This is the circuit I’m using for a Dave Lawton style dual 555-timer circuit Stanley Meyer water fuel cell pulse width modulator (PWM). I’m using an LM556, as there appears to be a run on 555s. This is the ‘D14′ circuit. All the parts were acquired via Digi-Key.com , who continue to do an outstanding job… great web site, good prices, fast shipping.
27-JUL-2008 Something is wrong with the MOSFET bias. I’m not getting any amperage. I had this plugged into the test power supply I’ve been using, and while I’m seeing voltage, I can’t get any current flow. It should have blown the fuse. I’m thinking I’ll put a trimpot on the output of the second timer to the MOSFET. Schematic shown here updated. Quick fix for old circuit: cut resistor from MOSFET gate to Ground, it’s 1.1K, so brown-brown-red. There are two of them, cut the one that connects to the busbar running under the IC.
28-JUL-2008 It works. Schematic above updated.
01-AUG-2008 Here is a scope picture from my analog Tektronix 475, 5 volts per division vertical and 1 milliSecond / div horizontal. This is with the 28V supply, scope hooked to the output across a 4.7K resistor… so this waveform is about 200 Hz gate and 2900Hz hum.
I put a self-resetting circuit breaker in the box, I was blowing too many fuses. Also added was another LED with a 1.5K resistor across the breaker, this indicates when the breaker is tripped. At 14 volts, 6 amps would be 84 watts, 7 amps would be 98 watts, and the MOSFET is 100 watts, so I thought a 6 amp breaker would work right. Turns out it snaps (kinda makes a “ponk” sound) at a steady 2.4 amps, although it takes a while for it to heat up. This isn’t really bothering me, as I don’t really plan on running it at more than that, but it is a little curious. I suppose I should have expected it, but only experimentation really showed the result. The breaker is in series with the fuse holder, which is now a 15 amp fuse, this will provide some safety, but likely still blow out the MOSFET if the electrodes get shorted. With the zener diodes, maybe not. I suppose I will find out one day on accident, not sure I actually want to cause that yet, I’m wanting some mileage out of this thing before I have to redesign or scrap it. Then again, the incredibly awesomely named OSCILLATION OVERTHRUSTER circuit should run circles around this open-loop approach.
DOH! this isn’t a steady 2.4 amps, it’s an average 2.4 amps. Maybe the breaker is more reactive than I thought it would be, and is doing what it can with a pulsed current. Okay, I can’t blame it for that. Another theory: I damaged the breaker soldering the wire to the spade lug and it’s overly sensitive.