Power Supplies Really Power Converters

The Basics Power Supplies take 115VAC as input and output 3.3v, 5v and 12v DC. Held in place with four common screws It’s one of the easier items to replace, but figuring out that it needs replacing can be difficult. We have both AT and ATX style power supplies.

Basic Electricity The pressure of electrons in the wire is called Voltage and is measured in volts (V) The flow of electrons past a point on the wire is called current or amperage (Amps or A) The product of volts and amps, (V*A), is called Watts (W) or wattage Resistance to flow is measured in Ohms

More Basics Wires (and devices) can only handle so much power (watts) then they heat up and break (melt). We say a circuit can handle 10 A, the voltage (~115v) is assumed. We use this heat/break to our advantage and call them fuses. We need a ground, or zero point, in order to create DC voltage. Good safety practice also.

DC and AC DC – constant voltage In single direction AC – Alternating current, 60 cycles (Hertz)

Electricity Won’t hurt you as long as – it is contained, or –You are NOT part of the path to ground The kind of electricity we are talking about here COULD flow through you If you start with respect for electricity, you will seldom get into trouble

Securing AC What comes from the wall should be a steady flow of vAC Three wires: Hot, Neutral and Ground –Hot carries the voltage –Neutral returns it to the breaker panel –Ground provides a path, to ground, in case it is needed

Measuring Electricity Use a multimeter, or VOM (volt-ohm meter) Neutral Hot Ground

VOMs Can measure AC, DC, resistance (and continuity – a variation on resistance) Make sure you have the scale set to the right type/range BEFORE you touch the leads to wires Might want to have a special plug tester if you do a lot of new home installations, otherwise, use a lamp or other simple device to check outlet

Power If the power should go out, you will only loose what you have not saved to disk – not entire contents of disk. If power dips, or reduces, it’s a brownout. If power stops, it’s a blackout. If power surges up, it’s a spike. The critical point is when power comes back on – spikes and inrush current – so make sure computer is off.

UPS Uninterruptible Power Supply Designed to protect against spikes and sags in line voltage The less-expensive ones ($100-$600) are actually standby or SPS The expensive ones ($600 +) are true UPSs

Standby UPS Normally, line voltage flows through unit, with a little flow to battery to maintain charge. When line voltage drops, battery kicks in to provide replacement voltage. Wall outlet computer

True UPS Line voltage is constantly converted to DC, flows through battery, converted back to AC. Battery is never out of the circuit. Wall outlet Computer

Sizing UPSs UPSs are rated in watts, and volt-amps. Take your power supply (300 watts) and add monitor (52 watts for flat panel; 2.5a [2.5x115= watts for 17” CRT) to find rating needed. Don’t plug printer or speakers into UPS. Remember, all you want to do is save your work and shut down computer.

Surge Suppressors Good idea in areas prone to electrical storms or power spikes. They “clip off” or fail-safe when voltage level goes up; no protection for sags Around here, get an outlet strip (4 to 6 outlets) 15

Once Inside Power supply converts AC to 3.3, 5 and 12 volts DC for interior components. AT-style power supplies have a thick, black cord and switch 115v at the front of the PC ATX-style power supplies have the large, 20/24 pin P1 connector for power to the motherboard

P1 Connector Used on ATX motherboards 20- (or now 24-) pin connector

P4 Connector Named that way because it first showed up for P4 processors. Now used by both Intel and AMD. 12 volt x 2 Ground x 2

Molex connector Used to power hard disk drive, CD/DVD drive, Zip drive 5v G G 12v

Mini Connector Used to power floppy disk drive only 5vG 12v 10

SATA power connector

Power Supply Size Processor can draw watts, hard disk drives watts Michael suggests 500 watts for new systems. The “little” systems, with 200w power supplies are scary – too close to not enough The more it produces, the more AC it draws and the more heat generated and the more cooling fans you need and the more noise you get The issue of efficiency…

ATX-style Power Supplies Use a feature called Soft Power that allows system to power down, then back up again. Always have 5v on motherboard when system has power cord attached and switch is on Michael and his car key; not a good idea with new ignition key

Newer Power Supplies ATX12V 1.3 – Adds a 4-pin, 12 volt connector (the P4 connector) and/or a 6- pin flat connector (AUX) EPS12V – Used, for a while, in servers Rails – Increasing the power output ATX12V 2.0 – 24-pin main power connector, two 12-volt rails and SATA power connector(s)

Active PFC Power Factor Correction Because of the way power supplies convert AC to DC, the AC can get shifted (out of phase, or harmonics) It’s not on the boxes I have 5

Installing Unplug the old power supply from devices Just 4 screws at the back of system unit. Use same screws to attach new supply Reconnect power leads to devices

Cooling This is becoming a huge issue with new, hot CPUs and video cards Case (exhaust) fan a really good idea Keep slots covered Make sure power supply fan (exhaust) is working

Repair of Power Supplies

Don’t. Capacitors can hold a (big) electrical charge for quite a while Replacing a power supply is a lot cheaper than “fixing” one

Fans You can have too many – and too noisy Some fans you can control through the BIOS or a software application Bigger spins slower and thus quieter Keep the case closed for better air flow

When Power Supplies Die Sudden death – and may take other components with it (CPU, motherboard, hard disk drive) Slow death – System halts, blinks off, reboots – the key is intermittent issues

Fires Class A – wood or paper Class B – Gasoline, solvents, paint Class C – Live electrical equipment Class D – Combustible metals such as titanium or magnesium You can get ABC extinguishers today