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Topic: Can I use two 9V batteries in series to power an Arduino Uno? (Read 19224 times) previous topic - next topic

staticsan


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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.


Hey, could you chill a bit? This is an unpleasant welcome to the Arduino forums, even for someone who has been involved in both web-based forums and hobby electronics for many years, and even if you are absolutely certain of your facts.

I'm going to try to not let you scare me away from here.

Wade.

Grumpy_Mike

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I'm going to try to not let you scare me away from here.

Good. No attempt to do so was intended.

Paul__B


I'm going to try to not let you scare me away from here.

Well, you can't say you weren't warned!   :D

(The name tends to give it away.)

fungus



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.


I'm with grumpy: You're wrong. Batteries in parallel is a very bad idea and will absolutely not make them last longer (in fact they'll probably last a lot less then a single battery).

Advanced Arduino

staticsan



I'm going to try to not let you scare me away from here.

Well, you can't say you weren't warned!   :D

(The name tends to give it away.)


*sigh*

This is unfortunate. As was the fact I needed to say the quoted line above. I am comfortable being wrong. I am not comfortable being confronted with a dogmatic stance about it. I hope the forum is normally nicer to new people.

I stand by my original comment that two batteries in parallel are sometimes a viable solution. Just not a preferred one.

Wade.

AWOL

Besides which, two 9V batteries would have about the same volume as four AA cells, which be more preferable.

JimboZA

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two batteries in parallel are sometimes a viable solution


But isn't it true that if one is of lower voltage, and that is almost certain to be the case, then the higher one will try to charge the lower one. Without some electronics in place to prevent that, that can't be right, since not all batteries are re-chargeable. So to me- and I'm a mere civil engineer who doesn't profess to have any more electrical know how than my 18yo daughter- viable means it must have some electronics in place.
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

fungus

#37
Oct 10, 2014, 12:26 pm Last Edit: Oct 10, 2014, 04:59 pm by fungus Reason: 1

This is unfortunate. As was the fact I needed to say the quoted line above. I am comfortable being wrong. I am not comfortable being confronted with a dogmatic stance about it. I hope the forum is normally nicer to new people.


If you come in here saying "2+2=7" then people telling you're wrong isn't 'dogma', it's because you're 100%, flat-out wrong. The sum of 2+2 is not a subject open for debate.

If you're convinced you're right, fine, but come back with some experimental data that shows how you're right and we're wrong.

We too are comfortable being wrong. Being wrong is how we learn. All we ask for is evidence...
Advanced Arduino

Paul__B


But isn't it true that if one is of lower voltage, and that is almost certain to be the case, then the higher one will try to charge the lower one.

Mike - not without experience we understand - has a problem with things in parallel - LEDs and now, batteries.

I am sure people do from time to time successfully use batteries in parallel, though I cannot think of any such example myself.  It would seem reasonable if the batteries are from the same batch as they would tend to closely equalise their discharge.

A battery has an internal voltage and an internal resistance, what happens is that with discharge, progressively less area of electrode material becomes available and the internal resistance progressively increases so that the battery which is more replete will have a lower internal resistance and will provide more of the current, discharging faster until it matches the other.  This would seem to equalise out the discharge between the batteries.

The intrinsic voltage may change according to changes in the concentration of various reactants, which is why rechargeables in general hold their voltage better as the electrolyte is not a consumable; its concentration does not change until the end of the discharge (if then).  In order to charge a battery (which is to some extent possible even with "non-rechargeable" cells) you require a significantly higher voltage to reverse the electrochemical reaction, so parallel cells with different degrees of discharge are not particularly likely to charge or be charged by the other but will simply float to the higher voltage.

Grumpy_Mike


I am comfortable being wrong.

Good glad to know you are comfortable.

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I stand by my original comment that two batteries in parallel are sometimes a viable solution.

Glad to know you are comfortable about this.

However this is a beginners forum, and while you might be comfortable about this bit of "wisdom" you do have a responsibility to people who are just learning not to mislead them.
As you say you are new. All the answers given here are pear reviewed, that is there will be many members checking for the correctness of any statement. If they spot a wrong one then it is the ethos of this forum to inform the member of this.

Then we can have a debate and put forward further arguments. All I see from you is that you say:-
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I stand by my original comment


This is not a matter of opinion, it is a matter of fact. If you have some special circumstances where you think your original comment has some validity then state them. If it is just your opinion then in terms of scientific debate you have not got a leg to stand on.

You are welcome here to ask any question you want.
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I hope the forum is normally nicer to new people.

Yes it is, no one is ever given a hard time for asking the simplest of questions, and if they don't understand the answer they only have to ask for a more detailed explanation.

However if you want to give advice, it has to be correct. This is not a "blind leading the blind" forum that you see so much of on the net. This is a solid advice forum.

JimboZA

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All the answers given here are pear reviewed


.... which is maybe why some answers are pear-shaped....  :P
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

Grumpy_Mike


technix

Also, you will be burning off lots of energy on the linear regulator.

The Arduino takes 100mA under worst case scenario at 5V. Given the principle of linear regulators they will be pulling 100mA out of the batteries, and burn off that 13V of excessive voltage. This means 1.3W of heat dissipation and ~30% efficiency.

The AMS1117 on the Arduino is indeed rated for 100mA, but the SOT-223 package cannot really handle the 1.3W heat dissipation. Your board, running off 18V, can get hot real quick, and its life will be reduced.

Although replacing the AMS1117 chip is easy and cheap, but having a part burning off that much energy is not a good design.

If you have some other part of the circuitry that requires the 18V power, you should either drive the Arduino using only 1 instead of 2 of the batteries, or use an switch-mode DC-DC converter to derive the 5V voltage out of the 18V in a more efficient (usually 90+ percent) way.

jardane

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

AWOL


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

Welcome to the forum!

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