# Mean Well switch mode power supply how they work

I’m looking at the power supply below.

I have a few questions around the current output:

1. How do these power supplies increase the current to 40A from a 240v / 10A outlet or is there some other way these should be plugged into mains?

2. My plan is to have a WS2812B led strip connected to the output of this power supply, do I have to worry about the 40A output or will my led strip only draw what is required? Do I need to limit the current based on the led strip length?

Thanks.

Hi

It’s basic physics - conservation of energy.
Power = Voltage x Current
Assuming 100% efficiency (not true but close enough for an explanation) Power in = Power out

So, if power in = power out, but the voltage decreases on the output the current must go up proportionally. Mathematically:

Vin / Vout = Iout / Iin
(V is voltage, I is current, because that’s just a convention)

Just note that the one you linked is a 130W supply so it can provide 26A @ 5v (26 x 5 = 130) not 40A.

And question 2, yes you understand correctly. 26A is the maximum this supply can provide, but your circuit will only draw what it needs (in fact if your circuit needs more current it will try to pull it and damage the supply).

One last thing to note, you need to get an electrician to install this supply for you to make sure it’s safely installed.

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One more thing re 240V 10A outlets. 240V X 10A = 2400 Watts, about 1 X 3 bar radiator.
This 10A is TOTAL. Does not matter if there are 1, 2 or 4 outlets on this point you should not exceed 10A TOTAL LOAD. Failure to adhere to this will result in overheating and possibly actually blowing the point out of the wall. Possibly resulting in fire.

Oliver is correct, the efficiency of these supplies is usually 90% or better (varies slightly with load) and if you allow a bit of “fudge factor” (which you should anyway, about say 25%) can usually be ignored.

Cheers Bob

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OK thanks for that.

Two more questions.

1. So if a normal power outlet allows 240v @ 10a which is 2400w and connecting the above mentioned power supply 5v @ max 26A = 130w then isn’t that still well below the max 2400w allowed?
2. What exactly does an electrician need to do to install this power supply? Would it just be cutting a adequately rated power cord and connecting to the power terminals on this power supply?

Thanks

1. Yes it is. I just highlighted Max loadings as a precaution. How many times have you seen power multi boards daisy chained with all sorts of things plugged in.

2. Basically yes. Quality insulated crimp terminals should be fitted to the wires connecting to your power supply. Reasonable tooling should be used. Problems could arise when any old pair of pliers or similar are used. Using an electrician to make up and connect your cable would be recommended by Oliver as a precaution as your electrical qualifications and/or expertise and tooling available to you is unknown to the forum users and it is after all 240VAC we are talking about. Quite lethal.
Cheers Bob

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An electrician would also make sure the supply is correctly earthed (very important for safety), and since there’s mains voltage on the terminal block it’ll need to be placed inside another enclosure or behind a wall so someone can’t just stick their fingers in and zap themselves.

There’s some fairly hefty fines for doing electrical work on mains if you’re unlicensed in Australia:

You can be fined \$22,000 as an individual or \$110,000 as a company for doing unlicensed electrical work.

Everything on the 5V output side is fine, I’d just get an electrician to wire up and install the supply in an enclosure with a mains plug and some terminals for the 5V rail so it’s all nice and safe and you can just plug it in and move it around to your heart’s desire.

Thanks All,

I’ll find a local sparky once I purchase the power supply to set it up for me.

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Ah the laws. Sometimes seem a bit strange but a line has to be drawn somewhere. Mainly to stop people doing themselves what could be catastrophic injuries.
I say sometimes strange as during my working life I could not legally fit a 3 pin plug onto a piece of mains cable (unless inspected or supervised by a licensed electrician) but I could happily work on equipment with a DC power supply of 7000V or more. The overload circuitry did not start to get upset until the current started to exceed 10.5A. The minor HT supply was negative 1200V.
I think the States differ slightly with the rules. For instance some years ago WA had what was known as a Plug and Socket license which enabled technicians working in the industry to at least terminate mains cable with a 3 pin plug or socket. Progress.
Cheers Bob

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Yeah they’re strange at times! Usually written in blood though when it comes to safety. Usually.

But sometimes it’s just someone in middle management trying to make themselves be seen to be doing something which undermines the whole thing.

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