Magnetics question; and I don't have more info than presented

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,197
Suppose I have a coil of X size, number of turns and some specific voltage. Suppose that coil is going on a stackup of E-laminations. Suppose I'm supposed to have 47 laminations and order such a part.

The question is: How will the magnetics be affected if there's a 48'th lamination in the coil? The voltage should be 115 volts AC but I don't know the amperage or the VA. None of that is important; what I'm after knowing is will the extra ferrous material cause the coil to run hotter? Can it shorten the lifespan? Can it even cause a fire? These things I truly don't know, but it's important. For reasons of security I'm not at liberty to tell you more about what I'm inspecting. However, due to the fact that some engineer has decided to use 47 laminations, I'm wondering if the extra is going to be a problem.

The parts are rejected because they're not built to print. I'm just wondering if, and if so - how big an impact it may have.

Thanks.
 

AlbertHall

Joined Jun 4, 2014
9,333
It certainly won't cause overheating. All else being equal, an extra lamination will reduce the magnetising current and the core will be further from saturation in operation. I can't see any downside except the extra weight.
 

shortbus

Joined Sep 30, 2009
7,465
I'm going to give a different take on this. In all of my reading I never saw the number of lamination's in any formula. It's always been just the square inches or mm of the core, not the number of lamination's making up that value. If it takes 47 layers to fill the opening in the coil bobbin so be it, if takes 48 that's what it takes. Core lamination's come in different thicknesses/steel gauges but the square size number of the core is what is important.
 

crutschow

Joined Mar 14, 2008
24,405
The extra lamination will have no significant effect on transformer voltage output, but likely will cause a small increase in the transformer winding resistances due to the longer wire (roughly 2%) needed to wind a given number of turns for the primary and secondary(s) over the extra lamination thickness.
That's assuming the number of winding turns is unchanged from the specification.
This magnetizing current losses may be slightly less, but the winding resistive losses for a given load current would be slightly more (roughly 4% increase in resistive losses), and it would also have slightly poorer voltage regulation.
A measurement of the winding resistances would determine if this is a problem.

The extra lamination will also make it slightly larger, of course.
 

AlbertHall

Joined Jun 4, 2014
9,333
The extra lamination will also make it slightly larger, of course.
I took it from the question the size and number of turns (and hence wire length) were the same whether there are 47 or 48 laminations. If that is not the case then things do change slightly.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,197
Well, home now. Or "Hotel" now as it may be.

I'm inspecting cores that will become contactors. The coils are already wound, and the specifics of the size of the core is spelled out in "Maximum inches" (or partly thereof). The number of turns isn't going to change. The resistance isn't going to change. The purpose of the "MAX" is so that it will fit into the coil that will become the contactor. This is a very large contactor, industrial in size. Some of the cores I inspected were over size due to flaring out during riveting. A certain amount is allowable, but it starts off with 47 core laminates. Our supplier apparently doesn't mind giving away free material. Unfortunately they are not going to be usable and the supplier is going to have to remanufacture them. Correctly.

If the extra core reduces the amount of magnetic force holding the contactor in the closed position that may also become a critical issue, as this has to work in some rough conditions. Like "Combat" situations. So reliability means our boys can come home after the campaign. Failure may mean having to explain to some mother why her son didn't come home because one of our parts failed. We don't like doing that.

Anyway, this isn't a serious problem, just something I wanted to know. We have engineers here who are about as sharp as a fuzzy tennis ball. Literally. One of them asked me if it was OK to make a note on a blueprint. "No." I told him. "Make the necessary changes to the print and give it a new revision." And this kid has been doing - um - engineering for 10 years. Makes you wonder when an inspector knows more about blueprints than an engineer who's been doing it for 10 years or more.

It's nice to know something and be able to argue with an engineer why something is potentially a problem. Since I know nothing about the subject I thought I'd get some opinions here. Thanks all. From what I've read, the extra steel will lower the magnetic force holding the contacts in the closed position. Just wish I had an idea how much that would change. I know you'd need more info to be able to give me a better idea, but I just am not allowed to lay out anymore than I have. In fact, just giving you the number of laminates COULD be considered a violation of ITAR.
 

AlbertHall

Joined Jun 4, 2014
9,333
From what I've read, the extra steel will lower the magnetic force holding the contacts in the closed position.
If the number of laminations is the only difference then I don't think the force on the contacts would be reduced.
The magnetising current I referred to applies if this was a transformer and is the current drawn by the primary if the secondary is open circuit.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,197
Thanks Al. Probably not. But I like stirring up trouble. Especially for this particular supplier. Seems EVERYTHING I pick up from this supplier has issues, whether it's a dimension out of spec or a procedure not followed or documentation is lacking something. Really starting to turn my stomach when I see parts with their name on it. Means a whole lot of paperwork for me.

