Inrush current limiting necessary for EI transformers

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Hi Bama Slamma,
Let's just say that your power switch will last longer with an inrush current limiter. It depends somewhat on how much capacitance you have in there too.

You don't really "need" a limiter, but they are nice to have. You can always just use a large, high current power switch.

-Chris
 
Hi,
an advantage of soft start is the ability to use a close rated mains fuse giving better protection in event of a fault.

As an example your 320VA on 120Vac supply may run reliably with a T2.5A or T3A fuse when soft started.

Without soft start it may require a T6.1A or T8 just to get it started, or maybe worse.

BTW. are you planning to run 150W +150W into 8ohm speakers from a 320VA transformer?

Seems a bit low, particularly if the speakers are really 6ohm or 4 to 8ohm as has become popular of late.

Don't even think about using 4ohm speakers.

You can recover some of the amplifier ability by using larger than normal smoothing caps (or more in parallel) but this may aggravate the on-line starting.
 
I checked with the designer and he said a 320 VA transformer will run two amps for stereo. All my speakers are 8 ohm. Since the amps are class AB, don't they only draw max current at max output? What I plan to use my creation for is home listening at low to moderate volumes and maybe small PA system use. With +-56 volt rails, the amp is rated 230 watts rms at 4 ohms. A 320 VA transformer does seem undersized for running at max power int 4 ohms.
 
Hi,
your 320VA is underpowered for 150W+150W into 8ohm speakers, never mind the 4ohm possibility.

a normally sized transformer would be rated at about 1.5 times total output power into your chosen load. That equates to 450VA.

As I said before, you can recoup some of the PSUs ability by oversizing the smoothing caps. I would guess at +50% for that 67% transformer VA.

A normal transformer would fit my usual recommendation of 2 to 3mF/Apk of output current. i.e. 12mF to 18mF. and adding 50% to these gives 18mF to 27mF.

Looks like it would be worth trying 20mF or 25mF which also happen to give a sensible RC value of 160 to 200mS (just right for good bass.

If you think you might do party nights or light duty PA then fit BIG sinks. Heavier duty would probably need fanned sinks.
 
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