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Unread December 1st, 2019, 10:08 AM   #16
westom
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All those last posts are saying one thing. Why is a problem being solved when a defect (or threat) is not even defined? IOW a useful answer exists only after numbers and other relevant details are provided (as requested). What is this problem or threat? Why are MOVs even mentioned when a problem was never defined?
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Unread December 1st, 2019, 04:05 PM   #17
EMILLER233
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It's not that complicated really. Just wanted to make sure multiple surge suppression devices wasnt an issue.

The PLC will have relays between it and the solenoids. So I'm not worrying to much about power requirements for each solenoid or plc damage. I can change fuse sizes easily if required later once details are known.

We're just adding the surge devices since it's in the customers 'generic' spec sheet that we have to meet, which states solenoids shall have surge suppression

Last edited by EMILLER233; December 1st, 2019 at 04:08 PM.
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Unread December 1st, 2019, 06:50 PM   #18
Highland Controls
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Westom, a threat is defined by the very nature of valve coils. Yes, a suppression device is required. The OP is only asking if there are downsides to doubling up on the suppression(since he isn't sure if there will already be suppression provided).
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Unread December 1st, 2019, 07:13 PM   #19
westom
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Quote:
Originally Posted by Highland Controls View Post
Westom, a threat is defined by the very nature of valve coils. Yes, a suppression device is required.
That is the point. The nature (those necessary numbers) and other parameters define what is necessary and not necessary.

For example, AC coils typically do not need or have protection. DC coils may already include necessary protection.

Fuses clearly do not do anything to avert transient damage. That made obvious by datasheets and other ballpark numbers such as "I squared t".

Relays only provide protection when parameters are discussed. An example that everyone should be familiar with. 56K modems connected to telephone lines via a relay. Transients from AC mains would blow through that relay's PNP transistor. Current connected from that relay's coil to its wiper also destroyed the PNP transistor. Reasons why because numbers are required with engineering answers. That isolation voltage was less 500 volts. So transients easily blew through that relay.

What happens to a PLC? In one case, the transient caused a microprocessor software crash. Which opened all valves; not just the one that suffered a transient.

Another mentioned another significant fact that is missing. Dry contact relay? That also makes a serious difference.

Transient protection was not a solution. The solution became obvious after an investigation first collected numbers - that were ignored during design.

No honest answer, recommendation, or conclusion is possible here. The many necessary parameter have been withheld. So every answer can only be subjective, vague, deceptive, or speculation.
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Unread December 2nd, 2019, 12:43 AM   #20
James Mcquade
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westom ,

here is the problem that I have.

Are the valves ac or dc?
what is the quantity of ac and dc valves?
do they come with surge suppression or not? buy suppression terminals.

the really big issue - what is the size of the valves !!
plc outputs can only carry only so much holding current and has a surge current limitation! I have installed air valves that takes 3 or 4 amps just to hold in the valve, forget the surge current. valves like that must have an interface relay to power the valve. that means more panel space, bigger power supply / transformer. 100 3 amp valves means 100 interface relays, a larger transformer a bigger control panel additional wiring, design, cad labor.
failing to take this into consideration can be a disaster.

james
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Unread December 2nd, 2019, 02:25 AM   #21
GaryS
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To answer the original question Stacking surge suppressors
By that question I assume you mean parallel them
While you could stack them, but the question is why would you there in nothing to be gained by doing it.
As the old saying goes the strongest chain is only as strong as it’s weakest link this is true on all surge suppressors or any electronic component.
Even with the same suppressor there will be slight differences in the voltage level that they start to conduct. It is not possible to manufacture then to be exactly the same. Even with only .001 voltage difference them the lowest one will conduct first. The first one to conduct will dissipate the surge up to it’s limit and burn up the other devices will do nothing until the first one is destroyed.
If you think the device is not able to dissipate the surge then you should consider getting a higher wattage device.
Normally for 120VAC coil as 130V MOV is used and all DC coils a simple diode connected across the coil works best
Do not put a diode in series with the coil.
To be the most effective all surge suppressors should be located as close to the coil as possible.
When considering any surge suppressor you have to ask what at you trying to protect?
In most cases you are trying to protect the PLC output card from the voltage spike from the collapsing magnetic field when the power is removed from the coil, that surge can be very large normally they consider that voltage level to be over 10X coil voltage. If you are trying to protect the supply voltage to a device or panel then you should look at supplying a better power supply with surge suppression built in.
You can get MOV’s with very large power dissipation ratings if you feel you need them.
Just to be clear Fuses or Breakers are not surge suppressors they are current limiting devices by the time they open the damage has already been done they just isolate the damage to the local device.

