RE: Old questions, new member; new questions; item wanted; any interest in power xfmrs?

I can fill in a few bits:

> Hello:
>
> I hope someday I can be a help to someone here, what with all the
> questions
> I ask but not yet having a lot to contribute. Here are a few more.
>
> 1) Been reading about DRO project, but would would like to know
> if it still
> exists. I would like to read more about it.

You can read about the DRO and get the software at:
http://www.mcs.net/~kulaga/dro.html
If you want a PCB instead of wire wrapping you can get that from Dan Mauch
at Camtronics. He also sells complete kits. If you have never visited his
site or heard of his products you need to go to:
http://www.seanet.com/~dmauch/

> 2) I jumped on the tail end of a thread about using a scope to determine
> overvoltage for stepper drive. I never found out the procedure. I only
> caught the peripheral discussions about everyones' scopes.

I think this is the message you want. I seem to remember someone added more,
but this is a start:
From: Walter McCarthy <wmccarthy@...>

> Where can I get supplies to work with my 20 amp motors?
>
> How much power saving do you think I can have by changing power

supplies?

>
> I am confused on how to pick a power supply. The motors are rated at

less than 2 volts,
but are 12.7 amp and the larger ones are rated at 20 amps. I think the
Ah-ha supplies are 48
volt. Can I send 48 volt to a motor rated at 2 volts?

The over voltage you are supplying is supplied to shorten the turn on
time of the motors.

As the motors are only rated at 2 volts, 40 volts supplies 20 times the
rated voltage of the coils.

If you can hook your motors to an occilliscope, you can visually see the
turn on time of the motors you are working with. Watching the rise time
on the scope eliminates all the calculations and variables you don't
know in the design of the motor.
When you determine the rpm that you require for the application, you can
then reduce the voltage to the point that you will have a turn on time
that is less than the pulse width needed at your fastest rpm.
. What I have observed is that when the rise time of the voltage
approaches the full cycle of the pulse, the stability falls.

You may only need 20 volts for your application, depending on your rpm
needed and the rise time of your coils. The lower voltage saves on
components and voltage transients.

I have some 4 volt 1.4 amp step-syn motors. RMP tops out at about 110
with 35 volts on the power supply. That is the point where the rise time
of the pulse approaches the pulse width on this motor. This is with a 10
times overvoltage.

The Ericcson 3776 uses 20k cycle chopping for current limiting. At 20k,
the chopping frequency is much higher than the pulse frequency at 120
rpm on a 200 step motor. The ericsson chip has a max voltage of 40
volts. By picking high current FETs you can drive 20 amps from the 3776.

For a high amp, low voltage transformer, rewind a microwave oven
transformer. The primary is 110 volts with 700 to 1000 watts. If you get
a 1000 watt primary, that gives you 50 amps rms at 20 volts. If you need
more, rewind two. Most microwave ovens do not lose the transformer.
Often the fuse blows because it is tired or a transient pushes the fuse
over the edge and the oven is thrown out without having it even checked
by a serviceman.

Buying a scope is very interesting and is a great troubleshooting tool.

Best of building

Walter


Tim
[Denver, CO]