FAQ: Will <insert PSU model> Power Supply work with my system?

**DarquePervert** · 01-31-2006, 09:39 AM

The main factor in determining power needs is your CPU. Some CPUs draw lots of power, namely P4 and Athlon64 units. The CPU is the biggest variable in systems, as far as power consumption.

Look up your CPU on Chris Hare's PROCESSOR ELECTRICAL SPECIFICATIONS page. He lists the electrical specs of just about every CPU produced in the past ten years or so. Look at the Max Power Dissipation column. That's the peak power usage of the CPU under heavy load. Using this figure in your calculations will allow power overhead for the CPU to perform any tasks you throw at it without choking off your power supply.
(Note: He has divided this page into two pages, with older CPUs being listed here.)

Now that you know the max power draw of your CPU, you need to know how much power the PSUs provide on the 12v rail. The 12v rail is the one that will provide power to the CPU. It's stepped down to 1-2v (typically) with more amperage so the CPU doesn't burn up. There's circuitry on the motherboard for this.
Typically, the PSU will tell you how many amps it will output on the individual rails. To calculate wattage output, you multiply amps by volts (A x v = w). If the wattage output of the PSU on the 12v rail is less than the max dissipation for your CPU, it won't work.
Some will argue that the PSUs put out more than they are rated for, blah blah blah. This may very well be true, but do you really want to gamble that a $100 PSU will work for your desired setup based on a couple of watts difference?

The other thing you need to consider is other 12v devices. There aren't that many. 3.5" HDDs, full-sized optical drives, case fans, external audio like a Creative SB Audigy NX, possibly an LCD screen, etc. There are other power calculators that will give you power usage estimates for these devices. These need to be added to the total wattage load on the 12v rail to determine if the PSU will suit your needs.

EXAMPLE:
Let's say you want to use an Opus 150w PSU with a P4 2.8C CPU. If you look up that CPU on Chris Hare's page, you can see that the max power usage is either 68.4 or 69.7w, depending on flavor. Let's call it 70w for simple math. ALWAYS ROUND UP!!!!
So you look up the specs for the Opus 150w and it says that the output on the 12v rail is 5A. 12v x 5A = 60w.
You'd get 60w out of the Opus PSU and the CPU requires 70w. It's not going to work, so there's no point in calculating how much power the other components are going to draw from the 12v rail, as the CPU itself uses more than the PSU can supply.

See? It's simple!

Please note that the range of AMD AthlonXP CPUs are the exception to this rule. They draw their power from the 5v rail instead of the 12v rail, as do most other CPUs. As such, this method of determining an appropriate power supply won't work. A similar method for calculating the dar on the 5v rail would neeed to be used.

**DarquePervert** · 01-31-2006, 09:58 AM

Each PSU lists the rail, amperage output and total watts for that rail. All PSUs also have negative 12v rails and a 5v standby. For the purposes of calculating whether a PSU will work with a given system, these aren't necessary, so aren't listed here.
Links are provided to the manufacturer's website for each of the products listed.

Opus Solutions 90w
12v rail = 2.5A (30w)
3.3v rail = 6A (19.8w)
5v rail = 6A (30w)
(Note that the Opus 90w PSU is no longer in production. It has been replaced by the 120w unit. I include the information on the 90w here because there are plenty of them around and can be purchased used.)

Opus Solutions 120w
12v rail = 3.5A (42w)
3.3v rail = 8A (26.4w)
5v rail = 8A (40w)

Opus Solutions 150w
12v rail = 5A (60w)
3.3v rail = 10A (33w)
5v rail = 10A (50w)

Opus Solutions 250w
12v rail = 10A (120w)
3.3v rail = 15A (49.5w)
5v rail = 15A (75w)

Opus Solutions 320w
12v rail = 15A (180w)
3.3v rail = 15A (49.5w)
5v rail = 15A (75w)

Mini-Box M1-ATX
12v = 2A (24w)
3.3v = 10A (33w)
5v = 10A (50w)

Mini-Box M2-ATX
12v rail = 8A (96w)
3.3v rail = 8A (26.4w)
5v rail = 8A (40w)

