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| Math http://www.interceptradio.com/bbs/viewtopic.php?f=20&t=4161 |
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| Author: | Atomic Taco [ Fri May 07, 2010 4:09 pm ] |
| Post subject: | Math |
Here's another fun one. I'm no EE and my high school didn't have electronics class. I'm looking at picking up a power supply, but need to know how much current it's going to draw. The inverter has the specs of: AC Input: 100-204V 2.5A, DC Output 12V 6.6A max. Assuming 82% efficiency, how much current will it draw off the 120V AC line if I'm pulling 35 watts DC? |
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| Author: | chpalmer [ Fri May 07, 2010 4:40 pm ] |
| Post subject: | Re: Math |
Roughly 350ma off the cuff... |
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| Author: | kb7dqh [ Fri May 07, 2010 5:51 pm ] |
| Post subject: | Re: Math |
Hmmm.... in a perfect world, maybe... The PSU sucks 2.5A off the AC line when its dumping 6.6A into whatever... Assuming 120VAC on the line that 2.5A is 300W... 6.6 A X 12V= 79.2W... or 26.4% efficiency. :puke: My guess is the max current draw occurs with the PSU being fed with 100V... Thus... 100V X 2.5A = 250W, or 31.5% efficiency. Only slightly less :puke: So... a 35W load on 12V would be a snudge under 3A... (2.9167A;) Likely would still draw around an amp off the AC line with your hypothetical load... and two-thirds of the AC is heating up the transformer and the voltage regulator This assumes the suspect power supply isn't a switcher... If it was (and it were mine :mrgreen: it would likely end up at the other end of :chaingun: |
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| Author: | Atomic Taco [ Fri May 07, 2010 5:52 pm ] |
| Post subject: | Re: Math |
http://www.silentpcreview.com/article601-page1.html |
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| Author: | chpalmer [ Fri May 07, 2010 5:54 pm ] |
| Post subject: | Re: Math |
I dont argue the question... Just try to answer it. :mrgreen: Quote: Assuming 82% efficiency
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| Author: | kb7dqh [ Fri May 07, 2010 6:19 pm ] |
| Post subject: | Re: Math |
OK, those chinese power supply builders have a lot of nerve, both the 60 and 110W apparently draw the same current :?: Maybe the 2.5 amps is the inrush current when you plug it in? When it catches on fire? :roll: I givvup... Eric KB7DQH |
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| Author: | kb7dqh [ Fri May 07, 2010 6:21 pm ] |
| Post subject: | Re: Math |
Guess the only way to know for sure is to get one of those "brick" supplies, plug it into the AC ammeter, stick the 35W load on the 12V side and MEASURE IT :arrow: :mrgreen: |
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| Author: | SpudGunMan [ Sat May 08, 2010 9:24 am ] |
| Post subject: | Re: Math |
kb7dqh wrote: Guess the only way to know for sure is to get one of those "brick" supplies, plug it into the AC ammeter, stick the 35W load on the 12V side and MEASURE IT :arrow: :mrgreen: thats the real answer, math is for squares :mrgreen: in the time it takes to find your HP calculator I can clamp it and correct for efficiency and real world loss! |
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| Author: | Atomic Taco [ Sat May 08, 2010 10:17 am ] |
| Post subject: | Re: Math |
If it draws more than .5 amps, I can't use it, so I was trying to figure it out before I buy. Plus, the "real world" values are probably different than the theoretical values. |
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| Author: | SpudGunMan [ Sat May 08, 2010 11:12 am ] |
| Post subject: | Re: Math |
what is your application? can you put in a current limiter or just fuse it |
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| Author: | Atomic Taco [ Sat May 08, 2010 11:53 am ] |
| Post subject: | Re: Math |
Webserver |
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| Author: | chpalmer [ Sat May 08, 2010 1:33 pm ] |
| Post subject: | Re: Math |
Webservers dont need to be very substantial at all unless your Google or Intercept Radio... :mrgreen: Laptop could be set up to do it if all else fails. Fry's in Renton had a couple of those pico power supplies last time I was there on clearance.... Ive thought of running my pfSense box off a battery bank along with the rest of the network to keep it up during storms. But I did not get one while I was there... I can get a -48vdc supply to replace one of the redundant supplies in my server so would run the whole thing on -48 and regulate down to 12 here if I were to get serious. But my connection to the world goes away after roughly two hours during an extended power outage of the area so have that to consider. Why the 1/2amp limitation if you dont mind me asking?? |
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| Author: | SpudGunMan [ Sat May 08, 2010 5:26 pm ] |
| Post subject: | Re: Math |
Atomic Taco wrote: Webserver I guess a better question is where is the application, this going in a solar or mobile operation? |
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| Author: | Atomic Taco [ Sat May 08, 2010 5:33 pm ] |
| Post subject: | Re: Math |
It's on a shared circuit that is very near capacity. |
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| Author: | chpalmer [ Sat May 08, 2010 6:19 pm ] |
| Post subject: | Re: Math |
Hosting services are your friend. |
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