Question about transformers (DC, not robot) - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Insert BS here A place to discuss anything you want

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 08-19-2011, 01:11 PM   #1
Junior Member
Thread Starter
iTrader: (6)
 
Join Date: Mar 2009
Location: Los Gatos, CA
Posts: 120
Total Cats: 0
Default Question about transformers (DC, not robot)

I just purchased a 600w 12v transformer for outdoor lighting. Is the DC load going to directly determine the current draw (similar to AC)? Or is this baby going to suck down 600w no matter what the DC load is? It has an eerie hum with just the AC plugged in with no DC load, and itís warm, and itís huge (at least 20#).

Reason I ask: I only have about 200w worth of lighting that I need to power, but I opted for the larger power supply for the possibility of expanding, and it was only $20 more than a unit with half the capacity. Just wondering if the smaller unit would have been notably more efficient (300w unit driving 200w worth of lights versus a 600w unit driving 200w worth of lights)?

Thanks
Slayer is offline   Reply With Quote
Old 08-19-2011, 01:18 PM   #2
Senior Member
iTrader: (1)
 
revlimiter's Avatar
 
Join Date: Jan 2009
Location: ABQ, NM
Posts: 528
Total Cats: 92
Default

awww. I got all excited.

revlimiter is offline   Reply With Quote
Old 08-19-2011, 01:26 PM   #3
Boost Pope
iTrader: (8)
 
Joe Perez's Avatar
 
Join Date: Sep 2005
Location: Chicago (Over two miles from Wrigley Field. Fuck the Cubs. Fuck them in their smarmy goat-hole.)
Posts: 26,317
Total Cats: 1,914
Default

Quote:
Originally Posted by Slayer View Post
I just purchased a 600w 12v transformer for outdoor lighting. Is the DC load going to directly determine the current draw (similar to AC)? Or is this baby going to suck down 600w no matter what the DC load is?
Current draw will vary with load.

More lights = more current on the AC side.

The wattage rating on the transformer indicates the maximum that it can supply before it blows up.


Quote:
It has an eerie hum with just the AC plugged in with no DC load, and it’s warm, and it’s huge (at least 20#).
Yup. Transformers are not 100% efficient. They draw a small amount of current even with no load.

If you were to measure a transformer's primary winding with a regular DC ohmmeter, it would appear to be a dead short. It's just a big coil of wire connected directly across both legs of the AC supply. The reason it doesn't immediately catch on fire and blow a fuse is because it has a very large AC impedance, and impedance is basically a resistance to change in the flow of current (it's sort of like resistance, but applicable to AC only.) If you were to feed 120v DC into it, it would melt and catch on fire. This is the big reason why Westinghouse beat Edison in the War of the Currents- you can run AC it into transformers, and the electromagnetic properties of the transformer cause it to magically load-follow. With DC, you can't do passive voltage conversion.

Those poor elephants...



Quote:
Just wondering if the smaller unit would have been notably more efficient (300w unit driving 200w worth of lights versus a 600w unit driving 200w worth of lights)?
Very slightly, but you're not likely to notice it on your power bill.
Joe Perez is offline   Reply With Quote
Old 08-19-2011, 01:39 PM   #4
Ben
Supporting Vendor
iTrader: (33)
 
Ben's Avatar
 
Join Date: Jul 2006
Location: atlanta-ish
Posts: 12,689
Total Cats: 99
Default

P = I * I * R
Where P = power (measured in watts)
I = current (measured in amps)
R = resistance (measured in ohms)

So power varies with load.
Ben is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Raleigh: Fiberglass headlight scope, 1.6L ECU, AFM, Hardtop latches, more bigmackloud Miata parts for sale/trade 13 09-22-2017 01:34 PM
1994 Spec Miata Race Car SM/SM2/SSM For Sale Quinn Cars for sale/trade 6 10-23-2016 08:58 AM
Nuke Mars! Joe Perez Current Events, News, Politics 8 09-30-2015 05:41 PM
Low oil pressure after 1.8 swap and new turbo setup JesseTheNoob DIY Turbo Discussion 15 09-30-2015 03:44 PM
NA Seat Sliders and Seat Belt Receivers skipstr Miata parts for sale/trade 2 09-28-2015 11:53 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 08:52 AM.