Controlling 24V ball valve via relays and temp reading problems
I'm confident it's not a software issue either. My client and I are fairly sure it is an isolation/interference issue with the power supplies.
So just to really ask a dumb question: what exactly do you mean by tying the wires together.
Do we simply connect the 2 DC negatives together after relevant power supply terminal, or do we connect them both to ground?
So we would have both DC return wires come back to their relevant power supply, but then also connect those same wires together or connect to ground rail in power box. Tying those wires to ground rail would ground them out through 240AC ground
Yes, that is correct. All grounds should be tied to one point (STAR) to prevent ground loops.
If the DC PS's have an AC ground, they should be included.
Thanks for the assistance Peter. I am sure these are fairly simple questions, but we all start somewhere.
We are trying tying the DC negatives to each other as a starting point.
The 24V power supply has a 240V earth, so we will tie that to 240V GND.
The 12V power supply does not have a 240V AC GND terminal so I guess there is nothing we can do there.
If connecting the 2 DC negatives together works ok, we will them tie them both to 240V GND.
We are still getting temp fluctuations when 24V current is flowing
Does this diagram look correct?
- White box is 24V power supply
- Grey box is 12V power supply
- First pair of joiners (not sure what you call them) is 24V distribution out to ball valves
- Second pair of joiners is 12V distribution out to Arduinos
Are the DC negatives tied together (blue wires)?
The DC negatives are the brown wires. I should have mentioned that.
They are tied together by a loop under the joiners (not sure what you call them).
Should we tie them at the actual power supply?
I've updated the image with the common loop denoted
OK. At this point, I'm stuck. Without the schematic, devices being used etc., more pics, I can't venture much more. You might try shielding the probes.
Alternatively, email us... info then_the_at_sign brucontrol.com
Thanks again for your help.
I'll update my wiring diagrams and send them through when ready.
Turns out I bought a cheap shitty PT100 cable with no or poor shielding. At home, it was not coping with the electrical noise of the fridge compressor starting up, or shutting down.
I "shielded" the cable by **cough** wrapping it in tinfoil and earthing it to the arduino. Temp has stayed rock solid through about 25 cycles of my fridge. It was definitely tripping every time the fridge was turned on or off pre-tinfoil.
Now fingers crossed the same thing applies to my clients installation. May look at shielding foil/braiding if the tinfoil works though as it's probably not the best look for a brewery to have their cables wrapped in tinfoil. ha ha
Great to hear! I know of another user or two who sourced cheap probes and have noise... so this makes sense.
Might be worth adding a caution to the RTD wiring guide to mention shielded cables and earthing the actual shield may be necessary depending on electrical noise in surrounding area. It would have saved me a few days stress (and my client stressing).
Just upgraded to 1.1, but I'll have to leave testing the api until tomorrow night. I seriously need some sleep. I've been up until 1am the last few nights trying to get this problem sorted out.