mounting the transformer

fajimr · « **on:** 30 Nov 2005, 03:32 pm »

hi all...

I'm still in holding pattern here but I am slowly getting everything together so I can start to build

I just ordered the transformers from plitron and asked about the mounting washers. The reply was that since it came with potting (I assume this is the hole in the middle??) I didn't need any washers. The person there told me unless I was going to mount it sideways (haven't seen that yet) I wouldn't need them. But when I go through the gallery it seems like most builders have a washer to mount the tranformer. I also saw in Bill Menckle's site that he used both a metal and rubber (plastic?) washer...

what say ye?

soitstarts · « **Reply #1 on:** 30 Nov 2005, 06:15 pm »

Same here.... I ended up using a holesaw and drilling a piece of aluminium to make my washers up..

fajimr · « **Reply #2 on:** 30 Nov 2005, 06:21 pm »

Quote from: soitstarts

Same here.... I ended up using a holesaw and drilling a piece of aluminium to make my washers up..

hmmm, sounds like the washers would be a good idea then

soitstarts · « **Reply #3 on:** 30 Nov 2005, 06:30 pm »

Yep, I didn't like the idea of a bolt through the "resin" with a small washer. Not enough surface area in my humble opinion...

AKSA · « **Reply #4 on:** 30 Nov 2005, 08:35 pm »

Yep, a washer is a great idea, but you can get away with hard plastic or plywood. The resin is tough but not hard, and with no washer there could be distortion. But be assured any central distortion in the potting resin would have no impact on transformer operation, though it would make it loose and liable to cause mechanical damage if it moved around in transit.

BTW, when you mount a toroid with a bolt and washer you must be sure to avoid any electrical contact OUTSIDE the toroid betwen top and bottom of the attaching bolt. So, don't attach the upper bolt to anything on the case; the toroid will interpret this as a single shorted turn, and hundreds of amps will flow at switch-on, destroying the toroid and possibly even damaging the house wiring.

Cheers,

Hugh

wmeckle · « **Reply #5 on:** 1 Dec 2005, 04:39 pm »

Hugh said:
>BTW, when you mount a toroid with a bolt and washer you must be sure to >avoid any electrical contact OUTSIDE the toroid betwen top and bottom of >the attaching bolt. So, don't attach the upper bolt to anything on the case; >the toroid will interpret this as a single shorted turn, and hundreds of amps >will flow at switch-on, destroying the toroid and possibly even damaging the >house wiring.

Hi Hugh:
My Toroids (Plitron # 77019201) came with a neoprene washer on one side. I ordered another neoprene washer (# 670104) for the other side and two steel dish washers (# 680005), one for each side, and mounted them to a bracket with a 1/4-20 bolt & nut.
The bracket is bolted to the case/heatsinks, so I really don't understand what you mean by "OUTSIDE the toroid". The only electrical connection possible could be between the bolt and the hole in the toroid, and that hole appears to be filled with potting material, so ? Have had no problem ? ?
Yet ? ?

fajimr · « **Reply #6 on:** 1 Dec 2005, 05:56 pm »

opps sorry for destroying your last name Bill

when you said:
> I ordered another neoprene washer (# 670104) for the other side and two steel dish washers (# 680005), one for each side,

do you mean that you ordered a total of FOUR steel dish washers (2 x 2)?

thanks

wmeckle · « **Reply #7 on:** 1 Dec 2005, 06:29 pm »

Quote from: fajimr

do you mean that you ordered a total of FOUR steel dish washers (2 x 2)?
thanks

Hi Fajimr:
Yes, two (both sides) for each Xformer.

AKSA · « **Reply #8 on:** 1 Dec 2005, 06:34 pm »

Bill,

If one side of the attaching bolt is attached to the case, that's fine.

If both sides of the attaching bolt, head and nut at the other end, are attached to the case, then the toroid sees this as a single shorted turn and it's not fine.

Since you've only got one side connected, you should be fine, but if you have made a mistake you will soon know as the fuse will blow!

Cheers,

Hugh

lazyfly · « **Reply #9 on:** 2 Dec 2005, 12:29 am »

And now's a good time for a friendly safety reminder. Everybody is using a correctly rated fuse, right?

WOOHOO, my 5th post and still no Aksa gear :/

fajimr · « **Reply #10 on:** 2 Dec 2005, 07:48 pm »

just to let you know... I've followed up with Plitron and found their customer service to be EXCELLENT... very willing to work with me after the sale and make sure everything is right... highly recommended for those in N.America looking for a transfo.

from this reviewer

Jens · « **Reply #11 on:** 3 Dec 2005, 03:51 pm »

To avoid the problem Hugh refers to you can also use a non-magnetic bolt (brass, stainless steel). I prefer that anyway to ensure that the tranny doesn't get 'confused' about the steel core

Greg Erskine · « **Reply #12 on:** 3 Dec 2005, 09:50 pm »

Quote from: Jens

To avoid the problem Hugh refers to you can also use a non-magnetic bolt (brass, stainless steel). I prefer that anyway to ensure that the tranny doesn't get 'confused' about the steel core

Jens, that doesn't sound right to me, the bolt needs to be non conductive, i.e. plastic or nylon. Hugh is talking about creating a shorted turn.

regards
Greg

rabbitz · « **Reply #13 on:** 4 Dec 2005, 12:49 pm »

Has to be non magnetic like brass, austenitic stainless steel, most non ferrous materials.

