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Topic: powering the Arduino Uno with a 12V battery (Read 15804 times) previous topic - next topic

CTE_T

I am trying to power an Arduino Uno with a 12v battery. The problem here is that the Uno uses 5v as its operating voltage and we need to use a power source that will last longer than an hour while sending wireless signals. A 9v battery will not last a full hour (as far as I know) so we are using a smaller version of a 12v car battery and need to convert the power to 5v and to last a long time. I've thought about using a voltage regulator, but 12v to 5v will seem to give a overheating problem. Also, the thought of using resistors as a voltage divider has brought up the fact that the battery may only last as long as a 5v.

Does anyone have any suggestions or comments on how to power the Arduino for a long time on battery power at 5v with little or no cooling?

DVDdoug

The uno has a voltage regulator on-board.  12V is fine.

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Also, the thought of using resistors as a voltage divider has brought up the fact that the battery may only last as long as a 5v.
NO!!! ;)   A voltage divider is OK for low-current "signals", but it's a bad idea for a power-supply "reducer".   In order to work, the voltage divider itself would have to draw more current than the device being powered.

Linear regulators (like what's on the Arduino board) are sort-of like an automatically-adjusting resistor.   The aren't very efficient because the power consumed by the regulator can be more than the power consumed by the device/load.  (In fact, with a 12V supply, you've to 7V across the regulator,and 5V across the load and there is more power used in the regulator.)

Switching regulators are more efficient.  With a switching regulator, the current  from the supply/battery actually decreases if you boost the voltage.    (But, a switching regulator shouldn't be necessary with a small lead-acid battery.)

dc42

Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

CTE_T

So I can just wire a positive wire to the Vin on the arduino and a negative wire to the ground pin from a 12v battery? I was worried that the arduino would fry up or something.

retrolefty


So I can just wire a positive wire to the Vin on the arduino and a negative wire to the ground pin from a 12v battery? I was worried that the arduino would fry up or something.


The Vin pin is designed to accept the same voltage range input that the external DC connector is, approx +7-12vdc.


Lefty

CTE_T

I will take that as a complicated way of saying yes. Lol.

retrolefty


I will take that as a complicated way of saying yes. Lol.


LOL of course yes. Just an attempt to educate rather then just give yes and no answers for you to memorize.


Lefty

CTE_T

Alright. Thank you! I've spent the last 3 days trying to figure out how to power or convert power to work at 5v on the arduino.

One more quick question, do you think the 12v battery will last more than an hour?

dc42

To answer that, we need to know the specification of the battery, and how much additional current you will be drawing from the +5v line and/or directly from +12v.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

CTE_T

The battery we have is a NP7-12, 12v, 7.0Ah : Sealed Rechargeable Lead-Acid Battery. It says genesis on it and www.enersys.com

We need the Arduino to pull information off (separate) 12v car batteries and send that information wirelessly through Xbee for an hour.

I have not had the time to look up the battery's specifications yet, but I will later.

Any help is appreciated.

retrolefty


The battery we have is a NP7-12, 12v, 7.0Ah : Sealed Rechargeable Lead-Acid Battery. It says genesis on it and www.enersys.com

We need the Arduino to pull information off (separate) 12v car batteries and send that information wirelessly through Xbee for an hour.

I have not had the time to look up the battery's specifications yet, but I will later.

Any help is appreciated.


Well a basic arduino board draws about 50ma for it's own uses, so maybe 140 hours from that battery. But I suspect you may be powering other external devices and components that draw power from the arduino +5v pin or directly from the +12vdc battery? If so that current consumption would also have to be factored in to get a total battery run time estimate.

Lefty


John_S

I would just get one of there:
DC-DC adjustable switching regulator module.
http://www.ebay.ca/itm/LM2596-DC-DC-4-40V-1-5-35V-Step-Down-Adjustable-Converter-Power-Module-/270922360466?pt=LH_DefaultDomain_0&hash=item3f143b2692
http://jsrintervalometers.blogspot.ca

CrossRoads

Or one of these if you'd like to get it sooner rather than later.
http://search.digikey.com/us/en/products/OKI-78SR-5%2F1.5-W36-C/811-2196-5-ND/2259781
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Daanii

#13
Feb 29, 2012, 05:15 am Last Edit: Feb 29, 2012, 06:52 am by Daanii Reason: 1

The battery we have is a NP7-12, 12v, 7.0Ah : Sealed Rechargeable Lead-Acid Battery.


