Powering Arduino with Car Batteries (classic topic)

Hello,
I have already spent some time on [all this good topics ](http://car batteries site:http://forum.arduino.cc)in order to understand the best way to make Arduino work with 12v automotive batteries.

The majority of them are about making Arduino work inside a car, so running together with the car engine.
In my case, I use Arduino outside a car, so the board is the only thing connected to the battery.

I need to power Arduino directly to the vin, so I bought this DC-DC step down converter. It can span from 4,5 to 30v with 12A. I hope it's not oversized for the project.

The problem is: Is there any risk of inverted polarity and spikes (for ex. when connecting the battery to the circuit) anyway?

If so, what kind of configuration can I use between the battery and the DC-DC to prevent it?
My Arduino is connected to a GSM module and some Led-matrices, so it would draw 0,1 - 1A

Thanks

Definitely oversized. You could also use this: http://www.pololu.com/product/2850 or if 1 ampere really is enough, this http://www.pololu.com/product/2831

The problem is: Is there any risk of inverted polarity and spikes (for ex. when connecting the battery to the circuit) anyway?

If that ever happens, the module is worthless -- send it back.

Thank you for the answer.

If that ever happens, the module is worthless

I am using the DC-DC only to bring down the voltage.
My question is how to protect the DC-DC (and Arduino, eventually) from any potential spike or polarity inversion (is there any risk though?) by configuring a protection circuite between the battery and the DC-DC.

My question is how to protect the DC-DC (and Arduino, eventually) from any potential spike or polarity inversion (is there any risk though?) by configuring a protection circuite between the battery and the DC-DC.

A diode in series between the battery and DC/DC converter will protect against a reversed battery connection. A fuse wouldn't hurt, but most of the time fuses blow after something is damaged.

I think a reversed battery is the only significant risk.

I've got an Arduino running some "disco lights" in the ceiling of my van. It's running directly off the 12V, using only the Arduino's on-board voltage regulator. (In my application, the Arduino is only driving a few LEDs and solid-state relays. Since you are also powering a GSM module and drawing more current, the DC/DC converter is a good idea.)

Sorry, I misunderstood the question about polarity reversal and spike protection. Both are absolutely necessary unless the DC-DC module already has them built in.

For protection from spikes, which can reach hundreds of volts in automotive circuits, special Zener diodes are available (often called TVS for Transient Voltage Suppressors) and are very inexpensive. See attached application note from Vishay.

tvs.pdf (199 KB)

filipporosso:
Hello,
I have already spent some time on [all this good topics ](http://car batteries site:http://forum.arduino.cc)in order to understand the best way to make Arduino work with 12v automotive batteries.

I would suggest a 7805 regulator. On the input side, do this:

[+12 volts in]-->[1.5 amp fuse]-->[1 ohm, 5 watt resistor]-->[1N5402 diode]-->[1000uF, 25v cap]-->[7805 input]

The negative side of the cap goes to ground, as does the ground lead of the 7805.

And of course, the diode needs to point in the right direction! :slight_smile:

The purpose of the parts:

  • 1.5 amp fuse - fire and short circuit protection
  • 1 ohm resistor - surge protection
  • 1N5402 diode - reverse polarity protection and negative spike isolation
  • 1000 uF cap - storage during negative spikes and noise filter
  • 7805 regulator - gives nice, clean 5 volts regulated power, overcurrent and overheat protection

You can build all of this in a small aluminum box. Since the tab of the 7805 is ground, just attach it to the box (it will act as a heatsink).

You say the car won't be running, but if it ever is (or if you turn on some accessory such as headlights or blower) the 12 volts will get a momentary downward spike. The diode will block this negative spike and the capacitor will supply power during the spike.

The combination of resistor and capacitor will also protect you from high voltage, short duration spikes (which you may also encounter).

I've used this circuit for years on various car powered goodies and it works flawlessly.

Good luck!

Thank you all for the very useful replies.

Please notice that I’m not connecting the circuite to a car. I’m only using a car battery to power Arduino, so I guess there are not going to be current spikes (but only voltage spike and reverse polarity) right? If so, what is the utility of a fuse?

@DVDdoug

A diode in series between the battery and DC/DC converter will protect against a reversed battery connection.
A fuse wouldn’t hurt, but most of the time fuses blow after something is damaged.

Shouldn’t I put a put a zener in parallel like this?

@Krupski

I would suggest a 7805 regulator.

I have already bought this DC-DC. I guess it has already some built in components of your list, but maybe I’m wrong?

Thank you!

If you are using a "naked" automobile battery, there will be no voltage spikes unless your circuit generates them. If you connect it the right way around, polarity reversal is not a problem.

filipporosso:
Thank you all for the very useful replies.

Please notice that I’m not connecting the circuite to a car. I’m only using a car battery to power Arduino, so I guess there are not going to be current spikes (but only voltage spike and reverse polarity) right? If so, what is the utility of a fuse?

@DVDdoug
Shouldn’t I put a put a zener in parallel like this?

@Krupski

I have already bought this DC-DC. I guess it has already some built in components of your list, but maybe I’m wrong?

Thank you!

Wiring the zener the way you drew it will either fry and short the zener, or it will blow the fuse. Which happens first is a tossup.

Zener diodes are of limited value, especially for what you want to do. They aren’t meant for your kind of usage.

The little board that you bought is a switching regulator. It will certainly work, and indeed it is more efficient than a linear regulator (i.e. the 7805).

Regardless of what you do, I would suggest sending the battery plus through a fuse and a diode. I don’t know if your switcher regulator has reverse polarity protection, and a fuse is absolutely essential. A car battery can provide SEVERAL HUNDRED AMPERES if short circuited. If you don’t use a fuse and you get a short, SOMETHING will burn. It’s better to safely pop a fuse than to have molten, dripping, flaming vinyl coming off your wiring!

jremington:
If you are using a "naked" automobile battery, there will be no voltage spikes unless your circuit generates them. If you connect it the right way around, polarity reversal is not a problem.

You are 100% correct, but a diode is cheap insurance against a casual mistake. Plus the 0.7v drop will make the regulator's job a bit easier! LOL! :slight_smile:

And (IMHO) a fuse is absolutely essential when dealing with a car battery, which can easily put out several hundred amperes of current into a short circuit. If a fuse doesn't blow, something else will, and it probably won't be pretty.

Check ebay for UBEC voltage regulators.

Krupsky wrote:

Wiring the zener the way you drew it will either fry and short the zener, or it will blow the fuse. Which happens first is a tossup.

Good to know :wink: Then what kind of diode should I use and how?

And (IMHO) a fuse is absolutely essential when dealing with a car battery

Again, what fuse should I use?

Sorry for the ultra-basic questions.

Thanks!

zoomkat

Check ebay for UBEC voltage regulators.

This as well looks like a proper solution.
Does this module cover what I want to achieve with fuse-diode-DCDC, or it's simply just another form of DCDC?

Does this module cover what I want to achieve with fuse-diode-DCDC, or it’s simply just another form of DCDC?

It is a power converter for RC components like servos, etc., and not made for your specific needs.

Ok. Thank you anyway.

I guess the proper solution is adding a fuse and a diode on the plus.

1,5amp fuse and 1N5402 diode, as Krupsy is suggesting?

Thanks a lot