Unless anyone has experienced it. What would happen if that thick aluminium sheet, nominally stuck as screening, to the chipboard interior of a band amp carcass , drooped down and touched the top of the coachbolt that holds the mains transformer to the chassis ?
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I imagine that if the aluminium sheet is earthed via the chassis there would be some smoke due to a single shorted turn.
Gareth.
SPLATTTTT (maybe) Fizzzzzz (possibly) POP as the fuse blows.
All of the above assuming that it is a toroidal transformer and that aluminium foil is connected to the chassis
How? The OP says the coach bolt is holding the transformer to the chassis. Everything is at the same potential, presumably earth.
-- Regards - Rodney Pont The from address exists but is mostly dumped, please send any emails to the address below e-mail ngpsm4 (at) infohitsystems (dot) ltd (dot) uk
You'd end up with a new metallic pathway (chassis, up through the bolt, into the aluminum sheet, and then to the chassis again) which forms a loop going through the center of the toroid.
In effect, you would have added an unwanted one-turn secondary winding to the transformer, and then shorted it... just as if you had looped an isolated wire through the center and then soldered its ends together.
You'll end up with a *lot* of current flowing in this one-turn secondary winding, and (as a result) through the primary... just as you would have if you had short-circuited one of the "real" secondary windings.
It'll be a good question whether the mains fuse/breaker will blow fast enough to keep the sheet from arc-welding itself to the top of the bolt. In any case, it'll probably be reasonably spectacular.
--
Dave Platt AE6EO
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eDepends on the resistance of the total loop. Bolts are usually steel, and steel is rather high in resistance.
In your typical transformer, with say three turns per volt, you now have something like 300 millivolts AC running into anything from 0.1 to 1 ohms. Taking the worst case, E^2 / R is about 1 watt. That will cause a little local warming but not much else.
Hmm, I hadn't thought about the field. I suppose a lot would depend on how good a contact the aluminium sheet that had fallen made with the rest of the chassis.
-- Regards - Rodney Pont The from address exists but is mostly dumped, please send any emails to the address below e-mail ngpsm4 (at) infohitsystems (dot) ltd (dot) uk
Well, if it closed a circuit one hell of a current would flow through a single shorted turn and the magic smoke might come out (depends on if the designer knows how to fuse equipment properly).
Graham
Not the ones that go through toroids !
In a power amp ? Much more volts/turn than that. At least a volt from memory (typically).
Graham
Never forget the field !
True. Bad luck would probably ensure a good contact.
Graham
So what DID happen ?
Graham
aluminium
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I've no idea , its a thought experiment. Could not find the current carrying capacity of a 3/8 inch steel bolt, assuming the worst case would be something like one turn of a 3/8 inch steel ring.
I see where too many owners pull these amps out of their housings and then not know how to use an old vinyl record sleeve or couple of steel rules or similar to reintroduce amp to casing.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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