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Topic: 12 V Rechargable battery (Read 875 times) previous topic - next topic

j_derius

-Hi guys,

I have to find a solution for the project I'm developing which consist in 1 arduino uno, 12V stepper motor, 1 miniservo and 1 lcd shield. My problem is how to supply the energy in order to make it as portable as possible: the idea is to make it fully indipendent from external energy.
Of course the first Idea is to use a rechargable 12 Volt battery (possibly cheap and small).
So, I'm very ignorant in this matter, I don't really know which kind of battery I would need or if there are limitations, I just like to know what you think about the battery I've found here:
http://www.diotronic.com/alimentacion/pilas-y-baterias/baterias-de-plomo/bateria-800ma-12v-96x25x61-5_r_358_8434.aspx
http://www.diotronic.com/alimentacion/pilas-y-baterias/baterias-de-plomo/bateria-800ma-12v-96x25x61-5_r_358_8434.aspx

Are they compatible with the project I'm doing? Then do you think is it possible to recharge it with a common DC 12V power supply? or do I need something different? or maybe I'm totally wrong?

Thanks a lot

jd

cr0sh


-Hi guys,

I have to find a solution for the project I'm developing which consist in 1 arduino uno, 12V stepper motor, 1 miniservo and 1 lcd shield. My problem is how to supply the energy in order to make it as portable as possible: the idea is to make it fully indipendent from external energy.
Of course the first Idea is to use a rechargable 12 Volt battery (possibly cheap and small).
So, I'm very ignorant in this matter, I don't really know which kind of battery I would need or if there are limitations, I just like to know what you think about the battery I've found here:
http://www.diotronic.com/alimentacion/pilas-y-baterias/baterias-de-plomo/bateria-800ma-12v-96x25x61-5_r_358_8434.aspx
http://www.diotronic.com/alimentacion/pilas-y-baterias/baterias-de-plomo/bateria-800ma-12v-96x25x61-5_r_358_8434.aspx

Are they compatible with the project I'm doing? Then do you think is it possible to recharge it with a common DC 12V power supply? or do I need something different? or maybe I'm totally wrong?

Thanks a lot

jd


Your main thing would be knowing how much current in total your project will draw; once you know that, then you can decide how long you want it to run on battery, in order to figure out what the total amp-hour rating of the battery should be.

For instance, that battery is an .8 Amp-Hour (800 mAh) battery; what this means is that if your circuit draws (on average) 800 mA, you will get 1 hour of run-time (this is simplified - more on this later). If your project only draws 400 mA, you would get 2 hours of run time. If it draw 1600 mA, you would get .5 hours of run time. See how that works?

Now - the reality of the situation is different. You will -never- get that perfect run time; due to internal resistance of the battery, and other factors (external temperature and the heating up of the battery as it is used, among others), the actual run-time will be much different. You also should adhere to the C10 rule of charge/discharge - otherwise the battery could be over-stressed and ruined. The best way to figure out all of this, would be to consult the datasheet for the battery; it will have all the information you need to determine whether it will fit your application (of course, you -must- know how much current your project will draw before you can do anything - so figure that out first).

Now - as far as charging a lead-acid battery? Once again, you need to follow the C10 rule for the battery; if you don't you can damage the battery. If you can follow it, then you can plug in an appropriate 12 VDC wall-wart capable of supplying the C10 current needed (or less - you never want to go greater, unless the battery is rated for it, or you don't mind shortening its life - this is a so-called "quick-charge" mode, some batteries can handle it, some can't - but in just about all cases, it wears the battery out quicker) - and then charge it for the needed time (but no longer - you can just plug it in and let it go).

This only applies to lead-acid batteries, by the way - if you want to use NiCd or NiMh (or if you want a "plug it in and forget it" charging capability with lead-acid), you would need to build a charger. If you want to use a rechargeable lithium battery of some time (Li-ION, Li-Poly) - those need special chargers, and are really outside the scope of a beginner (because if it isn't done right - such batteries have a nasty habit of explosion and fire).

:)
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

j_derius

Thanks a lot cr0sh!

Your explanations will be very helpful.

the stepper motor I'm using draw about 250 mA, I don't know about the servo since I can't find the datasheet, not even in the product website, the same about the Lcd but I guess they draw very few current (the servo is a micro servo). The point is, they will never work in the same moment, so I think I shouldn't need something that give me more than 500 mA,then the device shouldn't work for more than 1 hour.

About charging, that's a issue I really don't know much. I've googled a bit this c10 rule but I didn't find anything explain me precisely what you mean then I would need to know something more about it.
some quesitons:
can I charge a 12V 800 mA battery with a  DC 12V wall-wart power supply without damage the battery?
Is there a time limit in charging it?
how can I ensure the battery is fully charged?
can I plug the charger in the way I can use it as a power supply meanwhile I charge the battery?

For sure I'm not skilled enought to build a charger so I have to find the easer solution.

thanks again for your attention

jd

a.d

To get a rough idea of current usage you could hook up a multimeter in ammeter mode.

Si

It may be an old technology, but I have come to the conclusion that I like using lead-acid batteries. They are a lot less fussy about how they are charged than NiMh's or LiPos. I used them in my solar radio (http://srmonk.blogspot.com/2011/09/arduino-solar-radio.html) mainly because they are quite happy being trickle-charged with a current that frequently varies by a factor of 10 depending on the weather (I live in England).
--
My New Arduino Book: http://www.arduinobook.com

j_derius

Thanks SI,

I think I finally use one of them as from what I've learnt during  the last days it seems much simpler.
Thanks

jd

MarkT


It may be an old technology, but I have come to the conclusion that I like using lead-acid batteries. They are a lot less fussy about how they are charged than NiMh's or LiPos. I used them in my solar radio (http://srmonk.blogspot.com/2011/09/arduino-solar-radio.html) mainly because they are quite happy being trickle-charged with a current that frequently varies by a factor of 10 depending on the weather (I live in England).


Unfortunately lead acid batteries cannot tolerate over-discharge, even for short periods, and they lose capacity and lifetime if you let them fully discharge.  NiMH are much more resistant to this I think - so it rather depends on whether you expect the battery to become fully discharged.  Lead acid should be stored fully charged and regularly topped-up in storage.
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