Lights stay dim with inductive load, not with resistive load

rlane00 said:
Sorry for the long absence, and also for all the ideas and input. The circuit is wired in #14 with a total length of about 150'. At 8.8 amps of load (when vacuum is running) the calculated voltage drop is 5.9%, even though the actual drop measured was 10v or 8.3%. However, the voltage drop with the resistive load was much higher (18v drop or 15%) - and all the lights work fine at that lower voltage. The problem seemed to be the combo of the inductive load and only those certain fixtures/bulbs.

Since the homeowner needed to keep the inductive load option, we tried some other LED bulbs - hoping that a more "forgiving" bulb would be able to handle the inductive load without dimming. Fortunately we found a bulb that worked fine. They dim just a bit at startup (due to inrush), but then recover to essentially full brightness even with the vacuum or hole hawg running. The builder and homeowner are now happy, so for them the problem has been addressed.

However, I'd still like to understand what it was about the inductive load that caused those bulbs to dim when operating at 110v, but not dim when operating at 102V due to resistive load.
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An inductive load inherently means you are going to have current lagging behind the voltage. This really only effects sensitive electronics.

There is also the possibility that the voltage drop is resulting in the biasing of the the driver to periodically become unstable, dampen or oscillatory.

It is much easier to show this stuff in a lab setting where you can control the loading but in a home, it is very difficult to pinpoint an issue like this. That is where the easier / cheaper fix usually is the first option. Find a better designed LED bulb. They are not all designed or made the same. Some have more thorough designs that will result in less issue or increased efficiency.

There are resources online that show some of the LED bulbs being torn apart and you can see the different levels of intricate design.
 
I actually thought about renting an oscilloscope to see what the waveform looked like, how much the current lagged, and how/if it varied at different points in the circuit. But then I realized that even if I had that information, there wouldn't really be anything I could do about it other than possibly adding a capacitor in parallel to offset the lag, but have never even considered how that would be actually be implemented in a residential setting.

Thankfully the better LEDs did the trick.
 
rlane00 said:
I actually thought about renting an oscilloscope to see what the waveform looked like, how much the current lagged, and how/if it varied at different points in the circuit. But then I realized that even if I had that information, there wouldn't really be anything I could do about it other than possibly adding a capacitor in parallel to offset the lag, but have never even considered how that would be actually be implemented in a residential setting.

Thankfully the better LEDs did the trick.
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That's the hard truth.

Even if we could isolate the issue, the correction might be more expensive that just finding a better bulb. Replacing wire, installing a Capacitor etc. would be more expensive. Adding equipment puts another point of failure in the circuit that might need to be replaced, maintained, etc.

Though, if given the time, it would be interesting to find the bottom out point / minimums for a cheap bulb vs a more expensive bulb.
 
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