how to reduce output from 32 vdc power supply

[LarryH]

I am working on a project that has a 32 vdc stepper motor for which I have a power supply. However, I would like to use the same power supply to power a 24 vdc, 6W solenoid.

Is there a simple, inexpensive way to reduce the 32 vdc to 24 vdc?

I saw a diagram utilizing two resistors in series. The stepped down lead came from between the two resistors and one of them went to ground. Would something like this work and if so, how do I calcualte the resistance?

I am a total novice so need all the help I can get with this.... TIA

 

[Reloadron]

All you need is an LM7824 simple 3 terminal voltage regulator. This is the data sheet for the LM78XX family. It cost literally a few USD.

Ron

 

[duffy]

If you want to use a resistor, use Ohm's law like this: A 24V, 6W coil, will have a resistance found by V^2/6W = 96Ω. Then you divide the 24V by the 96Ω and find the coil uses .25A of current. You want to "burn off" 8V (32V-24V) so divide that by the .25A and presto! 32Ω. 33Ω is the closest standard value, so use that. The resistor will need to be 8V x .25A = 2W, so make it a 5W to be on the safe side. A 5W resistor costs less than a buck.

 

[Reloadron]

Yeah, matter of fact if all you have is the solenoid and nothing else, do as Duffy suggest.

Ron

 

[4pyros]

Use a .25 amp, 12 volt lamp. Like a #158 Automotive lamp.

 

[LarryH]

Thanks, everyone. Really appreciate the quick responses.

Reloadron - tried to get a source for the part you linked to and Mouser and Newark indicate "obsolete and therefore unavailable" - this was only for the 24v. You seem to know this stuff - is there another part number for perhaps a newer model?

Thanks again

 

[4pyros]

Thanks, everyone. Really appreciate the quick responses.

Reloadron - tried to get a source for the part you linked to and Mouser and Newark indicate "obsolete and therefore unavailable" - this was only for the 24v. You seem to know this stuff - is there another part number for perhaps a newer model?

Thanks again

https://www.amazon.com/7824-24V-Voltage-Regulator-TO-220/dp/B0002ZPX78
Search without the "LM".

 

[duffy]

In stock at DigiKey -
http://search.digikey.com/us/en/products/LM7824CT/LM7824CTFS-ND/1923055

 

[LarryH]

Thanks, 4pyros and Duffy.

While thinking it was unavailable, found an adjustable regulator at the local Radio Shack and got it tuned in perfectly. However, the 24v sounds easier.

Is there basically any difference in using the regulator vs. using a resistor? Would they both allow the same amount of current in the circuit?

Thanks again, it is really nice to be able to post a question and get answers so quickly.

 

[colin55]

The cheapest is use a string of 1N4004 diodes.

 

[duffy]

The resistor will fire the solenoid more quickly - the reactance of the coil at "time zero" is infinite, so the voltage it would see will be the full +32V instead of +24V, which is why the L/R time constant is lower. Usually this is an advantage with a solenoid, sometimes it is not.

If you have anything ELSE that may want the +24V, you need to use the regulator.