New comer needs any and all help

[TinselKoala]

You don't need faith, all you need is patience and a bunch of spare parts.

I presume the transistors you got are 2n2222a types, little black plastic ones not little metal tophat cans. You got a good deal, but what are you going to do with all those transistors?

I use 2n2222a types myself as relay drivers or inverters; they are one of the types that are very useful for general purposes like switching and amplification, a little higher performance current-wise than the 2n3904 type. I don't think they can take the strain of the Bedini high voltage, though.


I just came back from RS myself and I am not too pleased. I got two 2n3055 transistors, they look good, have manufacturer's label on them, usually a good sign ... but one failed within two minutes of installation, at an input voltage of 24 volts, which I can use with no problems at all on all my old ones. It stopped switching and went into an oscillation mode that made high-freq waveforms very similar to a Joule Thief.... but at high current, like one amp, and no drive pulses. I could hear the oscillation, increasing in frequency like a bomb about to go off... so I pulled it and put the other new one in. I'm kind of scared to run it up to 24 volts..... I can't afford to be tossing away three dollars every time a transistor fails. But it's pulsing fine, a little weak on the HV, but it does run both ring oscillator loads at 16 or 17 volts input.

I think that if I hadn't gotten lucky that first time and picked the best transistor out of my bunch to start with, I might have concluded that my motor didn't work. Without instruments like the scope and the multimeter it would have been hard to tell at first. So the moral of the story is.... DON'T GIVE UP.

[jhsmith87]

I just got the transistors cause it was such a good deal. I could at least use them in the jt.

[TinselKoala]

That is true, although the 2n3904 works at a bit lower voltage. However, as I always say, you can't be too rich or too thin, or have too many 2n2222a's.

I found this website that has more information about Bedini motors and variants than anyone needs to know, and he's got schematics and also drawings of his circuits for you to look at, from the simple ones that we are dealing with to ones that are much more complicated.

http://www.fight-4-truth.com/Schematics.html

I've just used my motor to charge up two AA batteries that were depleted to below the point of lighting a JT. Now they will. I charged them in series; they started at below 2.4 volts for the pair and I stopped charging when they read 3.5 volts under charge, then they relaxed down to about 3.1 volts. This was not a serious attempt at charging; I'll use the SLAs for that once I'm happy with the circuit. I don't have a tuning pot in mine yet, I have to put one in and try it, to see if I think it's necessary.

The page I linked above has all kinds of different core materials. I like the "black sand" mixed with epoxy, it has a suitably cosmic connection, since much of the black magnetic sand one can harvest by the methods he lists, is actually micrometeorite debris.

Oh, I forgot to mention... I went to a 470 Ohm, one Watt resistor for the base resistor, after I looked at the B - E waveform on my scope. It too has large HV spikes, and the max rated B-E voltage of the transistor is only supposed to be seven volts. It's a good thing the spikes are short duration.

[TinselKoala]

Ok.... .now I've started using my 2, 12 V 5 A-H SLA batteries. I'm running on one, called "B1", and when it hits 11 volts I'll take it out, put "B2" in there to run, and hook up "B1" to be charged. We'll see what happens.

I also decided to try the variable pot - light bulb combo for the base resistor. I have a good "Type J" pot that is 2.2 K, so I put it in series with a small light bulb and a 10R resistor as shown in the Bedini variant diagram below. This allows "tuning" the circuit, and I can show on the oscilloscope just what this tuning does. It does indeed have a "sweet spot" or narrow range of resistances for best performance.  The basic pot setting varies the duty cycle, that is, the length of time that the Drive pulse is "on". So if you turn the pot one way, the duty cycle decreases and the motor slows down. If you turn the pot the other way, the duty cycle increases and the motor speeds up BUT--- you quickly get to a point where the High Voltage spike decreases in amplitude, in other words the charge rate will drop off and your High Voltage devices won't work properly. So there is a sweet spot for the base resistance, and I imagine this changes with winding turns number and overall circuit resistance (wire size) and also input voltage.

I'll shoot a short video showing the effect of varying the base resistance on the scope trace from Collector wrt Ground (emitter), in other words across the neon.

ETA: there are so many different diagrams. Some show a 10 R and some show a 100 R.... but since it's the total resistance that matters here and you have the pot, you can use whatever is handy in that range I think. Obviously with 100 R in there I am not going to be able to get my motor to the HV decrease point of 73 ohms. A resistor of some value should be in there to limit current if you inadvertently turn the pot to its zero resistance value.

[TinselKoala]

OK, here are some numbers from the Base resistor tuning test.

I am using the "B1" battery which is at 12.61 volts under the running load. I put a small 12 volt auto dome light bulb in the base resistor, it measures 8.8 ohms cold. I put the 10 ohm resistor and the 2.2K ohm pot, all in series. This then is the total Base resistor.

I start the motor and let it come up to stable speed. Then I tune the pot, first for the "sweet spot" of best running, max RPM. Then I disconnect the power, unsolder one end of the total Base resistor and measure its value with the Fluke 83 DMM.
Then I resolder the resistor, re-hook up the power and restart, allow speed to stabilize, then I tune for the "multiple pulses" point, disconnect, unsolder, measure, resolder, restart.
Then I tune for the HV dropping point, ditto.

Here are the results:

Sweet Spot: 1125 RPM, 311.3 Ohms total Base resistor, 80 mA current draw from battery.
Multiple Pulses: RPM weak and decreasing, 1554 Ohms total Base resistor, 50 mA current draw.
HV Decrease: RPM not recorded but near 1000 and dropping, 72.9 Ohms total Base resistor, 110 mA current draw.

The motor would not start from reasonable starting spin at the "Multiple Pulse" setting, and would start only with difficulty at the "HV Decrease" setting. The added light bulb is dark, but starts glowing dimly, as the resistance is decreased, just before the HV Decrease value.

So to tune for the sweet spot without a scope, start with the resistance at around 500 ohms, then turn the resistance lower  until the little bulb just barely starts to glow: this is the HV Decrease point. Turn the resistance up from this point until you hear the sound change (Multiple Pulses, I can hear the difference easily) and RPM drops, then back off on the pot about 1/3 of the way back to the HV Decrease point. This will be close to your "sweet spot" and should give a current draw about halfway between the values at HV Decrease and Multiple Pulse points.