Thing I don't get is how they get hammered and nobody is calling them to the carpet over it. Why don't they learn that crap is not going to pass through receiving inspection?

Oh well. Monday I have another job waiting for my rejections. Badly formed crimps. And engineering says "It'll be fine." OK. I'm happy enough with that. As long as an engineer is signing off my reject. I'm not going to. Learned that lesson back in 2003 when the Railroad Safety Buereau came investigating why their passenger cars were catching fire. Company I was working for made the connector pins that handle high voltage and current. The chemistry was off on the material and caused it to have a different sound than normal. I couldn't find any reason for the difference but I rejected it anyway - based solely off the sound. Almost got laughed out of that shop. I was shamed into signing off my own rejection. The federal investigator told me he could put me in prison for that. I think he wanted to scare me because nothing happened to me. But the company had to pay a hell of a fine. Shortly after that we had enough work to hire two new temp's then didn't have enough work to keep me. Their loss.
 

AlbertHall

Joined Jun 4, 2014
9,333
I think you are right, they should be rebuilt. The 'new' version has not been characterised and there may be unforseen problems. One possibility is extra pressure from the laminations on the bobbin damaging or even splitting it, especially over an extended temperature range.
 

nsaspook

Joined Aug 27, 2009
6,960
The percent of increase and change are both about 2.1%. That's easily within the normal circuit variation for something electromechanical like contactors.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,197
That's easily within the normal circuit variation for something electromechanical like contactors.
I'm sure it is. At least commercially. However, military may take issue with that. And believe me, there's real potential for these contactors to be operating in violent seas with ships taking hits. I don't think they want any chance the part could fail. Can be the difference between coming home and going to the bottom of the ocean.
 

ebp

Joined Feb 8, 2018
2,332
Until a contactor is "sealed" (armature has slammed home) the inductance of the coil is totally dominated by the air gap and a 2% difference in the lamination stack would mean nothing. Even if it did, I'd wager the variation in the force of the spring that holds the contactor open would be substantially greater.

You wouldn't catch me in a million years trying to reject the contactors based on the difference in lamination count alone unless it was very clearly in the specifications or I could provide sound evidence from proper measurement that it made a detrimental difference. If I were the vendor and the lam count wasn't exactly spelled out and the inspector couldn't provide evidence, I tell him where he could cram his rejects and hall that receptacle into court, where I'd make him testify that he didn't know what he was doing. Especially after he published his malicious intent and evidence of his lack of knowledge on the internet - which is forever.
 

nsaspook

Joined Aug 27, 2009
6,960
I'm sure it is. At least commercially. However, military may take issue with that. And believe me, there's real potential for these contactors to be operating in violent seas with ships taking hits. I don't think they want any chance the part could fail. Can be the difference between coming home and going to the bottom of the ocean.
If that part fails because of a 2.1% (or even 20%) variation of pull strength then you've got bigger worries than 47 or 48 lamination's in those conditions.

I've been there on a ship at sea. I worried a lot more about something falling on my body, drowning or burning to death than any possible transient electrical failure from a missile, shell or violent sea wave.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,197
@ebp Did I offend you somehow? I'm never ashamed to admit when I don't know something. However, I DO know this: The blueprint specifies the exact number of lam's that are to go into the build. On that basis alone, the supplier is poiked. And if I were called to court to prove ineptness, I'd have a file as large as a 4 drawer office file cabinet full of rejects from this one supplier.

You don't need PROOF of me not knowing something. I'll freely admit it every time. I believe it's better to admit a lack of knowledge or understanding than to try and spout some intelligent sounding crap that can be easily disproved. THAT would call into question even the things I DO know. Hence, I ask this question. You want to hang me for that? WOW! Didn't mean to strike a cord with you.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,197
I've been there on a ship at sea.
Well, I haven't. I don't know the thrills of being in such situations. But it must be nice to not have to worry about equipment failure. My boss has been a submariner. Been shot, stabbed drown twice. He has an interesting take on the products we build. He says he KNOWS our products will always get the seamen back home. He's been under the polar ice cap. Been to the deepest parts of the ocean. Never once did he think something might fail and leave him stranded on the ice or at the bottom of the ocean. He's a man of whom I have great respect. Come Monday when he looks at the reject I suspect he'll still side with me. The best equipment is only the best when it's the best. Anything less is not the best.

