InterceptRadio.com Forums

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?

Roughly 350ma off the cuff...

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"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

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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That is how the people at DARPA think. they take things and use them in unconventional ways, to see what happens.

I dont argue the question... Just try to answer it. :mrgreen:

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"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

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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That is how the people at DARPA think. they take things and use them in unconventional ways, to see what happens.

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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That is how the people at DARPA think. they take things and use them in unconventional ways, to see what happens.

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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If I had an antenna, I would; but I can only transmit on 160 meters.
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DE K7MHI

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.

what is your application? can you put in a current limiter or just fuse it

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If I had an antenna, I would; but I can only transmit on 160 meters.
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DE K7MHI

Webserver

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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"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

I guess a better question is where is the application, this going in a solar or mobile operation?

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If I had an antenna, I would; but I can only transmit on 160 meters.
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DE K7MHI

It's on a shared circuit that is very near capacity.

Hosting services are your friend.

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"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."