Strange RTC reset on VIN power up??

Other Hardware General Electronics
1

This is my first post on here, so hello....I'm Craig!

I've been playing with various arduinos for years and know my way around electronics. I have built a project that measures three phase voltages (safely....transformers, resistors, fuses etc) and it records to an SD card with date/time stamp from DS1307. The unit is normally powered by a separate psu, but I was getting a strange reset of the date and time to default 2000,01,01,00:00:00 etc...

My first thoughts were backup battery...checked and all fine!

I then plugged the arduino into my laptop and turned just the arduino board on via its separate PSU and set the time, turned power off...waited a minute and turned back on, it worked!

Through various testing, as soon as I turn the three phase voltage on, the RTC resets back to default. Now the incoming voltage is dropped down to 3.5v MAX via transformers, diode rectification, capacitors, resistor/variable resistor decider and fuses. There are no differences in voltages between the three smaller voltages (I.e they aren't a on a different wave cycle because they are fully rectified DC signals) but I cannot work out why when I only turn the voltages on, it would reset the RTC which is something completely separate??

Just a random thought, are RTC's susceptible to interference from EMF??

Any thoughts would be greatly appreciated!!!

Craig

2

This isn't a programming question, so I'll move it.

Can you post a circuit diagram? It sounds like something electrical.

3

Try providing a separate power supply to RTC & then try. Also keep 0.1 mfd cap parallel to Power supply.

4

After the incoming voltages have been converted to 3.5VDC max, how do you monitor that with the Arduino? It may be that the Arduino is being partially powered from these voltages via the pin protection diodes. If so, then a fix is to add series resistors. Post your schematic.