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Low-Power Solar? - Page 2

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Posted by Vaughn on January 31, 2012, 11:49 pm
 
On 1/31/2012 3:55 PM, Anon wrote:


I probably should have been clearer.  Above I said "Connect cable to a
12 volt DC power supply."  It may have been better to say: "Connect
cable to a 12 volt DC power supply rather than to a landscape lighting
transformer."

Vaughn


Posted by Jim Wilkins on February 1, 2012, 12:15 pm
 


How about running 24VAC from a control transformer through the long wire and
converting to 12V at the destination?
http://www.altex.com/24VAC-to-12VDC-Power-Converter-w-Screw-Terminals-500mA-max-PIAD-AC24-P143407.aspx

You gain better voltage regulation and more watts down the wire, but the
equipment is a little harder to find and set up.

jsw



Posted by j on February 14, 2012, 4:35 pm
 On 2/1/2012 7:15 AM, Jim Wilkins wrote:

http://www.altex.com/24VAC-to-12VDC-Power-Converter-w-Screw-Terminals-500mA-max-PIAD-AC24-P143407.aspx

That's not a bad idea for those reasons. The 350mA might be a little
tight on his current needs though. 24 volt transformer are readily
available.

I found this online calculator:

http://www.stealth316.com/2-wire-resistance.htm

200'  of 18 gauge @ .5A = .65 volts (note I am not sure that calculator
does do 2 wire, it is in the name though)

Probably a volt or two of loss is acceptably as 12v supplies are a volt
or two above 12V, unless heavily loaded.

   Note that a simple supply off a 12v transformer, will put out
something close to 18V DC under no load. Too much for many electronics
with 16 volt caps!

Jeff




Posted by clare on February 15, 2012, 1:25 am
 

http://www.altex.com/24VAC-to-12VDC-Power-Converter-w-Screw-Terminals-500mA-max-PIAD-AC24-P143407.aspx

I'd go with 18 or 24 volts AC down the line with a 2:1 transformer,
rectifier, and regulator at the end. The 18 or 24 volts will lose less
in the cable because of lower current, and have more headway to play
with at the bottom end.

A small Variac will work well for the bottom end transformer, allowing
you to "taylor" the ratio. Use a full wave bridge on the secondary and
run it through a 1.5 amp  regulator chip (7812 in a TO220 case on a
good heat sink). Set the voltage just a few volts high (say 15 volts
DC) so the regulator works but does not need to dissipate much power
as heat.  Small Variacs are generally available surplus, at not bad
prices.  
Alternatively, just run the 18 volt doorbell transformer and the
bridge rectifier and bare regulator at the bottom end.

The bridge rectifiers are dirt cheap too - or you can make your own
with 4 regular diodes (salvaged from an old PC power supply if you
want to be "cheap")
Some old PC supplies even had the 7812 available (or 7912 - regulates
the - instead of the +, but can be used just as well.)

Posted by Gordon on January 26, 2012, 4:49 am
 

You can buy a solar powered motion sensing light at Home depot.
Turnkey, all set to go.

That's half your battle.

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