Charging Lead-Acid Battery in Parallel with Arduino

Hi,

I'm building a system that is physically located far from an outlet and can be periodically disconnected from external power supply.

So, I took the naive approach to put a 12V lead acid battery and plug it in parallel to Arduino Mega with Ethernet shield while AC charger is connected by a 30m wire. I know that I'm shortening the battery life due to bad cycle for such battery types, but I don't care here.

This approach didn't work at all, Arduino (or W5100) somehow manages to drive voltage down to 7.5 volts and completely to discharge the battery instead of maintaining charge.

I tried different types of power supplies, from transformer based to computer PSU with voltage ranging 12-14V -- nothing worked for me.

I only can use one pair of wires and I'm pretty much despair about the solution to that. Right now I'm trying to use car charger and power the whole thing from USB; seems to work but you know, it's ugly and unreliable. And I don't know how Ethernet behaves with that low voltage.

TL;DR. I'm certainly doing something wrong and missing something. What's the correct way to split single 12V power supply to charge a lead acid battery and powering Arduino simultaneously without any interference between them?

Thanks a lot!

Hi, sorry but we will need a diagram.

Can you please post a copy of your sketch, using code tags? Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png or pdf?

Connecting a mega directly to a 12V battery is not a good idea.

Tom..... :)

If the charger can provide a little more current than the average used by the Arduino it should keep the battery topped up and the Arduino functioning. If the charger cannot provide enough current then, inevitably, the battery will eventually discharge.

As long as the charge voltage is not too high a constant charge won't do a lead acid battery any harm - when the battery voltage is nearly the same as the charge voltage the charge current will be very small.

...R

You refer to a 30m wire but no information on the type or size of the wire. If you are using network cable you will have problems due to the resistance of the cable.

Weedpharma

Robin2: If the charger can provide a little more current than the average used by the Arduino it should keep the battery topped up and the Arduino functioning. If the charger cannot provide enough current then, inevitably, the battery will eventually discharge.

This ^^^ And all that wasted heat in the onboard regulator isn't doing him any favors.

faxik: Hi,

I'm building a system that is physically located far from an outlet and can be periodically disconnected from external power supply.

So, I took the naive approach to put a 12V lead acid battery and plug it in parallel to Arduino Mega with Ethernet shield while AC charger is connected by a 30m wire. I know that I'm shortening the battery life due to bad cycle for such battery types, but I don't care here.

This approach didn't work at all, Arduino (or W5100) somehow manages to drive voltage down to 7.5 volts and completely to discharge the battery instead of maintaining charge.

I tried different types of power supplies, from transformer based to computer PSU with voltage ranging 12-14V -- nothing worked for me.

I only can use one pair of wires and I'm pretty much despair about the solution to that. Right now I'm trying to use car charger and power the whole thing from USB; seems to work but you know, it's ugly and unreliable. And I don't know how Ethernet behaves with that low voltage.

TL;DR. I'm certainly doing something wrong and missing something. What's the correct way to split single 12V power supply to charge a lead acid battery and powering Arduino simultaneously without any interference between them?

Thanks a lot!

If your battery in draining down to 7.5 Volts due to the load from the Arduino then that tells me that your 30 Meter wire pair is doing absolutely NOTHING (ie open circuit?). Even with very thin 26 AWG wire you should not have more than a 2 Volt drop when drawing 1 amp across 30 Meter wire pair.

Do this ... Measure the voltage at the Arduino board, while running via 30 Meter wire WITHOUT the 12v battery connected. Now, is the voltage above 12 Volts or is the voltage below 12 volts?

Also, the Float voltage of a Lead Acid Battery is more like 13.2 Volts, not 12.0 Volts.

A fully charged lead acid battery will have an initial voltage of 14.6V.

Your supply should be designed to be able to supply this.

14.6 is too high to feed into an arduino I think but it depends on current draw. You need a regulator th step down to something more comfortable like 8 v.

If the voltage of the la battery dropped to 7.5 V you will have damaged it probably severely.

in this application I would suggest a constant current source driver with voltage limiting. This can be say a 20 v supply with a resistor so long as 20 v is not dangerous where you are. this is not the best arrangement but the addition of a 14.5 v Zener at the battery end will protect the battery from overcharge..

This by the way is a typical arrangement used for solar charging.