Voltage present when fuse has blown with no continuity.

[Patrick84]

Can anyone help with the below, there's probably a simple explanation but it's driving me mad.

Why I would be still measuring 24v DC at a 24v motor terminals after the fuse had completly blown? And there being no continuity across the fuse at all? This was also the case on the terminals of a lamp holder on a e-stop circuit.

 

[Wilko]

Hi - have you got a wiring diagram?

 

[HandySparks]

Got to give us a bit more of a clue than that. If there is 24V across the motor terminals I assume that the motor is still operating?

 

[Patrick84]

No the motor wasn't working and the lamp wasn't on.

No drawings unfortunately. The motor circuit consists of a reversing contactor which is controlled via a PLC output card.

The e-stop lamp circuit is separate to the actual e-stop circuit but is just a standard lighting circuit.

I was measuring the voltage with a fluke T110 voltage indicator.

 

[PEG]

Has the lamp blown?

 

[HandySparks]

If you're not measuring voltage across the motor terminals, you need to tell us exactly which two points you were measuring this 24V between.

 

[Patrick84]

Lamp hadn't blown and was disconnected when I was measuring voltage between the lamp holder terminals +/-.

On the motor I was measuring between +/- terminals.

 

[dmxtothemax]

You are simply measuring ghost voltage or phantom voltage or induced voltage.
Your probably using a digital volt meter or even some form of no contact tester.
These units have high impedance inputs,
and can register very small induced voltages.
Try using a low impedance anologue type volt meter. or a wigi !

 

[Pete999]

Lamp hadn't blown and was disconnected when I was measuring voltage between the lamp holder terminals +/-.

On the motor I was measuring between +/- terminals.

Does your test meter measure DC? I assume it's DC as you have measured across +/-

 

[Patrick84]

You are simply measuring ghost voltage or phantom voltage or induced voltage.
Your probably using a digital volt meter or even some form of no contact tester.
These units have high impedance inputs,
and can register very small induced voltages.
Try using a low impedance anologue type volt meter. or a wigi !

The meter is an analogue contact volt meter (not sure about the impedance).

 

[Patrick84]

Does your test meter measure DC? I assume it's DC as you have measured across +/-

Yes, DC and AC.

 

[Pete999]

Yes, DC and AC.

OK thanks

 

[HandySparks]

If you're measuring 24V DC across the terminals of a 24V DC motor and it's not rotating then, unless the motor has some sort of control system built in, either your meter's knackered or the motor's knackered.

How about doing us a sketch of the circuit around the motor and light?

 

[rapparee]

Is the 24vdc, on the brake circuit?

I'm assuming this is some sort of stepper motor.

Coincidentally I was working on a servo motor with an absolute encoder circuit a while back, it was 400v 3 phase, but when the motor wasn't in motion, a small DC current was put down the phases to lock it in position to prevent the motor from moving.

 

[Patrick84]

I'm back in work tomorrow so I'm gonna do a few checks with a different meter and hopefully dig some drawings out.