Gecko's limited to only 20A ?

[samualt]

I take it the Gecko G320 is limited to only 20A: "0 to 20A current limit adjust range".
I'm guessing that means I can never reach my theoretical maximum of 1500 oz-in with the following drives:

Reliance Electric DC Brushed Servo Motors, Model E712
37.51 Oz-In/A
25.0-30.5 V/KRpm
Motor Terminal Resistance .75-1.02 Ohms @ 4A.
Maximum Terminal Voltage 60V
Maximum Continuous Speed 2100 RPM (No Load)
Maximum Peak Torque 1500 Oz-In.
Maximum Peak Current 44.5A
Maximum Continuous Stall Torque At Max Motor Temp 300 Oz-In.
Maximum Continuous Current 8.9A

Is there any way around that? Or, should I just not worry about that at all?
Also, does anyone here have any experience with these motors? Will the encoder that comes with them work with the Gecko?

[kong]

Rutex offer some drives that run upto 40Amp motors, but they are twice the price of the geckos. You must be planning one big machine to want 1500 oz/in?!
edit - just a thought, if you could run them at 20Amp, losing half the torque, you could run them on a reduction pulley, halving their speed, but boosting your torque back up. Obviously you'd need to go for a course ballscrew to regain the speed loss.

[HuFlungDung]

Samualt,

I wouldn't get too distracted by the big numbers of max peak torque and peak current. Those are design limit parameters, not optimum running conditions.

The motors will stand 9 amps continuous at 60 volts, so that is what you need, plus a little reserve. If the power supply has a capacitor or two, it may give you the capacity for the peak surges, which are only momentary conditions.

[balsaman]

I am with Hu. 10 amps at 60 volts is close to 2 HP. That's a whack of power.

Kong,

Using a 2:1 reduction and then using half the pitch is mechanically the same as twice the pitch and no reduction.

Eric

[ToyMaker]

At 746 Watts per horsepower, 10A x 60V is a little shy of 1 hp.
Which is still a healthy amount of power.

robotic regards,

Tom

[HuFlungDung]

Yup, you can easily break off a 3/4" endmill with 1/2 hp twisting on your screw.

[samualt]

Hmm...I'm still a little confused.
The Gecko's say no more than 20A.
So, do I build one power supply for all three motors? If so, what Amps should it output (because its going to 3 motors)?

Do I build a single power supply at 60V @ 60A (for all three motors)?
Or, should each motor have its own 60V @ 20A power supply?

[ToyMaker]

samault:
three 60v20a pwr sups might be cheaper than 1 60/60 but you will have to shop and see what's available.
speaking of high current supplies, what kind of voltage does a small (<100A) cracker-box welder put out?

robotic regards,

Tom

[HuFlungDung]

Originally posted by samualt Hmm...I'm still a little confused. The Gecko's say no more than 20A. So, do I build one power supply for all three motors? If so, what Amps should it output (because its going to 3 motors)? Do I build a single power supply at 60V @ 60A (for all three motors)? Or, should each motor have its own 60V @ 20A power supply?

Neither: one 30amp/60V supply should do.

Chances are slim that you are going to be pushing all three motors that hard at once, depending on whether you want jack-rabbit acceleration, or not.

FYI, I've run Knee mills for years with 12 amp servomotors, and never had a trip out because I was using all three axis at once. Most of the time, the motors have it pretty easy, and are barely warm to touch. The Z axis gets the most workout, if drilling a few hundred deep holes on a peck cycle. My entire controller package runs off a simple 15 amp, 110volt circuit, and I've never tripped a main breaker yet.

[balsaman]

Originally posted by ToyMaker At 746 Watts per horsepower, 10A x 60V is a little shy of 1 hp. Which is still a healthy amount of power. robotic regards, Tom

You are correct, my quick math was a little too quick...

Eric

[turmite]

samault may I ask a question here that is real close to what you are needing? I don't want to hi-jack your thread.
turmite

[samualt]

turmite:
Hi-jack away! I don't mind. Really!
I think I have a good idea of what to look for now (I wonder where I can find some of those time-sequential dilithium warp-field amplifiers though? ;-)