Testing alternator output with DMM

iis_iis

iis_iis

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Where to post... also a consideration. Tippie kind posting, had me going over charge system testing. Given most of you do not have high current measuring equipment, most DMM only run to 10Amps. Fabricate from resistance wire, 3 resistors in a Delta connection scheme, 1 Ohm in value for each arm or leg ( yes i know English...grin ), with a standard DMM on AC volts, you can read a stator power output on each leg of the Delta load resistors, each volt represents one amp of charge current.

Most common fault with stators is a "shorted turn" and this test will help indicate if a shorted turn is unable to supply balanced output voltage to the load resistors, this has to be an on motor test of course, yet that is good, simple test ( test jig not so much ). The resistors will need to be in the 100watt rating, in these cases i use a jar of water for the resistors, for cooling. Need to bring out 3 fly wires to measure the 3 voltages. Or a terminal block will serve the purpose prior to the load resistor water jar.

As my memory recalls the ND stator is Y configuration internally, Delta load for the RR connected. HTH j.

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piranha-bro2 said:
Foreign language to me John! One thing I've never become majorly competent is electronics - fine with electrics generally, but ... I'd love to know what's inside one of those little blue or brown cylinders - if you break one open what do you see?
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Smoke, mostly Chinese smoke, could be opium smoke...have suffered the odd dizzy spell when "cylinder" fails..... used to be not weird... blame the trade, grin. Dont sell yourself short, others may do that to you, i wont. j
 
iis_iis said:
Where to post... also a consideration. Tippie kind posting, had me going over charge system testing. Given most of you do not have high current measuring equipment, most DMM only run to 10Amps. Fabricate from resistance wire, 3 resistors in a Delta connection scheme, 1 Ohm in value for each arm or leg ( yes i know English...grin ), with a standard DMM on AC volts, you can read a stator power output on each leg of the Delta load resistors, each volt represents one amp of charge current.

Most common fault with stators is a "shorted turn" and this test will help indicate if a shorted turn is unable to supply balanced output voltage to the load resistors, this has to be an on motor test of course, yet that is good, simple test ( test jig not so much ). The resistors will need to be in the 100watt rating, in these cases i use a jar of water for the resistors, for cooling. Need to bring out 3 fly wires to measure the 3 voltages. Or a terminal block will serve the purpose prior to the load resistor water jar.

As my memory recalls the ND stator is Y configuration internally, Delta load for the RR connected. HTH j.

View attachment 85094
Click to expand...
I am in the same boat as Quentin, it is a bit above my pay grade, but I do like the scraps of electronics I do know, and wished we had gone a bit more in depth than our simple intro at maritime college.
Could you make a simple diagram of just how this diode assembly would be connected with the multi meter and the stator/regulator connection. And what values we could expect to get. How can you have these diodes in a jar of water and measure anything, or is it demineralised water that does not carry current?
 
Put together some hopefully useful basic connection scheme and test jig fabrication, photographs for testing the stator only.

Tippie, the load test for the stator is done with resistors, nothing to do with RR or similar active components, if i understand your message above. j.
 
Stator test is good. I am not sure how the multi meter connects to the resistor set, or how it works with the resistors immersed in water.
 
The resistors are put in water to keep them cool. If you were to use even higher wattage resistors, cooling them with water would not be necessary. the DMM is connected across each resistor one at a time to measure that windings current output. The higher the voltage measured on each resistor indicates a higher current output.

The stator being a Y connection, if any winding is open, two resistors will show a voltage lower than normal and one will show a voltage higher than normal on a delta load.

Now as for a winding with a short. If the entire winding is not shorted out you will see decreased voltage on one resistor. If the winding is completely shorted out................. I can't remember what voltage you will measure on each resistor as there will still be current flow. Been 42 years since I left engineering school. Need to research and edit my post.
 
As Bruce indicates, the water cooled load resistor is an economy for infrequent fault test time, on ebay you can purchase 3 by 100W 1 Ohm resistors for about $25 and fabricate a delta load bank with air cooling, expediency the water cooling, i would use say 10W resistors in water for a 30 second full load test, which i have in stock or on salvage discarded pcb's.

The most common fault on stators is a "shorted turn" DC resistance test will not show when a shorted or partial shorted turn fault is present. We used a device called a "growler" in the days, not for discussion here...grin. The enameled copper wire insulation on adjacent turns fails and causes this shorted turn which is low impedance and draws significant current under excitation ie circulates within the shorted turn and by implication causes a lower voltage on that arm of the Y configuration output, mentioned in another post the importance of a reference measuring point, with a Y or Delta configuration you are using the other arms of the stator to measure this lower voltage, ie not obvious which arm is the effected one, there are ways...another time... HTH j
 
John,

Another option is to use a clamp meter on each lead from the stator to measure the output. Then there is no need to make a test load and you don't need to disconnect any wires on the bike. Now this assumes the RR is working properly.

As for shorts in the windings, I use a LCR meter. But most people don't have one of them so a growler is a good choice. You are dating yourself by mentioning this piece of equipment as most people have never seen one. I have one made in the 1950's and it is a very usefull tool. If you have a 750 with the generator, you need one.

Bruce
 
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