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Author Topic: Isolate all the Iron?  (Read 4778 times)
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KD1SH
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« on: June 29, 2022, 11:09:05 AM »

    Laying out plans for retirement projects. Got all the Gates iron - power and mod - and working up drawings for how to lay all this stuff out. Power supply and modulator will be on separate platforms, rolling on casters. I figured to order myself some heavy aluminum plate - 3/8" or 1/2" thick - and mount the iron and associated parts on that. But then I got to thinking: for one, that aluminum is pricey, and for another, it would be easier on that old iron - both the power and mod iron - if I keep the transformer cores isolated from ground. In that case, I could simply use some really heavy plywood, much cheaper, as the bases.
    I know isolating the mod iron has been discussed here before, but how about the power iron? I'll admit that floating high voltage parts gives me the willies, but it's not like I'm going to be sticking my hands into the cabinets. Has anyone else done this?
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Jim/WA2MER
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« Reply #1 on: June 29, 2022, 11:37:13 AM »

My power supply and modulator iron is mounted on a plywood sheet in the bottom of my rack cabinet, as you can see in a photo that was taken during construction. I used heavy braid to provide an electrical ground for the PS negative side to the cabinet, but I did not ground the transformer cases. Never thought about it, really. All works well without transformer case grounding. Safety? I don't know if grounding the cases would provide a margin a safety, but like yourself I don't spend much time sitting atop the iron when the unit is powered up.


* B6EC9B76-56C1-43B9-9698-64F11544E746_1_201_a.jpeg (422.31 KB, 1600x1200 - viewed 230 times.)
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KD1SH
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« Reply #2 on: June 29, 2022, 12:43:55 PM »

Nice looking layout. I like your homebrew clamps for the oil caps. Some of my caps have factory brackets and others don't, so I'll likely wind up using your approach.
That's a lot of heavy iron - your plywood must be at least 1/2", I'd imagine. Plywood is certainly cheaper than 1/2" or 3/8" aluminum. I was going to say that plywood doesn't exactly grow on trees these days, either, but obviously it does, just very expensive trees.
I agree, I can't really think of any safety advantage that grounding the transformers would provide under normal circumstances; it just seems like the "traditional" thing to do.

My power supply and modulator iron is mounted on a plywood sheet in the bottom of my rack cabinet, as you can see in a photo that was taken during construction. I used heavy braid to provide an electrical ground for the PS negative side to the cabinet, but I did not ground the transformer cases. Never thought about it, really. All works well without transformer case grounding. Safety? I don't know if grounding the cases would provide a margin a safety, but like yourself I don't spend much time sitting atop the iron when the unit is powered up.
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Jim/WA2MER
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« Reply #3 on: June 29, 2022, 01:34:52 PM »

I don't recall the thickness of the plywood because I used a scrap piece I had laying around the shop. It's probably at least 1/2 in. becuase I installed 1/4-20 speed nuts on the bottom so that I could bolt the transformers to to it from above. The capacitors of course had no mounting holes, hence the brackets. Anyway, the plywood thickness didn't matter in my case because it lays flat against the floor of the rack cabinet.

The more I think about it, grounding the transformer cases might provide a bit of safety in the event that a transformer winding might somehow short to the case. If the case were grounded then a fuse would likely blow, instead of you becoming the fuse.
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KD1SH
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« Reply #4 on: June 29, 2022, 02:12:34 PM »

That's true, but I'm thinking that a winding is less likely to short to the transformer core when there's no potential between the two, thus giving the voltage on the windings no "incentive" to arc to something.

The more I think about it, grounding the transformer cases might provide a bit of safety in the event that a transformer winding might somehow short to the case. If the case were grounded then a fuse would likely blow, instead of you becoming the fuse.
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Jim/WA2MER
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« Reply #5 on: June 29, 2022, 08:51:16 PM »

That's true, but I'm thinking that a winding is less likely to short to the transformer core when there's no potential between the two, thus giving the voltage on the windings no "incentive" to arc to something.
There is truth in what you say, but I was thinking more of physical contact rather than an arc, something that might happen when insulating material breaks down and things touch that shouldn't. The plate transformer in the upper right portion of my photo shorted and provided some of the best fireworks I'd seen in recent years. A post mortem revealed a breakdown in the paper insulation on the secondary to the extent that refugee (migrant?) electrons were flying around furiously looking for a place to land. The carbon tracks were impressive. I'm glad that I never keyed the plate voltage unless the cabinet was closed.
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Anything worth doing is worth doing to excess.
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KD1SH
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« Reply #6 on: June 30, 2022, 08:25:53 AM »

We often use the flow of water as a crude analogy to the flow of electrons, when explaining current flow and voltage drops to newbies. However vague this analogy may be, there's no doubt that water molecules and electrons share one thing in common: when a whole bunch of them get together and head in one direction in a big hurry, it never fails to get your attention.

