Re: [ATM] question about reducing dc voltage

[Mark Holm <mdholm@telerama.com>]

1. Check the specs on the drive.  It is possible that it will be OK on 
12 volts.  Remember that a fully charged 12 volt lead acid battery runs 
nearer 13 volts, so the specs should allow that much overhead to be safe.

2. If you use a linear regulator (transistor that acts like a variable 
resistor in this setup), you will lose half the energy in your battery. 
  (It turns into heat.)

3. On the other hand, modern DC-DC converters are quite efficient, small 
and not terribly expensive.  In this case, you will need what is called 
a "buck" converter (as opposed to a "boost" converter.)  There are 
probably three design criteria:

	a. ~ 12 volts in  (they are usually quite flexible in this regard) and 
6 volts out.  You may have to do a bit of minor circuitry, such as a 
resistor, to program the output voltage.

	b. Enough current capacity to power your drive.  Check the specs again 
for that.

	c. Input, output and control connections are on leads, or screw 
terminals rather than circuit board contacts.  This keeps you from 
having to build a circuit board.

Your drive probably isn't taking a large amount of power, so at the 
typical high efficiency of modern converters, you probably won't need a 
heat sink.

-- 
Mark Holm
mdholm@telerama.com

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