Testing motor

[Goober11]

Ha, Everyone. starting a new post on my 2006 Ezgo PDS. my first one was about the solenoid. Solenoid was good controller bad. Did a search and came up on a reply from JohnnyB. How to test cart before installing controller.(PDF form).
All cables off motor
A1 to A2 should be .3 to 1 reading was 0
F1 to F2 should be 1 to 2 reading was 1.6
A1 to F1 should be open reading was open
F1 to motor case must read greater than 5M reading was 6M
So the A1 to A2 reading bad. Amy I right to say the motor is bad and also took out the controller.

[JohnnieB]

Looks like the armature is shorted, so you need a motor.

It depends on what controller is installed. If it is a stock PDS, it is likely to be a goner also. If it is an Alltrax XCT, it is probably okay since the XCT does have shorted output protection.

[Sergio]

Are You sure about the resistance specification on the Armature coil?

The Club Car ADC Sepex motor Armature resistance specification is 0.012Ω, 0.3Ω seems to be an order of magnitude too high.

[JohnnieB]

Originally Posted by Sergio

Are You sure about the resistance specification on the Armature coil?

The Club Car ADC Sepex motor Armature resistance specification is 0.012Ω, 0.3Ω seems to be an order of magnitude too high.

No I'm not 100% sure, but the info came from reasonably authoritative source (FSIP)

See attached PDF

If you have some better info, I'm all ears.

[Goober11]

Originally Posted by JohnnieB

Looks like the armature is shorted, so you need a motor.

It depends on what controller is installed. If it is a stock PDS, it is likely to be a goner also. If it is an Alltrax XCT, it is probably okay since the XCT does have shorted output protection.

Yes JohnnieB it is a stock PDS.

[Sergio]

Originally Posted by JohnnieB

No I'm not 100% sure, but the info came from reasonably authoritative source (FSIP)

See attached PDF

If you have some better info, I'm all ears.

The 0.012Ω resistance I posted is straight out of the ADC EJ4-4001 stock motor spec sheet used on Club Cars.

The numbers on that FSIP document don't seem reasonable to me, at 1Ω Armature resistance creating a dead short on the Armature with 48v would only draw 48 amps, does that seem reasonable to you for a Golf Cart motor?

I would personally do a "run test" on the Motor since most multi meters would not be very accurate at that low resistance.

[JohnnieB]

Originally Posted by Sergio

The 0.012Ω resistance I posted is straight out of the ADC EJ4-4001 stock motor spec sheet used on Club Cars.

The numbers on that FSIP document don't seem reasonable to me, at 1Ω Armature resistance creating a dead short on the Armature with 48v would only draw 48 amps, does that seem reasonable to you for a Golf Cart motor?

I would personally do a "run test" on the Motor since most multi meters would not be very accurate at that low resistance.

I've wondered about how an armature (or field) can draw more amps than Ohm's law says it can, but it obviously does.

I don't have the exact DC resistance of the Armature and Field of my D&D motor handy, but IIRC it is about 1Ω for the armature and about 3Ω for the field and on a dyno the armature can draw 444.8A at 1914RPM with 25A of field excitation and 40.2V applied. That figures out to a dynamic impedance of 0.090Ω. Of course the dynamic impedance increases as RPM increase due to back EMF, so the faster the armature spins the few amps it can draw.

I suspect the secret is the armature is not moving when you measure the DC resistance with an Ohmmeter, so you are measuring the resistance of only one coil of wire, plus the carbon brush/ copper commutator interface. When the armature is spinning, you have about two dozen coils of wire effectively in parallel, or something akin to being in parallel.

Also, the output of the controller is pulsed DC which has some AC like characteristics, but at 100% duty cycle it is effectively DC, so those anomalies don't apply at WOT.

Asking why armature can draw more than their apparent DC resistance allows is a question on my bucket list to ask a motor manufacture. Just haven't got a round to it yet.

[JohnnieB]

Originally Posted by Goober11

Yes JohnnieB it is a stock PDS.

Chances are it is a goner.

[Sergio]

The maximum Motor current should occur during a stall or 0 rpm since You have the full battery voltage on the motor and only the resistance of the Armature winding to limit the current.

As the motor turns the back EMF that is generated has the opposite polarity of the battery voltage and reduces the voltage on the armature which in turn reduces the current.

I don't have a spec sheet for any D&D motor so I don't know their Armature resistance but if it is as high as 1Ω I need to revisit my DC motor operation theory.

[JohnnieB]

Originally Posted by Sergio

The maximum Motor current should occur during a stall or 0 rpm since You have the full battery voltage on the motor and only the resistance of the Armature winding to limit the current.

As the motor turns the back EMF that is generated has the opposite polarity of the battery voltage and reduces the voltage on the armature which in turn reduces the current.

I don't have a spec sheet for any D&D motor so I don't know their Armature resistance but if it is as high as 1Ω I need to revisit my DC motor operation theory.

I'll measure the armature resistance of my ES-76-51 and email Eric at D&D, asking what the true DC resistance ought to be and why the armature can draw more amps than Ohm's law allows.

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There is another anomaly that made me a bit cross-eyed until I figured it out. Armature amps can be higher than battery amps when controller output is less than 100% duty cycle.