Your battery is 7 Amp hours, which means that it can more or less deliver 7 Amps of 12 Volt power for one hour. You should have plenty of power for what you want to do.

UPDATE:

Let me give you some figures.

I looked up the XBee and XBee Pro. They take 50 mA and 300 mA (respectively) of 3.3 Volts. The Arduino will take about 50 mA of 5 Volts.

Your battery will provide 84 Watt hours of power.

So if you use two relatively high efficiency switching voltage regulators (one to give 5 Volts to run your Arduino and one to give 3.3 Volts to run your XBee), in theory the XBee will take 165 milliwatt hours, the XBee Pro will take 990 milliwatt hours, and the Arduino will take 250 millwatt hours. So the XBee/Arduino combination will run for about 200 hours, and the XBee Pro/Arduino combination will run for about 65 hours.

Even if you just use linear voltage regulators instead of switching regulators, you should have plenty of power. The XBee/Arduino combination will run for about 70 hours, and the XBee Pro/Arduino combination for 20 hours.

CTE_T

Quote
Well a basic arduino board draws about 50ma for it's own uses, so maybe 140 hours from that battery. But I suspect you may be powering other external devices and components that draw power from the arduino +5v pin or directly from the +12vdc battery? If so that current consumption would also have to be factored in to get a total battery run time estimate.

Lefty


I had not thought of how I am going to power the other devices (specifically the Xbee) but the plan I believe was to use the battery to power the arduino, and then the arduino to power the Xbee.

Quote

It's not clear to me from this, but I assume the overheating problem is on the 5V regulator on
the Arduino board, due to its dropping a full 7V when the 12V battery is used.

7V * (whatever current is being drawn) = Pd, the power-dissipated in the v.reg.

For tiny SOT223 v.regs used on Arduino boards, Pd can be only .3W or .5W before the regulator
starts getting really hot. So, that means current in the range of only 50-mA or so before heat
starts rising. XBees and XBee Pros draw a lot more current than that when transmitting.

As others mentioned, linear v.regs are not very efficient. As you mentioned, 9V batteries
like the little 1" sized things, won't run your system for more than a few minutes.

Short of going to a switching regulator, I would try a series-R rather than a voltage divider,
pre se. With a full v.divider, the resistor going to ground will suck your battery dry in no time.

Rather just try using a series-R alone, with 4-5V being dropped in the resistor. Then, the
series-R will get hot instead of the v.reg, and that's a much better deal.

4V/.250Amp = 16 ohms or thereabouts. It needs to be at least 2W size.

You're still wasting a lot of battery in the series-R, as compared to using a switching
supply, but at least it should work.


Quote
I would just get one of there:
DC-DC adjustable switching regulator module.


Quote
Or one of these if you'd like to get it sooner rather than later.


I thought I didn't need any kind of converter now? I can just plug 12v into Vin and negative to ground right?

Quote
Your battery is 7 Amp hours, which means that it can more or less deliver 7 Amps of 12 Volt power for one hour. You should have plenty of power for what you want to do.

UPDATE:

Let me give you some figures.

I looked up the XBee and XBee Pro. They take 50 mA and 300 mA (respectively) of 3.3 Volts. The Arduino will take about 50 mA of 5 Volts.

Your battery will provide 84 Watt hours of power.

So if you use two relatively high efficiency switching voltage regulators (one to give 5 Volts to run your Arduino and one to give 3.3 Volts to run your XBee), in theory the XBee will take 165 milliwatt hours, the XBee Pro will take 990 milliwatt hours, and the Arduino will take 250 millwatt hours. So the XBee/Arduino combination will run for about 200 hours, and the XBee Pro/Arduino combination will run for about 65 hours.

Even if you just use linear voltage regulators instead of switching regulators, you should have plenty of power. The XBee/Arduino combination will run for about 70 hours, and the XBee Pro/Arduino combination for 20 hours.


We are going to use Xbee Pro and Arduino Uno. These calculations are accurate to just plugging into the Vin and ground right? Without any kind of converter? 20 hours is more than enough if this is true. Also, if your saying this will work for 20 hours, we ALSO have a camera/camcorder wired with the same battery but it is only for convenience and doesn't look like it will be a problem with 20 hours of power.

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