How is this question turning into an argument? I just wanted to know more about the possible effects the extra lam would have. Since when is it a sin to say "I don't know - how WOULD this affect something?" It's not a dumb question. It's dumber to NOT ask than it is to ask and learn something. Even if I learn the effect is negligible. Bottom line, the part is not to print. Not per the BOM.
 

nsaspook

Joined Aug 27, 2009
6,960
Well, I haven't. I don't know the thrills of being in such situations. But it must be nice to not have to worry about equipment failure. My boss has been a submariner. Been shot, stabbed drown twice. He has an interesting take on the products we build. He says he KNOWS our products will always get the seamen back home. He's been under the polar ice cap. Been to the deepest parts of the ocean. Never once did he think something might fail and leave him stranded on the ice or at the bottom of the ocean. He's a man of whom I have great respect. Come Monday when he looks at the reject I suspect he'll still side with me. The best equipment is only the best when it's the best. Anything less is not the best.

How is this question turning into an argument? I just wanted to know more about the possible effects the extra lam would have. Since when is it a sin to say "I don't know - how WOULD this affect something?" It's not a dumb question. It's dumber to NOT ask than it is to ask and learn something. Even if I learn the effect is negligible. Bottom line, the part is not to print. Not per the BOM.
It's not a argument, I'm stating my opinion.
I would respect his opinion too. Completely separate from possible BOM build/contract issues, that doesn't change the fact that electrically and mechanically it's hard to see how safety is compromised with one extra lam because of how contractors operate.
 

Reloadron

Joined Jan 15, 2015
5,140
I'm sure it is. At least commercially. However, military may take issue with that. And believe me, there's real potential for these contactors to be operating in violent seas with ships taking hits. I don't think they want any chance the part could fail. Can be the difference between coming home and going to the bottom of the ocean.
One of the more interesting periods in my life involved FRAUD IN THE SUB PIPELINE: VICTORIES FOR PROSECUTORS. Fortunately I was not involved with the bad guys. I am pretty sure when a nuclear propelled submarine submerges the crew would like to believe it will surface as advertised. When the parts in the story were nickel plated the test coupons were also supposed to be plated. Then the coupon was bent 180 degrees (looking like a horseshoe) the idea being the plating should not flake. However, you could expect a slight wrinkle in the coupon (test part). The test coupons were flawless, go figure. There was much more to the story than the published article but I have never forgotten that incident. Heck, a Google of government fraud will reveal hundreds of similar stories. Working to Mil-Spec can be fun, one saying I always liked was MIL-T-FD41 which is Make It Like The F'ing Drawing For Once. :)

We would prefer our submarine force not to be like K-19: The Widowmaker which darn near had a full reactor meltdown. Sort of a Chernoble at sea.

I will now return you to the regular thread. :)

Ron
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,197
When the parts in the story were nickel plated the test coupons were also supposed to be plated. Then the coupon was bent 180 degrees (looking like a horseshoe) the idea being the plating should not flake.
No, we don't get test coupons. We only get test reports and Certificates. Or as I sometimes call them "Sorta-fake-it's" Got one the other day with the wrong rev on the part and on the fake-it. The fake-it had the wrong part number too. On top of all that, the plater's cert had the right part number and revision but someone changed it with a pen and a strikethrough of the (what was the) correct rev and hand wrote in the wrong rev. What stands out in my mind is "Who changed it? Was it changed by the plater or did the company we were buying from change it without the plater knowing?" If the plater was unaware of the change to their document - that's a federal crime. In our purchase orders we demand the statement be present on every cert - "Fabricating, false or fictitious information is a federal crime punishable by prison according to article xx-xxx section x-xx-x." (X's in place of the article and section numbers). Or maybe I got the article and section reversed. I see them so often I don't even look at them. As long as they're there - - - . But a few of our suppliers - I really have to ask "What are they thinking? ARE they thinking? Are they even breathing?" Lot date codes that don't match the certs, quantities that fall short of the quantity shipped. Things that call into question the validity of the cert in the first place. The problem has been that for so long the company has just accepted the parts the way they were and we fixed the issues in house, never putting the pressure on the supplier to make it right for once.

One supplier got angry at me and said in a stern and somewhat raised voice "We've been making that part for 20 years and there's never been a problem!" My response: "Yeah. That's what NASA said just before they blew up a public school teacher in front of her students." You could SEE the steam coming off his collar. But he knew I was right. That's why my signature says "Right is right and wrong ain't!" That's when I love my job the most - when some high up and superior intellect spouts off and I shoot him down. LOVE it. Chalk one up for the little guy.
 
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