> I need to produce a single spark at a very precise time
> My problem: The FET heats up beyond reason.
> How would I trigger a single spark from a coil, using a 555 timer,
> based on a repeating trigger (The trigger is located on a rotating
> shaft which houses the sparkplug... but I only need one spark).
Try a 25-30 amp FET. The on state resistance should be about 0.06 ohms
and will dissipate only 2 watts at 6 amps.
Or, you can use a CDI arrangement, but you need a high voltage supply
which could be made from a 555 and a buffer to drive a transformer.
The supply impedance (R) needs to be high enough so the SCR turns off
when the coil discharges. Otherwise it will trigger once and leave a
short on the supply.
R 1-2 uf 400 volt non polorized
+300 volts DC <--------\/\/\---+-----+----| |----+
V |
--- )
Trigger pulse <--------\/\/\-------/ | 10 amp ) Ign coil
(+12) 510 ohms | 400 ) primary
| volt )
| SCR |
| |
| |
common negative <------------------+-----------+
Bill
Date: 1 Dec 1995 16:57:31 -0500
Original Subject: Just one spark!