Date:         Sat, 7 Aug 2004 15:46:59 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: voltage converter needed.  12vt to 3vt
Comments: To: Doug in Calif <vanagon@ASTOUND.NET>
In-Reply-To:  <001401c47cb2$28b2dcd0$49d2ea42@ttower17def>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 15:10 8/7/2004, Doug in Calif wrote:
>Hi all,
>I am looking for a good simple reliable way to run a 2.4 volt cordless
>screwdriver motor hard wired to the vanagon 12 vt system.
>
>The only thing I have found is a converter at radio shack that costs 20
>bucks that will convert 12 vt to 3 volt at 1.2 amps.
>
>I want to run a cordeless screwdriver motor hardwired to 12 vts.  I need a
>couple amps. at 2.4 or 3 vt would be okay.

If you can get a bunch of one-amp or bigger diodes free or cheap, a string
of them in series will lose about 0.7 volts per diode (and dissipate 0.7
watts per amp of current).  If you need to parallel two strings, put a
small resistance -- I think a quarter-ohm would be plenty -- in series with
each string.  At two amps, a quarter-ohm will drop half a volt and one
watt.  Can use nichrome for the resistor, or copper wire if you have
to.  50-volt diodes should be enough to take care of the inductive kick
when you shut off the driver, since you'll be running eight or ten in series.

Virtue of this is you get a fairly constant voltage.  Otherwise, a
resistor...you want to drop say 10.5 volts at two amps, that would be R = E
/ I = 10.5 / 2 = 5.25 ohms and would dissipate 21 watts.  Trouble is, at
half an amp that will only drop about 2.5v, so the tool will run away on
starting.

david


>Any simple suggestions like using a heater blower resistor?
>
>Doug

--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage," '85 GL "Poor Relation"