oops and update of Re: SP-3/HT (dropping resistor calcs)

Hello,

I'm not sure why, but I went back to the stepperworld site. I noticed
that I had missed a detail or two. Oops! So here's the update:

The sp-3/HT (Forgot that HT in the subject line of the post) DOES
HAVE the power resistors (with a pic). Sorry I missed that the first
time around...

So I'm looking and trying to think of why you can't go faster, as the
setup is pretty much an optimised 5804 setup. Looking at the board
printing, I see that you have the "dipswitch" option of hi-torq(HT),
wave drive(wd), or halfstep(HS). Now WD will be faster than HT or HS,
but will have less torque since it is a "one-coil-on" type of drive,
whereas HT will be "two-coil-on" and HS will alternate between one
and two-coil-on... And with these relatively lo-torque motors, you
don't want to go "one coil on", IMO. But you can try it and see if it
works for you.

Then I noticed that the motors offered are DIFFERENT with the HT
system! The nameplate (hard to read, so these are best guess) on the
superior(brand) motors shown as being sold with the sp-3/HT system
are 12v,0.4A! If true, this is good news! These motors have a higher
inductance than the 5V,1A motors offered with the "plain" sp-3
system. This will make them slower than the 5v,1a motors!

Why stepperworld would double the supply voltage for speed, and
then "give it back" by using these motors, I can only guess... <G>

Remember the wattage calc from my last message? With these motors it
becomes 24 volts x 0.4A = 9.6 watts. This means they can use a
cheaper 10 watt power resistor by using this motor. The aluminum
finned case type shown in the pic can be pricey. And there are six of
them.

So here's what I would do (if the nameplates on your motors match my
assumptions). Ask stepperworld to trade your superior motors for the
5v,1a type. If they won't, these 5v,1a motors are VERY cheaply found
at most surplus electronic suppliers (about 5 or 10 bucks each).

You will then need to replace the included power resistors(let's do a
calc here to double check) Using my assumptions for the new motors,
the original resistors will be:

24-12-1/.4 = 27.4 ohms (so they could be anywhere from 27 to 35
ohms, or so) and are prob'ly 10 watt.

Using the calcs from my last message for the 5v,1a motors, you need
to get six 18 ohm (or something close like 20 ohm), 25watt power
resistors. digi-key or mouser can have 'em to you next day (both are
online). Simply replace the old with the new, and you're set.

Hope this helps.

Ballendo

P.S. Remember the "squarish" and "gritty" description I gave for
power resistors? That type is sometimes called "sand", and may be
less expensive than the finned aluminuum type. In either case(pun
intended), the new resistors will be larger in size than the old
ones. So you may have to modify how they are arranged on the metal
plate stepperworld has used as a heat sink to get them to fit. The
sand type will need to be held down to the plate by a simple metal
bracket to utilise the plate as a heat sink. The bracket(s) needed
could be easily made, or purchased. The alum. type already has
provision for screws to hold it down. Both types will work in this
application.

--- In CAD_CAM_EDM_DRO@y..., "ballendo" <ballendo@y...> wrote:
> Woodknack,
>
> Reducing the voltage will DECREASE motor speed. Look elsewhere for
> the speed "limit", IMO.
<snip of relevant post>