Strange power problem

I have an Adruino Mega2560 with Ethernet shield and two Nano's all connected to each other through I2C. The power supply comes from a 12v DC source which is put through a 9v regulator to power the boards via Vin. When I power the Maga through its USB and the Nano's from the 9v everything works perfect, but when I change the Mega to run from the 9 volts the SD card gets corrupted on any attempt to read or write it. I have also tried powering the Mega through the jack socket instead of Vin but still the same problem.

Tried running from the 12V directly? Also did you swap power inputs while the Arduinos were running?

KandS: I have an Adruino Mega2560 with Ethernet shield and two Nano's all connected to each other through I2C. The power supply comes from a 12v DC source which is put through a 9v regulator to power the boards via Vin. When I power the Maga through its USB and the Nano's from the 9v everything works perfect, but when I change the Mega to run from the 9 volts the SD card gets corrupted on any attempt to read or write it. I have also tried powering the Mega through the jack socket instead of Vin but still the same problem.

Show a diagram of your connections. Could be an earth problem between the various power supplies and your computer

Noobian: Tried running from the 12V directly? Also did you swap power inputs while the Arduinos were running?

Everything was powered down before swapping. Running it off the 12v, after a quick test seems to work, in the finished design the 12v supply can vary between 11v and 15v would the higher voltage not be a problem

Boardburner2: Could be an earth problem between the various power supplies and your computer

That was my first thought so I have checked and rechecked and everything has a common ground. I don't have a drawing as such but could do one tomorrow

You can NOT power a Mega (~70mA) with ethernet shield (~160mA) directly from 12volt. The onboard 5volt regulator will overheat and shut down (if you're lucky).

A 5volt cellphone charger (connected to the USB socket) is a good option. But it all depends on what else you have connected. Post a full diagram. Leo..

Wawa:
You can NOT power a Mega (~70mA) with ethernet shield (~160mA) directly from 12volt.
The onboard 5volt regulator will overheat and shut down (if you’re lucky).

That is my concern with using the 12v supply

Wawa:
A 5volt cellphone charger (connected to the USB socket) is a good option.
But it all depends on what else you have connected.
Post a full diagram.
Leo…

A USB charge is not really an option, that is why I have the 9v supply

I am guessing (lack of proper information) that you power everything (whatever that is) from a lead-acid battery.

The most efficient way (minimal heat) would be to bypass all the 5volt regulators on the Arduinos. Use a (reliable) 5volt buck converter, and connect it's output to the 5volt pins of the Arduinos. Leo..

Hi,
OPs circuit


What is your 9V regulator and do you have any bypass capacitors around it?

A more informative circuit would be a picture of a hand drawn circuit in jpg, png?

Can you post a picture of your project please?
So we can see your component layout.

Thanks.. Tom.. :slight_smile:

Wawa: I am guessing (lack of proper information) that you power everything (whatever that is) from a lead-acid battery.

The most efficient way (minimal heat) would be to bypass all the 5volt regulators on the Arduinos. Use a (reliable) 5volt buck converter, and connect it's output to the 5volt pins of the Arduinos. Leo..

The normal power supply comes from a 12v psu but has the potential to change over to a lead acid battery in the even of mains failure

KandS: ...to change over to a lead acid battery in the even of mains failure

In that case a 5volt buck converter is a better option than linear regulation. A switching buck converter basically halves battery drain. Here is an example from Pololu. Cheaper (lower quality/specs) clones on ebay. Leo..

Hi, Please answer post #8.

Thanks.. Tom.. :)

Ok after getting my wires crossed and blowing up the Mega board, I have rebuilt hoping the original problem wouldn't be there but it is. So what I have found out is the 9v causes the mega to corrupt the SD card no mater where I apply it ie Vin or the jack. 12v on the jack works ok, but this is not a long term option due to the load on the on board regulator. 5v to the vIn, so far has not caused any problems to the SD card, so this looks like the solution, I can just add a 5v buck regulator.

It would have been nice to know why the SD card was corrupting under certain power configurations but I suppose that just life

TomGeorge: Hi, Please answer post #8.

Thanks.. Tom.. :)

That diagram is basically it, stick 2 nanos and a mega onto the 9v, connect their I2c's together and that's it. The regulator is an LM7809 and a 0.33uF on the input and a 0.1uF on the 9v side

Hi, What is your 11V to 15V supply?

Tom... :)

TomGeorge: Hi, What is your 11V to 15V supply?

Tom... :)

It will normally be a 12v 15A but will have a lead acid battery as a backup in case of mains failure

TomGeorge: Hi, What is your 11V to 15V supply?

Tom... :)

It is a per-made 12v 15A psu but will have a lead acid battery to take over in the event of power failure

KandS: It is a [u]per-made[/u] 12v 15A psu but will have a lead acid battery to take over in the event of power failure

Sorry what is per-made? Tom... :)

Is your 9V supply able to provide enough current?

Smajdalf: Is your 9V supply able to provide enough current?

The total peak current draw is around 380mA so the regulator is operating well within its range