Effects of Recirculating BEMF to Coil

[gotoluc]

Error

[poynt99]

Luc,

It would be a tough call to identify exactly what happened there without actually being there and examining the setup for burn marks etc. Also it would be prudent to use a volt meter and measure the voltage between your soldering iron tip and either of the leads or wires of the coil that may have come in contact with the iron.

But if I was to guess based on your description of what happened, I would say that you had either 120VAC alone (due to contact with the soldering iron), or a combination of 120VAC and 170VDC going through your coil for a brief instant. It all depends on earth ground paths etc. Not sure about the flash you saw, but it was more than likely a spark/arc from the transient high voltage and current.

.99

[gotoluc]

Hi .99,

thanks for the reply

that's true! it could of been a mix of AC and DC. The flame left no markings what so ever. It was orange in color, much like Hydrogen burning.
In my setup half the full wave bridge rectifier positive side goes direct to the coil and the negative side goes through the mosfet. The soldering Iron goes to ground, so if I touch the coil on the mosfet side I activate the coil with half the DC voltage (80 vdc) of positive side of the bridge.

Let me know if you think this is worth reproducing to study it more.

Thanks

Luc

[poynt99]

Luc,

Are you sure only half of the full wave bridge goes to the coil? I'm not sure I understand what you mean. I thought you had  +170V at the coil?

If your negative side of the 170V supply is tied to earth ground, then by touching the iron on the MOSFET side, you are applying 170V across the coil and fully discharging your capacitor into it. Yep, this would give the neo quite a kick!

You could try this again, but in a controlled manner (i.e no MOSFET present and don't use the iron as the ground path) just to prove that this is what most likely happened.

.99

[gotoluc]

Hi .99

yes a total of 170vdc is at the capacitor but if I put my voltmeter between Earth Ground and each of the leads going to the coil (leads now disconnected from coil) I can only measure the positive side of the capacitor as the other side is blocked by the mosfet. So I can only be sure half the capacitor voltage is going through but since the mosfet fried when this originally happen then it is quite possible the full 170vdc of the cap was at the coil.

I hope this help you to understand

Let me know

Luc