For you application I would install inter-pole relays with a 6 Amp or more contact rating in your panel, have your PLC outputs control the relays. That would provide you with total isolation between the PLC and the real world devices. Simple and easy to trouble shoot and cheap to replace if necessary. You still should use surge suppressors in the outputs of the relays and to the solenoid coils to help extend the life of the relays. That surge can damage the relays contacts even with the correct current ratings.

I see here that some are recommending Zener diodes or avalanche diodes they are both old school attempts but they will not work. Back when they first came out zener diodes were called avalanche diodes before they settled on zener
They are always used with a series resistor to limit the current through them. The way they work is with the voltage in forward polarity they act like any standard diode and pass current with the normal .7v voltage drop across the diode but with the voltage in the reverse polarity they block current until the threshold voltage is exceeded then all current is passed through the diode “Avalanche” without a resister to limit the current the diode would burn up in about 1 second or less, not much protection to be had there.
For an AC coil an RC suppressor can be installed and they do work very well, the problem is they are difficult to size for each coil, there is no universal RC for coils the only way to select the correct one it trial and error using a scope to see what works for each coil. Not something you want to do in the field.
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Unread December 2nd, 2019, 11:12 AM   #22
westom
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Quote:
Originally Posted by James Mcquade View Post
here is the problem that I have.

Are the valves ac or dc?
what is the quantity of ac and dc valves?
do they come with surge suppression or not? buy suppression terminals.
We are saying the same thing. I am simply defining a problem that most people demonstrate. They want answers. But do not first provide or learn necessary parameters. Numbers were not provided. So an informed answer is not possible.

You have simply listed some examples of this common problem. Most want answers - solutions - but do not realize their answers will only be as good as the information first provided.

He did not even list this parameter: are valves AC or DC? One (of many) major difference between an informed answer and answers only based in hearsay and wild speculation.

As GaryS also says, "When considering any surge suppressor you have to ask what at you trying to protect?"

We do not even know that. We do not even know what the PLC output terminals are driven by - relay, optocoupler, open collector transistor. And, of course, numbers even for that must be provided.

Why did we engineers know that Saddam did not have WMDs? We learned the numbers. He clearly did not. Why did most know those WMDs existed? They ignored or did not demand simple parameters (ie numbers). Instead made conclusions only from speculation and hearsay.

Why was the Challenger launched? They could not find one engineer who said it was safe to launch. So they ignored all parameters (ie numbers) to kill seven astronauts. It was no accident. It happens when one wants a conclusion and cannot be bothered to first learn parameters.

We are saying the same thing. I am also saying this "conclusion without facts" is not limited only to the OP's problem. We are all suppose to learn that conclusions (solutions) are only as good as the parameters that are first provided. It applies to everything in life.
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Unread December 2nd, 2019, 07:35 PM   #23
dogleg43
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Quote:
Originally Posted by westom View Post
We are saying the same thing. I am simply defining a problem that most people demonstrate. They want answers. But do not first provide or learn necessary parameters. Numbers were not provided. So an informed answer is not possible.

You have simply listed some examples of this common problem. Most want answers - solutions - but do not realize their answers will only be as good as the information first provided.

He did not even list this parameter: are valves AC or DC? One (of many) major difference between an informed answer and answers only based in hearsay and wild speculation.

As GaryS also says, "When considering any surge suppressor you have to ask what at you trying to protect?"

We do not even know that. We do not even know what the PLC output terminals are driven by - relay, optocoupler, open collector transistor. And, of course, numbers even for that must be provided.

Why did we engineers know that Saddam did not have WMDs? We learned the numbers. He clearly did not. Why did most know those WMDs existed? They ignored or did not demand simple parameters (ie numbers). Instead made conclusions only from speculation and hearsay.

Why was the Challenger launched? They could not find one engineer who said it was safe to launch. So they ignored all parameters (ie numbers) to kill seven astronauts. It was no accident. It happens when one wants a conclusion and cannot be bothered to first learn parameters.

