit. So, I will be glad to hear from you experts what will the best way be to bench test such a unit?
Thank you all in advance Michael.

 

[Joe Malovich]

It could be you had the meter in DC but the alternator was putting out 12V AC, the heat-sinked unit is a single phase rectifier. when you hooked up your mutimeter in DC you were only seeing the RMS of the top of the sin wave.

Perform your test again with the rectifier wired in blue to blue, 12vdc should be output from the red/black

 

[07wingnut]

Try running it at about 1000 rpm. Kubotas usually idle at around 1000, and the dynamo pulley is smaller than the crankshaft pulley, meaning that the dynamo is turning faster than the engine.

 

[steinmann]

The way I measured it:
I run the unit on the lathe, while holding it in the jaws of the chuck, on 1000 rpm, and measure between the 2 wires getting out of it.
Resistant checked between them and found ok with 0,4 ohms.

That's what I did.

 

[mddorange]

:welcome:
To the TBN forum. Glad that you joined.

As you can see people here are ready to help. Did you try Wingnut's suggestion?

 

[steinmann]

:welcome:
To the TBN forum. Glad that you joined.
As you can see people here are ready to help. Did you try Wingnut's suggestion?

Thank you!
I'm glad I'm here. People here seem to be very friendly, professional and willing to help. I appreciate it very much.
As I wrote before - yes, I tried it at 1000 rpm's as Wingnut suggested but with no luck (Thanks Wingnut).
Slopecarver: Thanks for your time, but I'm sure I had the meter on AC rate.

I have a strong feeling that I'm doing something wrong at the check process.
I would like to mention it again, that the unit is not installed yet, and that I'm looking for a way to test in on the bench.
Appreciate your efforts.

 

[07wingnut]

The output of that unit should be in excess of 20vac. Note that the frequency of the output is related to the rpm and may be above 1000 cycles per second. Any chance your meter isn't measuring the voltage accurately at that frequency?

 

[David_Kb7uns]

Your too slow read this thread.

Alternator output? - Yanmar Tractor Support Message Board


David

 

[steinmann]

I returned to update as there is a progress:
You guys where right!
The PM-Generator seems to be ok: The 1000 rpm of the lathe where simply not enough: we turned it with our impact wrench (compressed air) and got 26 volts out of it! We do not know at what rpm, though... You are great and I'm happy you could help.
But now we are facing a new problem: The rectifier is dead and nothing comes out, leads me to think that we do not wire it correctly (we did it as the pictures show and as shown in the pdf, the 5050 unit). As mentioned we did not hooked the system to the bike, yet. It is all methodic on the bench (BTW, is there a chance that we baked that rectifier?)
1. I will appreciate very much any kind of help or advice regarding correct wiring. The motorcycle is negative chassis, the minus pole of the battery is connected to the frame.
2. Is there a need to fuse the wires? If so what line and fuse value?

Many Thanks! Michael

 

[Dave M7040]

I returned to update as there is a progress:
You guys where right!
The PM-Generator seems to be ok: The 1000 rpm of the lathe where simply not enough: we turned it with our impact wrench (compressed air) and got 26 volts out of it! We do not know at what rpm, though... You are great and I'm happy you could help.
But now we are facing a new problem: The rectifier is dead and nothing comes out, leads me to think that we do not wire it correctly (we did it as the pictures show and as shown in the pdf, the 5050 unit). As mentioned we did not hooked the system to the bike, yet. It is all methodic on the bench (BTW, is there a chance that we baked that rectifier?)
1. I will appreciate very much any kind of help or advice regarding correct wiring. The motorcycle is negative chassis, the minus pole of the battery is connected to the frame.
2. Is there a need to fuse the wires? If so what line and fuse value?

Many Thanks! Michael

As a previous owner of old British motorcycles, (until in 1981 I decided to start riding and end fixing and bought a GS1100 Suzuki) I can feel your pain.

Kubota has several versions of what they call a Dynamo. Permanent magnets rotating around a stationary coil.

On some machines they have three wires leaving the Dynamo, all producing 3 phase alternating current. Two phases completely by pass any rectification and supply the lights with AC which comes as a big surprises to owners who start installing LED lights.The other phase is rectified to charge the battery.

Other models like the two wire you you purchased have limited output and need to be paired with a matching rectifier.

There is no voltage signal back to the Dynamo. Current in excess of need is turned to heat not unlike the zenor Diode arrangement on my unit construction BSA, an A10 if my memory is correct. the diode was in a heat sink between the two fork legs.
Stumbling around with anything electronic, like a rectifier can produce junk is milliseconds.

As far as fuses go, it is the battery circuits that may need protection not the dynamo.

What Kubota model is the Dynamo supposed to be for?
What Kubota model is the rectifier supposed to be for?...

I looked at the wiring diagram for a B5100 series and then a B7100 series.

The B5100 series has two output wires on the dynamo and a total of 4 wires on the rectifier one of which is a ground.

The B7100 is a completly different story with a rectifier with more than 3 wires and a ground.

My sense is you have married incompatible parts. A very knowledgeable person might make the many wire rectifier work with a two wire Dynamo but that is a rare person.


Dave m7040