Power Supply Section in A+ Book

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Hey guys

Just hit the power supply section in Mike Meyers A+ book - and suddenly realised a potential problem...

Im in the UK and hes talking about American plugs, voltages testing equipment etc

Do i just learn this? Or if i do the A+ test in the UK am i expected to know UK voltages?

Thanks for any help!

Steve

 

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There is *very* little in that section that is US specific. And some parts that detail the differences between European and N American stuff.

Just remember that in N America the voltage is approx 110V at a freq of 60Hz, whereas in Europe the standard is 230V at 50Hz.

The PSU and the mains socket are the same - Meyers give info on the voltage change switch.

Harry.

 

He does use the American terms for neutral, earth and live if I remember. I can't think what they are at the moment though.

 

i think it's just positive, negative and earth... although could be wrong.

 

the only thing you need to remember is that switch at the back.. keep it on 230v for the uk and europe and rest of the world and when you head to the us switch to 110v other than that the concepts the same.

 

The US plugs are 3 pin,have a 'hot' wire (we call it live),a nuetral and ground.There is a section in the MM book that will instruct you about the different voltages used and frequencies related to them,a little further down the chapter if memory serves correctly.

As mentioned,know that the PSU will covert AC to DC,typically output +-12v,+-5v and 3.3volts and has a voltage selector switch to change the input AC voltage from 110v to 220/230/240v (some psu's sometimes have 110/220,others can show 110/230 and 110/240,they're all good though!).

If you're power supply fan fails to turn...CHANGE THE POWER SUPPLY...no repairing psu's for the rest of your A+ training,KAPICHE?

 

That's what it says, hot.

 

Thanks for the tips guys!

I just had a flick through it before i read it and saw mentions of US voltages so i panicked slightly

Also thought i saw US plugs but that might have been the computer power cable plugs

Thanks again!

Steve

 

Allow me to add in a question here please. According to the book [if I understand this correctly], if a person plugs in a 115v piece of equipment into a 220v outlet, the equipment will be safe but if you plug a 220v piece into a 115v outlet, you will fry the piece, is this correct? If so, why? Should be the reversed because if you have an outlet with 220v of pressure in it and you hook up a piece which requires only 115v of pressure then you would be sending twice the required amount of pressure into the piece, is this not so?

Alternatively, if you plug a piece which requires 220v into an outlet that has only 115v of pressure in it then this should be safe becuase you don't have enough pressure to run the piece of equipment much less, do any damage to it. Can anyone explain this to me please?

 

Plugging a 240v AC rated device into a 110v AC rated socket will produce little,if any functionality from the device,but is highly unadvisable and,with care,avoidable.

Plugging a 110v AC rated device into a 240V AC rated supply may well land you in the nearest accident & emergency unit,or worse.EXTREMELY UNADVISABLE.

 

So then I am correct? Seems to me, you and I are both saying the exact same thing? If so, then I don't understand what he means on the book or can it be I misinterpreted his words? Here is exactly what is written on page 291:

" Caution
Flipping the AC switch on the back of the power supply can wreak all kinds of havoc on a pc. Moving the switch to ~230v in the U.S. makes for a great practical joke [as long as the pc is off when you do it]-the pc might try to boot up, but it probably won't get far. You don't risk damaging anything by running at half the AC. In countries that run ~230 standard, on the other hand,, firing up the pc with the AC switch set to ~115 can cause the power supply to die a horrid, smoking death. Watch that switch!"

Am I wrong or is MM saying the exact "opposite" of what we are saying, anyone?

 

read it again.It's saying what I said.

 

Ok, let's get straight to the point, I would appreciate if someone can confirm this, is Mike Meyers wrong, yes or no?

 

No, MM is right. You are reading it wrong as Mal said.
What you said here...

...is wrong.
If you are in the US and you set the PSU to 220v and then connect it to the 110v supply, you are unlikely to damage it. If you are in Europe and you set a PSU to 110v and connect it to the 220v supply, say good bye to your eyebrows and probably a good portion of the rest of your face.

 

To put it clearly he's saying this,

If you are in the US and you have the switch set to 110V your ok.
If you're in the US and you have the switch set to 230V you'll have barely enough power to power up.

If you are in Europe and you have the switch set to 230V then you're ok.
If you are in Europe and you have the switch set to 110V then you're putting twice as muce Voltage into the system as it can handle and will cause your power supply ( and possibly other stuff) to self destruct.

 

ok, got it now, MM is referring to "setting the switch" on a unit, looks like I was missing this, thanks everyone for clearing this up!

 

2 other issues please,

1] If I understand this correctly, on the section about "Wattage Requirements", it says that if you install a new hard drive and the pc doesn't power up, to determine if insufficient wattage is the problem, unplug the drive and power up the system. If the new system comes up, you can suspect the power supply.

My question here guys is, does this mean that the hard drive is drawing a lot of power from the system so the pc does not have the power to boot up?

2] MM gives a formula to determine wattage requirements of individual "devices" but how do you determine which power supply you will need when building a new pc since power supllies come in ranges between 200-600 watts?

 

I think the answer's in the question there mate. Yes.

Add up the total approximate wattage of all devices you will be using, add a bit more and buy a PSU that supplies at least that much power. I would say to get the most powerful one you can because you never know what power-hungry devices might come out in the future. It could get expensive buying a new PSU every time you want to add a piece of hardware.

 

Yes but MM advises against doing that because of "heat" and other issues which is why I am asking the question.

 

I don't remember him saying that but a PSU is always going to have an adequatly sized fan to dissipate any heat it generates so I don't think that's an issue.
Also, a modern ACPI/APM PSU will (I think) only supply as much power as needed so an 800w supply that is only having 400w drawn from it will only get as hot as a 400w supply. Factor in the fact that the 800w supply will have better cooling and it should be less of a problem.(This statement is pure speculation on my part so someone feel free to correct me ).