We are saying the same thing. I am also saying this "conclusion without facts" is not limited only to the OP's problem. We are all suppose to learn that conclusions (solutions) are only as good as the parameters that are first provided. It applies to everything in life.
Wow, while itís nice to completely analyze all of this stuff, none of my projects had either the time ( = $$$$) or need for this type of over thinking. Maybe your customer/end user is requiring this but IMO, it seems unnecessary.
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Unread December 3rd, 2019, 08:43 PM   #24
EMILLER233
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The details do not matter for this discussion, I have those already handled or will be during install...

Plc will have interfacing relays on the outputs. Solenoids will be powered directly from a power source. Power to the solenoids have fuses for protection of the wires.Design is/has been figured out (this info was already posted, maybe it was missed?). There are both, AC and DC solenoids. I have quantities. This was also posted previously,

The only question that needs discussed/answered is the original one posted: if it is acceptable to have multiple surge suppression devices(sizing is irrelevant), and IF it is not acceptable, why not???

Last edited by EMILLER233; December 3rd, 2019 at 08:53 PM.
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Unread December 3rd, 2019, 10:28 PM   #25
GaryS
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What's acceptable is what you and your client will accept
laying out the facts weighting all the information it's up to you.
One down side is that any technician coming after you finished could be confused
if you need to have the job inspected then check with the inspector
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Unread December 3rd, 2019, 11:02 PM   #26
EMILLER233
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What does surge suppression have to do with an electrical inspection of a system install?
What would be confusing if the documentation matches the as-built equipment?
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Unread December 4th, 2019, 12:15 AM   #27
GaryS
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Quote:
Originally Posted by EMILLER233 View Post
What does surge suppression have to do with an electrical inspection of a system install?
What would be confusing if the documentation matches the as-built equipment?
As I said before it's your call what you want to do
I have been on jobs that simply changing a light switch required an inspection
others you could rewire the plant and never get an inspection
it all depends on the local code and what the client wants
we have no way of knowing that here

As for the confusion I have seen and worked with drawings that even a well seasoned technicians were confused as to why something was done the way it was. Double surge suppressors would rise some questions most places
some clients have very strict standards that must be followed others don't care what you do.
You need to know what everybody involved will accept there standards every job may be different
it sounds like you are trying to get somebody to take on your responsibility and for free.
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Unread December 4th, 2019, 06:11 PM   #28
Highland Controls
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Holy ****, this place is becoming like Facebook. A simple question was clearly asked and we are getting dissertations that never answer the question.
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Unread December 4th, 2019, 07:21 PM   #29
westom
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Quote:
Originally Posted by GaryS View Post
Double surge suppressors would rise some questions most places some clients have very strict standards that must be followed others don't care what you do.
Most who recommend a surge protector only do so because wild speculation, brainwashing by hearsay, subjective accusations, and total technical ignorance has recommended it.

What dogleg43 calls too much time and too much money is, in reality, done in seconds or minutes. Resulting in massive cost reductions. But too complicated and hard for one who has never done this stuff. Who makes conclusions anyway (as taught in business management school).

A first time designer may take an hour - to learn how to be an informed designer. Then future designs only take seconds or minutes - to do what dogleg43 only wildly speculated as too much time and money.

Nothing says he needs surge protectors. In part, because relevant fact were never provided. Others, using only what they want to believe, will make recommendations. Rather than state what parameters are required to have an informed reply.

Had he selected a correct part and output, then no surge protector parts are required. How does that happen? So many parameters are learned long before making any design conclusion.

Most inspections are only for human safety. Surge protectors are for hardware protection. As EMILLER233 so rightly asks, "What does surge suppression have to do with an electrical inspection..."

Hardware protection is found/verified in design reviews. What does a design review always need? Those parameters. A design review demands parameters - so that hardware does not fail. Completely different purpose from an inspection.

OP has the only possible answers - because he did not even state if those were AC or DC coils. The electrically naive are always quickly identified. They complain it is too hard rather than learn why this stuff is always known (read and learned).

This is America where a music major is now head of computer and other security for a major credit reporting company - that has all our private information. And released that data to hackers. Why? She also could not be bothered to learn parameters or how things work. She was a music major. In many places, that alone means one can make expert recommendations - by using speculation as if parameters.
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Unread December 4th, 2019, 08:36 PM   #30
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IMO, the answer, in general is that doubling up on surge suppressors is fine, provided they are MOVs or diodes. Doubling up on RC snubbers may provide worse results than a single snubber, but certainly better than none.

Westom, you've mentioned a few interesting stories of non-engineers making poor engineering decisions. Would be curious to hear more about those.
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