Re: Modular 3, 4-axis Bi-polar Chopper Driver Help

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "learningcnc"
<learningcnc@y...> wrote:

> I want to build the 4 amp 48v driver and parallel card on Steve
> Blackmore's website http://www.pilotltd.net/cnc.htm his design is
> based off of Hans Wedemeyer's design http://www.hans-w.com/cnc.htm
>
> 1.) Can these drivers fry my motherboard, if so what can I do to
> prevent it?
> 2.) What would be a good power supply?
> 3.) Should I use a separate motor power supply for each axis?
> 4.) Are there any design changes I should make?
>
> I'm not an electrical engineer and I have a lot more time then
> money right now so any advice is much appreciated.
>
> Thanks

1. As Steve points out the design is not opto isolated so your PP on
your PC is at risk. The design assumes all grounds (motor ground, PC
ground, circuit ground are all common. If they are you should have
minimal problems with fried parallel ports. If you are concerned buy
a cheap add-in port card and run from that. You can add a 74lS541
octal buffer chip between the parallel port pins and the motor drive
circuit to give you added protection and better drive
characteristics. It has 8 inputs and 8 outputs. It needs to share a
commmon ground with the PC

2. Virtually any power supply that puts out unregulated DC at the 4A
or greater range. You can use a regulated supply, switching supply,
simple transformer and bridge/filter cap combo. It does not have to
be finely filtered or have a regulated output. There are some
surplus 48 regulated supplies avaliable since that is a common
voltage in the phone industry. If you do use a REGULATED supply put
a high current (12 to 20A) silicon rectifier in series with the
regulated output to keep back motor EMF from raising the DC voltage
above the regulated output and reverse biasing the pass transistors.
Check www.mpja.com for surplus power supplies.

3. While there is nothing wrong with using separate supplies for
each axis it is ususally more convenient to use one large supply.
Either approach works fine. If using separate supplies they need to
share the same ground if using Steve's circuit.

4. I have not built Steve's circuit but others have and can offer
advise on design changes but the design appears well thought out.
You should consider opto isolation on any limit sensors you plan on
using with your PC port.

I AM an EE but there are many days I wished I were not and that
computers were still just science fair projects! The feelings pass.