That's true, but I'm thinking that a winding is less likely to short to the transformer core when there's no potential between the two, thus giving the voltage on the windings no "incentive" to arc to something.
There is truth in what you say, but I was thinking more of physical contact rather than an arc, something that might happen when insulating material breaks down and things touch that shouldn't. The plate transformer in the upper right portion of my photo shorted and provided some of the best fireworks I'd seen in recent years. A post mortem revealed a breakdown in the paper insulation on the secondary to the extent that refugee (migrant?) electrons were flying around furiously looking for a place to land. The carbon tracks were impressive. I'm glad that I never keyed the plate voltage unless the cabinet was closed.
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« Reply #7 on: June 30, 2022, 01:03:54 PM »

Hey I'm a firm believer in insulating older or well-used components. I like to mount the components rather than sit them in place, though there's nothing wrong with either.

2x4s are cheap enough to just cover or make the whole cabinet floor with them as-is. It only takes two 8-footers for most racks.

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W1ITT
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« Reply #8 on: June 30, 2022, 01:24:24 PM »

I'm trying to think of all the big transmitters I've peered into over the last half-century-plus and I can't think of any that had HV componentry sitting on wood.  A couple months ago I was on Tinian and Saipan and Guam and I'm thinking that there were large transformers sitting behind chain link cages and there were big honking ground wires connecting the transformer frames to Mother Earth. If people float commercial transformers, it's rare.
Of course these transformers are purpose-built, bought new and they've been (mostly) well cared for over their lives, not stored in a damp cellar or old barn.  We hams get our transformers mostly where we can without pedigree and hope for the best.  I ground my HV transformer frames here because, if something starts arcing or burning, I want to have some certainty that a fuse or breaker will open up before the house goes aflame.   
A certain Mr Smith of Skowhegan has a method using a pressure cooker and a vacuum pump where he impregnates transformers with some sort of varnish to extend their life.  If the pressure cooker were not large enough, there are pressure canners that might suffice.  It might be worth looking into.
Do what you want, but consider the risks. 
73 de Norm W1ITT
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KD1SH
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« Reply #9 on: June 30, 2022, 02:20:28 PM »

Oh, absolutely, if I were building all new equipment using all new parts, and if mod and power transformers grew on trees (definitely hard-hat territory), leaving those parts floating would be virtually unthinkable. Exigencies often dictate, though.

I'm trying to think of all the big transmitters I've peered into over the last half-century-plus and I can't think of any that had HV componentry sitting on wood.  A couple months ago I was on Tinian and Saipan and Guam and I'm thinking that there were large transformers sitting behind chain link cages and there were big honking ground wires connecting the transformer frames to Mother Earth. If people float commercial transformers, it's rare.
Of course these transformers are purpose-built, bought new and they've been (mostly) well cared for over their lives, not stored in a damp cellar or old barn.  We hams get our transformers mostly where we can without pedigree and hope for the best.  I ground my HV transformer frames here because, if something starts arcing or burning, I want to have some certainty that a fuse or breaker will open up before the house goes aflame.   
A certain Mr Smith of Skowhegan has a method using a pressure cooker and a vacuum pump where he impregnates transformers with some sort of varnish to extend their life.  If the pressure cooker were not large enough, there are pressure canners that might suffice.  It might be worth looking into.
Do what you want, but consider the risks. 
73 de Norm W1ITT
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« Reply #10 on: June 30, 2022, 04:12:24 PM »

It is interesting to study everyone's point of view on this subject.  It essentially appears to be a judgement call between personnel/property safety and equipment/component reliability.  Personally, I realize and respect the technical advantage of floating the core and frame of vintage modulation transformers, modulation reactors, and filter inductors.  I am not sure there is any realistic advantage to floating the core of a plate transformer, since the primary winding is within 120 volts of ground at each end.  Newer hardware likely does not need any help to survive in the amateur transmitter environment, but iron that is older than the operator who is over half a century in age probably needs all the help it can get.  But NOT at the expense of the safety of the operator or the dwelling.

I run old Stancor, UTC, and Thordarson iron.  The 90-year-old Thordarson CHT driver and modulation transformers are grounded/bonded  to the chassis, but I run them at half their rated voltage and power.  Hipot tests revealed no impending leakage or insulation problems when the rig was restored.  But I cannot replace these vintage items, so I do not push them for another half an S unit at the receiver.  I plan to run the UTC and Stancor iron insulated from the chassis, on ceramic insulators.  The main concern here is that the voltage peaks at 100% modulation are double the resting plate supply voltage. 

There will be no flammable substances within or near the transmitter cabinet.  The cabinet is properly bounded to an approved ground, and the requisite fuses and breakers of the proper size are in all the appropriate places.  In addition, modulator and final plate currents are monitored and will trip the primary breaker off upon any overcurrent condition.

