Active Monitor blowing transformers.

[abbey road d enfer]

anyway, what about putting a smaller fuse (~500mA) and use a inrush limiter?

That would be good.

what surprised me is how they used a 35VA one????

That's based on the consideration that music has a very high crest factor (typically about 12dB). It means the average power is about 1/16th of the crest power.
Bob Carver made a business model of it, 1kW amplifier with a 200W transformer.
With switch-mode amps, it is the norm to evaluate the power with burst signals that make the amp deliver its max power for a few hundred mlliseconds before the psu collapses.
This expalins how a 20kW amp can be powered from a 117V 25A socket (3kVA).
Running these amps continuously results in stress to the PSU.
It is not supposed to happen with musical content, except that in a multiway system, the bass and sub amps are submitted to signals that have a lower Dynamic Range, particularly when using compressors.

 

[aviel]

Just curious, what is the Triad transformer model and can you link the specs?

it is VPT48-2040,
spec are here:
ttps://www.mouser.com/datasheet/2/410/VPT48_2080-781492.pdf

 

[aviel]

That's based on the consideration that music has a very high crest factor (typically about 12dB). It means the average power is about 1/16th of the crest power.
Bob Carver made a business model of it, 1kW amplifier with a 200W transformer.
With switch-mode amps, it is the norm to evaluate the power with burst signals that make the amp deliver its max power for a few hundred mlliseconds before the psu collapses.
This expalins how a 20kW amp can be powered from a 117V 25A socket (3kVA).
Running these amps continuously results in stress to the PSU.
It is not supposed to happen with musical content, except that in a multiway system, the bass and sub amps are submitted to signals that have a lower Dynamic Range, particularly when using compressors.

veey interesting! so when they say 100W it means peak of 100W for few msec? so if i give it pink noise at full volume i will blow it?

how does that affect my inrush current limiter selection? for the calculation i need a steady state power. shall i use 100W? its basically saying im expetcing  500mA current

 

[abbey road d enfer]

veey interesting! so when they say 100W it means peak of 100W for few msec? so if i give it pink noise at full volume i will blow it?

Pink noise has a crest factor too. It's 6dB. That means its continuous average power is 1/4th of the peak power. It shouldn't blow the fuse (or amp) but it will certainly produce some heat.

how does that affect my inrush current limiter selection? for the calculation i need a steady state power. shall i use 100W? its basically saying im expetcing 500mA current

Calculation of fuses is very approximate. There's a lot of trial and error needed for finalizing. You want the fuse to blow for a hard fault, like a shorted winding or a shorted cap or diode in the bridge. You can rely on the fact that the transistors protect the fuse, not the other way round.

 

[aviel]

so to conclude this, would you do anything apart from buying a new transformer? even in rush limitter will be problematic. since current will depend on volume of listenibg.

 

[abbey road d enfer]

Buy a bunch of fuses of various ratings and experiment. The CTN in-rush limiter is a good option.

 

[aviel]

Buy a bunch of fuses of various ratings and experiment. The CTN in-rush limiter is a good option.

for inrush limiting, i need to plan it to be hot at normal operating l, right? so using max volume current will result in it being cold at lower listening levels, isnt that a problem?

 

[abbey road d enfer]

When the NTC has been heated by the surge current, the idle current is generally enough to maintain it in the low resistance state. This is with a properly dimensioned NTC.
You need to experiment for the right value.

 

[murrayatuptown]

https://www.ametherm.com/inrush-current/ptc-thermistors-for-inrush-current-limiting
Some good reading at this link & elsewhere on Ametherm website. This article discusses PTC and some NTC thermistor approaches to inrush current limiting.

I was looking for their article on sizing such devices based on power requirement.

Since transformers are VA rated, continuous power is probably more relevant than extrapolated 'need' calculated from crest factor...just my opinion.

I could not get the toroid link to open, even after fixing the broken URL posted. I wanted to look before asking if the windings were unprotected by an outer wrap of some kind of insulation, or the photo was after accessing the magnet wire.

Murray

 

[aviel]

https://www.mouser.com/ProductDetai...6AAo3Kz/HBbyNKLcruHAmTm50IbLqDgtY6XrciFPc8g==
i took out the first winding. it was insulated. maybe the fact that traffo is overrated could cause this?