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Topic: PSU Ampere Calculation (on the wall with 230V) ?? - page 2. (Read 6407 times)

sr. member
Activity: 378
Merit: 250
Why is it so damn hot in here?
I am a bit puzzled again. Apologies if this has been answered before.

I am using 230V.

The PSU has 850W, I am currently using around 640W at the 12V rail. Lets assume for a moment I'd be drawing the complete 850W.

The PSU has 88% efficiency typical at this load (= 12% inefficiency).

850*1.12 = 952W.

At 230V that means the PSU should require a current of 4.14A (952/230). Why does the PSU say the following on the box:

AC Input:  100-240V~ 11-5.5A  60-50Hz

I know it's 240V not 230V, but 10V difference make 1.36A???

How am I supposed to estimate how much power it draws, how many of them I can connect to a single 13A or 16A outlet, etc? If I go by the 5.5A number, I can only connect two PSUs :/

Does anybody feel like teaching a dork like me some basic electrical skills?


It's more about the total wattage it can provide, the voltage and amperage are just the two parts to that.  120 Volts at 11 Amps is ...  1320 Watts.  240 Volts at 5.5 Amps is...  1320 Watts still.  So if your actual voltage is 230 volts, you max amperage would be...  5.74 Amps for the PSU max and 6.5 amps at the wall.

Your total amperage is dependent on what your actual voltage is.  Which can fluctuate quite a bit, so always be on the safe side and error on the side of caution.  Electrical fires are a real bitch.
rjk
sr. member
Activity: 448
Merit: 250
1ngldh
PSUs that allow a range of voltage without a switch tend to become more efficient as the voltage rises, due to how they work internally. Likely, that 5.5 is just an absolute max, and not what it will be pulling. Try it and see.

Additionally, the efficiency also varies with load - so with a different load and a different voltage, you could get a very different efficiency.

11 Amps at 100 volts is also a worst case scenario. All those are based on full load, and running at full load often reduces the efficiency a lot in less-expensive PSUs.
hero member
Activity: 489
Merit: 500
Immersionist
I am a bit puzzled again. Apologies if this has been answered before.

I am using 230V.

The PSU has 850W, I am currently using around 640W at the 12V rail. Lets assume for a moment I'd be drawing the complete 850W.

The PSU has 88% efficiency typical at this load (= 12% inefficiency).

850*1.12 = 952W.

At 230V that means the PSU should require a current of 4.14A (952/230). Why does the PSU say the following on the box:

AC Input:  100-240V~ 11-5.5A  60-50Hz

I know it's 240V not 230V, but 10V difference make 1.36A???

How am I supposed to estimate how much power it draws, how many of them I can connect to a single 13A or 16A outlet, etc? If I go by the 5.5A number, I can only connect two PSUs :/

Does anybody feel like teaching a dork like me some basic electrical skills?
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