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Topic: Can I use two 9V batteries in series to power an Arduino Uno? (Read 19223 times) previous topic - next topic

jardane

The worst case scenario is I can run some of the devices from a secondary battery that is not connected to the Arduino. I can run the DAC on a secondary battery without issue and I might also run the SD card reader off that as well.

Grumpy_Mike

Quote
I can run the DAC on a secondary battery without issue and I might also run the SD card reader off that as well.

You can but I would assume that your DAC requires 5V and your SD card requires 3V3 so you need some regulators as well.

Instead of all this fannying about why don't you just calculate the current you will need?

JimboZA

Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)
Dr Perry Cox: "Help me to help you, help me to help you...."
Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0

polymorph

Do you have more room? Can you fit something slightly larger in, maybe something longer? A 6 cell AA pack will last a lot longer than a 9V radio battery.

9V alkalines don't pack much punch, note that the best on this list is 490mAh at 100mA draw but that is for a brand I've never heard of. The other alkalines are more in the range of 300mAh, with capacity going down a lot at 500mA current:
http://www.powerstream.com/9V-Alkaline-tests.htm

Whereas a 1.5V AA alkaline is over 2Ah at 100mA, and still over 1Ah at 500mA:
http://www.powerstream.com/9V-Alkaline-tests.htm

6 cell AA holders:
http://www.amazon.com/Philmore-Battery-Holder-Standard-Connector/dp/B000LFVFU8/ref=sr_1_1?ie=UTF8&qid=1412789999&sr=8-1&keywords=six+aa+battery+holder

http://www.amazon.com/Battery-Holder-6-AA-Long/dp/B00LPXLDF2/ref=sr_1_2?ie=UTF8&qid=1412789999&sr=8-2&keywords=six+aa+battery+holder

http://www.amazon.com/TOOGOO-Battery-Batteries-Holder-Storage/dp/B00H8KVHT8/ref=sr_1_5?ie=UTF8&qid=1412789999&sr=8-5&keywords=six+aa+battery+holder

Enclosed with a power switch:
http://www.amazon.com/Spring-6x1-5V-Battery-Holder-Storage/dp/B00HG8EMM6/ref=sr_1_4?ie=UTF8&qid=1412789999&sr=8-4&keywords=six+aa+battery+holder

Powerjack for Arduino already installed:
http://www.amazon.com/Beautyforall-Battery-Storage-Holder-Arduino/dp/B00L0642SE/ref=sr_1_6?ie=UTF8&qid=1412789999&sr=8-6&keywords=six+aa+battery+holder


Or use an Ultralife Lithium 9V battery.
http://www.batterymart.com/p-ultralife-9v-lithium-battery.html

Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

staticsan



You can put identical batteries in parallel, then the combination will last about twice as long.

No you can't.
They will cross charge and heat up.


That would not be putting two batteries in parallel, but in series and then shorting them. Two batteries in parallel is both positive terminals together and both negative terminals together. They can then supply 9V to the circuit for twice as long as a single battery.

And they only need to be the same capacity (Ah) and voltage; they don't need to be "identical". The same brand bought at the same time would be enough.

Wade.

JimboZA




You can put identical batteries in parallel, then the combination will last about twice as long.

No you can't.
They will cross charge and heat up.


That would not be putting two batteries in parallel, but in series and then shorting them.


I'm 106% sure that Grumpy_Mike knows what it means to put batteries in parallel, and what the risks are.
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)
Dr Perry Cox: "Help me to help you, help me to help you...."
Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0

staticsan





No you can't.
They will cross charge and heat up.


That would not be putting two batteries in parallel, but in series and then shorting them.


I'm 106% sure that Grumpy_Mike knows what it means to put batteries in parallel, and what the risks are.


Well, I don't know Grump_Mike since I'm new here but I do know using batteries in parallel is widespread, common and safe. But I don't want to start an argument, either.

KenF

You would be better off using one of those batteries to power the uno and the other to provide power to the ancillaries that you're connecting.  But these things really do have poor performance for anything other than very low power consumption over a long time.  So for multimeters and fire alarms they're fine.  Anything else, they're a waste of time.

You're better off with a pack of c or d cells.

KenF

#23
Oct 09, 2014, 06:08 am Last Edit: Oct 09, 2014, 06:10 am by KenF Reason: 1



That's better!
Am I the only one with a small screen :)

polymorph

Oops, sorry. I linked that from an external source and had only a few minutes to post all that.

I can type fairly quickly, but, well...
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

Grumpy_Mike

Quote
Well, I don't know Grump_Mike since I'm new here but I do know using batteries in parallel is widespread, common and safe. But I don't want to start an argument, either.

If you know that then you know wrong.

Connecting battries in parallel is a bad thing and can lead to all sorts of problems.

Yes it is done and it knackers the batteries, depending on what sort they are the damage done can be large or small.

When you need extra current or capacity and have to connecting batteries in parallel it is common to connect them together through diodes to prevent problems. But basically they cross charge causing excess heat and loss of capacity and with certain types of battery damage to the battery.

Battries in seriese are fine and that is common, that increases the voltage not the capacity.

Paul__B

It's not rocket science.


If on the other hand, you want rocket science:

Use two 18650 rechargeables.

polymorph

Grumpy_Mike is correct. Although you may find people using batteries in parallel, it is a bad idea without isolating them with diodes.

There are a lot of bad ideas on the internet. Heck, there are a lot of bad ideas in some books!

Better just to use higher capacity batteries.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

MarkT



You can put identical batteries in parallel, then the combination will last about twice as long.

No you can't.
They will cross charge and heat up.


Not if they are identical, from the same batch, but its better to get a bigger battery.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

Grumpy_Mike


Not if they are identical, from the same batch, but its better to get a bigger battery.

Yes, a fundamental law of physics is that nothing is identical.

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