wow, friday night, late, and a good few beers under the belt.

So why dont you guys all use Eudora? never a risk of viruses, no tagging
problems, simple ascii....

gonna ramble....(to Colin (always open to correction))
steppers are not too picky about voltage, but total power dissipation. You
have running current, giving you sufficient torque, and holding current,
keeping it where it was.

Best to run a stepper off a something like a L297, configured correctly in
current limit mode(use all those pins). So if your motor is rated at 240mA,
then set Iquiescent on Isense to 240mA. So now, as the motor runs faster,
the back EMF from the motor will rise , and a greater source voltage will
be required to overcome it to maintain the same torque. So you can run a 5V
motor with about 40V if you're expecting to run at high speeds, but the
motor will always be seeing the same current. Of course, the total power
will increase, and this will be the limiting factor, like how hot it gets,
and how fast you can get rid of that heat.

Now when the motor has stopped, you may wanna pass less than 240mA, just to
keep the motor cool, but that depends on the mechanics. If there's lots of
shuddering about, you'll have to hold it harder.

So often, steppers will be powered with a voltage supplying close to (or
less than) their rated current, to hold, but as soon as movement is
required, a much higher voltage will be turned on, to provide the torque,
as shown on the MC3479, where two resisitors are used to set the bias
current, Rb and Rb1.
But all this and more you'll find any any decent stepper drive app. note.

You don't need the LM317 if you set Rb and Rb1 correctly and use them, but
if you do use the 317, put a diode back to the source, and use enough
heatsinking, especially on the TO220 package.

Regards
Roland

At 09:44 AM 27/02/04 -0700, you wrote:
>Hi,
>
>I've got a stepper motor that's rated at 9.2V (240mA).  I'm just wondering
>how picky these things are about the voltage.  Could I run it off a 9V wall
>wart? Unregulated? Should I maybe add an electrolytic?
>
>I'm using an MC3479 to drive the motor.
>
>At the moment I'm using a 15V wall wart into an LM317 set to 9.2V, which
>works OK except that the 317 runs pretty warm.
>
>Thanks guys,
>Colin
>
>_________________________________________________________________
>Protect your PC - get McAfee.com VirusScan Online
>http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963
>
>--
>http://www.piclist.com hint: The list server can filter out subtopics
>(like ads or off topics) for you. See http://www.piclist.com/#topics
>
Regards
Roland Jollivet


JeM Electric cc
PO Box 1460
Kloof
3640
Kwazulu Natal
South Africa
Tel: +27 31 7024412
Fax: +27 31 7011674
Cell: +27 83 255 6017
Email: enquiries@caon.co.za

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics