Power line filtering in a vintage car

[amyk]

It's interesting to see that early import cars, particularly UK ones, used electric fuel pumps; the customary American layout is a mechanical one driven by the camshaft, which was used from the 20s through at least the 70s until fuel injection started becoming common.

[robzy]

Zero surprise that the generic 1117 blew up.  It had no chance of surviving.  Did it fail shorted so that everything attached died as well?  Because that is their superpower.

Just got the new ESP32 today - and confirmed that it killed the rest of the circuitry.

It was only a TC74 temperature sensor, but it was a righteous pain-in-the-backside to solder it to the end of a cable, and also has my only appropriately-sized magnet epoxied to it already.

[robzy]

Thanks everyone! It worked an absolute treat! I now have the cleanest 5V supply attached to Lucas electronics

I ended up with an LC filter feeding a voltage regulator with a TVS protecting the input pin. Between the LC filter and the voltage regulator was a resistor to help the TVS bleed some power if need be.

I was going to put a diode between the filter and the regulator to protect against negative spikes, but I forgot. It shouldn't be necessary though, because the filter should be beefy enough to absorb any negative spikes, and even if it isn't the TVS should catch it.

Photo attached. Don't judge my soldering. Will clean it up and apply liberal amounts of hot snot when I'm happy with the circuit.



Just FYI components were:

• 2.2 mH inductor, ferrite/750mA/880mΩ
• 0.47uF film capacitor, X2 275V
• 0.1Ω wirewound resistor, 3.75W
• ON Semiconductor LM2931DT-5.0G
• SM15T36CAY TVS, bidirectional 36V

In all cases I chose those components because they were cheap(-ish) and readily available If I were to do it again I might use a higher value resistor, given the low current of my application, and only a unidirectional TVS to clamp the negative voltages even closer to 0.

[jfiresto]

... I might use a higher value resistor, given the low current of my application, and only a unidirectional TVS to clamp the negative voltages even closer to 0.

If you do, you might check what wattage resistor you will need if someone hooks up a battery, backwards, so that +12V becomes -12V for a few minutes. That is one of the  faults people design for, from the standard catalog of automotive electrical horrors.

[trobbins]

robzy, you didn't identify where you connect to the car's voltage supply (eg. direct to battery, or some distant point in a harness with some of those other noise sources on the same feed)?  You also didn't indicate if there was a possible ground loop concern, depending on if your load is isolated or somehow connected to other parts/equipment/chassis.