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Topic: Can I use two 9V batteries in series to power an Arduino Uno? (Read 19386 times) previous topic - next topic

technix


It's not rocket science.


If on the other hand, you want rocket science:

Use two 18650 rechargeables.



The two 18650's packs quite a punch!

I have 5 of those wired in parallel in a phone charger pack, and during wiring I accidentally shorted it out for a split second, and it blew out some of my solder joints immediately and heated up the wires to the point that I dropped them. I used lead-free solder that contained silver, which should be the lower resistance type already. The batteries are fully charged before this incident so maybe that is the reason why it bit so hard.

jboyton

Energizer has an application note on the subject. They recommend using "fresh" batteries if you're going to put them in parallel to minimize the chance of problems. And if you can't be trusted to do that to use Schottky diodes. They also warn about shorting the batteries if you install one backwards.

http://data.energizer.com/design_hints/pages/dhints_seriesparallel.html

Paul__B


The two 18650's packs quite a punch!

I did not choose to refer to it as "rocket science" without excellent reason!


I have 5 of those wired in parallel in a phone charger pack

So you are saying that is actually a commercial product, and they are wired in parallel?  Or this is your own concoction?


I feel like this stopped being about my question a long time ago.

But the fact is, you were answered (a long time ago).  Your original idea was totally impractical, and you have been given the proper recommendation - six alkaline AA cells, or if you really want performance, the two 18650s.  That's not so bad.  And you now know more about batteries.   :D

spicetraders

Darn I better tear down all those solar powered sites that I have put in the last 20 years as the batteries are all in parallel.  Oops there goes the car battery.

Yes I will give the fact that parallel does have issues once a cell fails or starts to fail, but so does series.
So unless we can run all things on simple one cell batteries we will be prone to the eventual doom.


If space is an issue ro weight is an issue two nines in parallel will do for increased run time.
If space or weight is not an issue then use the battery trays listed several time through out this post.
Or run on the 7.2  or 9V RC hobby batteries.

polymorph

It hasn't been said, but putting rechargeables in parallel is entirely different than putting non-rechargeables in parallel.
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


Darn I better tear down all those solar powered sites that I have put in the last 20 years as the batteries are all in parallel. 

Yep designed by a moron, who knew nothing about batteries and considered a design a success if it didn't immediately blow up.

Having said that Lead Acid batteries do suffer the least form being abused in this way because the charging requirements are quite simple. However, the batteries will degrade faster if you connect them directly in parallel than if you do it properly. Also the efficiency of the storage of the hard won solar power is less than it could be. 

spicetraders


When someone asks for help I assume it is practical help they want, not theoretical help that postulates impossible conditions.

You are right he did ask for practical help, not negative help

spicetraders

[quote author=Grumpy_Mike link=topic=271346.msg1916136#msg1916136 date=1412978139

Having said that Lead Acid batteries do suffer the least form being abused in this way because the charging requirements are quite simple. However, the batteries will degrade faster if you connect them directly in parallel than if you do it properly. Also the efficiency of the storage of the hard won solar power is less than it could be. 
[/quote]

Who said they were lead acid?
And I guess 10 years of heating up has been why the desert is hot here.


jardane

Can someone close this thread so people stop fighting?

polymorph

Sometimes positive help is negative help.

As for paralleled cells, I've seen a lot of battery packs with rechargeable lithium ion or lead acid cells in parallel. But those are rechargeables. Different situation.
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

fungus



When someone asks for help I assume it is practical help they want, not theoretical help that postulates impossible conditions.

You are right he did ask for practical help, not negative help


And he was given exactly that ... before he started telling us we were wrong.

Advanced Arduino

fungus


As for paralleled cells, I've seen a lot of battery packs with rechargeable lithium ion or lead acid cells in parallel. But those are rechargeables. Different situation.


Disagree. "Rechargeables" are almost certain to be at "different states of discharge" because they all have slightly different capacities, leading to (from the Energiser notes posted earlier).

Quote

Batteries connected in parallel should be at the same state of discharge.  If batteries at different states of discharge are installed into a device using a parallel battery configuration, the battery with the higher voltage will charge the battery with lower voltage until voltage equilibrium is reached in the system.  This charging could lead to leakage, elevated temperature, or other damage to the lower voltage cell.


It might be acceptable to put batteries in parallel when you want very high current and you're not expecting a long lifespan (rockets, helicopters, etc. Stuff that lasts 20 minutes...) In this case the current being drown will drown the charge being passed between batteries.

If your aim is to get "longer life" though, you're doing it very, very wrong.
Advanced Arduino

polymorph

You can disagree all you want. I work with 18650 LiIon rechargeable packs every day that have three cells in parallel, four of those in series. They are assembled at the factory. I've also taken apart a few high capacity laptop power packs that put 2 and 3 cells in parallel.

Say two non-rechargeable alkaline cells are connected with slightly different capacity/voltage: one cell pushes current into the other. A bad thing, which shortens the life of the cell having current forced into it, and using up charge from the higher voltage cell. Since the one cell is damaged, it shortens its life, shortening the life of both cells. So you don't get double the capacity.

Two rechargeable LiIon cells in parallel, one has slightly less charge and therefore voltage. The more charged cell merely recharges the one with less charge, thereby balancing the cells. Neither has its life shortened. Since the voltage of a LiIon cell correlates pretty well with state of charge, charge balancing naturally occurs when recharging and discharging.

Please don't give me ridiculous examples of paralleling a dead and a fully charged cell, or a new cell with an old worn out cell. I think everyone here knows you never mix batteries in different states of charge and/or lifecycle, even in series.
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

Peter_I



I feel like this stopped being about my question a long time ago.

Welcome to the forum!


Indeed, that is how forums are.

You got an answer:
- no, it is not a good idea to use two 9V batteries, neither in series nor parallel
- There is no reason to feed your Arduino 18V
- If space allows, it is better to use a pack of 6 AAs


Be happy that you got a good answer, then lean back and enjoy, as the thread takes off in whatever direction it chooses.
That's just the way it is.

:%
"Nothing is foolproof to a sufficiently talented fool"

JimboZA


Be happy that you got a good answer, then lean back and enjoy, as the thread takes off in whatever direction it chooses.
That's just the way it is


Well said....
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

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