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Registered Member #186
Joined: Thu Feb 16 2006, 07:22AM
Location:
Posts: 42
Finally got my 555 driven boost converter working.
Charges a single 450v 470uf capacitor to 450v from a 12v lead acid battery within three seconds. (I have 17 more for my bank, so charging time shouldn't be too bad.) Not sure of the max voltage, but it's definately well above 450v.
Anyway, if anyone wants specs, I'll post em later. Right now, pics!
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Nice one! Now add a 5k resistor in series with the 1M, compare the voltage across that with a reference voltage and get it to switch off once it has reached a set voltage.
Registered Member #186
Joined: Thu Feb 16 2006, 07:22AM
Location:
Posts: 42
One wierd thing that I've noticed, though.... the inductor whines at the frequency of the 555. It sounds like it might be arcing, but there's no visible evidence of that.... though I can't keep it on long, since it'll over-voltage the caps after a couple of seconds.
Banned Registered Member #110
Joined: Fri Feb 10 2006, 12:23AM
Location: Banned City
Posts: 85
Ah closure. Was wonder if my previous advice was thrown out the window. See, 97% duty is not needed to boost 12v to 450v. Appears the signal is 1.5kHZ at ~70% duty. 47 Joules / 3 seconds showes this to be a 15 Watt charger. Not bad after overcoming a few problems.
The noise is just the frequency of oscillation. Try running at 20kHZ and the whine will dim down to inaudibility. There are techniques to suppress the noise for lower frequencies. 1. Keep the inductor away from proximity with metal surfaces. The noise will just be amplified. 2. Wrap a layer or two of double sided clear scotch tape around the ferrite core. I use ferrite beads because the coilforming is faster and layers are easy to form. 3. Make shure the coil windings are tight. A thin coating of epoxy or CA glue helps.
As always, the frequency must match the inductor. The higher the frequency, the lower and possibly smaller the inductor.
Registered Member #186
Joined: Thu Feb 16 2006, 07:22AM
Location:
Posts: 42
Haha. You should see the graveyard of parts I have. I overlooked a connection the first time around on the pcb and completely melted an IGBT, burned up multiple 555's (Oh well, I only have about 30 more of those... ) a capacitor, a few resistors (still good, but charred), and a few other IGBT's that are damaged, but not completely destroyed.
Anyway, I've come to a good balance for my frequency. It's high enough to limit current enough so the IGBT doesn't heat up too badly, and it's low enough to get good output. I've tried playing with the duty cycle a bit, but only with minimal gains in output with seemingly large amounts of heat increase. I even tried a < 50% duty cycle (Placed a diode across r2 and increased r2's resistance) with no clear advantages.
As for the whine, I've just wrapped it in tape after soaking it in a little CA... I somehow made it louder. Not sure how that happened. Oh well, as long as it doesn't interfere with performance, I'm fine with a little whine.
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Woooohooo! (Boost converter success)
