Products > Dodgy Technology
Another Aliexpress special, the AC DC eliminator
johansen:
--- Quote from: Andy Chee on July 19, 2024, 06:26:17 am ---I refer to the attached electronic ballast circuit:
(Attachment Link)
Note that C17 is effectively a DC blocking capacitor. The value of C17 and L2 must resonate at the correct frequency for the tube to operate.
If the aliexpress capacitor is installed in a similar position in a magnetic ballast system, who knows what the resonant frequency is.
Using the aliexpress value of 20mF and ballast inductance of 400uH, the resonant frequency is 56.3Hz. Uncomfortably close to mains frequency.
I don't know what the inductance of a magnetic ballast is.
--- End quote ---
Please examine the rest of the circuit...
Gyro:
--- Quote from: SeanB on July 19, 2024, 04:30:11 pm ---I have used a capacitor as a current limit in a flourescent lamp circuit, and for small tubes it works well enough, though it was running the tube slightly high in current, so it did suffer from sputtering on the ends rather rapidly. However you also got them used as part of the ballast in lag lead use, where you use a single ballast for 2 tubes, and the capacitor provides a phase shift on the second tube, so that with the combination you get absolutely no flicker in the light output from the fixture, though unfortunately you have to use T12 tubes, as T8 have too high a strike voltage to operate like this, and you also need a grounded reflector close to the tubes to keep them lit reliably as they age, or use the special tubes with a starter strip on the glass that is used with a contact touching the caps, to provide an electric field to ensure reliable striking every cycle.
--- End quote ---
I have an 8ft 125W florescent lamp in the garage that has a traditional inductor ballast and a capacitor in series. That possibly does form a tank circuit to improve striking voltage, I don't know. The configuration was in the old Philips lighting catalogue for long tubes. Circuits for other (shorter) tubes just had the series inductor, with the capacitor across the mains input for PF correction.
P.S. The starter strip tubes were also used for dimmable installations, where the heaters were powered from separate, well isolated, secondaries of a transformer. They were pretty rare though. Winding a length of fuse wire along the length of the tube and tying the ends to the end caps (or even a pin at one end!) was an old bodge for getting tubes to strike reliably when the supply was a bit on the low side.
Circlotron:
--- Quote from: Gyro on July 21, 2024, 11:58:16 am ---I have an 8ft 125W florescent lamp in the garage that has a traditional inductor ballast and a capacitor in series. That possibly does form a tank circuit to improve striking voltage, I don't know. The configuration was in the old Philips lighting catalogue for long tubes. Circuits for other (shorter) tubes just had the series inductor, with the capacitor across the mains input for PF correction.
--- End quote ---
Maybe this? -> https://maker.pro/forums/threads/capacitor-in-series-with-fluorescent-ballast.55257/
madires:
--- Quote from: SeanB on July 19, 2024, 04:30:11 pm ---However you also got them used as part of the ballast in lag lead use, where you use a single ballast for 2 tubes, and the capacitor provides a phase shift on the second tube, so that with the combination you get absolutely no flicker in the light output from the fixture, though unfortunately you have to use T12 tubes, as T8 have too high a strike voltage to operate like this,
--- End quote ---
There are special starters for in-series setups, e.g. Osram ST151 or ST172.
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