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Power line filtering in a vintage car

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robzy:
So I have a problem: I connected an ESP32 to the 12v voltage rail of a vintage car (~70 years old) and let the magic smoke out. The module's AMS1117 voltage regular is rated up to an input voltage of 20v, but the module stopped working when the car was running, and the AMS1117 literally snap crackled and pop.

I want to solve the problem.

I think that the problem is the huge transient voltages caused by oldschool ignition systems. Even my multimeter can't handle voltage measurement of the car's power line, it shows around 12V, but then goes all glitchy.

What is the best way to create a cleaner 12V rail from an old car for an ESP32?

I have done some searching and I haven't found a lot of information. These are the thoughts that have occurred to me so far:

* Coils and capacitors: Currently my preferred option, but I can't find any information on the design of such filtering circuits
* MOVs: They don't seem ideal, because it looks like they are generally used for irregular voltage spikes and the car would just hammer them
* Industrialised voltage regulator ICs: I haven't found anything that seems rugged enough for this use case, I've found some IC's that claim to be able to protect themselves against higher voltage input levels, but nothing that seems ideal for this particular case

Psi:
LM2937IMP regs are automotive rated and have built in 60-V transient protection. (buy them from legit source, there are fakes out there which are just normal regs)


If you want a bit more protection, add a 0.1 ohm 5W series resistor and chunky ~3000W  ~40V TVS diode to GND on the input side of that reg.

tautech:
Not only are ignitions the noise source, generator brushes and electromechanical regulators are noisy too.
Generally the solution was to suppress at the source and just the addition of caps was sufficient.
IIRC 0.22 - 0.47uF 200V caps were used.

DBecker:
Many '1117' regulators are rated for *far* less than 20V.  Some are rated at 6V or 8V -- fine for dropping a regulated 5V supply down to 3.3V, but few other use cases.  The real AMS1117 is rated for a maximum of 15V, but I've blown them out (more likely, a counterfeit) with a 12V wall wart supply.

Some are also thermally vulnerable, and dropping 14V down to 3.3V might result in the thermal limit circuit not responding in time (assuming that a generic regulator even has a thermal shut-off).

Automotive power supplies should be rated to survive at 28V continuous, with a brief load dump to 35V or more.  There are plenty of medium-priced automotive chips that can reliably do this.  What are your voltage and current requirements?  Do you need the module to work during cranking transients?


duak:
There are usually two capacitors (AKA condensors) on a Kettering or points style ignition system.  One is across the points to reduce arcing.  The second is connected to the other low voltage terminal on the coil to reduce RFI.  This vehicle probably has a generator with an electromechanical regulator.  These systems usually have caps on the generator and/or the regulator to reduce RFI.  These caps usually have a value of 0.18 to 0.22 uF.  I think I've seen these caps on horns and electrical fuel pumps too.

For a filter into the electronics I would be looking for something like a 1 to 5 mH inductor in series and something like 10 to 22 uF in parallel with 1 uF to circuit common.  These were available at car stereo shops at one time.

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