Problem with relay board connected to battery powered Nano.

I am attempting to use a 5v relay board with a Nano. When I have the Nano connected to and powered from my PC through the USB port the relay board functions as it should.

To clarify,

relay board Vcc to Nano 5v pin
relay board Gnd to Nano Gnd
relay board 1 signal to Nano I/O 7
relay board 2 signal to Nano I/O 8

All works perfectly until I power the Nano with my battery. It is a 1800mah 7.2v nimh 6 cell (for 1:10 scale rc trucks).

The battery connects to the Nano through Vin and Gnd. When I use the battery, the Nano seems to work fine. I get 3V from the I/O pins when they are set to HIGH. The relays will not fire though. The indicator LED’s on the relay board light up (very dimly) indicating a signal, but the relays will not fire.
I even tried connecting the relay board Vcc and Gnd directly to the battery + - (slightly over-volting them) and the same thing happens.

Anyone know what I am doing wrong here?

The relay I’m using is:

http://www.ebay.com/itm/231982434720?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

The battery is:

Thank you.

You need to investigate why you are only getting 3 volts from the Arduino pins. Should be close to 5 volts. The dim LED is another clue. Something is not wire as you have written that it is.

Paul

Just making sure, powering nano thru vin pin with 7.2v dc is within acceptable limits, right?

moses1592:
Just making sure, powering nano thru vin pin with 7.2v dc is within acceptable limits, right?

Right! But the 3v on the digital pin?

Paul

Bad nano regulator? With everything disconnected from the nano except the battery pack to Vin and GND, what voltage do you get at Vin and at the 5V terminal?

Only 3.2v at the 5v pin. I know that's not correct. For some reason though it works when powered through usb port.

With nothing connected and 3.2V at the 5V pin, nano's regulator is fried or you need a new battery for your multimeter.

I have another nano lying around and will try again with that one. One mistake I realized i had made was that I accidentally had the battery plugged in to vin while the usb port was connected to the pc. Only happened once but perhaps that could've blown the regulator.

Thank you for the help!

moses1592:
I have another nano lying around and will try again with that one. One mistake I realized i had made was that I accidentally had the battery plugged in to vin while the usb port was connected to the pc. Only happened once but perhaps that could've blown the regulator.

No. There is no problem powering the board from VIN and USB at the same time.

// Per.

You probably should do this to lighten the load from nano's regulator:

Thank you I will give that a try!

Well I got it work using another nano. Same thing happened though with the 5v pin, this one was only showing 3.8v for some reason. It still would not work using the 5v pin to Vcc. What ended up working was connecting the battery directly to the JD pin (with no jumper) on the relay board and omitting the 5v pin entirely (connecting ground, of course). Only issue is the relay board is being slightly over-volted by about 2.2 volts, hopefully this wont be a problem long term.

Could you post a picture?

It's the same setup as in your diagram above except the 5v is not connected to vcc (and no diodes between battery + and VD).

The setup is already installed in an rc truck. I posted some photos but I don't think you'll see much.

Here is the setup

For reply#4, what voltage did you get at Vin? (wondering if it dropped significantly)

Vin always stayed at 7.2v.

Are you by any chance having your program set the pin high and low very rapidly and your meter is just showing the average voltage?

Paul