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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › How much power can an AC outlet deliver?
08-01-2007 07:03 PM  13 years ago
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gullie667

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Brooklyn, NY

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How much power can an AC outlet deliver?
I have heard that you can convert a computer power supply into a 12v power supply to power your battery charger.

The question is, how many watts in a power supply is the point diminishing return?

They sell 1000watt power supplies but can an AC outlet actually handle that kind of amp draw?

Gullie
Helicopters - 1000 parts flying in formation.
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08-01-2007 07:06 PM  13 years ago
Hydroman

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Kommifornia

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An AC outlet can only deliver what is rated in amperage from the circuit breaker.....

I am running a 45AMP PS from my 110 outlet....
just remember as you drop voltage, you can increase amprage....
everything seeks a median...
The older I get, the better I was
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08-01-2007 07:13 PM  13 years ago
Chopper

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Stow,Oh- oops, I mean St Louis, nope Stow again,

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A 110 outlet generaly is breakered at 15 to 20 amps. 110v x 15 a =1650. 1650 / 12 volts is 137.5 amps....minus line loss and power consumption of the transformer.Paul Soha is a free agent now. Wow.
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08-01-2007 07:17 PM  13 years ago
daijoubu

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Burnaby, BC - Canada

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North American standard is 120V with a 15A breaker. Thats 1800W. You shouldn't run a breaker at more than 80% of the rating for long (it may trip) so you have 1440W available. Most computer power supplies are terribly innefficient (about 60% efficient) so you can sustain 864W at the output. Realistically, you could push it up to 1100W at the output for about 30 minutes as long as the utility in your area was well regulated.
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08-01-2007 07:44 PM  13 years ago
Nick Jones

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anderson

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Would i be able to charge 6 cell 5000 batteries off a comptuer power supply?
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08-01-2007 07:59 PM  13 years ago
Heavy_Iron

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Wichita, KS, USA

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yes:

3.7Vx6cells=22.2V, 1C charge rate= 5A, 5A*22.2V=111W ONLY!
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08-03-2007 10:50 AM  13 years ago
SUB RAPTOR

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Galway Ireland

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You shouldn't run a breaker at more than 80% of the rating for long (it may trip)
If its rated for 15amps that means it will carry 15amps all day everyday. Of course that is if they rate them the same in the US as in the rest of the world. So the answer for one million dollars is YES. lol
Conor
"My piloting skills are proof that gravity does exist."
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08-03-2007 10:49 PM  13 years ago
AltecLansing

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North Carolina

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NEC code says that continuous loads must not be rated for more than 80 percent of a breaker rating. Any more than that and it may overheat the lines. Or if you are looking for the 80 percent in the code book, it says that for a continuous load, you have to use a breaker rated at least 125 percent of the load.Man, I miss the eighties.
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08-03-2007 11:23 PM  13 years ago
spog

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Ontario, Canada

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North American standard is 120V with a 15A breaker. Thats 1800W.
A 15 amp AC outlet at 120v is 1800VA, not 1800 watts.

For single phase AC
Power (avg) = V * I * PF (power factor)
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08-04-2007 12:00 AM  13 years ago
AltecLansing

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Ok, I can't resist. True power is measured in Watts. Apparent power is measured in volt amps. Power factors are involved with motors and transformers. Basically, anything with a coil of wire will have a power factor(efficiency) due to power lost in the coil. A standard house hold outlet has available the wattage that is calculated with voltage times current. Hence, a 20 amp circuit breaker at 120 volts nominal will have 2400 watts available. The only loss of power you get in circuit is from the resistance of the wire in the circuit. Resistance uses power. However, resistance of wire is generally not calculated in houses unless the distance great. Then you would determine voltage drop and resize the conductors accordingly. Which is all done for you when the house was built. Hence, you have 2400 watts available on a 20 amp circuit. But if you use any particular item for more than 3 hours at once, you will want to use no more than 80 percent of the circuit breaker or 1920 watts on a 20 amp circuit breaker. To make a long story even longer, yes you can use 1000 watts on a 20 amp circuit with little problem. If the breaker trips, check to see how many items you have plugged in on that circuit and unplug a few of them. Don't use a power strip for the charger though. Most of them are not rated at 2400 watts. Sorry to make a long post and nitpicking a little, but I don't talk any tech stuff at work since we build commercial and industrial buildings and I don't trouble shoot equipment any more.Man, I miss the eighties.
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08-04-2007 01:49 AM  13 years ago
spog

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Ontario, Canada

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Power factors are involved with motors and transformers. Basically, anything with a coil of wire will have a power factor(efficiency) due to power lost in the coil.
Power factor and efficiency are not the same thing at all. Power factor is a measurement of the phase relationship between AC voltage and current. The power factor of a load can be corrected with a capacitor or an inductor (depending on the device). A poor power factor results in higher losses because more current is required to provide the same power (watts). Many industries correct their usually lagging power factor using capacitor banks. Where I work, we correct our power factor by overexciting our 32000HP synchronous motors.
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08-04-2007 02:00 AM  13 years ago
AltecLansing

