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More Power! « Kevin's Projects

More Power!

For some, computer power supplies are a dark magick that are best not talked about; car electrical systems doubly so. Most people, if they deal with computer power supplies at all, just buy something high wattage, plug in the appropriate connectors, and then never think about it again. However, I’m hoping I can demystify things a bit by showing how I’m wiring my system up.

The power supply I’m using is an M2-ATX board I bought from LogicSupply, specifically designed to be used with automotive computer applications. It has some pretty slick features, such as ignition connection, timed shutdowns, engine crank undervolt protection, and audio amp protection. It takes in voltage from the car battery (anywhere from 6-28 volts, since car battery/alternator combos don’t usually provide a clean, stable voltage), and it outputs nice clean ATX voltages: 12V, 5V, and 3.3V. It can provide up to 160 Watts to devices.

Here’s the board itself:

M2-ATX Power Supply

M2-ATX Power Supply, in all its glory.

Notice on the right-hand side that there is a standard 20-pin ATX connector as well as a 4-pin P4 connector. The motherboard I am using requires a 24-pin ATX2 connector; this meant I needed a 20 pin to 24 pin power cable adapter. More on that in a bit. The P4 connector is the ATX 1.x standard, which outputs both 12V and ground, and that will be used to power the touchscreen monitor. The three two-pin connectors on the very far right of the board are two on/off switches (one to the motherboard and one external) and an LED connection.

In the upper left corner of the board, there are three large contacts: these are supply (+) and return (-) from the car battery, and an “ignition switch” which turns on the board when shorted with battery supply. For initial setup and testing, I will hook up an AC adapter that provides 12V to those terminals.

In the bottom left corner of the board is a set of jumper pins that control the board’s timers. Most PC power supplies supply a constant 5 volts all the time, to allow for software wakeups and so forth. However, in a car, that constantly-on 5 volts would drain your battery rather quickly, so the M2 provides some other options. In the default state, it acts like a standard PC power supply. When one or more jumpers are applied to the proper pins, it uses timers to control the voltage it provides. The timer will wait a certain number of seconds after it receives a wake-up signal (ignition pin shorted to battery supply pin) before supplying voltage to the motherboard, which allows you to crank the engine on startup and not worry about the low amperage during crank damaging the motherboard. The timer will also wait a certain number of seconds after receiving a shutdown signal (ignition no longer shorted to battery supply) before turning off the 5 volt rail, to allow the computer to suspend or shut down. Changing the locations of the jumpers changes the wait times on each end of the cycle.

Finally, that two-pin connector on the left is an audio amp protection signal; it only tells the audio amp to switch on after the initial timer is complete. That gets rid of the annoying “thump” you hear from an aftermarket audio amplifier when you turn the key and crank the engine.

Ok, enough about the power supply… lets hook some things up.

The Intel board I am using requires a 24-pin ATX2 connector, but the M2 power supply only has a 20-pin ATX connector. Luckily for us, the 24-pin ATX2 standard doesn’t require any voltages that ATX doesn’t already provide, so it’s just a matter of rewiring. I found an ATX pin description on Wikipedia and scavenged some connectors and wire from another couple of power supplies I had lying around. The additional 4 pins required one each of ground (black), 12V (yellow), 5V (red), and 3.3V (orange), so I split those off of existing pins. The result looks like this, with a standard Molex and SATA power connector added in:

Custom 20-pin to 24-pin ATX adapter

Custom 20-pin to 24-pin ATX adapter

Removing pins from connectors was a little tricky. There are two little metal tabs on either side of a pin that lock it into the connector, and they need to be pressed flat against the side of the connector before you can wiggle the pin out. Paperclips were too thick to fit, so I ended up using a couple of staples. Bend the staples out into an L shape, and then insert the longer end into either side of the pin from the connector side (not the wire side). You’ll have to wiggle the pin and play with it a bit before it comes loose. Once it’s out, you can bend the tabs back out again if needed, and the pins just snap right into another connector. To split off the 4 new pins, I needed to remove the metal socket connector from the end of the wire and re-crimp it with two wires in place. This required two pairs of needle-nose pliers and a lot of patience.

I also wired up the P4 connector to provide 12V and ground to the monitor, via the case’s external 8-pin connector (the one on the right in the photo below). This connector can be accessed from outside the enclosure, and contains pins for battery supply (red), battery return (black), ignition (white), audio amp signal (black and red), 12v monitor power (orange, two pins on the P4 to one pin on the case), and monitor ground (black, also two pins to one). The wires on the connector on the left will be sent to battery, amp, and monitor once it’s installed in the car.

P4, Battery, and Case External Connectors

P4, Battery, and Case External Connectors

Here is the motherboard and power supply with the new power cables in place, and the SSD connected via SATA cable:

Power Connections

Power Connections


Categories: Carputer