Can I use these motors as bipolar?

[Walky]

I got 4 of these 8-wire motors:

Lin Engineering 5718M-02E-03 unipolar stepper motor | Alltronics

I wanted to use them with a HobbyCNC Pro 4-axis board but Paypal doesn't show my country as an option on checkout and there was no response about it from HobbyCNC, so I'm considering a G540 as an alternative.

My question is: Can I be sure that those motors can be wired as bipolar? I know they should as they have 8 wires and are probably hybrid, but they're advertised as unipolar on their site and there's no clue on the description or motor's PDF about bipolar use, so I'd like to be sure before spending $250+ on the Gecko.

Haven't gotten a response from Alltronics about this, either.

Thanks!

[Mariss Freimanis]

Nice motors at a very nice price. They are rated a 3A per phase so you will be able to get significant mechanical power from them.

8-wire motors are universal motors meaning they can be connected bipolar series, bipolar parallel and unipolar. I looked at their sparse datasheet so I'm guessing the ratings are:

Bipolar parallel. 3A per phase, 1.2mH inductance. If you use the G540, 35VDC is the maximum power supply voltage for this connection.

Bipolar series. 1.5A per phase, 4.8mH inductance. 70VDC will get you exactly the same performance as 3A at 35VDC parallel. Can't use the G540 there because it can't go over 50VDC.

Unipolar. 2.1A per phase. 1.2mH inductance. 35VDC max supply voltage.

Bipolar parallel will get you the best performance using a reasonable supply voltage (24VAC secondary transformer gives 34VDC after rectification).

Mariss

[Walky]

Thanks Mariss, it's great to get some help from the "gecko guy" himself!

I've always used unipolar drivers (Probotix) for my machines so I was a little lost at bipolar. I understand that bipolar series loses torque faster than parallel, which can reach speeds similar to unipolar but with higher torque.

By 35V I guess you mean the estimated max voltage of the motors by the usual sqrt(inductance)*32 equation, and not anything to do with the G540 itself, right?.

About bipolar parallel, I was thinking about using the G540 with a 36V 10A switching power supply from Ebay (those have worked wonderfully for me and are slightly adjustable so I can even play safe and set it at 35V). As the driver is a chopper and should actually consume less than 105W (3A*35V), do you think it would reduce consumption enough to use that power supply to drive all four motors at 3A? (I'd probably still drive them at 2.5A to be sure and reduce heat). What would be the right resistor to install on each connector for both 2.5A and 3A? (I know that's in the manual, but I'd rather ask now than make a horrible mistake).

Thank you very much for your help.

[Walky]

I found some more info about the motors:

Lin Engineering - Step Motor Specialists

However, I'm still a little lost. According to the actual info from the site, unipolar amp/phase rating is 3A, and bipolar parallel would be 4.2A (assuming que "P" in "02P" means parallel and "S" means series, which makes sense, but I'm still not 100% sure if it's the same motors they're talking about, but it seems so). If it really is 4.2A at bipolar parallel, what performance can I expect from the motors when using the Geckos at 3A as compared to an unipolar driver running at the same current/voltage?. This doubt is the only thing that's keeping me from getting the G540 right now.

[H500]

It's probably not the same motor listed on the Lin's site. The phase inductance is different. But even if it's rated at 4.2 amps bipolar, the unipolar rating would be 3 amps.

The torque curves on Lin's site seems highly suspicious. They show 24v 4.2 amps, or about 100watts for the input power. But shaft power is 148 watts at 2000rpm. Unless I made a mistake in my calcs, the motor efficiency is 148%. Who needs cold fusion when we have motors like this?

[ger21]

If you use their Buy Now option, it lists a 5718M-02E, which is indeed an 8 wire, 4.2A bipolar parallel motor. So it looks like you're correct.

A unipolar motor has about 70% of the torque of the bipolar rating.
If you run a 4.2A motor at 3.5A (G540 max), you'll get about 83% of the torque.

The motor appears to be rated at 173 oz-in of torque, so running it with the G540 will give you about 143 oz-in, vs the unipolar rating of 129 oz-in.

[Walky]

If you use their Buy Now option, it lists a 5718M-02E, which is indeed an 8 wire, 4.2A bipolar parallel motor. So it looks like you're correct.

Thanks for that info, it probably is the same motor then. Why didn't Alltronics include bipolar rating is beyond me.

If I use a switchng 10A power supply what would be the highest absolute current I could provide to the motors (all four of them) with the G540? Usually one would say 2.5A, but AFAIK chopper drivers don't have a 100% consumption because of the PWM, but I'm not sure the actual % (I guess it changes between drivers, too). Might I be able to provide 3A or hopefully 3.5A?

[ger21]

Gecko's documentation states that a 3.5 amp motor will not draw more than .66% of the rated current, or 2.33amps per motor, if running them at 3.5amps. So 4 motors should never draw more then ~9.5 amps, and most likely will usually be drawing less current. So you should be fine with a 10 amp power supply.

I've read that the G540 has a 7 or 8 amp internal fuse, and that is the max it can draw. And even at 7 or 8 amps, it can still provide 3.5amps to 4 motors.

[Walky]

That's it then, I'm going with the G540!

Thanks for all your help, everything is much more clear now.

[Walky]

Well, I got my G540 today from HubbardCNC, all nicely packed. I've read the G540 heatsinking experiments, but I understand that those are under 48V, so I'd like to know... does the G540 need heatsinking at 36V @ 3.5A? What about 3A?

Thanks!