As you can see now (with the full schematic), the processor runs off 3.3v which it gets from a LM2576-3.3 switching power supply. The 7805 exclusively supplies the relays at this stage.(1) power your relays before the 7805 of your controller or from a different 7805
Is the power for the processor derived from the same supply as powers the relay coils?
I don't know anything about varistors, so I will investigate this option. Thank you!(2) use a varistor with correct voltage (130Vac or 250Vac) in parallel with the NO contact of each relay
To the same ground plane that runs under the relays and where everything else is also grounded....Where is the processor chip ground connected?
1K 1/4WWhat base resistors are you using between the processor and the transistor bases?
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To the same ground plane that runs under the relays and where everything else is also grounded....
I expected it, so the news isn't that bad. In hindsight I wonder how I didn't see this coming. Lack of experience, I reckon. Your advice regarding separate grounds makes a lot of sense and I will definitely be doing that with the next version of the PCB.You ain't gonna like this; but that is likely the problem.
I hope I understand your question here correctly. Let me first say that the pumps won't be directly switched by the relays on the PCB. Each PCB relay will switch another external relay which in turn switch 3-phase contactors which finally turns on the 3-phase pump motor. Single phase AC is 240V/50Hz in South Africa. In a distribution panel the neutral bus bar will be connected to earth, normally via a copper rod that is driven into the ground.Since in your application, the problem gets worse when you connect the AC loads, is the ground on the board connected back to earth ground? I am not familiar with how they do AC power distribution in your country, but it is possible that the pumps are inducing a ground current some of which flows through your pc board. That would require a thorough analysis of where every wire that touches your PC board ground goes...
The gist of my question about the power distribution grounds is this: Does your PB circuit board connect to multiple external devices, each of which find their own respective paths to earth ground?
If so, if there is any significant voltage gradient between the disparate ground locations, then you might have current(s) flowing from one edge of your pc board to the other which are induced externally, such as the inrush during motor starting.
edrean said:I mounted the same relay setup as I have on the PC board (relay, LED, 2N2222A, diode), on a piece of stripboard. From the stripboard I then pulled the needed 5V, the signal as well as ground from the RELAUX box header on the PCB (that's what it's there for ). I then wired a 240V 60W incandescent lamp through the relay. This seemed to work fine. I couldn't get the processor to act up again.
Extend your simplified drawing a little. Add the power supply which runs the processor. Where is it's AC input connected? Line to Neutral or Line to Line?
Is there an Ohmic connection from the processor ground symbol to "earth" ground, either directly or indirectly?
You will see on the schematic, posted previously, that there are two voltage regulators. One is a linear 5V regulator (7805) and the other is a 3.3v switching regulator. The processor runs off 3.3V and the relays run off 5v (thus different regulators). Both regulators get their input voltage from the PWR connector (refer schematic). A regular (transformer type) 12v DC adapter is used to provide +-12v to the PWR connector and subsequently to the regulators. The processor's ground is ultimately connected to the negative of the 12V adapter. The adapter is plugged into a regular mains wall socket.
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Could you temporarily supply the 12Vdc to the processor board from a small 12V SLA battery? That would eliminate the possibility that a transient is being coupled through the wall-wart's transformer (either inductively, or due to capacitance between primary and secondary windings).
I'm still trying to get you to tell me if the neg side of the 12V DC supply (when plugged into the processor board) has Ohmic continuity to the ground pin on the AC socket that the Wall-Wart is plugged into?
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