Modifying battery charger

[tdpomodoro]

Guys,

I'm new to the CNC game and am looking for a power supply for my stepper motors. The steppers will be controlled by a PIC and used in a basic guitar pickup winding machine. Both are identical astrosyn steppers and have the following ratings:

• Model:34PM-C007-07
• 5.5V/phase
• 1.25A/phase

I have located a possible candidate on ebay in the form of an electric bike charger

http://cgi.ebay.com.au/60v-60-Volt-B...#ht_3186wt_939

However i'm unsure of what the voltage output may be (am I correct in assuming 60V?) as all the information that is supplied is that it has an output current of 2.5A.

Will I be able to use this power supply coupled with a current limiting circuit for each motor? (possibly even some filtering of the voltage output if its not steady enough)

Any help would be much appreciated.

[dilbert0815]

You might be disapointed, but a battery charger is no power supply.
It might work but it would possibly require quite elaborate and sofisticated changes to replace a normal power supply with modified charger.

Also your question seems incomplete without posting your intended driver parts or circuit. It's mostly NOT the motor that define the power supply parameters.

[tdpomodoro]

Thanks for you reply dilbert0815

You might be disapointed, but a battery charger is no power supply. It might work but it would possibly require quite elaborate and sofisticated changes to replace a normal power supply with modified charger.

I looked further into batteries chargers for electric bikes and it would seem that the majority are, as you say, unusable with all sorts of voltage protection, trickle charging and all other sorts of circuits that would make it too complicated for my purposes. I was hoping someone may have been able to tell me that this style of charger may be a cheaper, straight DC output charger - one where the user must monitor the voltage level and disconnect the battery manually rather than peak voltage sensing.

Also your question seems incomplete without posting your intended driver parts or circuit. It's mostly NOT the motor that define the power supply parameters.

I had a lot more information in my post originally but I cut it out cause it was sort of overwhelming. The application for these steppers is for winding coils with wire around 42, 43 AWG. Guitar pickups mainly, possibly some speaker coils down the track. So the load on the motors are negligible as any appreciable amount of tension can snap the wire. What i'm going for is motor RPM so from readings it's the high voltage that will allow for high stepping speeds.

Do you mean that in a CNC application things like cutting speed and depth will dictate the power supply more than the motor?

Regards,

[dilbert0815]

Originally Posted by tdpomodoro Do you mean that in a CNC application things like cutting speed and depth will dictate the power supply more than the motor?

I wasn't refering to the application but the electrical driver cicuit you have chosen for controlling the steppers. You just mentioned using a PIC, but left out the more important output stage.
The motors are somewhat unimportant regarding power supply voltage. Most stepper driver circuits are current regulating circuits. That means you can apply as much voltage as this driver circuit will survive. You just set the current to the rating of your motor.

By the way there seems indeed a correlation of required power and the chosen application (speed and cutting depth), but that's outside my field.
May be some other expert here can give you an estimate.

[tdpomodoro]

I was proposing to tailor the circuit found on the following website to my needs. It's a MOSFET based current limiting circuit, one on the voltage supply rail for each motor.

http://www.apsolutions.com/Electroni...nt%20Limit.htm

The PIC will swtich on and off MOSFETs that can operate at the desired frequency that will energise the coils of the stepper.

[dilbert0815]

Originally Posted by tdpomodoro The PIC will swtich on and off MOSFETs that can operate at the desired frequency that will energise the coils of the stepper.

That's a linear limiter.
Are you aware of the power dissipation ?
Assuming using 60V and 1.2A you will get more than 60W in each driver. Per coil.
That's more than 250W total and requires quite a lot of efford to cool it.
Also very ineffective (ever heard of global warming ).

Almost all actual stepper drivers use chopper control (like a switching power supply) to avoid dissipating that much heat.

With a linear current regulation I would suggest realy finding out first how much speed/torque you realy need. Your power budget may be realy very tight in between the needed power and the max power dissipation you could handle.
With your application I would assume the speed/torque are correlated as you only need torque to overcome inertia of the winding maschine. However it's not negligible on motor side. On most applications the torque needed for overcomming inertia is larger than the output load of the tool.