Date:         Sun, 8 Aug 2004 08:41:37 -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>,
          laurasdog@WEIRDSTUFFWEMAKE.COM
In-Reply-To:  <6.1.2.0.0.20040807165055.02c19920@mail.gct21.net>
Content-Type: text/plain; charset="us-ascii"; format=flowed

>
>Thanks David,
>If I just use a simple resistor will it ruin the tool to have it "runaway"
>on start up?
>Doug

Most likely.  Better to use a constant-voltage arrangement.  Steve's method
below is the right way, really.  The diode trick is easy to understand and
workable if you have a bunch of diodes lying around.  I made up a set
ladder-fashion to get variable speeds on a little muffin fan, it's got a
clip lead to short out one or more diodes and raise the voltage.  Junk-box
science... :)

david


At 20:01 8/7/2004, Steve Delanty wrote:
>Doug,
>I'd use a LM350.
>It's a 3 amp adjustable regulator. It needs a couple external
>resistors to set the output voltage. I would also use a small
>ceramic capacitor from the input to ground, and the output to
>ground for stability. 0.1uF @ 100volts would be a good cap
>choice.
>
>It will NEED to be on a heatsink. If you want 3 volts at 2 amps,
>it means the regulator will dissipate 12.6V - 3V= 9.6V X 2A = 19.2 watts.
>
>Here's a data sheet for the LM350....
>http://www.national.com/ds/LM/LM150.pdf
>
>Steve
>
>
>---------------------
>
>At 12:10 PM 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.
>>
>>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"