At 2:12 AM +0000 10/18/03, olympus-digest wrote:
>Date: Fri, 17 Oct 2003 12:33:04 -0700
>From: Jim Brokaw <jbrokaw@xxxxxxxxxxx>
>Subject: Re: [OM] Re: [OT]Transformers (was Noisy T32 (wax potting))
>
>on 10/17/03 10:50 AM, Joe Gwinn at joegwinn@xxxxxxxxxxx wrote:
>
>[snip]
> >
> > CH suggested using real electrical potting varnish, which would certainly
> > work
> > very well, but as he said it's hard to get these materials, at least in
> > small
> > quantities. But CH does give me an idea -- ordinary shellac, available at
> > paint stores everywhere, would work and again isn't going to hurt anything.
> > Shellac can also be thin enough that it will simply soak into the
> > transformer.
> > Remove the shellac by soaking in alcohol.
> >
> >
>[snip]
>
>CH also mentioned that the T-32 transformer is a ferrite-core part. Hence no
>laminations, so the noise must be coming from something else. I'd be
>inclined to closely check the solder joints for vibration induced
>'cold-solder' effect, maybe touch them up anyway, then flood the coils with
>something that might damp out any vibration in the wire loops. I suppose wax
>or shellac or whatever could be used. If it isn't sounding like a 747 taking
>off I don't think I would make the effort... if you can hear it at least you
>know its working. <g>
What I forgot to mention about ferrite (and some kinds of transformer iron,
especially kinds with lots of nickel) is that depending on the kind of ferrite
and the intensity of the alternating magnetic field in the core material, the
core material itself may be changing size in proportion to the field intensity.
This effect is called magnetostriction, and if it's the problem,
bolting/clamping won't help much, and the only thing likely to work is potting
in some kind of not-quite-solid material with high internal acoustic damping to
muffle the noise. Wax is such a material, but shellac (which dries hard) is
not. (If one plans to use both wax and shellac, apply the shellac first.
Shellac contains a little wax, but not enough to help with damping.)
I don't think the solder joints can possibly be generating the noise, so I'd
leave them alone. Adding clamps and/or potting/damping material is probably
the only way to silence an existing transformer in an existing design.
I must admit I prefer some noise from the flash, so I can be sure that it's
charging. But not too much noise; I don't mind having to bring the flash up to
my ear.
At 2:12 AM +0000 10/18/03, olympus-digest wrote:
>Date: Fri, 17 Oct 2003 23:15:25 +0100
>From: "Julian Davies" <julian_davies@xxxxxxxxxxxxxx>
>Subject: Re: [OM] Re: [OT]Transformers (was Noisy T32 (wax potting))
>
>Yes, drilling ferrite cores would be a neat trick! My guess would be that it
>is the entire coil bouncing as a unit on the core. A few loose turns on the
>coil won't usually produce too much additional noise, assuming that they are
>neatly wound (which may well be an assumption too far, of course)
>Where I would be concerned in covering the entire coil with shellac or
>similar is that this will rapidly impinge on the heat dissipation of the
>coil, which is already marginal (hence the overheating issues on rapid -
>firing sequences), so go sparingly.
Drilling ferrite is easy -- with a diamond bit, lots of water, and patience.
Just like drilling ceramic tiles or glass. If the hole is deep (as measured in
drill diameters), a drill press is required.
CH mentioned that often the ferrite core pieces aren't clamped securely
together, and so vibrate against each other. This can be tested by pinching
the pieces together with the fingers, to see if the noise is affected. (Beware
the high voltage on the circuit board.) Potting with shellac or wax will fix
this problem.
As CH also mentioned, potting acutally improves heat dissipation, as the
potting agent is always a far better conductor of heat than air. The final
limit on dissipation is watts of heat generated per square centimeter of
surface area, as the heat must be carried away by heat transfer to the air.
The fact that the transformer is prone to overheating implies that the field
intensity in the core material is quite high. This is typically done for cost
reasons, to allow use of a smaller core.
I must say I'm amazed by how many people in this, a photo group, have direct
knowledge of transformers and their manufacture, an arcane art to be sure. I
suppose I shouldn't be amazed, after discovering a hard-rock miner turned
photographer, and so on. And the fact that this group is dedicated to a
mechanical silver-based camera system from the 1970s. But it all shows how
widely based a group this is.
Joe Gwinn
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