Mini-Box M3-ATX
This is a very small PSU, similar to the PicoPUS, but accepts a wide range of inpuyt voltage. It is rated for 125w total output, but Mini-Box provides no details as to the voltage output for each rail.

zootjeff's DSATX
12v rail = 12A (144w)
3.3v rail = 10A (33w)
5v rail = 12A (60w)

Keypower KP-DX250H
12v rail = 10A (120w)
3.3v rail = 14A (46.2w)
5v rail = 25A (125w)
(It's important to note that the Keypower states lower efficiency (60%) than the other models and does not include the other features such as startup/shutdown controller and battery protection that the othyer DC-DC power supplies provide)

**DarquePervert** · 01-31-2006, 10:12 AM

PicoPSU-120 & PW-200M
These units are designed to power a miniITX motherboard, such as the VIA EPIA-series motherboards. They are small (especially the PicoPSU), which gives them a decided advantage for vehicle installations, where space is usually at a premium.
However, these units do not regulate the 12v line. That means that whatever voltage goes into the power supply is also fed to any 12v devices that are connected to the power supply.
You might be asking why this is so bad, since a car's electrical system is also 12v. True, but the car's electrical system fluctuates quite a bit. The power output will drop to around 9-10v when you crank the engine, as most of the power is fed to the starter. When the car is running and the battery is fully charged by the alternator, the voltage typically runs around 14v or even higher.
When the voltage drops below a certain level, a motherboard will simply shut off. When the voltage is too high, it will destroy components.
The advantage to these tiny PSUs is that there's no maximum output for the 12v line, because it's not regulating it. The maximum is only deetermined by the components it's made of. However, in a vehicle, you want a steady, regulated 12v current going into one of these power supplies. One maker of regulators specifically for vehicle computing applications is Carnetix.

Mini-box.com is also producing new versions of the PicoPSU line that accept a wider range of voltages, which are more suited for a vehicle environment. they have the same features as the PicoPSU above, except for the ability to accept a range of input voltages. Because of the low output wattage, the PicoPSU is only suggested for very low-power systems such as those based on the lower-end Via C3-based motherboards like the M10000.

PicoPSU-60-WI
60 watts / 80 watt peak
6-26V wide input

There are also 90w & 120w variations of the PicoPSU WI series, but they are not as well-suited for a vehicle application, as they require a minimum input voltage of 14v & 12v respectively. Because the voltage of a typical car 12v electrical system will drop below the 12v threshhold, these are not recommended.

Carnetix Power Supplies
Carnetix realized the shortcomings of these widely distributed micro power supplies and made a product to work in conjunction with them. The term 'power supply' isn't entirely accurate. They act more as a regulator to provide a consistent 12v stream of power to a PSU that isn't regulated, such as the PW-200M and others.
The CNX-P1260 provides 5A of 12v current, for a maximum output of 60w.
The CNX-P1290 provides 6.3A of 12v current, for a maximum output of 75.6w. It also provides 3A of 5v current (15w) for those devices that require it.

They also make a different product line that includes the CNX-P1900 and P2140. These are designed for mini-PCs like some small formfactor HP units, Mac Mini, Cappuccinos and the like that have a 'transformer brick' type of power supply. They also work very well with many models of laptop that require a single input voltage. The CNX-P1900 & P2140 provide a user-selectable consistent voltage of 18v, 19v or 20v, as well as a secondary output of 12v, 13.5v or 5v.
For building a system based on one of these miniature systems or a laptop, these power supplies will give you all the bells and whistles as the better ATX power supplies from Opus Solutions, including a startup/shutdown controller, acceptance of a remote turn-on from a car stereo or car alarm and more.

CNX-P1900
+18v @ 6.32A (113.76w) or +19v @ 6.32A (120.08w) or +20v @ 6.32A (126.4v) [Primary output]
+5v @ 3A (15w) or +12v @ 3A (36w) [Secondary output]
(Be aware that use of the secondary output at 12v will detract from the current available on the primary output!)

