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Topic: Power Arduino with lead accumulator? (Read 794 times) previous topic - next topic

exkoria

First post here! I'm just starting out arduino develompent and I'm trying to build a time-lapse dolly. So for the electronic I use an arduino board, an easydriver stepper control and a stepper motor.

So, this thing needs to be a bit portable so I want it to be powered by a lead accu because the time-lapse should be able to run for at least 3h or so. I can of course power the arduino board with seperate batteries but I was hoping to skip that and power everything from the same source.

What do I need to take into consideration if connecting the arduino to a rather big lead accu? Let's say 6V, 4Ah. Do I need to do anything so that the arduino is not fed to much power or so?

Thanks for help!

DVDdoug

#1
Jan 14, 2013, 11:45 pm Last Edit: Jan 14, 2013, 11:50 pm by DVDdoug Reason: 1
Quote
Let's say 6V, 4Ah. Do I need to do anything so that the arduino is not fed to much power or so?
Actually, you'd like to have a bit more voltage.

The actual current "drawn" by the Arduino depends on the Arduno and what's plugged-into it.   The amperage (or wattage or volt-amps) for a battery or power supply is the maximum it can supply.  For example, if you connect the Arduino to a 12V / 500 Amp car battery, it will still use only a few milliamps.  Typically the voltage is (relatively) constant, and the current depends on the load.  (Ohm's Law.*)   

Or if you touch the terminals on your car battery, you won't even feel it, because 12V can only "push" a few microamps through the megohm resistance of your body.   (You can get a dangerous shock while connecting/disconnecting a car battery because the coils can generate lots of voltage.)

The specifications say that the Arduino can run from a 5V regulated source, or from an unregulated source of 6-20V, with a recommended minimum of 7V.     The regulator needs some "extra" voltage to work, so you could have problems as your 6V battery starts to discharge and falls below 6V.    You can run it from 5V, or from 6-20V, but you should not run it between 5V and 6V.





* We don't actually know the impedance/resistance (Ohms) of the Arduino, and it varies depending on conditions.   But if we measure the voltage & current, we could calculate the effective impedance, if for some reason we wanted to.  The important thing is to understand the relationship between Volts, Ohms, and Amps...   If you want to increase current (Amps), you usually need to increase the voltage, or lower the resistance.


arbutus

Exactly.  Start with a 9v or 12v battery - I suggest a sealed lead acid type which do not off-gas and can be safely used sideways without leakage. These are commonly available.

Secondly you should use a voltage regulator to suit your MCU, normally 5v but some are 3.3v.  Simple regulators are available such as LM7805 which will take a supply voltage and output a fixed voltage for the MCU.  All you need in addition to the regulator are some capacitors.  Check out http://www.digikey.com  or  http://www.mouser.com  etc for some components.  The manufacturers datasheets show example circuits. 
Don't breath in the magic smoke!

MarkT

With batteries like lead-acid or lithium-polymer which can provide very heavy currents should a short-circuit
happen, you should have a fuse - otherwise a short could damage the battery or wiring or  start a fire.
[ I won't respond to messages, use the forum please ]

exkoria

Thanks for the replies! The reason I want to use a 6V accu is because the stepper uses 4.5V. The easyDriver stepper controller has a built in regulator so I should be able to connect the 6V just as is and the easyDriver board takes care of that. If I use a 12V accu it feels like a lot of heat will be generated from the EasyDriver regulator?

Perhaps I can connect the 6V to a regulator that outputs 5V and use the USB connection instead? Would that be better?

Thanks again

Leon Heller

Or, connect the 6V to a switching boost converter delivering, say, 9V. They are available quite cheaply on Ebay.
Leon Heller
G1HSM

exkoria

Thanks for the reply. I guess I can do that also but what is the advantage of that over my suggestion?

Thanks again

Leon Heller

Leon Heller
G1HSM

dc42

Most Arduinos these days use low dropout regulators, so running them from 6V or even 5.5V should be fine, provided you are not drawing much power from the 5V pin. Look up the datasheet for the voltage regulator on your particular Arduino. If it isn't a low dropout type, use an external low dropout regulator instead.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

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