Hot in line resistor, old motor

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EkW

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Hot in line resistor, old motor
« on: 15 Jul 2018, 05:58 pm »
I noticed that the in line resistor for my 20 yr old WT Classic with round motor gets very hot even though the motor isn't running. It is normal for it to get warm during operation but now it is almost too hot to hold. It seems to me that a motor that isn't turning shouldn't be pulling that much current. Should I just unplug it when not in use or look for a fix?
 
Replacement motors are hard to find so I was considering the Origin Live motor kit, which can get expensive. Does anyone have any experience with the OL kit?
Thanks,
Eric

avahifi

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Re: Hot in line resistor, old motor
« Reply #1 on: 16 Jul 2018, 06:28 pm »
1. Determine the value of the resistor, both its resistance in ohms and power rating in watts.

2. Measure the voltage on each side of the resistor.  Subtract lower value from higher value.  This gives you voltage drop across resistor.

3.  Use formula power equals voltage drop squared divided by resistance.  This tells you how much power the resistor is actually dissipating.

4.  For long service life, the resistor should have a power rating of at least three time the power it is actually dissipating.

If the resistor is dissipating too much power then there is a problem.  Either something in the circuit is a problem or the resistor was not appropriate for its use.

Frank

EkW

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Re: Hot in line resistor, old motor
« Reply #2 on: 17 Jul 2018, 03:25 am »
I strongly suspect that the resistor is properly spec'd unless the manufacturer made a big mistake. My concern is that the resistor heats up when the motor is off. That means that there is current flow through a switch that is supposed to be open or there is a fault ahead of the switch. I may need to do a little disassembly and check for proper operation. If I ruin it I know that I can replace it with an Origin Live or other kit.