Softstart (new guy) Question

[greenm01]

Hello,

I'm working on my first DIY gainclone project, and have a simple question:

If I'm using a softstart, is it good practice to still use a fuse on my unregulated 500 VAC power supply?

/Mason

[CanAm Man]

Are you using an in-rush limiter, as your softstart device?

If so, the answer is "yes". The in-rush limiter "limits" current flow while the flux field is initially building in your trasformer core upon start up. It does this by introducing a resistance (while the in-rush limiter is "cold). Shortly after power is applied, the in-rush limiter resistance drops (ans the limiter warms), and effectively removes itself from the mains circuit.

The fuse is there for over-current and/or catastrophic failure under operation. Don't depend upon the in-rush limiter to "open" and remove mains voltage--this is a function of the fuse, so include it in your design.

To respond in another way--if commercial designs use both in-rush softstart limiters AND fuses (and so do good DIY designs....), then you should, too? Yes?

[greenm01]

I appreciate the clarification. I plan to use this softstart board from sjostromaudio, but will also utilize a fused power module like this one on my chassis.

Thanks!

[AndrewT]

That ON/OFF switch combined with Mains Fuse and IEC socket is a good idea.

It allows back panel control of OFF and front panel control, at low voltage, of Standby/ON.

The soft start you have chosen is a relay bypassed version. Exactly the type I recommend.

[CanAm Man]

Yep... Considering you're going with a relay bypass softstart (and not a thermistor one, as I had assumed....), Andrew T is giving you good advice.

Go for it.......