The neon bulb basically acts like a spark gap and is just a safty precaution in case the charging battery becomes disconnected so that the flyback voltage will have a way out of the coil, otherwise it is going to plow a hole through your transistor no current can flow through a neon unless there is at least 90v across the terminals, unlike an LED that will conduct at practically any voltage. Putting an LED across the emitter and collector is basically shorting the circuit, bypassing the transistor.
I've built a few of these fan motors (not performing as well as my big motor unfortunatly, though still fidling with different designs and coil configurations) and I don't think the neon is as essential for an average sized computer fan. I took the neon out of the circuit on one fan to see how high it would charge a capacitor and the transistor held up fine even after the capacitor was disconnected.
I've also tried recovering some seriously dead batteries and found the voltage reading isn't an indication of charge in the battery AT ALL! lol at first when you try charging a seriously dead battery, you are effectively just putting a resistor on that part of the circuit so the voltage will immeadiatly shoot up, then as the sulfation on the battery starts to break down, the voltage will start to drop again, then level off (takes about 24h depending on the condition and size of your battery). After it has leveled off it will slowly start rising again though it will probably take at least a month of charging and discharging for the battery to be in any kind of usable condition. and that is only if the plates haven't warped! Oh, the fun of it all!
I've built a few of these fan motors (not performing as well as my big motor unfortunatly, though still fidling with different designs and coil configurations) and I don't think the neon is as essential for an average sized computer fan. I took the neon out of the circuit on one fan to see how high it would charge a capacitor and the transistor held up fine even after the capacitor was disconnected.
I've also tried recovering some seriously dead batteries and found the voltage reading isn't an indication of charge in the battery AT ALL! lol at first when you try charging a seriously dead battery, you are effectively just putting a resistor on that part of the circuit so the voltage will immeadiatly shoot up, then as the sulfation on the battery starts to break down, the voltage will start to drop again, then level off (takes about 24h depending on the condition and size of your battery). After it has leveled off it will slowly start rising again though it will probably take at least a month of charging and discharging for the battery to be in any kind of usable condition. and that is only if the plates haven't warped! Oh, the fun of it all!
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