limiting voltage from DC power supply

[bsoder]

I'd like a way to provide myself a constant 11.1V supply to test motors with. I have a 25A DC power supply already; according to my charger it's putting out 14.05V. I was thinking that a really easy way to do this would be to put an adjustable load (rheostat?) in series with my wattmeter/ESC/motor/receiver stuff on my test stand, then just adjust it until my wattmeter reads 11.1V input. Does that make sense? Any suggestions as to what to use for the load? If I'm understanding things correctly, it'll need to handle 2-4V at up to whatever amperage I'm going to be testing - I'd want it to be able to handle up to the limit of the power supply, 25A.

Mabye there's a better way to do this? Feed the entire load through some sort of voltage limiter?

[z-matrix]

3-4 parallel connected bd250 ( balanced using 5w 0.1 ohm resistors at the emmitters ), 1 lm 317, the high current metal can version, and 2 resistors at the feedback pin ( use potmeter to make it adjustable ).
you can get the datasheet and some sample circuits at
www.national.com => LM317 (http://www.national.com/pf/LM/LM317.html)

[bsoder]

You're somewhat over my head here - it's been a LONG time since I did any circuit design. Are you talking about a limiter here or just an additional load?

[vintage1]

Don't put resistors in series...it will upset brushless controllers.

Use a proper linear regulator, and a fat capacitor on its output.

[Acetronics]

Hi, Bsoder

A really stupid ( nowadays another word for simple :D ) way is to use on the mains side of the supply a simple dimmer for Halogen lamps or inductive loads ...
Note you will find such a design (auto - regulating ...) on mains side of High power linear supplies ... to get an acceptable heating of the ballasts.

as Vintage says, a big capacitor on your supply output will kill your lasts fears ...

That's also the cheap way to trim the foam cutting wire temp. ;)

Alain

[bsoder]

How about this for a solution: the power supply I have is a pretty standard deal - 25A radio shack switching supply. I opened it up, and there's a 1K trimmer pot (102 stamped on it.) I adjusted that pot from 0-1000 while checking the output, and at 1000 ohms the output drops to perhaps 12.5V. If I replace that trimmer with a pot that goes to say 2K, will I hurt anything if I use that to reduce the voltage?

[bsoder]

Nevermind, tried it. I could drop the voltage to about 11.8V but below that the supply goes funky. I've put the original pot back in.

Alain, are you talking about basically reducing the incoming AC voltage to my power supply using a dimmer switch?

[Terry S]

Adjust a pc power supply.

Terry