Uninterruptable power supply for Controllogix PLCs?? 2

[bdn2004]

We are installing a network of Contrologix PLCs. They are to help us diagnose the cause of a power failure.

We are intending to put these on a separate AC power supply from the power system that we are monitoring. This separate AC system has two power sources that are switched by a manual transfer switch.

The problem with this arrangement is that the separate AC system is not a make before break operation, so the power is interrupted for a split second during switching.

Without introducing maintenance-heavy UPS systems...is there anything out there that could keep these PLC's running through the switching procedure? perhaps even chassis mounted?

 

[dV8r]

How much time are you talking about? Seconds or milliseconds? What voltage?
If the latter time period and DC, maybe capacitors?

 

[jraef]

Many of the DC power supply mfrs have what is called something like an "extended ride through" option, basically a capacitor. I use Siemens Sitop power supplies because on theirs you can gang up the modules to extend your hold-up time and/or current. But to dV8r's point, these are good for a few seconds, not a few minutes. You need to further define your problem.

There are also several options for DC UPS systems to go behind 24VDC power supplies as well, they are nowhere near as complex as AC UPS systems since you already have the DC power supply. They still have batteries though, and batteries need to be replaced periodically.

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[catserveng]

For AC powered systems I have used the Allen Bradley 1609-S350NS UPS (120 VAC)a number of times. To date they have been rugged and reliable, but a tad pricey at around $395USD for a 350VA UPS.

Last system I retrofitted the AB UPS on was three ControlLogix PLC racks and two VersaView HMI's, they were feed from a non-critical ATS and transfer time was 25 seconds, to date no problems reported.

Hope that helps,

Mike L.

 

[bdn2004]

Thanks for the good answers.

I'm trying to find out the switching time. And its not just one switch. The plant has tried to create a low voltage power center source that can be relied upon in almost any scenario, by feeding it from alternate sources.

In talking to our IT guy he also indicated they've had lots of problems with small UPS units, particularly when the batteries go dead - the network goes dead. This doesn't sound like a very good design.

The voltage is 120VAC but we haven't purchased anything yet. We also have available 125VDC except there are issues with it as well, the 120VAC is considered more reliable.

 

[bdn2004]

This discussion is making me think of another alternative. I think I read where the A/B PLC will stay up on power loss for 6 cycles. What if we were to bring in two different 120VAC power sources connected to an electronic switching unit that would automatically switch to the other source within this time range?

Is something like this possible?

Or perhaps bring in the two sources so that we could do a hot swap on the 120VAC. Is this a common practice?

As you can may be tell...I'm a novice about stuff like this.

 

[djs]

Anything lasting more than a feww hundred milliseconds will probably require a battery. And batteries require maintanence and replacement on a regular schedule. Many AC type UPS allow the battery to be changed without interupting the output. Like jraef the simpliest UPS is a 24 VDC battery. I believe that you can get a 24VDC power supply for the ControlLogix.

 

[DLite30]

I believe all the control logix chassis are 120VAC powered. A small ups is your best bet.

 

[EddieWillers]

The 1756-series ControlLogix power supplies are available in 120/220V AC, 24V DC, 48V DC, and 125V DC versions.

I'm running a system right now where we used the 24V DC ControlLogix supplies and ordinary A-B 1606 power supplies with Phoenix Contact Quint UPS units. We can run the controller and a couple of I/O racks for twenty minutes with the AC line down, which keeps our data acquisition live in the event of a power interruption.

If you have a manual transfer and there will be only a few hundred milliseconds interruption in the AC line, the QUINT Buffer modules might be just the solution, so you don't need a central on-line uninterruptible AC source.