On Tue, 08 Jan 2008 17:25:49 -0600, John Fields
wrote:


---
Since you're driving the 12V, 100% duty cycle coil with 24V, that
mandates a 25% (or lower) duty cycle so, assuming it's going to be
working 100% of the time, I think a good idea would be to drive it
with something like a 555 wired like this:

+24----------------------------------------+
|
VCC--+--------------------------------+ |
| | +------+
[20k]R1 +---------+ | | |K
| |_ | | [COIL] [1N4001]
+-------------7-O|D Vcc|-8---+ | |
| R2 | _| | +------+
+---[82k]---+--6-|TH R|O-4--+ |
| | |__ | | D
+-[1N4148]-+-2-O|TR OUT|-3---|--G NCH
| | GND | | S
[C] +----+----+ [0.1µF] |
| |1 | |
GND--------------+---------+----------+----+

Note that a pot can be substituted for R1 and R2, so you can adjust
the frequency, as required, to accommodate the inductance of the
coil, by choosing the end-to-end resistance of the pot and then
choosing the duty cycle by cranking the pot.

---
Or, change the frequency by selecting an appropriate 'C', duh...


--
JF