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Messages - sam

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Hi all,
Thanks for the input.  I've got a nice system set up now, I'll describe below.

bkt, Thanks for the link to the valley fill circuit.  I had been wondering why there were 7 diodes on the pcb, and it's nice to know the source of the 60 Hz that's making it through the ballast. :)

Tesla500, nice idea -- very simple but I would have never thought of it.  I must say, I'm still a little confused how the DC is making it through the input filter on the ballast.  I thought there would be an isolation transformer that wouldn't let any DC pass... ?  Clearly not...

Nikon1, thanks for the schematic.  What is the transformer in this circuit doing?

Since I'd love to avoid depotting any more ballasts, I opted for Tesla500's solution, feeding an appropriate DC voltage into the ballast.  I didn't have a variac, but I borrowed a high voltage DC supply to test.  Sure enough, with ~100V DC, the ballast produces a constant amplitude 100kHz signal (TEK00115.PNG and TEK00113.PNG, attached) and the lamp lights without any flicker.  For a permanent solution, I ended up buying this power supply instead of building my own rectification circuit:  The controllability and current display is nice, and I'll definitely use it for other projects as well.  I think the appropriate voltage is around 105-110V -- after the lamp has warmed up this puts the power draw near 55 watts.

Here's a soap film video (3kfps) without any flicker:

Hi all,
I'm hoping to tap into the collective brain for a problem I'm working on.  I've been using my lab's Chronos for recording turbulence patterns in my soapfilm tunnel.  Here are some test videos I took:

The pressure distribution on the flowing soap film causes light and dark interference fringes when illuminated with a monochromatic light source.  Currently, I use a 55 watt Philips Low Pressure Sodium lamp (  To drive the lamp, I'm using a Fulham workhorse 5 (, as I saw many people had had success using this ballast with LPS lamps.  When I bought it, I thought I would be free from 60Hz flicker because it is advertised as an "electronic" ballast.  Unfortunately (as you can see in the videos), the 60 Hz flicker is alive and well...

I scoped the output to get a sense of what was going on, and I saw the nice ~100kHz waveform I had expected (TEK00110.PNG attached -- don't worry about the voltage scale; it's measured through a capacitive pickup, so the absolute scale doesn't mean anything).  When I zoom out in time I see the amplitude of this high frequency signal is modulated at 60Hz (TEK00111.PNG attached), explaining the flicker.  So, my ballast is indeed an electronic type, but it is passing through the 60Hz frequency content from the mains. 

Initially, I had assumed the circuit in the ballast was something like the block diagram here:
I thought the flicker could be coming from not having enough capacitance after the rectification to sufficiently smooth the signal.  So, I opened up the ballast and de-potted the pcb from the disgusting black tar... and found what looked like the diagram above (image attached).  My thought was just to replace the blue electrolytic capacitors with larger ones.  But, when I (carefully) probed the circuit, I didn't see what I had expected after the rectification stage.  Instead of a near-DC signal, I saw the sine wave clipped into positive and negative pulses before getting sent into the chopper.  So, I didn't know how to proceed...

So, I'm looking for some advice.

1. Does anyone in this forum has experience with LPS lights and their ballasts?

2. Anybody know other electronic ballasts that work with LPS that might have less flicker?  I tried this one (, but I don't think the striking voltage was high enough, as the arc never formed (just a halo around the electrodes).

3. Is there an external power filter module I can put in series with the lamp to filter the 60Hz (and avoid any depotting...)?

4. DIY no-flicker LPS driver? 

5. any other ideas?

Chronos User Discussion / Re: Let's talk lighting
« on: September 16, 2017, 06:10:41 AM »
Inspired by tesla500, I rigged up lights with the Chanzon 100W led modules ( here now, but this link moves around...).

I drive each of them with one of these constant current boost converters each.  This is probably overkill, but these are so cheap...  I mount the LEDs to the front of a cpu water cooling block, and the drivers to the back.  Right now I'm driving 3x100W LEDs, a water pump, and fan for the radiator with a 500W ATX power supply. 

Overall, this is ~25k lumens for ~$100.  It stays plenty cool, and works well, but I think there's lots of room for improvement.  And of course, now that my camera has arrived, it doesn't seem bright enough any more!

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