Re: router speed control

A Current Transformer or CT is just a large coil wrapped like a
torrid. Then you pass one AC line thru that and the flux field of
the AC will energize the coil and you can measure mA output from the
coil. put that into your comapritor and presto ! instant monitoring.

http://www.jameco.com/cgi-
bin/ncommerce3/ExecMacro/Jameco/searchResult.d2w/report?
sort=BKW&search=current+transformer

sorry for the long link, Jameco P/N 174887
http://www.jameco.com/ $4.25

Dave

(can I have my watch back now ? :>)

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "caudlet" <info@t...> wrote:
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> <davemucha@j...> wrote:
> > Hi all,
> >
> > I have a Harbor freight router speed control. this is a common
> > device sold for between $20 and $30 bux. listed as 15 amps max.
> > Brush motors only.
> >
> > I wanted to monitor the amps in the router and was wondering if
> > anyone has any idea of the best place to place my current
> trasducer. ?
> >
> > (or a better way to monitor amps)
> > Dave
>
> Do you want speed or current? You can get speed (RPM) from back
emf
> of the motor since it is a generator as well as a motor. If the
> speed control has any ability to maintain a constant speed under
load
> they probably use that method. If the motor slows down the more
you
> load it (no feedback in the control) back EMF from the motor is one
> way to sense the loss of speed, if you just want to detect if the
> motor is starting to get overloaded then you can monitor the AC
> primary current anywhere in the AC path to that device. One neat
way
> I have seen is to take a standard AC transformer and connect the
low
> voltage side of the transformer in SERIES with the hot or negative
> lead (NOT ACROSS THEM!) The secondary must be rated for the average
> current draw of the load. The 120VAC primary then becomes the new
> secondary and will output a small AC current in porportion to the
> current flowing through the low voltage winding. The current is
then
> imposed on a resistor or two ends of a pot and it used to trigger a
> voltage comparitor, meter or other device to sense the value. This
> is a poor man's current transformer. Down side of current
> transformers is they are based on the frequency of the AC waveform
> (60HZ in this case) so their size is dependent on that. Current
> transformers for high currents at 60HZ are pretty large magnetic
> devices.
>
> Don't you love guys like me that come up with all these ideas but
> don't tell you how to build it!! Were called "Consultants". We
> borrow your watch to tell you what time it is and charge you for
it :-
> )