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Topic: Best way to power Arduino Uno with 12V Lead Acid + monitor battery charge (Read 129 times) previous topic - next topic

mr_c265

Hey all,

I'm pretty green to this whole thing, but i've been researching it for a while and have come up with a pretty good idea (I hope at least) for a project.

I want to power an Arduino Uno as well as a few water pumps controlled via a relay with a 12V lead acid car battery (which is not attached to a car) I know the voltage at full charge starts off quite high and this could be an issue with respect to heating up the voltage regulator on the board. I've had a pretty good look around and seen this question answered many different times, many different ways, but from what I've found it's mainly been with the battery installed in a car and without concern for the efficiency.

Basically, I want the battery to last as long as possible and as I understand it the voltage regulator is fairly inefficient, particularly at higher voltages, so I wanted to try to avoid going from the battery straight to the Arduino. So I've had a few ideas:
Buying a cheap 12V to USB off ebay
Voltage divider (probably more inefficient than the regulator?)
LM7805 and caps

Which way should I go to give the longest time possible between charges?

And, whilst I am here, I would like a way to monitor the  battery to determine when I have to charge it again, being lead acid simply measuring the voltage should suffice, so it needs to be <5V, would it be best to use a voltage divider or is there a better way to do it with Zener diodes?

jremington

Here are my suggestions:

Use a resistive voltage divider to reduce the (up to) about 15 V down to about 5V. 220K and 100K will form a 3.2 to 1 voltage divider, without wasting much power.

Use a step-down switching regulator for maximum efficiency and bypass the barrel jack, as the onboard regulator wastes power as heat. To do that, use a 5V switcher and power the Arduino via the 5V terminal.

Power the relay(s) with a separate regulator, or use the battery voltage directly for the relay power, if appropriate. Observe the maximum current ratings of the regulators.

Here is a good selection of inexpensive, efficient step down regulators, from a trustworthy (non eBay) source: http://www.pololu.com/category/131/step-down-voltage-regulators
"It seems to run on some form of electricity"

tylernt

Good advice jremington. For the relays, I prefer to use relay modules that already have the transistors and flyback diodes. They are usually 5VDC so the coils can be run off the same supply as the Arduino (unless you want to energize a bunch of them at a time which may stress the power supply).

One more thing -- I don't recommend using a car battery. Car batteries are designed to deliver a lot (100s of amps) of power for a short (seconds) time. For a more moderate load for a longer period -- like, for example, water pumps -- a deep cycle marine battery would be far more suitable.

mr_c265


Here are my suggestions:

Use a resistive voltage divider to reduce the (up to) about 15 V down to about 5V. 220K and 100K will form a 3.2 to 1 voltage divider, without wasting much power.

Use a step-down switching regulator for maximum efficiency and bypass the barrel jack, as the onboard regulator wastes power as heat. To do that, use a 5V switcher and power the Arduino via the 5V terminal.

Power the relay(s) with a separate regulator, or use the battery voltage directly for the relay power, if appropriate. Observe the maximum current ratings of the regulators.

Here is a good selection of inexpensive, efficient step down regulators, from a trustworthy (non eBay) source: http://www.pololu.com/category/131/step-down-voltage-regulators


That's perfect thank you! Being in Australia, I might try to find a voltage regulator with cheaper shipping, but that looks like a good way to do it. Would I be better to hack a USB cable and power it through the USB port or just straight through the 5V?


Good advice jremington. For the relays, I prefer to use relay modules that already have the transistors and flyback diodes. They are usually 5VDC so the coils can be run off the same supply as the Arduino (unless you want to energize a bunch of them at a time which may stress the power supply).

One more thing -- I don't recommend using a car battery. Car batteries are designed to deliver a lot (100s of amps) of power for a short (seconds) time. For a more moderate load for a longer period -- like, for example, water pumps -- a deep cycle marine battery would be far more suitable.


Absolutely, I already have a relay module with all the transistors that runs on the 5V, I think they're only 20mA each and looking at 2-4, so not too much draw.

I was only leaning  towards a car battery as I had a spare. I might go for one of those smaller SLA battery's then, I believe they can be drawn continuously.  Thanks heaps!

bluejets


mauried

The cheapest 12V to 5V switching regulators you can find are cigarette lighter USB adapters for cars.
They can provide up to 2A at 5V which is plenty for an Arduino.
Ive seen them for as low as $2 in places like the Reject Shop.
Auto shops also have them.

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