PLC Brownout

What sort of pre PLC power supplies do you generally use to protect from brownouts spikes etc? Switchmode?
Do you normally supply the whole control cabinet with protected power, or only the PLC itself?




Just curious:
How much rain do you get a year?
We get >3000mm/120in.

http://www.southerntraverse.com/

We have several large UPS systems installed in the MCC's, that we run all of our control systems from. We kind of backed into having many versus one large one, but it has made the system more reliable. One UPS failure will not shut down everything. As time goes by, we will run out of capacity and add another UPS etc....


Ken

BTW
Rainfall in Upstate South Carolina is about 50-55 inches a year.

The wet, shaky isles.

24 VDC battery systems almost exclusively with 24/24VDC switchmode power supplies to power the PLC's. Very reliable, provided the battery banks are discharge tested regularly to detect any failing cells.

Sydney is pretty wet during summer - except for the last 3 yeras. Water restrictions now.

I spend a bit of time in Weipa - Far North Queensland. It is on the gulf side 1/3rd down from the tip. I was there just prior to Christmas 3 years ago. Sitting having a beer (or two) about 10 metres from an ablution block. The rain was so heavy we could not see the ablution block in the middle of the day. They had 7 metres of rain that wet season between mid November and early March.

Just a word of caution...

Depending on you PLC I/O you might need your UPS to produce a true sine wave.

Check out this thread here: http://www.plctalk.net/qanda/showthread.php?s=&threadid=8900&highlight=true+sine+wave

Thanks Guys,
Will keep all this in mind.

Constant voltage transformers are commonly spec'd for the PLCs on a lot of systems that we build.

Here's an example. http://www.sola-hevi-duty.com/products/powerconditioning/mcr_hard.htm

They're quite a bit more expensive than regular transformers, but they will help with dirty power, voltage sags, etc. I'd say they're a good go between if you don't want to go all the way with a UPS.

Mike is right about the quality of the Sine wave. This is the reason we always use industrial grade vs. commercial grade UPS systems. The industrial grades are always hardwired via distribution panels, instead of a bunch of plugs on the front. All of our UPS systems are fairly large 4.3-18kVA per unit, so the distribution system works great for us. Now if I could only find a cheaper source for the isolated orange outlets.

If your PLC cab be feed with 24DC Bob advice is the best.
If you need 100/220v take Mike advice.
Anyhow stabilized switchmode power supply is always recommended.

Last week I purchased a Sola STV25K surge supressor for a small control system I'm designing. I thought it would be a good idea to provide some protection for the PLC and other solid-state components. This one is larger than I need (at 20 amps). I had intended to get a Cutler Hammer model from AD, but the largest offered was 5 amp, which was right on the borderline, capacity-wise.

So I shelled out $185.50 for the Sola. I was shocked at how light the thing was when I got it! I couldn't resist the impulse to open it up to see what all wasn't in it. Here's what I found:





I'll be the first to admit how little I know about the electronics of surge supression, and maybe these components are more expensive than they look, and maybe they get hot enough in use to require all that extra space in the enclosure, but for 185 bucks, this sure looks like a whole lot of nothing.

Paula

[PS- The black box at the lower left of the second picture is a small relay for controlling a remote status indicator.]

Paula,

I'm sure I'm gonna get some disagreement here, but it is my opinion that these devices are about as usless as the proverbal mams on a goose.

Think about it.. The only real big benifit your getting from this device, over simply installing a $5.00 mov on the terminal strip, is a monator, (the $2.00 relay), to tell a remote device that there's a power failure..

So......

1) This type of production machinery is required to be equipped with power drop-out protection . Basicly a manually reset self-holding relay. (you can get your power falilure indication from this device)(the device in the link has surge suppression also, but you can just use a small contactor, and a couple of MOVs)

2) Transient protection is important, so simply buy a couple of 130 volt MOVs and install one on the power supply, (the input to the power-drop off relay), and one on the PLC power supply.

Mike,

Thanks for all the info, but you kind of skipped past the question I was asking. I'm not questioning the usefulness of these things (a good question all by itself), but what make this one cost $185.50? I noticed that among the technical specifications, Sola lists the weight of this item at 3 pounds. The one I've got weighs barely 11 ounces. I think it's basically a scam.

Originally posted by pstephens:
I'm not questioning the usefulness of these things (a good question all by itself), but what make this one cost $185.50?

Click to expand...

What's in auto insurance that I should pay $600/year for it? What's in a PLC that it should cost $600? Whats in a drive that it should cost $500? What's in your shear that it should cost what what you are charging your the customer?

As engineers we often fall into the trap of evaluating things purely on the basis of what it physically is as opposed to what it can do for us. Whis is mostly because we can. The population as a whole doesn't generally evaluate items based on parts cost but on capability.

Paula, you already stated you see the need for the device. Like Mike said, if you have the capability to provide the same functionality with discrete parts at a lower cost, then by all means have at 'er. However, $185 seems like cheap insurance for what the thing does form you (assuming it actually works). And unless you are going to put this protection on every machine you do and bulk buy your components I find it hard to believe you could pick and procure parts and draw the stuff in for less than the time equivalent of $185, if you charge yourself the same per hour rate that youm charge your customers.

Keith

pstephens said:

I noticed that among the technical specifications, Sola lists the weight of this item at 3 pounds. The one I've got weighs barely 11 ounces. I think it's basically a scam.

Click to expand...

Paula, I think you kinda answered your own question.... Looking up the MOVs I see that their 37 cents apeice!!! I cant justify the cost either.. maybe somebody else has a good explaniation.

They are and they arent, they will probably do what they are stated/designed to do. These kind of items are not in strong demand but offer the features that many want/need...indicator, relay, din mounting etc so you are paying more for packaging and features then what the device actually does. That and the fact all you have to do is connect a few wires which saves you time.

Thats why we buy off the shelf items, its overall cheaper than making our own. Also makes it easier to replace quickly if needed.

Keith,

Dont get me wrong. I would never reccomend NOT providing surge protection. However for $185.00 you can buy hundreds of MOVs. Properly placed, they will do just as good outside of the little box.

Besides Paula MUST provide power drop out protection. If she purchases a commerical ready made unit, it will likely be equipped with a surge suppressor also.

Mike.