CNX-P2140
+12v @ 11A (132w) or +18v @ 7.5A (135w) or +20v @ 7.5A (150w) [Primary output]
+5v @ 3A (15w) or +12v @ 3A (36w) [Secondary output]
+5v @ 3A (15w) or +12v @ 3A (36w) [OPTIONAL third output]
(Be aware that use of the secondary output at 12v will detract from the current available on the primary output! The CNX-P2140 also has the ability to accept 24v input to allow for greater primary output amperage. Consult the user manual for more details.)

Carnetix has gone to great lengths to write an excellent document about how to choose the correct power supply for your vehicle PC project. It's freely available on their website here: http://www.carnetix.com/regulators/h...coose_psu.html

**meddler** · 01-31-2006, 10:13 AM

Mastero v4.5 (sproggy)
+5vdc @ 12A 60W
+3.3vdc @ 12A 39.6W
+12vdc @ 10A 120W

Note: This is a make it yourself design. Most of the required info is on Mastero's site linked above.

**MatrixPC** · 03-22-2006, 11:58 AM

Regarding to Mastero(Sproggy) PSU.
You built the way you want it which I did. The chip used list 6A max each and 5A normal. So the number list below is normal/continuous.
3.3V @ 10A (2 chips)
5.0V @ 15A + 5A (Additional 5A is for HD/DVD drives)
12.0V @ 5A x 2. (One for HD/DVD drive and one for mobo)

**didiet78** · 05-10-2006, 03:47 AM

Originally Posted by MatrixPC

Regarding to Mastero(Sproggy) PSU.
You built the way you want it which I did. The chip used list 6A max each and 5A normal. So the number list below is normal/continuous.
3.3V @ 10A (2 chips)
5.0V @ 15A + 5A (Additional 5A is for HD/DVD drives)
12.0V @ 5A x 2. (One for HD/DVD drive and one for mobo)

Or you can add more Amp with P-Mosfet(s) so
3.3V @10A-15A (1 chip + P-Mosfet)
5.0V @ 15A+ (1 chip + P-Mosfet)
12V @ 10A - with bobblick (3843 + N-Mosfet + little winding

) or
12V @ 10 - with LTC3780 + Mosfet(s) (very hard task

)

and don't forget pressly Forward Converter (change reguler ATX into Car ATX)

**DarquePervert** · 08-01-2006, 06:26 PM

Can I use a microATX motherboard?
Sure you can. The formfactor of a motherboard has little to do with power draw. MiniITX motherboards are popular because of their small size. The EPIA line of miniITX boards are also low-power motherboards, making them ideal choices for a vehicle installation.
However, microATX, Shuttle, FlexATX and even full-sized ATX boards are all perfectly fine for a vehicle and can be powered, so long as you follow the guidelines above and have the savailable space in your vehicle for the larger motherboards.

**PhilMayfield** · 10-09-2006, 04:29 PM

Thank you for this information. Its definately helping me to decide on my carpc components.

Just curious tho, in your example of the P4 2.8, you state the power usage is either 68.4 or 69.7w. Looking on Chris Hare's site, it looks like those settings are from the Thermal Design Power column.

Is it okay to use this column for calculating? I only ask because alot of the P4 entries are missing for the Est. Max Power Diss. column.

**DarquePervert** · 10-09-2006, 04:34 PM

Originally Posted by PhilMayfield

Thank you for this information. Its definately helping me to decide on my carpc components.

Just curious tho, in your example of the P4 2.8, you state the power usage is either 68.4 or 69.7w. Looking on Chris Hare's site, it looks like those settings are from the Thermal Design Power column.

Is it okay to use this column for calculating? I only ask because alot of the P4 entries are missing for the Est. Max Power Diss. column.

Yes. They are calculated differently, but are similar in nature.

**rsd212** · 10-10-2006, 01:38 PM

PicoPSU-60-WI - This model DOES regulate 12V, however the current is very low. Only for use on Epia boards (mobos using 5V for Vcore), and laptop drives.

12V rail = 0.4A (4.8W)
5V rail = 6A (30W)
3.3V rail = 6A (19.8)