[Oldmanandhistoy]

Hello,

I'll wait to see what they have to say to my last email... It is a bit irritating, because I can't do my electronics enclosure until I know what power supply I need, which depends on the motor current. Anyway...

Would I be correct in thinking that for an 8-wire motor, the coil resistance is equal to the unipolar phase resistance? The reason I ask, is because if that is the case, then maybe pminmo is correct and the given specs are unipolar ratings, since my coil resistance is 3 ohm and the datasheet says 3 ohm/phase. I'm not sure I'm willing to trust that, but it seems it could be a possibility.

John, I certainly don't know of any way to work out the specs. Surely to work out the current specs, you'd need to know something about the thermal characteristics of the motor?!?!?!?

Warren

Unfortunately I have hit the ceiling of my knowledge on stepper motor so can not add any more. Hopefully Piminmo will come back and advise.

John

[pminmo]

3 ohms coil resistance, 2.2Nm torque and 2.5A bipolar parallel fits. Assuming the 2.5A is the bipolar parallel rating then in round numbers 1.8A would be the unipolar rating and 1.25A bipolar series.

[James Newton]

Would it not be possible to just hook up a variac or other variable power supply and slowly (very slowly) increase the current flowing through the coils until the motor reached some reasonable heat limit, say 100'F and then call that the rating of the motor?

As far as I know, the issue is just how much heat the thing puts out. I suppose the maximum voltage before you get arc over is the other failure mode, but I doubt you would reach that high a voltage before the motor melted. In the end, you can set the current rating low and amp (heh... "amp") it up until it just doesn't melt.

[mcpltd]

From what i have seen, and who we are working with at the moment for steppers, the current on the name plate is the unipolar current. (Unless it is a 4 wire motor)
As an example the FL57STH76-2808 is a 2.8A motor in unipolar, and the name plate shows 2.8A.

[itsme]

Hi mcpltd,

The problem that I am having (which I'm sure you've realised by now), is that the the supplier says the current rating is for bipolar parallel, but the resistance rating clearly isn't for bipolar parallel. They haven't replied to my email, but I'll give them a call this week.

Warren

[pminmo]

Motors should be marked with coil specifications. If the motor is marked with coil specifications then every thing can be worked from there. It works for any motor regardless of wire count.