What gage wire?

[WilliamD]

I'm going to start wiring my Geckos and power supply up this weekend. I have the breakout board and motors also. I was wondering what kind of wire people use? My motors are 4 wire, so I was thinking about getting some surplus USB wire, and using it for the motors. Does regular 16 gage coated wire work? I don't see much mention of what people use. It's probably so obvoius and right in front of my face, I don't mind if you chuckle at me.

[NC Cams]

It all depends how much current you are drawing and how long your runs are.

If you are in the science project mode, take a proposed length and draw some current near your peak load and measure voltage drop across the length. Recall that E=IxR (a relationship we need to review every so often) and since you know/control I and can measure E. Is R too high or tolerable??? In a servo, whatever you do to keep E loss low results in free extra speed (and more torque).

For a few amps that approaches double digit levels, 16 is probably fine. Start drawing double digit current and you may want to step up (size wise) a gage or two to 14 or even 12 for heavier current draws. For flexibility, be sure to use the finest stranded stuff you can find.

We were running R/C car motors (4.8 volts at 20 amps DC) on 10 gage ultrafine strand with runs never over 6". Overkill??? Sure but a 0.2 volt drop reduced power by 4.2% and you can never have enough power.

Watch your jacketing as some wires don't survive coolant well.

[WilliamD]

Thanks for the info! I'll be running 300 oz steppers at 60 volts at first, and then will move up to some motors that draw the full 7 amps. So I might as well go with some 12 gage, so I won't need to replace wire in the future.

[Al_The_Man]

If you anticipate 7amps, 12 gauge is a bit overkill, especially that 6 conductors + ground can occupy over 3/4" circular diameter, depending on insulation, The electrical code shows 16g is rated for 10amps and 14g rated for 15amps.
If you use single conductor stranded, remember to twist together each pair of conductors over the whole length to cut down EMI.
Al.

[WilliamD]

What does "single conductor stranded" mean?

[vulcom1]

Single conductor stranded is like auto wire. One wire with multi strands inside the cover. You can use only one connector on each end. Multi conductor has more lines inside one cable. Hope I got this right.
I am not sure how long you want to make your cables but either 16 or 18 should work. What I would do is purchase some 4 wire multi-strand with a shield around the 4 cables and covered. If you ground the ends you get your shielding where you do not have to twist the cables.
John

[Al_The_Man]

Originally Posted by vulcom1 If you ground the ends you get your shielding where you do not have to twist the cables. John

However, if you buy multi-conductor shielded, it usually is twisted, also only ground one end of the shield, generally at the 'source' end, and set up a common ground plate for all grounds.
Al.

[gar]

060209-1809 EST USA

On wire size --- there are two limiting factors ---

Maximum voltage drop you want to allow. You can calculate this using data from wire tables. This will be length dependent.

Maximum cable temperature. This is determined by the current thru the wire, its insulation rating, and the thermal dissipation characteristics of the cable.

vulcom1:

Shielding and twisting wire pairs do not have much to do with each other. Twisting reduces magnetic coupling over an area of several lengths of the twist independent of any non-magnetic shielding. Conductive shielding if non-magnetic ( copper or aluminum ) provides shielding of electric fields. At very high frequencies and microwaves things are somewhat different, but we are not talking about that part of the spectrum. A magnetic material wrapped around the cable could provide both magnetic and electric shielding.

.

[NC Cams]

Perhaps oversimplified but this should answer the stranded wire/conductor question.

Lamp cord wire is typically 2 conductor (w/o ground) or 3 conductor (w/ground).

Each conductor of lamp cord is USUALLY made up of many fine strands of wire. This makes it flexible.

They add more strands to obtain the prescribed MCA (mill circular area) of wire to generate an appropriate GAGE size. IE: 18 gage wire has LESS strands of fine wire than 14 gage stranded wire and vise versa.

Stranded wire is MUCh more flexible due to many tiny wires as opposed to the more rigid single strand of so called "solid" conductor wire. Auto wire has more vibration potential so it is imperative that stranded wire be used.

Wire that runs thru conduit is gonna be pretty stable (vibration free) thus you usually run solid wire here. Wire that will see flexing (IE wires to a moving servo/stepper) needs to be highly flexible for obvious reasons.

Prety sure that stranded wire is less likely to generate RF issues than solid conductor wire due to "twist" inherent to its onstruction and/or the fact you have so many more wires generating a magnetic flux field which causes it to be more self disruptive.

[gar]

060213-0945 EST USA

WilliamD:

Find a copy of "Reference Data for Radio Engineers", by ITT Corporation. My edition is 4, and on pager 51 is Wire Tables, Annealed copper (AWG). #10 has 0.9989 ohms/1000 ft. #16 has 4.016 ohms/1000 ft. And #20 has 10.15 ohms/1000 ft.

Fusing currents of wires is on page 55. #20 is 58 amps, #16 is 117 amps, and #10 is 333 amps. You can not run close to the fusing current, but it sort of defines an absolute maximum. This is obviously ambient temperature dependent. Melting point of the insulation is of greater importance.

If you had #20 with 58 amps thru it, then you would have a dissipation of 33 watts per foot, or 2.8 watts per inch. Take a 2 W wire wound resistor, it is about 1" long, dissipate 2.8 W in this and you can not hold your finger on the resistor. Its surface area is vastly greater than that of the #20 wire. Thus, the #20 wire would be much hotter.

Now reduce the current from 58 amps to 7 amps and the dissipation of #20 wire is about 0.04 W per inch.

Suppose you have a 10 ft wire length from controller to motor, that is 20 ft of loop resistance. For #20 wire this is 10.15/50 = 0.203 ohms. The total voltage drop at 7 amps is 7 * 0.203 = 1.4 V. Not of great importance relative to your source voltage of 60 V. You are dealing with a complex AC waveform so these are only approximations based on DC values, but more than adequate to guide you.

NC Cams:

Multiple strands of copper wire to make one conductor, whether these are twisted or not, has nothing to do with the twisting of two conductors carrying the same current in opposite directions.

When you have a current flow there is a magnetic field created from this current. This current can be in a wire or an electron beam as in a cathode ray tube.

If I make a loop of wire from point A to point B and pass a current thru the wire I will have a magnetic field created all along the the loop and the field will be in the same direction. If I twist this loop every 1 ft, then at each foot I reverse the direction of the magnetic field. If I go a number of feet away from the loop, then I get the superposition of the magnetic fields from a number of the 1 foot segments. These alternating direction magnetic fields then cancel one another.

On an ordinary twisted cable the pitch will be in the fractional inch range. In a CAT-5 cable it is about 0.4, 0.5, 0.6, 0.7 for the 4 different pairs. The pitches are staggered to reduce mutual coupling between the closely spaced twisted pairs.

.

[BobWarfield]

William, you can get Speakon (also called Neutrik) cables already made up with locking connectors in 14 and 16 gauge. Take your pick. They're stranded and available in various lengths. They're designed for commercial grade concert sound purposes, including outdoor concerts. They use stranded conductors.

www.partsexpress.com and eBay are two excellent sources. Prices are reasonable. Just splice them onto your step motor wiring and protect with appropriate heat shrink tubing.

Best,

BW

[sdantonio]

I was just digging around on ebay and did a search on "4 conductor" (my motors are strict bipolar, 4 lead, 425oz) and came up with a lot of people selling 4 conductor, 14 gauge monster cable (speaker wire). 100ft for about $40. Should work fine.

You can probably find the same thing in 6 conductor

Steven