[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Controlling 28V relays

Estes, your idea is neat.  A manual voltage doubler.

Another circuit that occasionally comes in handy when you have
a 28V relay and a 12VAC winding is to use a conventional
voltage doubler, feeding a large electrolytic through a
dropping resistor.  With the relay off (no load on the doubler)
the cap charges up to 35VDC or so.  When you pick up the relay,
it snaps in smartly, then the voltage slowly drops off to a
nice holding voltage, limited by the dropping resistor.
When you drop out the relay, the cap again charges to 35V,
ready to snap in the relay next time.  I think it's a good
idea to use a scheme like this on relays in hot locations
(such as up in a box near your antennas) for long coil life.
John  W5EME

Estes Wayne-W10191 wrote:
> John Harrington wrote:
> Another very good approach to boost 12V to 17+ volts is to use
> commercial packaged DC-DC converters.
> Since the output is isolated from the input, you are free to put
> the 5V output in series with the 12V input and get 17V total.
> Wayne replies:
> That's a clever idea.  You can also use a passive circuit to control a 28V relay with a 12V power supply.  I'm surely not the first person to do this, but I did get it published in QST Hints & Kinks in Dec. 1995.
> I use a DPDT switch to latch a 28V coaxial relay with a 24V pulse, then keep it latched with 12V.  When the DPDT switch is in the OFF position, it charges a large Electrolytic capacitor.  When the switch moves to the ON position, it places the capacitor in series with the 12V power supply.  Current flows through a diode after the capacitor is discharged.
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org