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### Topic: Small battery with 50mA output, does it exist? (Read 9059 times)previous topic - next topic

#### Archelon

##### Sep 11, 2013, 07:24 pm
Hello once again Arduino folks!
I wonder if there is any small battery, size between coin cell CR2032 batteries and an AAA-battery, with a voltage around 3V or higher with a possible output current of 50mA?
I need a really small battery which can power an XBee, not for a very long time but a couple of seconds.
The battery doesn't need to have a very long lifetime but at least a couple of minutes.

Archelon

#### cmagagna

#1
##### Sep 11, 2013, 07:38 pm
How about a 123A, like they use in (some) LED flashlights?

#### Archelon

#2
##### Sep 11, 2013, 08:51 pm

How about a 123A, like they use in (some) LED flashlights?

thanks! do you know if there's any smaller batteries with almost the same capacity? 'cause its just a litle to big :/
thanks again!

#### Erni

#3
##### Sep 11, 2013, 09:18 pm
Maybe this one
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7567

#### Archelon

#4
##### Sep 11, 2013, 10:03 pmLast Edit: Sep 11, 2013, 10:07 pm by Archelon Reason: 1

Maybe this one
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7567

That one look like it's just the right size!
The questions are,
can I pull at least 50 mA out of it?
What is the voltage of that battery?
Considering the battery is used for helicopters with motors and so on it should work right?
Thanks again!

#### int2str

#5
##### Sep 11, 2013, 10:07 pmLast Edit: Sep 11, 2013, 10:09 pm by int2str Reason: 1
The RC battery has a "C" rating of 20. Meaning you can draw up to 20x100mA from it, which is 2A (!!).
Obviously it's not going to last long, but 50mA will be no problem at all.

Single LiPo cells are rated at 3.7V. In reality, 4.2V fully charged and I wouldn't discharge past 3.7V to be safe.

#### Erni

#6
##### Sep 11, 2013, 10:11 pm
Quote
What is the voltage of that battery?

Fully charged it will be 4.2V.

#### Archelon

#7
##### Sep 11, 2013, 10:27 pmLast Edit: Sep 11, 2013, 10:29 pm by Archelon Reason: 1

The RC battery has a "C" rating of 20. Meaning you can draw up to 20x100mA from it, which is 2A (!!).

Woow 2A thats alot, so if I only need 50mA to my XBee which I will power, will the battery force more current into the circuit than that?

Obviously it's not going to last long, but 50mA will be no problem at all.

Single LiPo cells are rated at 3.7V. In reality, 4.2V fully charged and I wouldn't discharge past 3.7V to be safe.

If my circuit only draw 50mA won't the battery last a little bit longer?
To be safe of what? That it will work?

Quote
What is the voltage of that battery?

Fully charged it will be 4.2V.

Thanks guys!

One more newbie questions since you seem to know these things about singe cell LiPo batteries.
How do I charge that battery since its a rechargeable?
Thanks! I promise to post a picture of the project I am working on if I can get it to work(Installing a remote in a lighter)

#### int2str

#8
##### Sep 11, 2013, 10:53 pm
Woow 2A thats alot, so if I only need 50mA to my XBee which I will power, will the battery force more current into the circuit than that?

No, that's not how it works.
That's just the maximum discharge rate. The XBee will only draw the current it needs.

Quote
If my circuit only draw 50mA won't the battery last a little bit longer?
To be safe of what? That it will work?

The battery is rated at 100mAh. So if you're drawing 50mA continuous, it would last for 2 hours.

LiPo batteries do not like to be deep discharged. If you completely discharge the battery, you risk a fire.

Quote
How do I charge that battery since its a rechargeable?

You need a LiPo charger.
http://www.amazon.com/Heli-Max-Charger-Novus-CX-LiPo/dp/B00272WUFC

#### retrolefty

#9
##### Sep 11, 2013, 11:06 pm
Quote
LiPo batteries do not like to be deep discharged. If you completely discharge the battery, you risk a fire.

I don't believe that is true. LiPo can suffer fire damage from overcharging or over current draw if no protection device(s) are used, but overdischarge just causes a cell failure such that it will no longer except a new charge, but not fire damage.

Lefty

#### int2str

#10
##### Sep 11, 2013, 11:28 pm
I don't believe that is true. LiPo can suffer fire damage from overcharging or over current draw if no protection device(s) are used, but overdischarge just causes a cell failure such that it will no longer except a new charge, but not fire damage.

Sorry, yes, you're absolutely correct.

#### polymorph

#11
##### Sep 11, 2013, 11:30 pm
Ohm's Law. It isn't just a good idea, it's the law.

;')

Regarding mAhr vs rate of current draw: most rechargeables seem to be rated at the total mAhr when the current draw is sufficient to cause 10 hours discharge time. When higher current is drawn, the mAhr capacity drops. So that 100mAhr cell might only last 1-1/2 or 1-3/4 hours at 50mA draw.

However, if 50mA is drawn intermittently, you may get something closer to the mAhr rating. Not sure.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8

#### Archelon

#12
##### Sep 12, 2013, 08:32 am

Woow 2A thats alot, so if I only need 50mA to my XBee which I will power, will the battery force more current into the circuit than that?

No, that's not how it works.
That's just the maximum discharge rate. The XBee will only draw the current it needs.

Quote
If my circuit only draw 50mA won't the battery last a little bit longer?
To be safe of what? That it will work?

The battery is rated at 100mAh. So if you're drawing 50mA continuous, it would last for 2 hours.

LiPo batteries do not like to be deep discharged. If you completely discharge the battery, you risk a fire.

Quote
How do I charge that battery since its a rechargeable?

You need a LiPo charger.
http://www.amazon.com/Heli-Max-Charger-Novus-CX-LiPo/dp/B00272WUFC

How do you know when to stop charging, does the chargers have some kind of indicator?

It seems like that kind of battery is sold out everywhere I look do you have any tips on where I could get some of 'em?
Thanks for the information guys! (:

#### fungus

#13
##### Sep 12, 2013, 08:48 am

How do you know when to stop charging, does the chargers have some kind of indicator?

Hopefully it has an Arduino in it to stop charging when the voltage reaches a cut-off point.

Similarly discharge - cut the power when you reach a certain voltage, don't drain it completely (I believe those batteries should be kept inside the 20%-80% charge range).
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### Grumpy_Mike

#14
##### Sep 12, 2013, 08:50 amLast Edit: Sep 12, 2013, 06:52 pm by Grumpy_Mike Reason: 1
Quote
How do you know when to stop charging, does the chargers have some kind of indicator?

Good point. There are various methods.
Charge for a fixed time based on the charge current and mAh rating.
Monitor the temperature of the battery and stop when it starts to rise.
Charge until the charging current drops.

But you have to apply the right technique for the appropriate type of battery.

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