Re: router speed control

--- 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 :-
)