From: Jim Newton (jnewton@laurel.com)
Date: Wed Apr 30 2003 - 23:26:38 PDT
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)
>>>
>>>
>>>
>>> _________________________________________________________________
>>> MSN 8 with e-mail virus protection service: 2 months FREE*
>>> http://join.msn.com/?page=features/virus
>>>
>>>
>>> ===Mil-Veh is a member-supported mailing list===
>>> To unsubscribe, send e-mail to: <mil-veh-off@mil-veh.org>
>>> To switch to the DIGEST mode, send e-mail to <mil-veh-digest@mil-
>>> veh.org>
>>> To reach a human, contact <ack@mil-veh.org>
>>>
>>
>> ===Mil-Veh is a member-supported mailing list===
>> To unsubscribe, send e-mail to: <mil-veh-off@mil-veh.org>
>> To switch to the DIGEST mode, send e-mail to <mil-veh-digest@mil-veh.org>
>> To reach a human, contact <ack@mil-veh.org>
>>
--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 Keyword Searching of 22,000 Electronic TMs at www.MILDOCS.com
This archive was generated by hypermail 2.1.4 : Sat May 07 2005 - 20:18:41 PDT