A teapot question about connecting an arduino project to a car's power system?

Question

Batteries

There is a car with a 12V electrical system. I want to make a project on arduino for him.
I want to make the project constantly working, even when the power is turned off from the car battery.
I'll admit right off the bat that I don't know much about electricity. So I decided to make such a hobby project - and understand it better, and spend time with interest.
Accordingly, as I understand it, you need to connect the project to the battery, and the battery to the charger, which will charge it from the car's network. Can it be done? At the same time, both charging and the consumer, so to speak. How?
So I found, for example, a NiMh battery, which is little affected by the “memory” effect, and it is at 9V, which is just the minimum for arduino. This battery produces 250 mAh.
Questions.
1) how quickly will the car battery run down from the operation of such a system if the car is not started at this time? and in winter?
2) if fast, what to do? Perhaps it's better to make it so that charging turns on only when the car is started? Those. to run the wire not directly from the battery, but through the ignition switch?
3) Where can I buy a 12V DC charger? (the connection will not be through the cigarette lighter, but from a separate wire)

Answer 1

I must make a reservation right away that I do not pretend to be the ultimate truth, and everything written below is just my subjective opinion.

1) how quickly will the car battery run down from the operation of such a system if the car is not started at this time? and in winter?

this question is difficult to answer without knowing the battery capacity, as well as the consumption of your craft

2) if fast, what to do? Perhaps it's better to make it so that charging turns on only when the car is started? Those. to run the wire not directly from the battery, but through the ignition switch?

I usually clung to the cigarette lighter, but when I had a “classic”, I turned off the device while the car was idle so as not to put the battery “to zero”, and now, having bought a miracle of the Japanese automotive industry, when the power is supplied to the cigarette lighter only when the ignition, such a need has disappeared.
Also, I would like to note that it is not good to feed directly from the battery, as evidenced by my deplorable experience of an incorrectly connected alarm, when the relay-regulator fails, and in connection with this, the full 18 volts in the on-board circuit from the generator, I have the alarm burned out (there was a direct hook from the battery without a fuse), which simultaneously burned 2 turn signal bulbs and all door servos (by supplying 18 volts from the generator), 1 of the servos, in turn, almost burned the whole car, but fortunately it cost only 1 a reflective on the door and thermal insulation, which burned out a little more than half.

3) Where can I buy a 12V DC charger? (the connection will not be through the cigarette lighter, but from a separate wire)

Again, I usually buy a charger for the cigarette lighter, and then I solder the wires to the contacts, and it turns out cheap and cheerful (and again, in such a design there is a fuse for working from the cigarette lighter, which does not hurt at all)

This battery produces 250 mAh.

Just in case, this capacity says that when using a device that consumes 250 mAh, the battery will last for an hour, and if, for example, 25 mAh, then for 10 hours. Make no mistake in choosing a battery, in my humble opinion, it is worth taking one so that the charge is enough for at least 10 hours (overnight)

Answer 2

Interestingly, in the version with the charger, there will be no failures when starting the engine. I remember that I made a power stabilizer on KREN-5 for a CD player, and at the start, playback stopped (either drawdowns, or impulse noise). I tried to suppress it with containers - it didn’t work out (although I’m not strong in filters).

Answer 3

Battery - cigarette lighter - charger - small battery - arduino.
For Arduino you need at least 5 or 3.3 volts, depending on the model. Some have an additional 9 volt input, but this is in addition to the 5 volts via USB. At 9 volts, the efficiency is too low.
If the temperature does not drop too low in winter, then you can use a simple power bank with one element (about 1600-2000 mAh) and charging from the cigarette lighter. Such power banks give out 5 volts.

Answer 4

Alternatively, you can hide the Arduino in the car radio, and use its own power lines for the standby connection / ignition.
It is important to note that it is not so easy to charge the battery - in the simplest case, you need a stabilizer for the charging current of 1/25 of the capacity.
1) If an alarm is installed in the car, then it will rather discharge the car battery, and not the Arduino. When consuming 30 mA for three months of winter, the car battery will be discharged with a 100% probability.
3) "Car charger for the phone." There is a lot of interference in the on-board network, the reliability of the Arduino will depend on how charging can cope with them.

Answer 5

Assemble the simplest voltage converter, from 13 volts to the required 5 or any other.
www.outme.ru/raschyot-preobrazovatelya-napryazheniya.html
There is little interference on an idle car, when the noise generator is running, there is plenty.
Directly charging from a car charger is fraught with either a fire or simply a failure of the arduino battery - a charge controller is needed, in phones they are on the phone’s board, but what comes to it from charging is not particularly important, for example, Nokia can be charged with a voltage of 5 to 9 volts, and some more, everything else is done by the internal power controller.
If you want to charge, charge - your right, but I myself saw how batteries connected directly to high current voltage flashed.

Answer 6

A feature of the car's on-board network with the engine running is the presence of impulse noise in the form of surges of positive and negative polarity, the amplitude of which can reach 160 V (decreasing after 1 ms). Pulses of positive polarity with an amplitude of up to 90 V also appear in the power circuit and fall off after 0.4 s.
... the duration of the transient process can be several hundred milliseconds, in some cases up to 1 s or more, with a maximum amplitude of voltage surges of more than 100 V, which is, to put it mildly, unsafe for standard semiconductor devices or, to put it bluntly, deadly.
...when the engine is running, impulse noise appears in the vehicle's on-board network (emissions of positive and negative polarity, falling off after 1 ms, the amplitude of which can reach 160 V). There are also pulses of positive polarity with an amplitude of up to 90 V, which fall off after 0.4 s.
catethysis.ru/pitanie-ot-avtomobilnoy-seti
www.russianelectronics.ru/developer-r/review/8627/...