I was researching protection circuits for a upcoming project for my car. When I ran across this blog.
It's very short so I copied the whole thing here.
The suppliers of automotive electronic devices are competing these days to lower the cost of theirs designs. This is a sample of rather expensive solution to ensure proper function of an automotive electronic device during transients on supply lines (12V Battery).
Sample of less expensive solution to prevent reverse polarity, load dump, and cranking pulse from disturbing circuits sourced from a 5V voltage regulator or directly from the 12V B+ line.
Since this is coming from a site " dedicated to Automotive EMC Testing for Electronic Modules" it seems it could be legit. But I am not even close to being qualified to judge if this "less expensive" circuit can do what is claimed. What say you?
If that is the cars 12V battery that starts the engine, the negative of the battery will already be connected to starter gnd.
That circuit will simply "fix" a polarity error, not stop or signal it, bad karma.
What is "cranking protection".
Keeping the battery negative above car gnd will cause problems with charging.
The diodes would have to be rated at very high current to work.
What sort of protection do you want?
A fuse and a reverse protection diode will provide the action you need.
Hi, @TomGeorge
Thank you for your reply, but that is not the circuit in question. The blog I referenced in the OP was posted by a company that I believe does electronics testing for the Automotive industry. As such I would think they know a bit about the subject.
They suggest that that this circuit:
will protect approximately as well as the circuit you reposted.
My question is could that be true?
I intend to but was just curious since I would think a person/place that actually does " Automotive EMC Testing for Electronic Modules" for the Automotive industry would be quite serious and quite unlikely to publish information that would fail their own tests for compliance. I would still like to see a cogent reply on this.
But Yes I do intend to implement a more common scheme to protect my circuit.
Does this look ok?
To me, that looks like some random person's blog. The person seems to go by the name of "Christian". There might well be some useful information in it.
It is on a 15A fuse currently. Are you suggesting a fuse solely for the Arduino? I have another circuit available in the fuse box. What size fuse do you recommend?
What coil current do those automotive relays have.
With a 470 ohm base resistor you shouldn't switch more than 100-150mA with a 2N2222.
If the relays draw more than that, then reduce the base resistor to 330 or 220 ohm.
A low-voltage 1N4004 is preferred over a high-voltage 1N4007, although it makes little difference.
That would depend mostly on the four relays.
Leo..
If there is no inrush current (motors), then the fuse rating can be close to the actual draw.
Say the circuit with four relays draws 1Amp, then a 2Amp slow-blow fuse would do.
Leo..
