# Need to drop from 38vdc to 24vdc

I need to drop from 38vdc to 24vdc (current unknown) to control a 24 relay. What is the easiest way to do this? All the regulators and buck/stepdown converters that output in the 24v range have a max input of 32 volts dc.

What is the easiest way to accomplish this?

Easiest ?

Add a 14 volt zener in series with the relay coil.

If you are only going to control a relay, you can use a resistor in series with the coil to drop the excess voltage.

herbschwarz:
If you are only going to control
a relay, you can use a resistor
in series with the coil to drop the
excess voltage.

â€¦but it will slow down the relay slightly

Actually, the relay will be [u]faster[/u] when driven by 38V, with a series resistor, than with 24V and no series resistor. In the "old days" the high voltage/series resistor technique was used to speed up the step rate of high impedance steppers.

moses1592: I need to drop from 38vdc to 24vdc ([u]current unknown[/u]) to control a 24 relay. What is the easiest way to do this? All the regulators and buck/stepdown converters that output in the 24v range have a max input of 32 volts dc.

What is the easiest way to accomplish this?

If the coil is DC, use a DMM to measure its resistance, then use Ohms Law. Tom... :)

More specifically, add a series resistor slightly more than half of the relay coil resistance. Will probably need to be at least a half watt resistor.

Don't forget the diode! :astonished:

jremington: Actually, the relay will be [u]faster[/u] when driven by 38V, with a series resistor, than with 24V and no series resistor. In the "old days" the high voltage/series resistor technique was used to speed up the step rate of high impedance steppers.

That means my CNC machine is old :confused:

Yes I guess it is, it is controlled with a program running on 'Windows 95' :zipper_mouth_face:

Have two more 95 machines incase the CNC one goes up in smoke. :)

What is the relays coil current or resistance or wattage?

Have two more 95 machines in case the CNC one goes up in smoke

Do you have a bottle of Scotch in case those go up in smoke ?

I have Frangelico :)

Just counted, I have a total of 4 Windows 95 machines so I think I can drink the liquor myself. ;)

You need to check again, I found buck converters with over 50VDC input. I found them on eBay for less then \$10.00. Try searching for high voltage input buck converter.