Soft Start Advice

[Jonathan]

I am a little perplexed why a soft start is required, if it is to avoid a spike at switch on/off then a triac with a zero crossing detector would seem to be better.

For 630VA you'd probably get away with it. More interestingly, the best point to switch on is actually when the mains voltage is at a peak - see here.

[paulus.v]

For 630VA you'd probably get away with it.

I thought the same but for no apparent reasons I am unable to turn on my router. My 16A main fuse is tripping. After a few attempts I managed to get it on but later on trying again I manage to blow the T4A fuse at the toroid.

The only reasons I could think about are the temperature drop in the workshop (7°C) or some alterations on the mains electricity supply.

[EddyCurrent]

Take a look at this;
http://www.ft-transformers.co.uk/wp-...ction-50VA.pdf

[paulus.v]

The T4A fuse was just fine, I'll change it with 6.3

I have to check if the MCB is type D. Until now I did not know that there are different types of mcb's based on the instantaneous tripping current.

But my question remains, if I want to implement a soft start will the cheap 10W resistors work?

[cropwell]

Now, after a little bit of digging around t'Interweb, I realise the problem- it's big toroidal transformers needing a high-current fix at switch on. As I haven't used a toroid for anything other than power supplies for pre-amps and mixers I have not had a problem like that to solve. I must pull the case off one of my 1KW PA amps to see what that uses to switch on the power to the toroid in it.

Never got round to that Laplace stuff at Uni, it was over 50 years ago and I studied Geomorphology

[m_c]

A contributing issue is CNC power supplies have a nice big capacitor to charge from nothing at switch on, which contributes quite heavily to the surge.
Placing a resistor inline, limits the surge until everything reaches working voltage.

[Clive S]

But my question remains, if I want to implement a soft start will the cheap 10W resistors work?

Have a read through this :- http://sound.westhost.com/project39.htm there are quite a few posts on this forum regarding " soft start " I have had many in my time usually after a .. Clive

[EddyCurrent]

Steady now, remember what happened last time http://www.mycncuk.com/threads/8251-...5238#post65238
I'm currently on with that myself but it's black nectar

[Clive S]

Steady now, remember what happened last time http://www.mycncuk.com/threads/8251-...5238#post65238
I'm currently on with that myself but it's black nectar

I just can't think what you are on about !! ..Clive