In my diagram, the line (inside the OEM PS box) between G and -24 was to show that there was an internal connection between them. I guess to be more accurate, the label on the OEM power supply should be: L | N | G | +24 | +24 | GND | GND | GND2 | +5 . There is continuity between G, the two GND’s and the case. GND2 only works with the +5 volts. The new one is labeled L | N | G | +V | +V | -V | -V with no continuity between GND and -V (or the case), so I think you make a good point, the new supply could be used for either polarity. Either way, it’s working as it’s currently wired.
Onward, to the next problem!
There are a couple of ways parallel switch mode supplies are used, either for redundancy or current sharing. In order to share current you need all of your supplies to be designed for it.
If you have redundant supplies you want there to be some difference in the actual voltage. The supply with the higher voltage will provide power to the load. When the voltage drops below the output voltage on the 2nd supply, the 2nd supply with start providing power.
This is a pretty common setup for PLCs.
I didn’t mention this in prior posts but you do need to have protection diodes to protect the supplies from flyback voltage but that’s also true for a single supply. These days, all decent supplies have inbuilt protection.
That is exactly what I pictured from your initial description.
I don’t see any issue with what you have there.
Those Arduino modules make switching so easy don’t they.
My next-door neighbor was the commander of the hospital at the Naval Acadamy. When his staff would tell him that they had a problem, Robert would say “There are no problems, just opportunities for solutions”. That statement had a profound effect on how I look at things.
Hi, I can’t confess to being an expert on engravers and adding power supplies. I have however spent my entire career working in the electronic security industry on all various voltages AC, DC, I volt to 440 volts. It was always common practice to connect all the common, ground, earth or any other name for the negative supply to each other. For example, if you were connecting a 24 Volt Fire Alarm activated Output to a 12 Volt intruder alarm and a 12-volt communication device you would ensure all the commons or negatives are joined together. The positive would be supplied by the correctly rated power supply and they are not joined like the common terminals. It is safe to join the two 24 Volt power supply ground terminals together assuming that the ground, common or earth is either a permanent 0 volts and doesn’t change polarity when any relays activate. I would recommend testing each common, ground or earth output before joining them together. Note, if the negative terminal is crossed with a voltage terminal it should only blow a glass or thermal fuse without damaging the power supplies. Relays normally use dry contacts and state what the incoming and outgoing voltage should be, along with the maximum load available in Watts or Amps. I hope this helps but if you have any problem send me some photos along with the specifications of everything you want to join together and I will draw you a circuit diagram on how to connect the commons, grounds or earths. INFO Different devices call terminals by different names but the following are all the same - Negative, Minus, -Volts, 0 Volts, common ground or earth. Hope it works ok regards, Carl
This Chinese junk doesn’t follow many rules… I’ve fried a controller because the ground was +40V above my house ground/common. I tossed the power supply. But I’ve gotten two, the second I sent back.
To communicate the signals they have to have some sort of common…
I always measure them before I trust them …
“Trust but verify.” RWR
Thank you @jkwilborn & @Carl27 for your wise counsel. I checked both supplies six ways to Sunday before tying them together. I spent the last 45 years in the aerospace industry, at both the Eastern & Western Missile Ranges (Point Mugu NAS and Cape Canaveral AFS) so I picked up a few things (including a mint condition Simpson 260 multimeter). The only thing that gave me pause was that the AC (earth), case, and -24V grounds were all isolated from each other. That was not the case with the OEM supply. Both supplies are currently (SWIDT) playing nice with each other, so, as with any upgrade I’ve made, I’ll be keeping a wary eye on it.
Always brings to mind a Sinbad movie where they say trust Allāh but tie up your camel. 