If this was a transmitter for commercial, rather than amateur use, I would also agree that the iron should all be grounded to the chassis.  In a commercial environment, there should not be any non-standard "surprises", as any unknowing person may be called upon for service.

In my case, with my amateur transmitter, any floating (ungrounded) iron or capacitor will be clearly marked with large red warning labels.  Even though I have plug-in coils for the final grid and plate tanks, I operate those rigs as "single-banders", because memory at over three-quarters century age is not what it was as a teen.  Swinging links are operated from outside the cabinet via a linkage with insulated and grounded external knobs.  In addition, all my transmitters have door interlocks that remove primary plate transformer voltage AND provide a dead-short to the high-voltage supply as the door is opened.  Not fully trusting mechanical interlocks or contactors, I ALWAYS remove the mains plug from the wall BEFORE opening the door of the cabinet, and ALWAYS use the "Jesus Stick" to verify there are no hazardous voltages within the cabinet before poking my fingers into the equipment.  I do not allow anything flammable to be used for mounting or insulation within the rig.

Bottom line, I do not believe that floating vintage iron is wrong, so long a proper steps are taken to prevent the potential dangers involved.  I do not believe a high voltage potential on the iron cores presents a hazard to the single operator when the above precautions are religiously followed, but I would never consider building a rig for another person with floating iron; that must be the decision of the individual builder-owner.  With everything properly labeled, the risk to the recipient of SK estate sale equipment is minimized, but, realistically, the recipient of any equipment acquired in this manner, especially home-brew equipment, should be duly cognizant and careful to consider all associated risks with unknown equipment.
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Rick / W8KHK  ex WB2HKX, WB4GNR
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« Reply #11 on: June 30, 2022, 06:33:48 PM »

I will refer you to my qrz.com page where I show my gates iron. All on the same platform. 2 layers of 3/4 in plywood. It is tight but fits. Works very well.
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« Reply #12 on: June 30, 2022, 08:31:42 PM »

Having high voltage potentially floating on a transformer core is a bad idea...
... unless there is a protection cage built around said iron that is both clearly labeled and
also able to keep hands and fingers off!

(yes I know that there are often HV terminals exposed on the transformer's topside...)

Perf metal is ok. Even 1/4" galvanized (chicken) mesh mounted by an angle iron frame or similar
would be fine.

Lucite/acrylic sheet - but it does not allow cooling if it is solid... (use some imagination).

So, NO to the plywood. Use suitable metal, and stand off the transformer a suitable distance from
the surface using an appropriate material - acrylic, hdpe, "solid surface" counter top material, ceramic, etc. are
all candidates.

The way to do it is to mount the transformer to a fitted PLATE of metal, and then put that plate
with suitable cutouts - the same way a ceramic feedthru does it - and matching insulating spacer above
with metal bolts and force spreading washers above... hope you can picture that?

Wood is a fire hazard for sure at minimum.

Imho, of course.
Ymmv.

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« Reply #13 on: June 30, 2022, 10:12:27 PM »

Yep, beware of termites in yer transmitter!

73DG
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« Reply #14 on: July 01, 2022, 06:38:53 AM »

my old iron is on teflon or plastic cutting boards. I figgered that would be a better insulator than wood since wood can be a desiccant to some degree and possibly become a leakage path.
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Bob
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« Reply #15 on: July 02, 2022, 06:46:38 AM »

I use Glastic and isolate all my iron from the metal


In the past I used cutting boards, plywood and other insulators.

Then I found out just how cheap real insulation materials where and stopped playing around with things that looked half assed.

Glastic insulators are cheap and I've used them with 3/8 bolts to isolate plate transformers weighing well over a hundred lbs.

--Shane
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KD1SH
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« Reply #16 on: July 02, 2022, 01:49:51 PM »

Good point about recipients of SK gear. I've seen some very weird and potentially dangerous stuff out there, including one big old HV power supply that had Millen jacks for the screen and bias outputs, but a chassis-mount SO-239 for the 2000V B+. I know some people use SO-239's for power connections, but at least label the thing - very conspicuously - as such. I also once came across a PL-259 with a - very nicely soldered with shrink-tube and all - length of AC zip-cord with a two-prong line plug on the other end. Huh


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Bottom line, I do not believe that floating vintage iron is wrong, so long a proper steps are taken to prevent the potential dangers involved.  I do not believe a high voltage potential on the iron cores presents a hazard to the single operator when the above precautions are religiously followed, but I would never consider building a rig for another person with floating iron; that must be the decision of the individual builder-owner.  With everything properly labeled, the risk to the recipient of SK estate sale equipment is minimized, but, realistically, the recipient of any equipment acquired in this manner, especially home-brew equipment, should be duly cognizant and careful to consider all associated risks with unknown equipment.
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