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Low Cost 5V Supply

Power MAP sensors, airflow meters and LED meters from this 5V car supply.

by Julian Edgar

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Most cars with engine management feed a 5-volt regulated supply to sensors. For example, airflow meters of the last 15 years almost universally use a 5-volt supply, as do MAP sensors. In addition, accessory LED and LCD panel meters often need a regulated 5V supply.

So what happens if you want to use a MAP sensor in a car that didn’t originally come with one, or swap a 12V supply airflow meter for a 5V design, or use a 5V LCD or LED panel meter in your car? The traditional answer has been to use a 5V regulator and a handful or other components to build a 5V supply on a small piece of punched board.

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But there’s a much easier way of doing it. You can now buy PC fan speed controllers incredibly cheaply – at the time of writing, on eBay the cost is AUD$4.39 including postage!

So? Well these controllers comprise an adjustable voltage regulator.

To get any voltage between 5 – 12V, all that you need to do is turn the knob. The voltage regulation of the one we bought was very good. When set to a 5.0V output, it maintained this with input voltages from 5.3 to 18V! And even when the load changed, the regulator continued to maintain its set output.

Making it Work

It is very easy to turn the device from a fan speed controller into a voltage regulated power supply. Two plugs are fitted as standard – these are designed to plug into the PC fan and the fan control cable.

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The input plug uses female pins and on the controller we used, the input had yellow, red and grey wires.

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The output plug has male pins, and used yellow, red and black wires

Make sure you identify the input and output plugs correctly – the description is by the shape of the pins and not the shape of the plug!

Label the input and output. Cut off the plugs are then feed battery voltage to the input wires – positive to red and negative to grey. Ignore the yellow wire.

On the output side connect the red and black wires to your multimeter. Again ignore the yellow wire. Turning the knob will allow you to set the voltage.

Connect the load and then check that the output voltage remains correct.

Bigger Loads

If you are driving a small digital panel meter or the like, the load current will be pretty small and no modifications to the unit will be required. However, larger loads will require a small modification to the device.

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The unit is rated to 1 amp but the internal heatsink (just a piece of square metal) is small. If you are running a current-hungry load, open-up the unit and feel the temperature of the heatsink – if it gets hot, fit a larger one.

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This is easy to do – just unscrew the standard heatsink and screw on a larger unit. Heatsinks are available from electronic component stores or can be salvaged from nearly any piece of discarded electronic equipment – for example, an old PC power supply can provide heatsinks that have plenty of heat dissipation ability for this application.

In addition to feeding a regulated supply voltage to a piece of electronics, the fan speed controller can also be used to dim small incandescent lights. Oh yes, and you can also use it in your PC to alter fan speed!


Buying the fan speed controller sure beats stuffing around with resistors, capacitors and voltage regulators – not to mention having to go to the shop to source the parts. This one is built, it works well and it costs next to nothing! Sounds good to us.

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