Power Quality

[mcraddock1210]

If I am using a PLC that has a 24 VDC power supply is that enough to provide good power quality or do I need a 120 volt UPS feeding that 24 DC supply to have good power quality?

 

[keithkyll]

Good enough. No need for UPS.

 

[Paul T]

If I am using a PLC that has a 24 VDC power supply is that enough to provide good power quality or do I need a 120 volt UPS feeding that 24 DC supply to have good power quality?

Good but limited. If you're using the PLC 24VDC source for your IO, make sure it can supply everything you're using.

Mostly, people buy a 24VDC separate power supply and use that to feed the IO and the PLC outputs. Check out

http://www.automationdirect.com/store/Home/Home

for all the things you're looking for for your project. You will not get better pricing unless you are already giving your local distributors a lot of business.

 

[Jeff23spl]

Yes 24vdc separate power supply from a good brand is well enought and usually better than most of the 120vac device

UPS are usually not filtering device!!! The entry level work with a quick relay that switch from AC line to a square wave pulse
Medium grade will have a better wave but manny time worst than ac line and the best one will be filtered (True sinewave) and will cost 500-1000$ (5-800VA) so not used when not absolutely necessary

 

[jraef]

Adding a UPS would be done to extend the control system hold-up time, and if you already have a 24VDC power supply, you can add it to the 24VDC side, it's better there.

Beware of cheap power supplies though, there is always a reason why they are cheap. Filtering is usually the first thing to go in cutting cost, followed by regulation and surge capacity.

 

[mcraddock1210]

All products including the PS will have to be AB as that's all we are allowed to use at this company unless we need something that AB does not make or have a very good reason for not using AB.

 

[marcinski]

Stick with A-B or SOLA power supplies and your good to go.
Use UPS if you have frequent power outages. I used UPS for powering up PLC, computer, HMI.

 

[Mark Snodgrass]

SOLA makes a good din rail mountable UPS that fits well in a control cabinet, both in ac and dc versions. One advantage to these are they also have some measure of surge protection, and being wired via a terminal instead of using receptacles and plugs in your cabinet(yes, I have seen that done). Here is the link:

http://www.solahevidutysales.com/uninterruptible_power_supplies.htm

 

[Paul T]

All products including the PS will have to be AB as that's all we are allowed to use at this company unless we need something that AB does not make or have a very good reason for not using AB.

Wow. That would be nice. AB is way too expensive for us on commodity items. We use them for software, PLC and HMI when we can, but small stuff we may not.

For breakers, PS, terminals, fusing, that sort of thing I have done very well with Automation Direct for the last eight years. I've tried their safety relays and light curtains in the last year and had no problems. The SR is half as much as Guardmaster (well, at my multiplier anyway) and the light curtains are about 2/3 of what Keyence wants. Both worked perfectly well, although you do have to buy a particular SR they sell for use with the light curtains they sell.

I work for a medical device company, though, so all of my stuff goes into a clean room. In a different environment I would change some of the less expensive parts I buy to more expensive ones.

 

[jraef]

All products including the PS will have to be AB as that's all we are allowed to use at this company unless we need something that AB does not make or have a very good reason for not using AB.

Then you are good to go, the A-B power supply has VERY good filtering and regulation.

 

[meghnesh]

UPS is not required.
wat source of 24V DC are you using ??
Make sure that your source has got enough AMPERE capacity to drive all your IO's and maybe external digital & analog sensors too...

 

[Mark Snodgrass]

UPS is not required.

Sometimes a UPS can be handy if your plant is located in a remote area and you have power quality issues. We had a PLC5 that would sporadically lose its program, after talking with our integrator we installed a UPS we had (plug in style, but that's what we had) and the issue went away. We are now using the SOLA UPSs for our PLCs, they only maintain power for a few minutes, but that is enough to ride through most flickers and keep from losing data (positioning, product data that shifts with conveyor line, etc...).

 

[Jeff23spl]

Sometimes a UPS can be handy if your plant is located in a remote area and you have power quality issues. We had a PLC5 that would sporadically lose its program, after talking with our integrator we installed a UPS we had (plug in style, but that's what we had) and the issue went away. We are now using the SOLA UPSs for our PLCs, they only maintain power for a few minutes, but that is enough to ride through most flickers and keep from losing data (positioning, product data that shifts with conveyor line, etc...).

when you are stuck with a 120vac plc it may be the only solution as long as you have a true sinewave UPS because the usual battery backup model with a relay won't be of any help.
The true sinewave is a battery charger and a DC to AC power supply that use the dc power at all time VS the tcheap battery backup that let you connected to AC line until it see a blackout and, only then, switch to battery-pulses...
AB still do both so be carefull and chosse de right one

IMO the best configuration is a 24vdc powered plc connected to a good 24vdc ps that will handle surge and voltage variation until it burn without burning the plc itself...If the panel is alone outside or not powered by a well grounded and surge protected source, it must be done at panel level also...

 

[Jeff23spl]

All products including the PS will have to be AB as that's all we are allowed to use at this company unless we need something that AB does not make or have a very good reason for not using AB.

are you involved in a petrol/gaz plant or a governement facility ?