DC power supply and generator

[edexlab]

Evening all I'm looking at a machine which has a B&R HMI 24v not working,
The usual display is replaced with a page saying a product code needs entering and the touch screen is not responsive,
So it looks like we will be replacing it as it's under warranty still.

However after talking to different operators each with varying versions it transpires that there was a backup generator test yesterday

There's 2 identical machines, both not turned off at the time, and according to one guy they couldn't restart this one

Another said it wasn't used again as no product required

Another says it ran perfectly but took longer to reboot than usual and started fine this morning

All sounds a bit fishy

I would think a DC power supply would just shut down or have internal protection for devices downstream

Is it a possible this could have caused the HMI to develop a problem?

 

[James]

It is a make of plc that i avoid wherever possible, in my experience, they have a failure rate far higher than others that i have used.

It is possible for a power supply to fail and damage down stream equipment, when ever i have come across similar things in the past, it has often been the case that a 230v power supply has been used between phase and neutral, a momentary or prolonged failure of the N can destroy the PSU, a 3 phase psu or 400 to 230v transformer normally prevents such issues from re occuring.

 

[edexlab]

Sorry I forgot to say the power supply is still functioning there is 24v present

So maybe the question should be
can there be issues caused downstream while the Psu is not damaged by an event?

Re B&R
I had never heard of B&R Plc's before moving to this company ( still relatively new to this )and we do have issues on this particular machine where questions have been put to B&R about glitches in the IO and they admitted they were aware of it and don't know what is causing it

 

[James]

it is sounding like a power surge or similar has either corrupted the memory or somehow put the device into shipping mode where a code is required by the commissioning engineer to make it work.

unfortunately the best people to give you advice are B&R,
however i have found there sales team about as scrupulous as a double glazing salesman
and there after sales team about as useful as a box of chicken nuggets at a vegans convention.

 

[edexlab]

Ok so it is feasible that a surge could have left the Psu intact but affected devices it powers

I would hope my company will have decent cooperation from B&R as they spend a very large amount of money to them each year

Thanks for your input James!

 

[James]

Remember, some spikes, surges, transients, (same "poo" different words) can come down the earth cable destroying devices connected also to "real earth" or phase/N cables.

 

[Lucien Nunes]

Ok so it is feasible that a surge could have left the Psu intact but affected devices it powers

In my own experience this is vanishingly rare as far as incoming voltage transients and brownouts giving rise to out-of-spec DC output are concerned. I run hundreds of DC PSUs on dodgy power from all sorts of generators, inverters etc, feeding studio equipment, and I am not aware of any downstream damage ever having been caused. I have had probably 50 or more PSUs blown up by 400V but nothing downstream was affected. I have seen adverse power events cause circulating ground currents to blow signal interconnects open, where equipment on different power sources is interconnected with single-ended signals. But if this panel is in the machine or fed from it, that seems improbable.

Therefore if there was a link to the genny test, it is more likely to be that the equipment or PSU had not been turned off for a long time and there was a brownout that triggered a latent problem that would have shown up as soon as the next restart occurred. This I have had many times - something appears to be working fine and you power-cycle it either intentionally or accidentally while doing some maintenance, and it does not come back up. You assume it's something you did, but it's actually an issue that has been lying in wait for years.

 

[DPG]

In my own experience this is vanishingly rare as far as incoming voltage transients and brownouts giving rise to out-of-spec DC output are concerned. I run hundreds of DC PSUs on dodgy power from all sorts of generators, inverters etc, feeding studio equipment, and I am not aware of any downstream damage ever having been caused. I have had probably 50 or more PSUs blown up by 400V but nothing downstream was affected. I have seen adverse power events cause circulating ground currents to blow signal interconnects open, where equipment on different power sources is interconnected with single-ended signals. But if this panel is in the machine or fed from it, that seems improbable.

Therefore if there was a link to the genny test, it is more likely to be that the equipment or PSU had not been turned off for a long time and there was a brownout that triggered a latent problem that would have shown up as soon as the next restart occurred. This I have had many times - something appears to be working fine and you power-cycle it either intentionally or accidentally while doing some maintenance, and it does not come back up. You assume it's something you did, but it's actually an issue that has been lying in wait for years.

The curse of the switch-mode power supply - capacitors dry out and you only become aware if ever the power fails. A place where I used to work had a really old pabx system which nobody ever dare power off in case it never came back on.

 

[Lucien Nunes]

Or sometimes the start-up bootstrap resistor, the high value one that trickles a bit of rectified mains into the SMPSU control supply reservoir cap to get it running long enough to provide its own hot-side ELV rail. Often something like 100kΩ 1W; if they have skimped and used carbon film instead of metal, it's more likely to be open

I have a story about a rather high-profile piece of kit that went haywire when it was power-cycled for the first time in years. About half of its fifty 12V 1kW power supplies did not restart, and it took weeks and a high 5-figure bottom line before it worked properly again. I won't clutter the thread up with that though.

 

[edexlab]

Psu is still functioning and the HMI is around 4 mths old as there were some software issues on the old version and a new version was installed into a HMI and sent over during 1st lockdown
So maybe an underlying problem with the device as suggested

The machines are left on all the time as keeping the panel warm helps with reducing condensation building up inside, it's a machine which washes a reusable plastic tray for food industry so lots of water and the panel is on top if the processing section

I've seen a much older one recently where a customer has rebuilt a complete panel away from the machine as the panel components were disintegrating from moisture getting in through damaged/ missing seals.

Generally the operator can reset the machine or power off and reboot if nothing else works so they tend to be left on.

However there are approx 500 of these machines globally, and I've been told this is the first time they've seen this problem