Works like air core inductors in speakers. Put a bolt up the middle of an air core inductor, and the inductance goes up.

Are Jens and me talking about the same thing as Hugh?

jules · « **Reply #14 on:** 5 Dec 2005, 04:11 am »

This one has always perplexed me but thanks to Hugh for the "shorted turn" explanation.

This being the case I agree with Greg in that the only solution is a non-conductive bolt.

We aren't talking about a situation like an air core/iron core inductor but simply the creation of a giant closed turn through which induced current could run ... through the floor ... up the sides ... back into the top washer/plate ... down through the bolt ... wham, short! Copper would probably be the worst possible material in this situation [edit: if an accidental short occurred] and as Greg says, a non-conductor like nylon, the best.

jules

rabbitz · « **Reply #15 on:** 5 Dec 2005, 06:07 am »

OK.... shorted turn it is. Isn't it just a matter of installing the toroidal as per the manufacturers instructions..... bolt through the chassis and into the top metal washer with no contact of the bolt on any other part of the chassis?

Nylon bolts don't exhibit a great deal of strength and if I want a toroidal standing up, I use a timber locating / supporting spiggot attached to the side of the case. You then don't have to worry about loads being taken by a bracket / top washer or bolt as the spiggot does all the work.

jules · « **Reply #16 on:** 5 Dec 2005, 06:48 am »

I agree

It was far too narrow of me to suggest that the "only solution is a non-conductive bolt". Wooden top, wooden floor, spiggots, insulated washers etc etc.

The thing about this particular problem is that it isn't obvious unless it's pointed out but can be very destructive. I think someone here mentioned the possiblity of inadvertently creating a short by resting a metal lid on top of a case simultaneously touching the transformer bolt by accident.

The standard arrangement is fine, in relation to this problem anyway, so long as the risks are known.

jules

AKSA · « **Reply #17 on:** 5 Dec 2005, 09:27 pm »

Jens, Peter and Jules are all correct, but there are two phenomenon here. One concerns the magnetic permeability of the securing bolt, which alters the inductive properties of the core, while the other is a shorted turn, reliant only on electrical continuity through a shorted turn.

Jens is correct, a ferrous bolt will actually alter the core properties of the transformer. HOWEVER, the core material is a coiled strip, surrounded by copper turns, and the magnetic circuit is therefore contained within the doughnut of the toroid. A ferrous part inserted axially into the center won't have much effect since the copper turns concentrate the magnetic field inside the toroid rather than within the centre, which is free space.

As for the shorted turn, just be sure that the securing bolt is attached to the chassis at one end only, not both. Then there can be no shorted turn.

Cheers,

Hugh

wmeckle · « **Reply #18 on:** 6 Dec 2005, 10:09 am »

Quote from: AKSA

Bill,

If one side of the attaching bolt is attached to the case, that's fine.

If both sides of the attaching bolt, head and nut at the other end, are attached to the case, then the toroid sees this as a single shorted turn and it's not fine.

Since you've only got one side connected, you should be fine, but if you have made a mistake you will soon know as the fuse will blow!

Hugh

Ok, Hugh, you've given me the idea that it is not a good idea to have a steel Xformer mounting bolt. So, I just ordered from McMaster-Carr some 1/4-20 cap screws, 3" long brass and the same size in PVC. Will try both. Seems like cheap insurance to me ?

PSP · « **Reply #19 on:** 6 Dec 2005, 02:28 pm »

Consider a wire which is carrying a current. If we now run that wire through a conductive loop, current is induced in the loop. This is how "clamp" ammeters work.

We can do the same thing by running a wire through the center of a torroid and connecting the ends of the wire somewhere outside the torroid to form a conductive loop. When we apply power to the torroid, enormous currents can flow through the wire loop. Do not try this at home!

The "shorted turn" condition will occur anytime we have an electrically conductive bolt (it could be made from pickled herring if the salt concentration was high enough) running axially through a torroid and we provide an electrical path that:
(a) connects the two ends of the electrically conductive bolt, and
(b) runs outside the torroid.

This could be a wire attached at both ends of the bolt or it could be the chassis--if the chassis is electrically conductive and if the mounting bolt is connected to the chassis at both ends.

I use a 1/4 inch stainless steel bolt attached to the floor of the chassis. Plitron supplies a large rubber mounting gasket, and I use a large metal washer on the outside of the chassis to spread the mechanical stresses. This allows me to firmly mount the heavy xfmr without deforming the chassis.

Peter