How many amps would an 850w PSU draw using a 300v power cord?

TheSilverKing · October 31, 2020

The power cord for my computer is labeled as 300v, my PSU is 850w, I know it won’t use the max all the time, but what max am I looking at? I’m trying to power my pc off of 1 15 amp outlet that also has a tv (1amp), Cable box (3amp), modem (1amp) and router (1amp) on it, but I’m not wanting to trip the breaker in the trailer I’m temporarily living in.

WereCatf · October 31, 2020

12 minutes ago, TheSilverKing said:

The power cord for my computer is labeled as 300v, my PSU is 850w, I know it won’t use the max all the time, but what max am I looking at? I’m trying to power my pc off of 1 15 amp outlet that also has a tv (1amp), Cable box (3amp), modem (1amp) and router (1amp) on it, but I’m not wanting to trip the breaker in the trailer I’m temporarily living in.

The rating of the power-cord is an irrelevant detail here, since what matters is the voltage at the wall. The 300V-rating only means that that's the maximum the cord has been designed to be able to handle safely, it doesn't say what voltage actually is traveling through it. So, the question is: what's the voltage at the wall? 230V? 110V? Something else? At 230V, 850W would equal to ~3.7A, whereas at 110V it'd be ~7.73V.

Wattage is calculated by Voltage * Amperage, so you can also do the reverse: Amperage = Wattage / Voltage, or Voltage = Wattage / Amperage.

Spotty · October 31, 2020

12 minutes ago, TheSilverKing said:

The power cord for my computer is labeled as 300v

Doesn't matter what the power cord is labelled. That's just the max voltage it is rated for. The voltage will be whatever your mains power is. What mains power do you have? 230V? 115V?

The power that your computer draws won't necessarily be 850W with an 850W PSU. It will be however much the system needs at any given time, which will depend on your hardware.

If your system draws saw 400W for example under load and you're on 115V mains that would be around 3.5A. If it's 230V that will be half that, 1.75A.

Watts / Voltage = Amps

SnowyMus · October 31, 2020

I'm going to assume you're using 120 V AC or 240 V AC, as most PSUs only support 100 to 240 V AC. The cable doesn't have a voltage difference on its own. It's probably just rated for up to 300 V.

Anyway, current depends on your PC's power draw.

Current (A) = Power (W) / Voltage (V)

If your PC draws its PSU's maximum current at 850 W and it's, say, 82% efficient at that load, then it draws a total of around 1037 W.

1037 W / 120 V = approx 8.64 A

1037 W / 240 V = approx 4.32 A

It's unlikely your PC will draw that much. It'll probably just draw 450 W or so if it's a typical gaming PC. If your PSU is 90% efficient at that load, then it draws 500 W total.

500 W / 120 V = approx 4.17 A

500 W / 240 V = approx 2.08 A

Some inputs are 115 V or 230 V. If so, take the current from the closer of the voltages and multiply it by 1.0435.

October 31, 2020

6 hours ago, TheSilverKing said:

The power cord for my computer is labeled as 300v, my PSU is 850w, I know it won’t use the max all the time, but what max am I looking at? I’m trying to power my pc off of 1 15 amp outlet that also has a tv (1amp), Cable box (3amp), modem (1amp) and router (1amp) on it, but I’m not wanting to trip the breaker in the trailer I’m temporarily living in.