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I need to connect some circuitry in a car, which needs 12V. It's my understanding that when a car starts, the power spikes well above 12V, and the battery itself can have a charged voltage of ~14V.

What is the ideal way to provide 12V to my devices?

Additionally, what is the best way to connect to a car's electric system? Must I do it via the dashboard, or is it there a better place, like near the tail lights?

Ask for further clarification if needed - the devices are just some speakers, an amplifier and some LEDs.

Thanks:)

  • What is the car you are dealing with? Year/Make/Model, please. – Pᴀᴜʟsᴛᴇʀ2 Jan 3 '17 at 23:21
  • A Kia Picanto from 2004. I'd be interested in a highly detailed datasheet for this car. – user400344 Jan 3 '17 at 23:45
  • I need to pull a peak 40-45 watts, most likely 25-30 on average. This may affect where I can pull power from. I don't know the location of fuses etc. – user400344 Jan 3 '17 at 23:47
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When properly installing an amplifier a large gauge wire is run from the battery to trunk area. A fuse is installed as close to the battery as possible. The amplifier then connects to that wire. If multiple devices need to connect use a fused distribution block.

Don't forget to run a remote wire from your head unit to the amplifier to turn it on and off when needed.

An automotive battery can range from 9v when fully dead to 12.6v nominally to 13.4v ish when surface charged. An automotive charging system will range from 13.9v to 14.4v normally.

Any component installed into a car needs to be able to handle from 9v to 15v. An automotive amplifier is meant to do just that. Don't use a non automotive amplifier. It will not be happy in a car.

EDIT: There are effectively two answers to your question, an automotive answer and electrical engineering answer and i'm not sure if you'd like either one.

Automotive: No one here develops their own accessories. Accessories are bought already equipped with a power supply that can tolerate an automotive environment. You could try and steal a power brick from existing LEDs or just buy LEDs meant for a car.

Electrical engineering: A DC to DC switching regulator is the best option. Always have a fuse at the input. Then a TVS diode, a zener diode and a MOV all chosen to be just under the maximum input voltage of the DC to DC converter will protect you from spikes. Capacitors at the input of the DC to DC but after the input protection will filter out brown outs. (a couple 220uF aluminum, a couple 10uF and 1uF ceramics ought to do it, output capacitance would also be needed) You might be able to find a prebuitl evaluation kit from Linear Technologies or Texas Instrument. That's all just to make 12v. Then to run a microcontroller you would need a 5 or 3.3v rail and you can accomplish that with a linear regulator like a 7805. A common mode choke or ferrite bead at the input might be nice too.

  • Good - what about circuitry to protect a microcontroller and LEDs from voltage spikes? What is best practice? – user400344 Jan 4 '17 at 11:42
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    @user400344 I believe this might be part of the reason for large capacitors with big sound systems. A capacitor should smooth out the spikes and dips. Not 100% sure that's how its done, but something to look into. – rpmerf Jan 4 '17 at 12:06
  • Yes, I agree. I will use several to soak up spikes. – user400344 Jan 4 '17 at 12:29
  • Whst is your definition of 'large capacitors', both in voltage and farad? – user400344 Jan 4 '17 at 12:36
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    @user400344 i edited my answer to include more info. – vini_i Jan 4 '17 at 12:50
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In addition to vini's answer, I always run a relay. Run the switch side from the battery to the trunk to power the amp / sub. Put a fuse right at the battery. I always switch the relay using the radio's ignition wire, so it is only on when the key is in the on or accessory positions. There might be another more appropriate wire to use.

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