Matching the electronics

[Parameter]

Hi,
I got my mill 80% done, the controler based on UCN5804 is completed (1.5A) AND my power-drivers board is almost done (4A). Still, I worry about plugging the good motors in and Poof...

I tested the boards with 12v motors on 12v, using about 300ma MAX so the allegro chips did'nt heat and the driver board neither... Nice to see all works fine...

Now, what will happen when I plug my 3v motors to my 5v power source (for a start)? I know I need to put a resistor, could someone confirm my understanding?

Motors are 3v, 3.5 Ohms, SO, current should be v/r=I so 3 / 3.5 = .86 Amps per phase? But then I use the resistor calculator and it tells me I need 2.2 amps per motors... does'nt sound right to me...

A single unipolar motor (6 or 8 wires) is 4 phases right? So I should be more on the 3.4 amps or so... how-come the difference? I tried the calculation at 3v ps but no difference.

The mill is about to be wired so I would really appreciate to clear that detail now...

Thanks in advance for your help

Para

[Parameter]

As for the resistor, I find it costly to need 60 watts resistors to bring my 3v motors on the 38v power input so I might just test a bit before using 5v input.

The recommended resistor is around 2 ohms at 5 v, do you think I could go without the resistor just for some testing?

Even 2 ohms at 30 watts are not given, for a test especially
eh... maybe I'll build these pwm modules I wanted to. Anyone has a good recommendation as for chopper power boards?

Para

[H500]

Look in the open source forum. There's an allegro 3977 based chopper design that's easy, low cost and works well.

[pminmo]

If it is an 8 wire motor it can be run several different configurations. You will get the most power out of bipolar parallel, but you can also run them unipolar, or bipolar series. If you want to roll your own have a look at my website: http://PMinMO.com.

Phil

[ViperTX]

Originally Posted by Parameter Hi, Motors are 3v, 3.5 Ohms, SO, current should be v/r=I so 3 / 3.5 = .86 Amps per phase? But then I use the resistor calculator and it tells me I need 2.2 amps per motors... does'nt sound right to me... A single unipolar motor (6 or 8 wires) is 4 phases right? So I should be more on the 3.4 amps or so... how-come the difference? I tried the calculation at 3v ps but no difference. Para

So, nominally the motors will use .86 amps per phase. If you're driving the motors off of 5 volts you'll need to calculate the R that will give you 0.86 amps from a 5 volt supply. So, R=V/I......5/.86 ~ 5.7 ohms. Remember that this is not useful for Gecko....since they have their own internal current limiting circuit, which requires different values.

Also remember that with steppers you only energize 1/2 of the coils at the same time....

What is the resistor calculator?

[Parameter]

Here is the Stepper Resistor Calculator software found on this forum.

To who the credit goes, this is a great app!

Para

[Mat-C]

If you are worried about your motors, how about this:
The worst case is the steady state on case (only one winding active, inductors don't stop DC current).... so measure the winding DC resistance. Then use a (power) resistor and an ammeter to measure the current your circuit outputs. If it's within spec for the stepper then no problem. Generally the max current is listed on the stepper, and max voltage is there to fill up space on the label.