On Wed, 21 Nov 2007 08:20:59 -0800 (PST),
wrote:

Hi. thanks for the detiailed response JF.

I'm using the following solenoid: www.radionics.ie : RS Part number
search (top of page): 431-7560
(19mm push, 12V)

I'm looking at about 3.5% duty cycle.
It says on the datasheet( http://docs-europe.electrocomponents...6b805c2a1f.pdf)
that the wattage increase by the square of the increase in voltage.
12-72 = 6x increase so 36x increase in wattage. (1/36 for the duty
cycle)
7W at 100% duty @ 12V so we're looking at 252W on 72V on a 3.6% duty
cycle.

Unfortunately they don't mention current or resistance in the
documentation but I can go and measure tonight.

I found this,:

http://docs-europe.electrocomponents...6b805b88ed.pdf

so if yours is the 12V nominal unit it'll have a coil resistance of
20.7 ohms, so the current with 72V across it will be:

E 72V
I = --- = ------- ~ 3.5 amperes,
R 20.7R

and the power it'll be dissipating will be:


P = IE = 3.5A * 72V = 252 watts,


so the duty cycle must be limited to:


Pnom * 100% 7W * 100%
D = ------------- = ----------- = 2.778%
Pon 252W

or less to keep from overheating the unit.

So now we have enough to look at the power supply again,
but the energy stored in its magnetic field is going to generate a
nasty spike when the thing turns off and the field collapses. I
didn't see any inductance spec's in the data sheets, so can you
measure it or find out what it is?


--
JF