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Topic: Tips for using a 12v power source (Read 961 times) previous topic - next topic

tjjunior

Hi all,

I'm fine with the programming side of things, but the hardware side is still pretty new to me.  I'm going to be running some gauges (fuel, temp, oil pressure, etc) in a sailboat.  As a result, everything will be powered off of the batteries (unless I use a very very long extension cord...). 

From my research I know using 12V directly from the batteries is a bad idea given that they will be used to start the engine and such and I need to de-couple the power supply.  There are a couple of different options I've come across, wondering if there is any benefit one over another, or if I should use several in conjunction.  I understand why it's necessary, just trying to figure out the best way to implement it.

Question 1: Better to use a 2.1mm plug with incoming 9V-12V or "clean" the incoming power to 5V and wire it in directly?  I'm guessing the plug so that the Arduino can use it's internal regulating as backup.

Question 2:  Any thoughts on the best way to clean the power supply?

  • Option 1: Use a car USB adapter and rewire it.  By doing this, though, it gives 5V not 9V, does that mean I'd then need to boost it up to 9V-12V?

  • Use something like the LM2596S adjustable power supply (http://www.ebay.com/itm/180947008880?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649)  If I use something like this, do I need to also add a heatsink?  I'll most likely mount it on the inside of a locker that's easily 3'x3'x3' and not airtight

  • Use some capacitors to filter out low and high levels



Any tips would be greatly appreciated!  I'm just trying to come up with a reliable power source for long-term use.  It would almost never be used for more than a couple of hours (at which time we recharge the batteries), so I'm hoping it's not going to be a significant battery drain.

Thanks!

DVDdoug

Quote
From my research I know using 12V directly from the batteries is a bad idea given that they will be used to start the engine and such and I need to de-couple the power supply.
When you start the engine, the voltage may drop below 12V (perhaps below 5V).    That's why your lights dim, if you have yoru lights on when you start your car.  The drop in voltage may cause your Arduino to reset, which may, or may not, be a problem.

I have an Arduino in a vehicle, and I haven't actually noticed if it resets when I start the car.   If it does, it's not a problem in my application.    Once the car is running, I never get a "glitch".

There is already a regulator on the Arduino board, but the regulator can only hold the voltage as long as there's enough voltage coming in (about 6V).   

If resetting is a problem... a capacitor (1000uF or so) on the Arduino power input, with a diode to prevent the diode from discharging into the other stuff on the boat  may help, depending on how long it takes to start the motor...  But, the capacitor-charge will probably only last for a couple of seconds, so the best solution is probably a separate back-up battery (probably with diodes or something so that the Arduino can run off the main battery most of the time). 

terryking228

Combine those ideas and you're in pretty good shape:

- Diode from "+12V"  (can go from 7 to 14 volts extremes) to a large capacitor (maybe 10,000+ uF at 25 volts)
- From the capacitor to a voltage regulator similar to what you showed, with an output of 6 or 8 volts, to the Arduino Vin
- The Arduino regulator takes it from there to 5V

Google "Car Computer" and "Power Supply" and you'll get LOTS of hits... Those guys are doing it for a long time now.
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

tjjunior

Thanks for the tips.  So something like:

12V battery -> 12V diode -> capacitor -> adjustable power supply at 8V -> Arduino vin

I'm not that concerned about resetting from a user perspective, just from a prevent-damage-to-the-arduino perspective.  None of the information is mission-critical (sounds similar to your usage, Doug), my plan is to turn the chip on only after the engine has been started.  But of course mistakes happen, so better to be prepared so I don't fry it.

Thanks for the suggestions! 

terryking228

Quote
12V battery -> 12V diode -> capacitor


The Diode can be a typical Silicon diode.  Voltage ratings are usually 400V or more.. no problem. The Current rating should be 1 Amp or more.. 3 Amp would be good.  Capacitor charging current will be high. 

1N4006 or 1N4007 1 Amp diodes easy to find
1N5408 3 amp diodes fairly common.

Examples: http://goo.gl/nbvdJ   


DISCLAIMER: Mentioned stuff from my own shop...
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

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