Damaged Triac before Transformer by an Amplifier - why and what purpose?

[Buffi]

Hi
in a previous experience with triac used to power inductive loads the only way to make triacs survive was an RC snubber in parallel with the triac itself.
Commercial items can be purchased, and usually they consist of an X2/Y1 grade capacitor with embedded resistor. 250Vac types should work fine. Exact values for CAP and RES are not so relevant.

 

[tiefbassuebertr]

I can't quickly spot any triac in the schematic, but in general zero volt switching a transformer (and in particular a toroidal transformer) is about the worse way to do a "soft start". If the zero cross over switching is carried out on a core that is already saturated from previous operation, extremely high currents can result. The order of magnitude of these currents can be as high as the mains voltage divided by the primary DC resistance, so many hundreds of amperes.

You would need a zero current switching, but then this is not what a triac would work nicely with.

thank you for this advice. In this case I have found this:
http://www.te.com/commerce/Document...v&DocNm=13C3206_AppNote&DocType=CS&DocLang=EN
check out also this threads:
http://www.diyaudio.com/forums/pass...r-solution-large-toroidal-transformers-2.html
and post #28 under
http://www.diyaudio.com/forums/power-supplies/152527-large-capacitors-inruish-current-3.html
Concerning SSR's this pdf file is of interest:
http://www.crydom.com/en/tech/newsletters/solid statements - ssrs switching types.pdf

 

[jean-paul]

Why do you imagine that?, the supposed 'change' to 230V was actually no such thing - you still have 220V and we still have 240V.

The only 'change' was the specification for manufacturers, who have to supply equipment that works across a wider range, including below 220 and above 240.

Well I am located here so I should know, we have 230V AC for many many years. This was arranged in 1985 to reduce losses over cabling and also to harmonize with the UK that had chosen 240V. It was agreed that it would go slowly, the norm was that it could take 20 years for everyone to adapt ! This was easier for manufacturers of electrical stuff. The transition took way less than 20 years. In the course of time different taps of the distribution transformers were chosen to "up" the mains voltage (when maintenance was done).

Since I am in the energy sector I see 230V +/400V + (3 phase) readings every day. So I imagine not so much. Strange thing is that everyone still refers to mains voltage calling it "220" and "380" for 3 phase. Old habits... The energy sector itself wants higher voltage but this time it will take more time as there is quite some equipment out there that can't have 250V. Meanwhile there has been a switch to DC high voltage for distribution in some areas, also to limit cable losses.

http://www.3sat.de/page/?source=/hitec/141010/index.html

https://de.wikipedia.org/wiki/Hochspannungs-Gleichstrom-Übertragung

 

[Nigel Goodwin]

Well I am located here and we have 230V AC for many years. This was arranged in 1985 to reduce losses over cabling and also to harmonize with the UK that had chosen 240V. It was agreed that it would go slowly, the norm was that it could take 20 years for everyone to adapt ! This was easier for manufacturers of electrical stuff.

Since I am in the energy sector I see 230V + readings every day. So I imagine not so much. Strange thing is that everyone still refers to mains voltage calling it "220".

Interesting Jean-Paul, it's the first suggestion I've heard of actual 230V - apparently the current spec is 230V +/-10% to accommodate either 220 or 240, every time I've checked here it's been close to 240.

Interestingly, I've driven through a place a few times recently, that used to generate their own power (and supply the local area) until relatively recent times (not that many decades ago) - and they actually supplied DC, at something like 200V or so I believe?.

 

[jean-paul]

In the UK it has been 240V all along. Here the current specification is 230V -6%/+10%. Whenever I get old equipment in my hands I adjust it to the 240V tap (if it has that) as voltages above 230V are common. The older 220V standard is still in use in China, which explains why many chinese devices sold on the web have 220V (tightly specced as more copper windings means higher cost) transformers that may hum if used in Western Europe. 230/240V was a wise choice compared to 110/115/120V grids as the latter need higher current rated stuff with higher losses which makes it a more costly affair and they're also more prone to failure. Higher inrush currents etc.

I have never seen low voltage DC power distribution except for the old but still very popular - 48V DC ( + to Ground) standard in telecom equipment which is elegant in its simplicity. Just a 230V AC to 24 V DC rectifier and 4 x 12 V batteries in series and you are done. Simplest UPS in the world 😉 Low voltage AC/DC power distribution means heavy switches, heavy fuses and thick cabling. In energy distribution voltages are nearly always high to very high. The higher the voltage the lower the current which makes a difference in losses and cost price of building, maintaining, repairing and exploiting the network.

 

[Nigel Goodwin]

In the UK it has been 240V all along. Here the current specification is 230V -6%/+10%.

Hi Jean-Paul, I think you've got that the wrong way round - there was a transitional period where the UK was 230V -6%/+10% (to better cover 240V), but 220V countries (like Germany) were 230V +6%/-10% (to better cover 220V).

But once the transitional period ended the spec was unified to +10%/-10% - which when you think about just uses the worst case for both.

Historically here in the UK we had major transformer failures in German equipment, such as Grundig (we used to be a major Grundig dealer), or anything that was 220V and no tapped transformer for 240V.

Certainly it's a LOT better now, but of course the proliferation of switch-mode supplies would have cured the transformer problem in most electronic items.

I have never seen low voltage DC power distribution except for the old but still very popular.

There were various voltages and frequencies used here, along with DC in places - probably the same in industrial countries everywhere, systems had to develop before standards could be set.

I don't know if you ever noticed?, but lot's of Japanese equipment used to always be switch-able 120/240V as after WWII their infrastructure was rebuilt by the UK and USA, so the UK rebuilt it as 240V, and the USA as 120V 😀