Hi hi !,
Wow Terry! Thanks for the detailed response, this helps me a lot.
You really need some high-voltage transient suppression! The MegaSquirt is a serious approach to this. Overkill in combat with Bad Stuff that could happen and kill your Fuel Injection system at midnight on Route 95 in New Jersey is not a bad idea.
That I can believe ;-) Also not here in the Alpes :-)
I have been reading a lot today about this topic. The hazards in a car summed up:
- Load Jump -> battery gets disconnected from the power line while the alternator is charging.
- Jump Start -> using "double battery" to start the engine when the car battery is low. Then you end up with a voltage of 24V instead of 12V.
- Cold crank -> battery voltage can go as low as 5V (oil is thick).
- Reverse polarisation -> connecting the battery in the wrong way.
- Disturbances from the ignition, injection, alternator, load switching, etc.
I found following solutions during my search:
-Discrete protection circuit using a TVS (transient voltage suppressor) or Varistor (for transients like load dump, etc.) in combination with a fuse or Diode (reverse polarisation). For repetitive low-energy negative transients (induced by a relay or a solenoid switch) they use a capacitor to filter. How do you calculate which capacitor should be used? Also how to choose the TVS or Varistor?
- Active Transient-Protection: MAX16013. This IC monitors the voltage input on the supply rail, and isolates the load from the the input when transients (or faults in general) occur. This is done in combination with 2 pFETs. Here they also use a capacitor to filter out the low energy higher frequency disturbances.
I also found this one: looks also a good solution: http://www.eeweb.com/news/overvoltage-protection-controller/
Good News is that this is such a common problem there are some good solutions. Texas Instruments has a nice voltage regulator, the LM2940 which is available in different output voltages. I would pick 9V output to run to the external power jack on an Arduino.
But your solution looks even easier and cheaper than what I found today. I will go for this one. In this way I only need the LM2940T and 2 capacitors? Do I see this correct? Will this protect my Arduino DUE from all these hazard I listed at the beginning of this post? Or do I need to add other extras as well?
And does the 9V-regulator provides enough current for the Arduino DUE? Its input voltage is recommended between 7-12V. And its current specs say the following:
- Total DC Output Current on all I/O lines 130 mA
- DC Current for 3.3V Pin 800 mA
- DC Current for 5V Pin 800 mA
----> does this mean that the DUE can deliver a total of 800+800+130=1730mA? Than the 1A that the LM2940T delivers would not suffice,...?
One more question -> do I need to use a heatsink with this component?
Thank you for your help :)