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
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.
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:
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.
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?
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?
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?
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!
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.
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?
Then what kind of diode should I use and how?