Author Topic: Wall Transformer Power Consumption  (Read 6546 times)

0 Members and 1 Guest are viewing this topic.

tcrenshaw

  • Jr. Member
  • **
  • Posts: 76
Wall Transformer Power Consumption
« on: December 30, 2004, 04:54:11 PM »
I'm working with CCFL lighting and using a wall transformer to go from 120V AC to 12V DC. I'm a bit confused about the input and output on the back of the transformer. The transformer Output reads 12V DC 0.3A - okay no problem understanding that, about 3.59 watts. The Input though says 120V AC 11VAC - I'd like to know what the current used is. Would it be still be the 0.3A?
« Last Edit: December 30, 2004, 04:54:11 PM by (unknown) »

chux0r

  • Jr. Member
  • **
  • Posts: 56
Re: Wall Transformer Power Consumption
« Reply #1 on: December 30, 2004, 10:59:13 AM »
0.3A at 12V is 3.6W, so your input must be at least 3.6W at 120V which is 0.03A (your current will go down if voltage goes up).  But of course there are losses, so if your input is 11VA (smarter people know the difference between VA and W, but I don't!), so let's round your current to about 0.1A.


That's notable loss, BTW...  Those wall warts suck. :)

« Last Edit: December 30, 2004, 10:59:13 AM by chux0r »

patty3

  • Newbie
  • *
  • Posts: 7
Re: Wall Transformer Power Consumption
« Reply #2 on: December 30, 2004, 11:35:20 AM »
If VAC means what I think it does,[volt, amp, constant duty] then it has nothing to do with the current consumption of the transformer. Usually what you get out of a transformer is the same as what you have to put into it + any losses and can be checked with an amp meter. My curiosity has always been how much current a transformer consumes when at idle and the only way I know of to find this out is to put an amp meter on the 120 volt side when nothing is hooked up to the 12 volt side. 3.6 divided by 120 = .03 amps, which would be fairly close to what your current consumption would be when the lights are on.  Pat!
« Last Edit: December 30, 2004, 11:35:20 AM by patty3 »

tcrenshaw

  • Jr. Member
  • **
  • Posts: 76
Re: Wall Transformer Power Consumption
« Reply #3 on: December 30, 2004, 12:02:30 PM »
Okay, what you both say makes sense - watts is watts. What I'm trying to figure out is how large of a 12v DC supply I'll need to run two to four of these CCFL lamps I have. I've read that the CCFL lamps I'm using really take about 5 watts for full brightness. Zero documentation with them so I'm not sure what they really require. In my case I'm at 3.6 watts so this also explains why the transformer is getting pretty warm. I'm pushing it harder than its rated for. Or am I way off on this?
« Last Edit: December 30, 2004, 12:02:30 PM by tcrenshaw »

RatOmeter

  • Full Member
  • ***
  • Posts: 144
Re: Wall Transformer Power Consumption
« Reply #4 on: December 30, 2004, 02:49:36 PM »
You're on the right track on everything except VAC.  That is simply Volts, Alternating Current. Read through the FAQs at otherpower.com on wall warts and maybe try a google search with the keywords "wall wart efficiency energy saving" or similar.


The upshot, wall warts do use energy even when plugged in but not powering some device.  Also any TV, stereo component or other consumer device that can be 'switched on' by a remote control is using (sometimes significant amounts of) energy while 'off'.

« Last Edit: December 30, 2004, 02:49:36 PM by RatOmeter »

tcrenshaw

  • Jr. Member
  • **
  • Posts: 76
Re: Wall Transformer Power Consumption
« Reply #5 on: December 30, 2004, 02:58:59 PM »
Yep, sounds good. Yeah I know about wall warts and it's pretty simple, the primary coils are always charged even when nothing is being used on the rectified side. What a waste of energy. I hear the newer ones are being designed with micro processors to detect when they should turn fully turn on. Even then, they will use a slight amount to power the detection circuits. What I plan on doing to minimize this is to have them plugged into either a power strip or wall socket that I'll turn on and off as needed. The good ole manual method of energy conservation. Now to order more CCFL's and play around some more. I like the idea of them lasting 15 to 20K hours. that kind of softens the expense. If I've got something wrong above, please point it out. I'm still in the learning mode.
« Last Edit: December 30, 2004, 02:58:59 PM by tcrenshaw »

