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I have a Despatch LBB 1-69 lab oven in my shop. It is a single-phase, 110-volt, 30-amp unit. It is wired to a 220 volt, 2-phase, 40-amp panel (on a single 110 volt phase), which is fed by the 100-amp main service. All wiring is appropriate or larger for the task at hand.

During operation, the element is switched on until the unit approaches the set point, then switches to a 1 or 2 Hz (approximate, not measured) pulse and maintains this mode until the heater is switched off or the set point is changed. The "on" period is substantially shorter than the "off", perhaps 10% or less of the period duration. It makes for a very stable temperature but I'm experiencing a nasty side effect.

Once the sun has gone down, there's a noticeable flicker in the garage's florescent lights, that coincides perfectly with the oven's operation, pulsing away. More problematically, every light on the same phase throughout the entire place displays the same behaviour. This is unacceptable, especially heading into the darker winter period.

If this were a fluid circuit, I'd add an accumulator to reduce some or all of the pressure fluctuations but clearly it's not. Would an appropriately sized capacitor (or bank) be a solution? Could they act as a sufficient reservoir to smooth out the fluctuations?

I'm not sure if this plays in to anything, but the voltage in the facility is quite high - on the order of 123 to 126 VAC at any given time.

Andrew M
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  • Capacitors are out for this (except maybe triac-switched ones), but they make AC voltage stabilizers. One for RV use might work for you, but 2 HZ fluctuation is not what most of these are designed for so check specs carefully. For regulators sized by wattage, you need about twice what your oven draws -- so about 7 KW. – Brock Adams Sep 13 '16 at 01:37
  • Also, check your wiring very carefully for voltage drop from the service entrance to the oven. You may very well have a marginal splice, or breaker, somewhere. – Brock Adams Sep 13 '16 at 01:42
  • Thanks Brock. Everything is coming up roses with the install, much to my dismay. The general consensus is that solving this would require a significant investment. An alternative put forward was to replace all the lights with LEDs. Sounds like a worthy hypothesis to test. – Andrew M Sep 17 '16 at 01:29
  • LEDs will flicker just as much (from experience, plus they have ballasts too, albeit at lower voltage). For just straight light replacement, incandescent bulbs will have much less flicker (if any) than either LEDs or florescents. – Brock Adams Sep 17 '16 at 01:39
  • Also has happened to me and worth a check: The lines to your building, and/or the power-company's transformer may be undersized for your (new) load. If the voltage fluctuates at the main service panel, make the power company fix it (their legal liability varies with jurisdiction). – Brock Adams Sep 17 '16 at 01:41
  • Flipping the problem: Your lights probably use much less wattage. So you could wire *them* to an affordable, line-regulating, UPS, or two, and solve the flicker that way (plus get emergency lighting). – Brock Adams Sep 17 '16 at 01:48
  • Now that's thinking outside the box! I believe that's the path to follow. Thanks Brock. – Andrew M Sep 17 '16 at 01:57

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