CAD CAM EDM DRO - Yahoo Group Archive

Re: Where to buy non induction resistors

Posted by beer@s...
on 2002-03-28 13:07:50 UTC
On 28 Mar, CAD_CAM_EDM_DRO@yahoogroups.com wrote:
> Message: 5
> Date: Thu, 28 Mar 2002 20:28:40 -0000
> From: "lenskeeper2000" <rnichol1@...>
> Subject: Where to buy non induction resistors
>
> Where can I buy non-induction power resistors? I'm using a simple
> L/R style drive circuit and want to step up my voltage but have found
> I have too much inductance to get my speed rate up. I'l thinking if
> I can reduce the effect of the wire wond reisitor's im using this
> will help.

Almost certainly won't help.

The very small inductance of the resistors, IN THIS APPLICATION will be
swamped out by the very large inductance of the steppers.

Now, when used as a sense resistor in a chopper scheme, the story
changes.

> I've seem lots of power resistors for sale (allied etc.) but none
> seem to be non inducting. Looking for 25 watt in the 20-25 hom
> range. Any suggestions?

Digikey sells 5 watt NI resistors .. you could parallel a bunch.
Or ...

> I'm trying to keep on a budget and am trying to learn electronics
> while upgrading my desktop CNC mill. so holding off going to a
> chopper curcuit as I want to design myself (will leikely eventually
> give in and by Gecko drivers).

Feel like a designing sort of mood ?

Replace the resistors with a constant current source. Things will spin
MUCH faster, as fast as any chopper setup with none of the chopper
headaches.

Before you do, though, spend a moment calculating power consumption.

In my case, they were 2 volt 5 amp motors that I was running from a
50 volt supply. The constant current source would therefore have 48
volts across it at 5 amps .. 240 watts per coil .. hmm, where's that
book on chopper design.

However, having some BIG heatsinks around from YAAANC ( yet another
audio amplifier never completed ) and more TO3s than I could shake a
stick at, I did spend the time. It DOES work.

Alan

--

Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta

Discussion Thread

beer@s... 2002-03-28 13:07:50 UTC Re: Where to buy non induction resistors