Ungrounded Lightning Rod

  • SuperHero Member
  • ******
  • Posts: 2865
Re: Wall Transformer Power Consumption
« Reply #6 on: December 30, 2004, 04:36:25 PM »
If VAC means what I think it does,[volt, amp, constant duty]


It doesn't.  It means Volts of Alternating Current, using the root-mean-square (RMS) method to characterize the AC's constantly-changing voltage.


My curiosity has always been how much current a transformer consumes when at idle and the only way I know of to find this out is to put an amp meter on the 120 volt side when nothing is hooked up to the 12 volt side. 3.6 divided by 120 = .03 amps, which would be fairly close to what your current consumption would be when the lights are on.


This is almost entirely "reactive current" - 90 degrees out-of-phase (lagging) with respect to the voltage.  (It's not exactly 90 degrees off - a little power is actually consumed heating the transformer.  The inductive current is 90 degrees lagging, the current feeding the heating is in-phase, and they add as a vector sum.


The "current consumption" when under load will be higher than that you calculate from the wattage.  That calculation gets you the in-phase current needed to feed the load's consumption.  It will also be added vector-style to the transformer's reactive current (which doesn't change).  So given that your reactive current is about the same as your expected load current, expect the actual current drawn to be about 1.414 times the current you'd expect for powering the load.

« Last Edit: December 30, 2004, 04:36:25 PM by Ungrounded Lightning Rod »

Ungrounded Lightning Rod

  • SuperHero Member
  • ******
  • Posts: 2865
Re: Wall Transformer Power Consumption
« Reply #7 on: December 30, 2004, 04:43:59 PM »
VA is Volts times Amps, without worrying about the phase angle between them.


Split the amps into "real current" (the part in-phase with voltage) and "imaginary current" (AKA "reactive current") (the part 90 degrees out-of-phase) and you can start calculating watts.


Watts = real current times voltage


VARs (volt-amps reactive AKA "reactive power") = reactive current times voltage.


Reactive power is said to be "consumed" by inductors or inductive loads and "generated" by capacitors or capacitive loads.  This is somewhat arbitrary, picked this way because reactive power is also conserved, so AC generators have to run out-of-phase to produce any reactive current needed by the loads.  Transformers and induction motors (the major loads on an AC utility) both present inductive loads.  So inductors are considered to consume VARs.

« Last Edit: December 30, 2004, 04:43:59 PM by Ungrounded Lightning Rod »

tcrenshaw

  • Jr. Member
  • **
  • Posts: 76
Wall Transformer Power Consumption
« Reply #8 on: December 30, 2004, 08:41:49 PM »
I actually checked out what the CCFL lamp was pulling tonight. I was right, I was pushing the wall wart harder than it wanted to be pushed. I have a 13.8vdc 2.5amp power supply I use for my HAM radios. I connected it up and what a difference. The CCFL lamp was almost twice as bright. Tossing a meter in there I found the voltage reading at 13.75vdc and the current at .92 amp or about 12.65 watts. It'll take a little more experimentation but I think with three of these 24" CCFL lamps I'll have more light in my bathroom than with the four 40 watt heaters (incandescent) bulbs that are there now. Even if I use five CCFL lamps I'm still only be a little over 10 watts above just one incandescent bulb. The bluish light is a little different but nothing that I haven't been able to adjust to.
« Last Edit: December 30, 2004, 08:41:49 PM by tcrenshaw »

tcrenshaw

  • Jr. Member
  • **
  • Posts: 76
Re: Wall Transformer Power Consumption
« Reply #9 on: December 30, 2004, 08:49:19 PM »
That's four CCFL lamps, not five as mentioned above.
« Last Edit: December 30, 2004, 08:49:19 PM by tcrenshaw »

