Date: Wednesday, December 10, 1997 10:38 PM
Subject: Re: MICO MOTORS


At 10:56 PM 12/8/97 -0500, Jerry Bellina wrote:
 Dynatol is one of the few command controls systems that puts pure DC to the
motor.  That's why they don't buzz, and also why the receivers (decoders)
run so hot.  They use op amps to supply a variable voltage, just like a good
power pack.

I believe most other command control systems, DCC (DIGITRAX, WANGROVE
etc),
CTC-80, Keller, and RAIL-LYNX, use pulse width modulation on the motor
drivers. This allows the drivers to be turned on completely (saturated)
with very little voltage drop, and thus low power disapation.

It also provides more torque at low speed than pure DC, because the peak
motor current is higher (due to full voltage being sent to the motor),
albiet for a short time.  The width of the pulse is varied to control motor
speed (0-100 %), and typically the pulse rate is around 50-100 per second
(this is what you hear).

I don't think this will harm can or micro motors, but cannot provide
evidence either way.

Regards, Jerry Bellina  RAIL-LYNX
-----------------------------------------------------

Jerry
A very accurate explanation except that traditional pulse width will indeed
harm coreless motors but not for the reason sited.  The problem is heat
buildup.

However now days there are more tricks available to operate motors.

Coreless motors have the problem that they can not disapate heat. The
problem is that traditional pulsed power creates motor heat and thus the
problem.  This is why normally there is a strong recommendation note to use
coreless motors on pulsed power.

Most traditional DCC decoders use traditional pulse width modulation as per

Jerry's message and i do not recommend these decoders for motors referred
to as ironless core motors.

However several DCC decoders are especially designed to handle these
coreless motors.

The first batch are Back EMF decoders,  The back emf control has a natural
tendency to randomize the pulse.  As many can remember from jump rope days,
if you randomize the pulse, you do not get a resonate frequency and thus
much less heat.  These decoders are considered safe by the coreless  motor
manufacturers.

A new generation of Back EMF decoders is just now coming on the market.
These decoders use a much higher frequency (16K-20K) which is above many of
our hearing range),  With a small capacitor inside the decoder, this high
frequency looks to the coreless motor like pure DC.  These decoders are
ideal for Coreless motors. They have the advantage of pure DC and the
advantage of pulse width modulation.

If you have a traditional DCC decoder you can improve operation by using a
circuit that is basically a capacitor to dampen out the high points of the
pulse,  this also reduces heat, but this is in my opinion not any where as
good as one of the two solutions mentioned above.

Hope that helps
Stan Ames