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    How to control the field current of an alternator by using PWM?

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    Alternative to Raspberry Pi 3?

    Get a Mini ITX board that you can plug a decent graphics card into. Just make sure that the boards work with Linux. That was the major problem with earlier VIA boards. It may have improved since then.
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    DC Motor drive

    eBay has loads of speed controlers. I suggest though, get a couple of Arduinos and learn a bot of programming while you use them.
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    3-Phase motor clarification.

    Blows fuse, probably because, with only one phase doing anything, the motor doesn't turn/stalled so no back EMF to counteract the input voltage.
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    Dual pump control circuit help

    Just buy a heavy duty pressure switch (eBay ?) that has DPDT of contacts. I replaced the little pressure switch on a water pump after it had failed twice. It is quite noisy when is switches, but it is universal and I can get at the contacts to clean them is that is ever necessary. It has...
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    Soldering Problem

    For flux, with corroded pins/pads, I use a white paste called Powerflow, by FRY. I have never come across a more effective flux. It works well at cleaning soldering iron tips too, just apply solder immediately after use.. However, I can't comment on possible corrosive effects over time, so...
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    LED array power queries

    It depends on whether you want to vary the number of LEDs that are illuminated, or the brightness. Usually, LEDs are driven by a current regulator rather than voltage. Most LED's need at least 10mA, and putting a very low value resistor with just a slight bit more voltage is not a good idea...
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    Why DC motor draws more current with friction?

    A motor generates back EMF dependent on it's speed. If speed is zero, no back EMF, so it is only the DC resistance that limits the current. Free running speed generates slightly less back EMF than the voltage the motor is rated for, so you get the input voltage, less the back EMF at that...
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    How to control the speed of a 24vdc pump from circulating water temperature?

    Buy a speed/brightness controller (eBay?) that has a pot to control the speed. Substitute a resistive PTC or NTC for the active side of the pot.
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    CDI repair

    The first thing to look for is electrolytic capacitors that have a domed top. A sure sign of being faulty. Capacitors, and especially electrolytics have a limited life, and that life is fairly predictable depending on load factor, AC current, and time in use.
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    Laminator for PCB's ?

    3D printer with conductive epoxy, then plate ? Inkjet with conductive ink, then plate ? It would be fairly easy to include a narrow connection so that all tracks are connected, then sever the links after (electro)plating. Plotter with dentists drill to rout ?
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    BBC Microbit

    People really shouldn't list the magnetometer chip as a compass. The only electronic compass that I know of is the fluxgate ones. Magnetometer are very sensitive to spurious magnetic fields.
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    Homemade PCBs with a Brother printer - 4mil Traces

    If your layout software can do it, it is well worth printing pads with holes.
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