RE: [CAD_CAM_EDM_DRO] Just an idea

NiCad batteries have a life based on how well you follow the charging and
discharging requirments for NiCad batteries. They live longer when fully
charged and then fully discharged. To apply them to peak power supply duties
as you have described is best done with two sets of NiCads and some
electronics to manage charging one set while the other is discharging as
needed to meet peak current demands of the servo system. You might think
that this is over-kill, however if you want to charge up a set for a job you
will want to discharge the set to zero before re-charging the set for the
next job. A simple electronic control system may do that for you.

As always, if the cost adds up equal to a bigger power supply to begin with,
you will find that the bigger power supply will save you replacing expensive
batteries from time to time. I am sure some operations with servo's can
demand peak power for extended times. I think you may find a different type
of battery might offer something resonable in all of this.

I have a Cosco deep cycle marine battery with a 36 Month warranty employed
in one application. I can live with the $40.00 to replace it every 3 years.
In other words, the average cost per year is under $15.00 and every winter
we loose power for 8 to 24 hours. This battery can handel peak power like
little else. Becasue 12V viechle batteries are so popular they tend to be
reasonable in cost. Servo power supply voltages are a stretch up.... If you
are just turning grey matter for fun, A car alternator connected to an old
washing machine 120 VAC Motor, can produce much more than 12 VDC after you
cluge up a simple adjustable regulator circuit and the current output will
be quite serious. In other words, in a similar package as a phase converter,
one could have a very high output DC power supply. Such a silly idea may be
reasonable for anyone with an old AC motor kicking around. Car alternators
don't cost much. The regulator circuit isn't bad.

-----Original Message-----
From: Mariss Freimanis [mailto:geckohall@...]
Sent: Friday, June 16, 2000 12:23 PM
To: CAD_CAM_EDM_DRO@egroups.com
Subject: [CAD_CAM_EDM_DRO] Just an idea


Has anyone used a battery in conjuntion with a servomotor power
supply?

Reason for the question:

Brush DC servomotors have peak torque values that are up to 10 times
their rated continuous torque, thus peak current draw can be up to 10
times the continuous draw. This peak current event can last from 10
millisec to 1 second and the duty cycle must be under 10% to stay
within the motor's dissipation rating.

Unfortunately the power supply has to be sized to this peak power,
when on average a supply 1/10 the size would do.

My idea would be to use a small NiCad or NiH battery connected to the
power supply output bus via a diode. During a high current pulse the
power supply voltage would sag, the diode would forward bias and pick
up the load for the duration. A quick-charge IC would handle the
charge restoration to the NiCad between the pulses.

Even little AA .5 AH NiCad cells would do; a 25 Amp, 1 second load
would discharge only .007 AH (25Amp / 3600 sec). The internal
resistance of a Nicad cell is on the order of .02 ohms, so they are
quite capable of supplying this level of current.

It seems a 100 watt supply / battery combo could replace a 1kW
supply. Has this been done before?

Mariss


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