Re: wire gauge and steppers

Hi Jan,

my origional post was concerning the wire between the transformer and
the cap, then between the cap and the terminal strip.

the wires from the terminal strip to the Geckos is limited to the
Gecko's amp draw, which is very small, and the wire to the steppers
is the same, very small.

Since the 8 inches between the transformer and the rectifier is 18ga
and the 2 inches of wire between the cap and terminal stip is 18ga, I
was wondering if I was getting too close to the ratings.

oddly enough, it seems that on the charts I did find, 18 ga wire can
handle either 7 amps, or 19 amps, depending on which chart is used.

I have only 18ga stranded wire and telecom wire, or 12 and 14ga solid
copper (Romex) for house wiring.

I was hoping to not have to run out to Home Depot for a few feet of
some wire. (hour drive and it is the only place open on sat and sun)

Dave

--- In CAD_CAM_EDM_DRO@yahoogroups.com, JanRwl@A... wrote:
> In a message dated 4/21/2003 10:21:07 AM Central Standard Time,
> madyn@i... writes:
>
> > #18 ok to 5 amps... again, guessing..... #18 is used for 10 to 15
> > amps at 117, so again, no big deal... Household runs are often
in the
> > 70 foot range, but at more voltage drop permissible....
> >
> > What the heck, #16 or #18 is fine...
> >
>
> Harvey & Dave:
>
> I have done such connections for years, both "unipolar"
and "bipolar". The
> new "chopper drives" may send an "average" current approaching the
motor's
> design-current, but since the DC voltage is much higher (didn't you
say 35
> VDC supply?), the actual current from that power-supply's
transformer and
> rectifier is considerably less. However, once the filter-capacitor
> (thousands of µF) is connected across that unregulated DC, the
current from
> there to the drives becomes effectively more.
>
> ANYway, for currents up to 3 amps, #18 is VERY adequate for the
kind of short
> runs you normally have between the supply and the drives or
switches or
> connectors. I would have no fear of using #18 for Size 34 and
smaller motors
> up to six feet, and probably all the way on up to 12' would be
OK.
>
> The only time I think you would need #16 would be for Size 42
motors, cables
> over, say, five feet.
>
> Now the old fashioned UNIpolar drives generally sent (usually-
nearly-) FULL
> winding-current to the motors, "wasting" the excess available
voltage over
> those big power-resistors in series with the +common leads to the
motors as
> heat. Modern BIpolar drives such as the Gecko G201 and G210 (and
other
> brands I know nothing about) "chop" the DC so those resistors are
not needed.
> Those better chopper-drives then DROP the current to about 1/3
the "max.
> rated" current when the motors are still for, oh, two seconds.
Thus, MUCH
> current is NOT flowing, anyway, so even if the wires were a bit
small (say,
> one gage-size smaller than "mathematically correct"), it'd be fine.
>
> Here's a tip for EVERYONE who never realized it: If some
particular AWG size
> (say #18) is "right" for a given current (say 3 amps), then simply
ADD three
> to the gage-number to indicate the size adequate for HALF that
current (that
> is, #21 would be right for 1.5 amps); and SUBTRACT three gage-sizes
for TWICE
> the current (that is, #15 would be right for 6 amps.) Of course,
these
> examples begin with the assumption that #18 is right for 3.0 amps.
(I think
> like a transformer designer).
>
> Conductors in a cable such as a motor's four our six-wire cable
might be
> rated for more current that the same gage-size used as magnet-wire
in a coil,
> but this is simply due to the fact that wasted heat is more easily
dissipated
> from a loose cable than from a tightly-wound transformer-coil! So,
in this
> instance, the thing to keep in mind is the voltage-DROP due to the
wire's DC
> resistance at whatever current.
>
> What did I miss? HTH! Jan Rowland
>
>
> [Non-text portions of this message have been removed]