[cnc1000]

I'm about to embark on converting a Bridgeport Series 1 mill to run on Gecko drives and Mach 3. I'm interested in the 8 amp per phase number you mentioned. If I run the Gecko, will it just limit out at 7 amps and therefore, I'd have 7/8 of the torque that the original Boss 5 controls gave it? If so, I can live with that. Any help is greatly appreciated. Thanks.

My $.02:

The stock steppers draw about 8 amps each at idle. Geckos will output 7 amps max so you are limited to 7 amps per motor there. Standby current is 70% of that so you are looking at 4.9A MINIMUM per axis or 14.7A total. If all axes are in motion, then you are at 21 amps.

If it were me, I would get a bigger supply, something you can get from Antek, as Jeff mentioned. I didn't look at the prices, but it looks like Keling might buy their supplies from Antek (pics look almost identical), which means you might cut out the middle man by going straight to Antek. I have bought at least 5 Antek supplies and could not be happier with their quality or performance.

Matt

[HawkJET]

If I run the Gecko, will it just limit out at 7 amps and therefore, I'd have 7/8 of the torque that the original Boss 5 controls gave it? If so, I can live with that.

I'm using Compumotor drivers rather than Geckos on my Boss 3 so there may be some differences in my experience, but I think it is representative.

First, low speed torque is not an issue with these machines. The 8 amps you refer to will really only be noticed at the low end.

Second, my machine runs better at 6 amps than it does at 8 amps. I believe the different current level affects the resonance characteristics of the motors. It so happens that this resonance is more of a problem at 8 amps. I discovered this with my own experimentation.

Third, the voltage will make more difference. This is because the limiting factor is torque at a higher speed. Stepper motors have a lot more torque at low speed than they do at high speed. These machines need more torque at the high end to be able to handle the rapid moves.

The inductance of the motor will limit the rate that the current can rise in the coils. At low speed, there is ample time to get to the rated current because the phase stays energized longer, before switching to the next phase. At higher speed, due to the rpm, the phase will turn off before the full current is reached. Since torque is a function of current and the number of turns in the coil, the torque drops off at higher speeds.

Increasing the voltage will "push" the current to rise faster, thus increasing torque at the higher speeds. Geckos do this well.

The bottom line is...

1. 7 amps will work fine
2. use as much voltage as the Geckos will handle
3. wire the motor in parallel
4. MAKE CHIPS!

[cnc1000]

Thanks for the info. Do you have a wiring diagram for the steppers, so I can wire them correctly? I assume they are to be wired as 2 phase motors with 4 wires coming out? I use steppers in my work, so I'm familiar with the basic idea. Are the Bridgeport steppers 8 wire models where they can be used as 6 wire unipolar or parallel each phase winding for bipolar? Do you know the color codes?

I assume also that there are limit switches on the Bridgeport. Do you know what those color codes are, or it is obvious when I dig into the machine? Many thanks. cnc1000

[HawkJET]

Do you have a wiring diagram for the steppers, so I can wire them correctly?

The attached image is a wiring diagram for a different stepper controller but it has the info you need. The color codes are for the other controller and are not applicable to what you have.

I assume they are to be wired as 2 phase motors with 4 wires coming out?

Yes

Are the Bridgeport steppers 8 wire models where they can be used as 6 wire unipolar or parallel each phase winding for bipolar?

Yes

Do you know the color codes?

No, I don't, but with the attached wiring diagram you can work it out....

I assume also that there are limit switches on the Bridgeport. Do you know what those color codes are, or it is obvious when I dig into the machine?

The limit swtiches are simple SPDT switches that are set up normally open (at least they were on my Boss 3) and it is safer to have them normally closed so I rewired mine. It should be straightforward.

[TarHeelTom]

Thanks for the info. Do you have a wiring diagram for the steppers, so I can wire them correctly? I assume they are to be wired as 2 phase motors with 4 wires coming out? I use steppers in my work, so I'm familiar with the basic idea. Are the Bridgeport steppers 8 wire models where they can be used as 6 wire unipolar or parallel each phase winding for bipolar? Do you know the color codes?

I assume also that there are limit switches on the Bridgeport. Do you know what those color codes are, or it is obvious when I dig into the machine? Many thanks. cnc1000

Here are pictures of a couple of different, but similar, steppers with the wiring cover plate off. Both are on different BOSS 5 machines. The first shows a color code, but it didn't match what was actually there. Didn't take long with an ohmmeter to figure out what was what.

http://tomwade.me/tw/machinist/nm/t4.php

http://tomwade.me/tw/machinist/nm/rf/page3.php

Roger tells me that all his limit switches are black/white. Haven't gotten into my limit switches yet.

Tom