Efficient Fan Speed Controller

A partial approach to quietening noisy PCs can additionally be to reduce the pace of interior cooling lovers. Low-cost fan speed controllers are available, however they continuously hire inefficient, heat-generating linear regulators and include no temperature remarks mechanism. This concept makes use of a with no trouble available, cheap in-car cell phone charger. The majority of these use common circuitry and require only minor amendments to function as efficient fan speed controllers complete with temperature feedback. Most in-car chargers are based on the nicely-known MC34063 DC-DC switchmode IC.

When used for charging cell phones, the open-circuit output voltage is in most cases set to between 7V and 9V. This is carried out with a easy voltage divider across the output, the centre level of which joins to the feedback input (pin 5) of the MC34063. To make the output voltage var-iable with air temperature, first exchange the higher resistor of the divider with a four.7kΩ resistor in collection with a four.7kΩ trimpot. The decrease half of the divider is then changed with a 470Ω resistor in sequence with a 500Ω NTC thermistor. These prices are simplest a information and may additionally be diverse to suit totally different thermistor and fan types.

Circuit diagram:

Efficient Fan Speed Controller Circuit Diagram

Note that component lead size should be minimised to avoid introducing noise into the remarks circuitry. Getting the best fan beginning voltage is a topic of trial and error. The prices shown on the circuit supply a beginning voltage of about 6.8V at room temperature however trimpot VR1 can be utilized to lift this voltage as vital. The output can then upward thrust to about 10V if the interior temperature upward viasts sufficiently. The 4.7kΩ resistor can be reduced to three.9kΩ and VR1 adjusted to give a lower beginning voltage if the fan pace is still too excessive at 7V. After operating for one hour or so, the fan voltage as set with the help of the interior case temperature thermistor on my PC settled at 7.4V.

Suitable chargers are to be had from Oatley Electronics, Cat. No. 2D0074. They’re presently listed at $5 for two, which is less than the associated fee of the MC34063 ICs alone! Data on the MC34063 can also be downloaded from www.onsemi.com and a useful construction aid is to be found at www.nomad.ee/micros/mc34063. Finally, note that now not all chargers have an output filter capacitor put in. Typically, this is a 220µF 10V or 16V electrolytic sort. To save just a few cents, the producers every so often go away this component out, relying on the mobile’s battery to operate the filtering process. If this element is missing from your charger’s PC board, it will have to be put in ahead of the availability is used.

http://www.ecircuitslab.com/2011/08/efficient-fan-speed-controller.html

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Speed limit Alert Circuit

Here’s a design circuit that can be used to alert the vehicle driver that he/she has reached the maximum fixed speed limit (i.e. in a motorway). It eliminates the necessity of looking at the tachometer and to be distracted from driving. There is a strict relation between engines RPM and vehicle speed, so this device controls RPM, starting to beep and flashing a LED once per second, when maximum fixed speed is reached. Here’s the figure of the circuit;

In this circuit, IC1 forms a differential amplifier for the electromagnetic pulses generated by the engine sparking-plugs, picked-up by sensor coil L1. IC2A further amplifies the pulses and IC2B to IC2F inverters provide clean pulse squaring. The monostable multivibrator IC3A is used as a frequency discriminator, its pin 6 going firmly high when speed limit (settled by R11) is reached. IC3B, the transistors and associate components provide timings for the signaling part, formed by LED D5 and piezo sounder BZ1. D3 introduces a small amount of hysteresis.

D1 is necessary at set-up to monitor the sparking-plugs emission, thus allowing to find easily the best placement for the device on the dashboard or close to it. After the setting is done, D1 & R9 can be omitted or switched-off, with battery savings. During the preceding operation R8 must be adjusted for better results. The best setting of this trimmer is usually obtained when its value lies between 10 and 20K. You must do this first setting when the engine is on but the vehicle is stationary. The final simplest setting can be made with the help of a second person. Drive the vehicle and reach the speed needed. The helper must adjust the trimmer R11 until the device operates the beeper and D5.

Reducing vehicles speed the beep must stop. L1 can be a 10mH small inductor usually sold in the form of a tiny rectangular plastic box. If you need an higher sensitivity you can build a special coil, winding 130 to 150 turns of 0.2 mm. enameled wire on a 5 cm. diameter former (e.g. a can). Extract the coil from the former and tape it with insulating tape making thus a stand-alone coil. Current drawing is about 10mA. If you intend to use the car 12V battery, you can connect the device to the lighter socket. In this case R20 must be 330R. Depending on the engines cylinders number, R11 can be unable to set the device properly. In some cases you must use R11=200K and R12=100K or less. If you need to set-up the device on the bench, a sine or square wave variable generator is required. To calculate the frequency relation to RPM in a four strokes engine you can use the following formula:

Hz= (Number of cylinders * RPM) / 120. For a two strokes engine the formula is: Hz= (Number of cylinders * RPM) / 60. Thus, for a car with a four strokes engine and four cylinders the resulting frequency @ 3000 RPM is 100Hz. Temporarily disconnect C2 from IC1 pin 6. Connect the generator output across C2 and Ground. Set the generator frequency to e.g. 100Hz and trim R11 until you will hear the beeps and LED D5 will start flashing. Reducing the frequency to 99 or 98 Hz, beeping and flashing must stop.

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