wooferhound

  • SuperHero Member
  • ******
  • Posts: 2288
  • Country: us
  • Huntsville Alabama U.S.A.
    • Woofer Hound Sound & Lighting Rentals
Re: Wall Transformer Power Consumption
« Reply #10 on: December 30, 2004, 10:44:31 PM »
I really enjoy the power savings and extra long life that a Compact Flourescent Light provides, but the color is a little wierd. It's good to still have a low wattage Incandescent in addition to provide the extra color
« Last Edit: December 30, 2004, 10:44:31 PM by wooferhound »

tcrenshaw

  • Jr. Member
  • **
  • Posts: 76
Re: Wall Transformer Power Consumption
« Reply #11 on: December 31, 2004, 05:18:46 AM »
That's one advantage CFL's have over CCFL's. They now come in a warmer color. My uncle uses CFL's throughout his house and I can't really tell a difference between them and incandescent. Plenty of light at low power consumption cost. The color is warm but bright.


CFL's are very efficient compared to pretty much all other forms of lighting that can be used fairly easily in the home, but they are not as efficient as CCFL's.


Here's the chart from Otherpower.com with the addition of other lighting. I found the extra information on the net so question some of its accuracy.


LPS lights--200 lumens/watt (poor color rendition)

HPS lights--140 lumens/watt

HID lights--100 lumens/watt (have horizontal/vertical position issues)


All three of the above are not really suitable for home interior lighting because of their size except HID's but presently HID's are kind of touchy about how they are oriented.


cold cathode fluorescent lights--75 to 90 lumens/watt

32 watt T8 fluorescent--85 to 95 lumens/watt

standard F40T12 cool white fluorescent--60-65 lumens/watt

compact fluorescents--low 30's to low 60's lumens per watt, usually 48-60

LED's (new technology) are reaching 50 lumens/watt

T3 tubular halogen--20 lumens/watt

white LED--15-19 lumens/watt

standard 100 watt incandescent--17 lumens/watt

incandescent night light bulb (7w)--6 lumens/watt

incandescent flashlight bulbs--dismal, less than 6 lumens/watt


T8 fluorescent's look very promising. There are two issues with them to deal with though. First, they run fairly warm to hot like any standard fluorescent and two, they are 1" in diameter so they do take up more space like a standard fluorescent. They do come in a neutral color though so color rendition is fairly good.


I haven't been able to find any company making CCFL's for home lighting use. Or at least not for primary use. Most are for internal PC case display, car accent displays, back lighting for LCD displays, some cabinet displays because of the very low heat generated and things along those lines. None yet for actual home or office primary lighting use. Well not entirely. I did find one desk lamp that uses a CCFL lamp and I did find one lamp that was a spiral CCFL encased inside a clear bulb that was shaped exactly like an incandescent bulb. It was 240v/7 watts.


I was thinking about tossing in a yellow CCFL with two whites to see what the mixed color would produce. The blue really doesn't bother me though.


Now that I've connected the lamp up to a power supply that exceeds its needs and pretty much doubled the light output I'm very pleased with the results. After power on it takes about 15 to 30 seconds for the CCFL to come up to full output. Once it does though it's very bright. I can now say that this one 12.65 watt lamp is producing more light than a single 40 watt bulb with ease.


I'm going to continue my experimentation (playing) and am looking into designing a few replacements for my incandescent lights in the house. It's going to be interesting to also calculate the cost break point compared to incandescent lights.

« Last Edit: December 31, 2004, 05:18:46 AM by tcrenshaw »

ghurd

  • Super Hero Member Plus
  • *******
  • Posts: 8059
Re: Wall Transformer Power Consumption
« Reply #12 on: January 03, 2005, 09:21:48 AM »
CFLs can be had in different colors or temperatures.

Some are nice, some are not. Varies by brand and model.

When you find one you like, get more before before they are discontinued or 'New And Improved'.

G-
« Last Edit: January 03, 2005, 09:21:48 AM by ghurd »
www.ghurd.info<<<-----Information on my Controller