Electronics > Projects, Designs, and Technical Stuff
Power line filtering in a vintage car
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John B:
I run a few microcontrollers in my car, and on each design I have put an RC filter on the input. R is generally ~100R. That makes it easier to implement basic clamping with zeners and caps, without having to worry about high instant power dissipation.
robzy:

--- Quote from: Gregg on January 07, 2020, 03:15:47 am ---I know from experience, I have a 1957 MGA.
--- End quote ---
Very nice! I've got a 1949 Morris Minor MM.


--- Quote from: Gregg on January 07, 2020, 03:15:47 am ---Edit: Additional information.  Perlux ignitors (may be listed as Pertronix  Ignitor) are available for most older vehicles and use hall effect sensors to replace the points.  Resistor ignition wires may be of some help.
--- End quote ---
I'm planning on fitting an Accuspark to replace the points.
DBecker:
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.

For an antique vehicle with DC dynamo you'll need to design for worse conditions than modern guidelines expect.  If the battery cable is making intermittent contact at high RPM with no other electrical load, the voltage transients will be far above what happens with an alternator.

Luckily you only have to supply a modest amount of power, and it's probably a carefully operated antique, so protection is far easier than the general case.

The simplest solution is a fast-blow fuse, TVS and the circuit board out of a switching USB lighter adapter, feeding into the 1117.  The next step up is a robust automotive linear voltage regulator on a heatsink.  A high end design would be using a SM15T33C TVS and the reference design of the TLE9471V33.

You'll have an excellent chance of surviving typical mechanical regulator transients. 
floobydust:
OP there is also a great danger if you use a car cigarette lighter phone charger, these are basic buck-converters that can't take much for automotive transients. When they fail short, your phone will be destroyed. So maybe put more in than just for the ESP8266?

In my own car I have a transient-protected module using series diode, industry standard 6,600W 27V TVS SM8A27, polyfuse etc. It clamps to 40V worst case so any Vreg IC should be good to that or a bit less.

Lucas RF95 is harsh on electronics, it could use capacitors across the contacts for longer life.
DBecker:

--- Quote from: floobydust on January 07, 2020, 08:40:19 pm ---OP there is also a great danger if you use a car cigarette lighter phone charger, these are basic buck-converters that can't take much for automotive transients. When they fail short, your phone will be destroyed. So maybe put more in than just for the ESP8266?


--- End quote ---

Many of the cheap lighter-to-USB buck converters are quite robust.  They are designed to work with either 24V or 12V systems, with margin.  They are certain *way* better than the sketchy low end linear regulators.

While the 27V TVS you suggest is OK in real life, it won't pass the tests that target a 28V jump start.  Those tests are why a 33V TVS is the usual recommendation.

A 28V jump start used to be a common tow truck trick to allow a quick start when long jumper cables were used with a good-but-discharged battery.  It became far less popular once cars started using ECUs that could be damaged by high voltage. Today it would be quite uncommon to see a mobile service truck use anything but a high end jump start box.
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