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### Topic: I have a "newbie" question about battery current (Read 3063 times)previous topic - next topic

#### Max_Maker

##### Jan 02, 2013, 02:58 pmLast Edit: Jan 02, 2013, 03:05 pm by Max_Maker Reason: 1
Hi everyone. I'm thinking about connect arduino to a 12 V DC battery car, but i have before to find out two things:

- An electronic device, when it's connected to a battery, only gets the amp required or the battery gives more and the device breaks?

- A voltage stabilizer is good or i need one with current limit?

The thing is that i want to connect to a battery car delicated electronic (12 V stabilized, no much current) and a lipo battery charger (11-15 V, a lot of current) and i don´t know if i can use a little regulator for the first thing or it must be higher because the battery.
All this it's because a battery have 13,8 V peaks, etc.

To sum up, i mainly want to know if a device "gets the amp required or the battery gives more and the device breaks" and if an stabilizer heat up although it require a little current.

Thanks!
Fácil, sencillo y para toda la familia.

#### fungus

#1
##### Jan 02, 2013, 03:21 pm

Hi everyone. I'm thinking about connect arduino to a 12 V DC battery car, but i have before to find out two things:

- An electronic device, when it's connected to a battery, only gets the amp required or the battery gives more and the device breaks?

The amount of current that flows will obey Ohm's law.

It can't give more than that without breaking the fundamental laws of physics.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### Max_Maker

#2
##### Jan 02, 2013, 04:22 pm
Estaba hablando de que si da más amperaje del que el aparato electrónico soporta.
I = V / R, aplicando al circuito si la intensidad interna de la batería es baja, podrá dar más amperios. Seguramente te estarás refiriendo a la hora de calcular la I que requiere una resistencia, como el aparato, y es I (requerida) = V (batería) / R (aparato), but i ask, get sure and don't break anything.
Fácil, sencillo y para toda la familia.

#### Grumpy_Mike

#3
##### Jan 02, 2013, 04:28 pm
Quote
An electronic device, when it's connected to a battery, only gets the amp required or the battery gives more and the device breaks?

It depends on the device you are powering. If the device is designed to be powered with 12V then that is correct. However some devices are dependent on being driven at the correct current not voltage. For example an LED needs to be driven at a fixed current not a fixed voltage.

Quote
A voltage stabilizer is good or i need one with current limit?

A voltage stabiliser is needed if the voltage you have is too large for the device you have. A stabiliser with a current limit is only useful for protection if something goes wrong. Once the protection kicks in it no longer has the same voltage output.

#### kf2qd

#4
##### Jan 02, 2013, 05:02 pm
If the current was controlled by the supply then each and every one of us would have a serious problem in our homes. The power company supplies MEGAWATTS and we use KILOWATTS, if the device using the power was not the limiting factor on our usage our houses would have all burned down yers ago.

#### vasquo

#5
##### Jan 02, 2013, 05:21 pm
If your load is using up 100 milliAmps (mA), then it will only draw 100 mA even if your power supply (in this case, a battery) is capable of supplying a lot more.

#### fungus

#6
##### Jan 02, 2013, 05:23 pm

Estaba hablando de que si da más amperaje del que el aparato electrónico soporta.

If you know the volts and the resistance then you know the current that will pass.

Is the current too much? That depends only the device, it has nothing to do with the power supply.

eg. If you have a 5V, 1000000000000000000000000000 amp power supply connected to a 100 Ohm resistor then only 0.05 amps will flow. No more, no less.

You seem to know Ohm's law, but you don't yet believe it.

I = V / R, aplicando al circuito si la intensidad interna de la batería es baja, podrá dar más amperios.

No. If the voltage is lower, the amps will be lower.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### Max_Maker

#7
##### Jan 03, 2013, 11:46 am
Ups, intensidad interna no, ¡resistencia interna!, se me ha ido la mano. Lo trabajo con las baterías Lipo, que pueden entregar mas corriente cuantos más "C" tengan, y estos dependen de su resistencia interna.

Thanks everyone for the replies, yes, was obvious:

If the current was controlled by the supply then each and every one of us would have a serious problem in our homes. The power company supplies MEGAWATTS and we use KILOWATTS, if the device using the power was not the limiting factor on our usage our houses would have all burned down yers ago.

But i want to ensure that. Electronics are so expensive... =)

Greetings.
Fácil, sencillo y para toda la familia.

#### AWOL

#8
##### Jan 03, 2013, 11:56 am
Quote
Electronics are so expensive

No, happily, they're about as ludicrously cheap as I can ever remember them.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

#### Nick Gammon

#9
##### Jan 03, 2013, 12:15 pm
Yeah, I bought 500 x zero-ohm resistors for \$4.

Can't do much better than that!
Please post technical questions on the forum, not by personal message. Thanks!

http://www.gammon.com.au/electronics

#### retrolefty

#10
##### Jan 03, 2013, 05:34 pm

Quote
Electronics are so expensive

No, happily, they're about as ludicrously cheap as I can ever remember them.

Correct, but I guess it depends on the users definition of 'electronics'. Apple iPhones are expensive but raw electronic components have never been cheaper in my lifetime as they are now, plus the internet opens up a worldwide seller/buyer connection making component selection and purchases easier then ever.

Bottom line, there has never been a better time to enjoy electronics as a hobby.

Lefty

#### retrolefty

#11
##### Jan 03, 2013, 05:46 pm

Yeah, I bought 500 x zero-ohm resistors for \$4.

Can't do much better than that!

Interesting. Usually these are used instead of simple bus wire runs when having to use auto insertion machinery, not for hobby use. But I did a quick search on 28 gauge tinned copper bus wire and couldn't find any cheaper per foot (assuming a 2.5" resister length) then your purchase price! Of course you are limited to the pre-cut lengths of the 0 ohm resistors, where with bus wire you can use any length you require to bridge two points.

So what was your reasoning for purchasing those, just couldn't pass up a bargain?

Lefty

#### JimboZA

#12
##### Jan 03, 2013, 05:51 pm
[zen]If a resistor has no resistance is it still a resistor?[/zen]
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)

#### retrolefty

#13
##### Jan 03, 2013, 06:09 pm

[zen]If a resistor has no resistance is it still a resistor?[/zen]

Of course it is, if for no other reasons then the lead wires have a finite resistance. Zero ohms is just a figure of speech, so zen that.

#### Max_Maker

#14
##### Jan 05, 2013, 04:03 am

Quote
Electronics are so expensive

No, happily, they're about as ludicrously cheap as I can ever remember them.

I wish but I am afraid I have to disagree with you.
Like Retrolefty said, it depends on the device. I want to connect a FPV system to my car battery, and that doesn't have the resistors price, haha. Also, the Arduino to control A/V and power supply switches.

Greetings.
Fácil, sencillo y para toda la familia.

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