From: geckodrive@yahoogroups.com [mailto:geckodrive@yahoogroups.com] On
Behalf Of Mariss Freimanis
Sent: Saturday, May 09, 2009 4:43 PM
To: geckodrive@yahoogroups.com
Subject: [geckodrive] Re: What comes with the g540?
It makes no sense to use a wire gauge greater than 22 for wiring the G540.
22-gauge wire has 0.016 Ohms resistance per foot and a 4-wire motor cable
will dissipate only 0.39W per foot for a 3.5A current set. By comparison,
a half-Watt resistor is 30-times shorter than 1 foot and is rated at 0.5W dissipation.
Mariss
Och sen ett lite längre med uträkningar etc.
Common sense should rule. While everyone is busy disassembling their motors
right now for God knows what reason, has anyone noticed the gauge of magnet
wire after they take their favorite motor apart? It should be worth a quick
look.
I'll bet it's 24-gauge or less and there is a hundred feet or more all
tightly wound on the stator slots.
After you have a look, common sense should prompt you to ask: "What
difference does 6 feet of my cable wire gauge makes when it connects to 100
feet or more of this skinny stuff wound on the stator?" The answer should be
"Not much".
Pick a wire gauge that is easy to use. It won't be too small. Bigger is not
better unless you are into hurting yourself soldering big fat battery
charger size wires onto a DB-9 connector.
Rule of thumb: A cable that dissipates less than 1W per foot is OK. At
1W/ft, it will not melt, it will not short unless you wrap it with styrofoam
or something. That makes 26-gauge as the minimum wire size at 3.5A.
For current calculations: Microstep drives use sine and cosine currents. For
I^2 * R calculations, remember 1 = sin^2 + cos^2. This means use the set
current as the value for I in I^2 * R. Convert it to R = 1 / I^2 for
calculating maximum wire resistance per foot given a 1 Watt limit.
Use the following:
#20-gauge = .010 Ohms/ft
#22-gauge = .016 Ohms/ft
#24-gauge = .025 Ohms/ft
#26-gauge = .041 Ohms/ft
#28-gauge = .065 Ohms/ft
#30-gauge = .100 Ohms/ft
Remember: Current goes to and from a load. Two conductors carry that current
and two conductor are dissipating heat.
Change the equation to R = 1 / (2 * I^2) and at 3.5A you get 0.041 Ohms.
Look at the table above and it says #26-gauge is the smallest acceptable
wire size.
Were it a 1A motor, the answer would be 0.5 Ohms and even #30-gauge wire
would be oversized. #30-gauge wire is approaching the diameter of a human
hair by the way. It is so small it gets difficult to use as well.
Bob, about documentation: This detail is one out of a million myriad things
that could be mentioned in documentation. Were it and the other 999,999
things mentioned, no one would read any of them. What I'm depending on is
you as an expert user and vendor is to convey this information to your
clients.
I have given you the background and it took a lot of words. Just make it
simple; say "Use #22-gauge wire; larger wire gauges will blow up the G540".
That should take care of it.
Mariss
