Running a microcontroller in car - power supply aspects

[stj]

Re: Running a microcontroller in car - power supply aspects

the resistance will be in the datasheet

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

the resistance will be in the datasheet

Right, though that's assuming there IS a datasheet for these things

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

Yes, turns out I was almost right: the specs give a 27ohm resistance.

[stj]

Re: Running a microcontroller in car - power supply aspects

nice parts, i like the way the contacts have low current pcb pins too.
you could use the mcu to detect relay failure or motor/wiring issues through those pins!

[Dannyx]

Re: Running a microcontroller in car - power supply aspects

Kinda running low on pins on the Mini TBH, though not a bad idea in the long run.

[redwire]

Re: Running a microcontroller in car - power supply aspects

You can use a resistor to lower the coil voltage from 12V to 5V. Like 47R and dissipating ~1.5W, regardless if a resistor or vreg or zener etc. the heat is made by something.
A relay coil is mostly a resistor anyway, just wirewound with copper. They need a constant amount of power (not current/voltage) to work, so a 5V coil and 12V coil are the same power.
If the relays are only on for a few seconds, then 1W resistors would work. Just takes up space.

[eccerr0r]

Re: Running a microcontroller in car - power supply aspects

put a reverse biased 7V zener diode in series
But yeah unfortunately damage's done, should have got the 12V units. Resistor is cheaper than zener, but you may need to calculate an appropriate value. And you can't get away with power consumption, it'll be significant, most of the relays I've seen when an option is given, the power consumption is the same when they're run at their rated voltages, meaning if you have to run on higher voltages, it will use more power overall.

... unless you PWM the input and filter it... HMM... heh heh heh...

[stj]

Re: Running a microcontroller in car - power supply aspects

it's not an issue, the buck convertor can easily drive the arduino and the relays.