From: Jon Shoop (shoop19@brick.net)
Date: Thu May 01 2003 - 02:28:58 PDT
Test..............
Jon
----- Original Message -----
From: "Jim Newton" <jnewton@laurel.com>
To: "Military Vehicles Mailing List" <mil-veh@mil-veh.org>
Sent: Thursday, May 01, 2003 1:26 AM
Subject: Re: [MV] 6volts from 12 or 12v from 24 volts
>
> Hi All...
>
> Just this afternoon I had the occasion to use 7805s and 7812s to build
> a power supply for a 2 amp load (a Cub Scouts Pinewood Derby track
> finish line system...is a Pinewood Derby car considered an MV? The
> Boy Scouts are a paramilitary organization, after all!) and it worked
> fine.
>
> My input voltage was 18.5 VDC at 3.5 amps\, so I hooked up 2 7812
> (12-volt) regulators in parallel (each similar pin connected), then
> took the output of those and ran it into 2 7805 (5-volt) regulators
> which were also in parallel. Common ground for all center leads.
> Worked great, but the voltage may fluctuate as the two 78xxs in each
> pair fight each other. Who cares?
>
> Remember the formula "VAW" (like the LAW of electricity but with a V
> for volts) when working with electricity...
>
> V * A = W (Volts x Amps = Watts)
>
> You can calculate a lot of stuff with this simple formula.
>
> With the 78xx regulators, the voltage drop that you get can be plugged
> into your formula. If you are dropping 24 volts to 12 volts and you
> drive a 1 amp load, your formula would be:
>
> (24 - 12) x 1 = 12 Watts
>
> Your 7812 will be giving off 12 watts of heat!
>
> If you hook up a 7805 (the 5-volt version) to your deuce's 24-volt
> power source, your formula would be as follows:
>
> 24 - 5) x 1 = 19 Watts
>
> 19 Watts is a lot of heat! That's gonna cook a 7805 pretty quick.
>
> 7806 regulators are a little harder to find than the 5 or 12 volt
> versions, but they are available as Dave says.
>
> >I've used those before but in a controlled situation - ie. soldered into
a
> >PC board, feeding some ICs, etc. How do they standup to overloads, and
> >electrical noise. If they are rated for 1 amp, do they open circuit at 2
> >amps, etc?
> >
> >Dave
> >
> >On Wed, 30 Apr 2003 10:37:16 -0700 (PDT), w7ls <w7ls@blarg.net> wrote:
> >
> >> Yes, those will work. They are available in higher power packages,
under
> >> different numbers. If you draw more juice through them for more lights
> >> or whatever, they will give off more heat, so a heatsink is a must. See
> >> Digikey.com, Jameco.com, Bgmicro.com, or if you're really desperate,
> >> Radio Shack. Jim
> >>
> >> "TA2 CNU" <ta4cnu@hotmail.com> wrote:
> >>
> >>> LM 78XX (xx= 06 for 6 volts, 12 for 12 volts)(negative ground)
> >>>
> >>> a simple transistor like chip can be used for getting 6 volts from 12
> >>> volts or 24 volts and 12 volts from 24 volts; but up to 1/2 amps. A
> >>> decent cooling fin will be needed...! (will cut out in case it gets
too
> >>> hot).
> >>>
> >>> this is a three legged item :
> >>> left leg + volts in,
> >>> mid leg - gronund,
> >>> right leg + volts out.
> >>>
> >>> also:
> >>> LM 79xx (xx= 06 for 6 volts, 12 for 12 volts)(positive ground)
> >>>
> >>>
> >>>
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>
> --
>
> Jim "Ike" Newton
>
> o 1984 M1007 CUCV Military Suburban
> 6.2 Liter (378 CID) Turbo-Diesel Engine
> 5/4 Ton Cargo Capacity, 4WD
>
> o 1971 M35A2 Military Troop/Cargo Truck "Deuce and a Half"
> 478 CID Turbo-Diesel Multi-Fuel Engine
> Air Shift Front Axle
> 2 1/2 Ton Cargo Capacity, 6WD
>
> See These Trucks at www.CUCV.NET
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>
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