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North Carolina

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You are right that power factor and efficiency aren't the same. Power factor is the ratio of true power and apparent power. I've also seen the capacitor banks used to counter inductive reactance. I've been lucky so far not have to correct inductive reactance. So many things I have let go since I only look at blue prints and run power to equipment and terminate them. Interesting that you are an electrical engineer, do you just work factories or have done design on blue prints?Man, I miss the eighties.
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08-04-2007 02:26 AM  13 years ago
spog

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AltecLansing, I am not sure I understand what you mean by "working factories". I have experience in electrical maintenance engineering and design engineering in industry. Maintenance involves more modifications, repair, troubleshooting, equipment replacement, but pretty much all enginering jobs involve design work. Maintenance engineering is a real meat grinder of a thankless job, I won't be doing that again.
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08-04-2007 02:35 AM  13 years ago
AltecLansing

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North Carolina

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My current boss is an electrical engineer. Yet, I don't think he would have the skills to do the maintenance in a factory. I'm sure if he studied up on it he could. He designs the electrical portion of a set of blue prints. Most blue prints use electrical engineers to determine the loads required in a building. A master electrician is suppose to be able to do the same thing, but seldom do. The biggest difference between the electrical engineer and master electrician when it comes to the electrical design in a blue print is being in the field. I find a master electrician better for designing the electrical portion of the print and an electrical engineer better for specific non standard equipment. Personally, I would rather get back to troubleshooting and repair. I like the challange more, I guess that's why I am learning to fly helis. Now if I could just figure out which way is up.Man, I miss the eighties.
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08-05-2007 03:43 AM  13 years ago
Heavy_Iron

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Wichita, KS, USA

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Ok, I'm not an EE but could you please elaborate how impedance and reactance relate to "power factor". is it equal to RMS product of I and V consumed over useful work produced?
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08-05-2007 04:36 AM  13 years ago
AltecLansing

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North Carolina

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does it really matter on what is available on a typical household circuit? go with the simple math and some common sense in plugging in multiple items and you won't have any problems with running a 1000 watt, 1500 watt, or 2000 watt item. I only made a comment earlier because I saw how everything was starting to get technical and I miss the techinical stuff.Man, I miss the eighties.
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08-05-2007 05:02 AM  13 years ago
Heavy_Iron

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you are absolutely correct that common sense is the key. could you please answer my question, i'm just curios. thanks!
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08-05-2007 05:37 AM  13 years ago
tadawson

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Lewisville, TX

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Reactance causes phase shifts in the relationship between current and voltage . . . If they is zero phase shift, the load is resistive, and then the power (wattage) is truly P=I*V. If there is reactance, then the current is phase shifted from the voltage, into what are described as real and imaginary components. The real component does work, and the imaginary is more of a circulating current, that loads the circuit, but is not able to do any work. Hence the difference in the definition of VA and watts . . . .

In a DC circuit, or purely resistive circuit, then VA = Watts. But not on AC . . . and, FWIW, a lot of power supplies are notoriously reactive . . . but not that it matters much at the low powers they draw. (Keep in mind that 20A at 120V is 2400 watts, or 200 amps at 12 volts with no losses . . . . and that will charge a s**tload of batteries!)

- Tim
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08-05-2007 05:51 AM  13 years ago
cudaboy_71

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sacramento, ca, u.s.

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the short answer is you CAN NOT charge a 6s 5000mah pack at 1C from a computer power supply. but, you can use your house mains with a proper power supply.

typical computer power supplies are in the ~7-12amp range on the +12v leg.

by the time you do the DC/DC conversion to get your 12v computer power supply up to the pack's 22.1v you'll double the amperage drawn from the power supply. so, you're really pulling 10amps from the power supply.

from personal exeperience i can tell you that a 11amp power supply trips pretty easily when charging an 4400mah pack at 4.4amps. now i'm no EE. but, logic should tell you there are some pretty heavy losses somewhere in the circuit between the mains and your pack. and, if pressed to hazard a guess i'd say it lies somewhere in the cheap, chinese-made computer power supply. (FYI, i was able to charge them fine at 1.2amps without tripping the breaker...it just took an eternity)

as soon as i got a proper 30amp power supply i had no problems charging 4900mah 6s packs at 2C from my 110v mains.
if it ain't broke, break it.
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08-05-2007 06:19 AM  13 years ago
Heavy_Iron

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Wichita, KS, USA

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edit: i looked everything up in a textbook from ten years ago. thanks for the info anyway.
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