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[on:]

Found a 12v 7Ah lead acid battery.  A multimeter reads it outputting 13v.  Will this damage an Arduino Uno if plugged into the power input?
Thanks in advance.

dp

[Reply #1 on:]

No. 5V regulator may get a little warm, it dissipates everthing above 5V as heat essentially.
Maybe consider a switching regulator at some point for more efficient battery use.
Check out Murata regulators at digikey.com, $4-5.

[Reply #2 on:]

as stated... heat is your only issue with 12V... I personally use a 9.6V R/C NIMH battery.

[Reply #3 on:]

No. 5V regulator may get a little warm, it dissipates everthing above 5V as heat essentially.
Maybe consider a switching regulator at some point for more efficient battery use.
Check out Murata regulators at digikey.com, $4-5.

I assume you mean this character: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=811-2196-5-ND
If so, thank you!  That thing is absolutely glorious.
If not, it's still glorious

[Reply #4 on:]

That's the one. I think RetroLefty pointed it out originally, I was not aware of them. I've only been keeping it in mind

[Reply #5 on:]

An SLA battery can go up to over 14V fully charged, so just be cautious when using a battery like that.  As long as you keep the load low on the 5V rail and make sure there is adequate airflow.  When exceeding the recommended voltage, you do risk shortening the life of the regulator.  Really, the killer is heat.  Keep it cool and there will be no problems.

[Reply #6 on:]

"Based on fi xed-frequency buck switching topology, the high effi ciency means very low heat and little
electrical noise, requiring no external components.
The ultra wide input range is 7 to 36 Volts DC.
Protection features include input undervoltage and short circuit protection, overcurrent and over
temperature shut down. The OKI-78SR is designed to meet all standards approvals. RoHS-6 (no lead)
hazardous material compliance is specified as standard."

I think he'll be fine.

[Reply #7 on:]

dpotthast, what else do you want to power from +5v? Powering the Arduino directly from the 12v battery is fine as long as you are not drawing much power from the +5v pin.

[Reply #8 on:]

"not drawing much power from the +5v pin" as in 800mA total - and that may require heatsinking to keep the regulator from going into thermal shutdown.

[Reply #9 on:]

Crossroads, where did you get the figure of 800mA from? As far as I can see, dpotthast has not stated how much current he wants to draw from the +5 pin (and/or the 3.3v pin, and/or Arduino pins that are sourcing current). The answer to his question depends critically on the total current draw on the +5v and +3.3v lines.

I measured the current consumption of a running Uno at 43.5mA including the power LED but with nothing else connected to it. If I were to run it from +14v then the regulator would dissipate 0.4W which is no problem. Looking at how the regulator is heat sinked, I would guess that 1W is a reasonable limit. So if dpotthast is using a Uno, he can reasonable draw up to 65mA or so in total from +5, +3.3 and Arduino pins before he needs to use an external regulator. If he's using serial comms or pin 13 as an output, he should allow a few mA for the extra on-board LEDs.

[Reply #10 on:]

Sorry, I was not clear. The 5V regulator is rated for 800mA.
If just the Uno is drawing current, 40-50mA, then no problem.
If a  bunch of LEDs, or transistor and a motor, are added, then current goes up & dropping 9V across the regulator may become a heat issue.

[Reply #11 on:]

800mA is under ideal conditions.  Usually you want to derate the regulator down a bit, anyway. 

[Reply #12 on:]

One way to deal with this if it is a problem is to use an external 10V regulator to step down the battery voltage to 10V before going to the Arduino.  That way the voltage drop across the on-board regulator is 5V rather than 7 to 9V, reducing the heat dissipated on board (at the expense of some heat in the 10V regulator.

A DC-to-DC converter would be more power efficient, but more expensive - in this case its worth directly converting to 5V and powering the Arduino directly by the 5V pin.  The on-board regulator then has nothing to do and generates no heat at all.  The typical efficiencies of these converters is 80 to 90% so overall much less heat is generated (useful if you put the electronics in a plastic box) - and battery life is extended of course.

[Reply #13 on:]

You can buy a switching UBEC from Chinese hobby stores for dirt cheap, FYI.

[Reply #14 on:]

You can buy a switching UBEC from Chinese hobby stores for dirt cheap, FYI.

Right your are, 5.5 to 26 volts input:

http://www.ebay.com/itm/Hobbywing-3A-UBEC-5V-6V-max-5A-Lowest-RF-Noise-BEC-US-/330587486141?pt=Radio_Control_Parts_Accessories&hash=item4cf88cb7bd