Hi guys, you may know the issue here.
I'm piecing together a high current 'mid-voltage' DC power source and I acquired a site transformer for the purpose (230V 1 phase to 115V 2 phase) and turned it into an isolation transformer by disconnecting the output centre tap to earth so the output floats. I have used two 3300uF 450V caps in a doubling configuration to take the 115 out and turn it back into 300V of DC.
(I tried loading a pic at this point, but the site still has this 'jpg size' bug, then it crashed 3 times loading a gif.)
OK, so in addition I added a 3800W voltage dimmer-triac type, off of Chinese ebay, in one of the two outputs on the site transformer. This dimmer works great with ohmic loads but I did try to 'dim' the input to the transformer and it didn't like it much. So I set it up to 'dim' the output. All works fine.
Now that I am running these two big caps, there are 'fluctuations' at certain voltages. So if I run a load off of the caps (to keep the triac switching) then I can control voltage smoothly from 50V to ~120V (across both caps), then the voltage goes 'bouncy' and unstable between 120 and 200 V, then it smooths for a while before going into a 10Hz or so oscillation at 'fully open' dimmer setting.
If I run the transformer directly into the caps (no dimmer) then no problem. Similarly, without the caps the dimmer works fine. So it appears to be an interaction between the dimmer and the caps. I figure this; the dimmer needs an actual current across it to switch, but the caps (being so big) end up pulling in all the current they need to reach some given voltage and the dimmer effectively turns off, then the voltage drops a little and the dimmer starts up again, etc...
I'd have thought the inductance in the transformer secondary would've kept current flowing.
Any thoughts/solutions? This voltage just isn't stable enough, but I would like (/need) voltage control.