Washer makes lights dance

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Here's my $ 0.02

'Back EMF' from the motor.

I have LED's in my office, and when I turn a fan from 'high' to 'medium' or 'low', the lights will sometimes dim for a split-second.

What happens is that the magnetic field in the fan motor collapses and generates a voltage opposite to the applied voltage ( THINK 'spike suppressor diode on a DC relay' for comparison), this opposing voltage generated is enough to dip the line voltage to make the LED 'stuitter'.

With the washer or treadmill referenced earlier, the motor(s) have a varying load, and generate an opposing voltage going from fully loaded to partially loaded.

How to verify ? I suppose you could plug the load into a large-enough battery back-up supply and run off that for a bit, although as a rule UPS's do not play well with motor loads.
 
220317-0825 EDT

Smash:

Using ohms law, resistance knowledge, load current, voltage measurements, and changes of voltage with load change provides you a means to study a circuit problem.

Copper wire, #12, per 1000 ft at room temperature is about 1.6 ohms. So if we took 1000 ft and made a loop 500 ft long, then for a 10 A current change in the loop the change in voltage at the 500 ft end would be 10 * 1.6 or 16 V. If the loop was 50 ft long, then the drop would be 1.6 V.

Suppose that my utility source voltage is constant at the utility transformer output terminals, not actually true, but a reasonable assumption to make, that there is a 50 ft distance from that transformer to the main panel, and that the service drop wire is #6 copper. A three wire # size change is about a 2 to 1 resistance change. Thus, the service drop is a resistance of about 1/4 that of the internal distribution wire.

Therefore in this example we have about 0,4 V drop from the pole transformer to the main panel, and 1.6 V drop from the panel to the 10 A load. Total change in voltage at the load is 2.0 V for the 10 A load change.

These are measurable voltage changes that you can obtain using a 1500 W space heater. 1500 / 120 = 12.5 A.

If you see a small change in the voltage at the main panel input terminals compared to the change at the end of your load, then you look for the problem in the main panel and/or wiring from the panel to the load.

Your loose connections, where ever they were, may well be your problem. Voltage change measurements may allow you to pinpoint the problem.

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I suggest checking for fall-of-potential readings on the neutral from as close as you can get to the meter (even the meter base itself) to the panel neutral busbar.

Also, check for pulsating voltage between this house's neutral and a neighbor's, if you have a piece of wire long enough.

Remember that only a neutral issue will cause an increase on one Ll-N voltage while the other L-N voltage decreases.
 
LarryFine said:
I suggest checking for fall-of-potential readings on the neutral from as close as you can get to the meter (even the meter base itself) to the panel neutral busbar.

Also, check for pulsating voltage between this house's neutral and a neighbor's, if you have a piece of wire long enough.

Remember that only a neutral issue will cause an increase on one Ll-N voltage while the other L-N voltage decreases.
Click to expand...
As load changes on the neutral it should change voltage difference to remote ground/neighbors neutral, should change by amount of voltage drop. If that drop is excessive for amount of load/length of run, there may be additional resistance in a connection somewhere.
 
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