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[Reply #15 on:]

The real danger here in using a car battery is not about too much current or voltage or whether a plug in USB power supply is OK or not (They aren't except for the same class of load as the reg on the Arduino board could handle (the NCP1117 is a 1A low dropout reg)... the real danger is from the hydrogen generated in the battery, if the battery is vented, so is the hydrogen and an air or worse oxy/hydro mix in the battery will if ignited, spread sulfuric acid about the area with a rather large force. Not highly desirable or advisable and Yes, I've done it, with a motorcycle battery... was charging it, forgot about it and put a lit cigarette near the gas discharge tube... blew up ALL over my kitchen.

Doc

[Reply #16 on:]

Whoa ....  explosion + sulphuric acid. Blecch.


Anyway back to the original question, I used to wonder if you could get "too much power" from something like a large battery (or a big power supply), but think of it like this ...

If you go into a hotel where they have a "buffet" dinner (where you help yourself) you can't have "too much food". You will stop eating when you have had enough, regardless of how many thousands of people there might be food for.

However you can have too little, like if there was a single biscuit.

So think of a power source as something you can't have too much of (current-wise anyway) but you can have too little.

Of course you can have too much voltage, or the polarity the wrong way around, or the wrong sort (eg. AC rather than DC).

[Reply #17 on:]

Finally, the sweet voice of Reason.

Doc

[Reply #18 on:]

put a lit cigarette near the gas discharge tube... blew up ALL over my kitchen.

Doc

Well, the Surgeon General did warn you that smoking is dangerous for your health, Doc

[Reply #19 on:]

I shall now forever associate 9 volt batteries with a single biscuit.

[Reply #20 on:]

Does that mean you can smoke biscuits too?

Doc

[Reply #21 on:]

Besides the charging dangers (actually shouldn't be a big problem if the correct charger is used), those are able to deliver a huge amount of energy. This means that you must be super mega extra careful about short circuits, which can easily happen even when we're super mega extra careful - we usually have our minds set in something else other than the battery wiring. It can melt a screw driver, and will spark and emit "lightning" like an arc soldering machine (that's actually the same principle). Ideal would be to get a small battery (under 7Ah) or rechargeable AA cells or a wall power supply. A fuse is a must have, with proper wiring and isolated & firm connections.

[Reply #22 on:]

Your Arduino can not handle that huge current.

I'm really starting to wonder where this misunderstanding comes from...    it's quite popular lately.

[Reply #23 on:]

It's always been popular.  It stems from people not understanding the fundamentals of electronics.

They try to run before they can walk.

One of the failings of the Arduino:  It encourages it.

[Reply #24 on:]

I'm really starting to wonder where this misunderstanding comes from

Not knowing ohms law and seeing that the arduino is "rated" at a small current and the power supply "rated" at a large current. They think the two ratings have to match before it is safe, like it is with voltage.
That is why I wrote this a few years back:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

[Reply #25 on:]

Hi all,
  I'm creating my first arduino project, and I'd like to power it with a car battery; it gives 12V-DC, and I think arduino can use it, but I have some external electronic components that need 5V (lcd, relay, etc).

Can I supply 12V to arduino, to Vin pin, and get 5V from the "5V" pin for external components?
It is a simple question, but I'm a newbie and I don't wont to break my arduino

Thanks

NO, DO NOT CONNECT 12volt to Vin Pin. You can only connect 5volt to Vin pin. You can safely connect the 12volt battery to the power in socket - positive centre negative outer.

[Reply #26 on:]

NO, DO NOT CONNECT 12volt to Vin Pin. You can only connect 5volt to Vin pin.

Sorry this is wrong.
Vin is connected to a voltage regulator. You can feed any voltage from 7.5V to 24V in this connection.

[Reply #27 on:]

Majenko, You have the Right of IT.

Doc

[Reply #28 on:]

I'm really starting to wonder where this misunderstanding comes from

Not knowing ohms law and seeing that the arduino is "rated" at a small current and the power supply "rated" at a large current. They think the two ratings have to match before it is safe, like it is with voltage.
That is why I wrote this a few years back:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

Mike on the subject of your tutorials, which I think are really good- except I was just reading the Power one, where you say this:

Power is defined in Physics as the ability to do work

Wouldn't it be more correct to say that

Energy is defined in Physics as the ability to do work, and Power is the rate at which that happens

(Energy and Work being in Joules, and Power in Joules/second....)

[Reply #29 on:]

Yes good point. I was trying o keep it simple, looks like I over simplified it which is not what I aim to do.