Arduino program won't stay on when connected to a 12v battery

Other Hardware General Electronics
1

I have an Arduino UNO connected to four relays (3 12v LEDs and 1 12v Motor relay).

For simplicity I'm using the same 12v to Vin on the Arduinbo UNO as powers the LEDs and motor.

I've built and tested using a 120VAC to 12VDC transformer for months. It works perfectly in that arrangement. When I changed to a 12V lead battery, the system would initialize then turn off.

I measured the voltage from the transformer at 11.88 vdc, the rating is 800mA max at 12vdc.

I measured the voltage from the battery at 12.85 vdc.

My question is why is this happening and, more importantly, how do I fix it?

Thank you in advance for your help.
Ken

2

This sounds like a grounding and possibly EMI (ElectroMotive Interference) problem.

If you disconnect the motor relay does the rest of it work?

If you ground the Arduino/System to a local ground does it work?

See some about EMI etc. on the ArduinoInfo.Info WIKI HERE:

3

The voltage regulator on the Arduino may be overheating and shutting down. 12.85 V is slightly above the allowed voltage of some boards. You can reduce the input voltage using diodes (1N400x) in series with the lead from the battery to the Vin input -- each diode will drop about 0.7 V.

4

ShowerMaster:
My question is why is this happening and, more importantly, how do I fix it?

Try putting your finger on the Arduino voltage regulator when it's running...

5

What about a L7808ACV voltage regulator? That puts the voltage to the ARDUINO mid range of the recommended.

BTW. Because the motor current is about 10 amps it has not connected

6

Voltage reg did the trick. Yeah! Thank you all. I found a nifty heat sink to mount it. I'm golden.