INRUSH CURRENT LIMITER

[AA4PB]

"light bulb savers" were disk rectifiers, you got DC at the bulb.  cut half the wave off, reduced light.

The "light bulb savers" that I have are NOT rectifiers. They are carbon resistance elements that are high resistance when cold and low resistance when hot. They cause the light bulb to turn on slowly (I can see the difference), thereby reducing the "shock" to the bulb filament. I got tired of using a ladder to get up to replace the bulbs in the fixture over the foyer every few months. I put in the "light bulb savers" over 10 years ago and have changed a bulb only once in that time.

[WB2WIK]

Inrush current limiting is not just to protect the power switch or other internal components.  It is needed to prevent transients on your AC line from damaging other equipment.  I watched our nearby big screen TV power supply fail as I turned on my computer, which had particularly bad inrush current (enough to make the lights in the room flicker).  Troubleshooting revealed the TV power supply switching chip had failed.

As we usually have little control over our AC line regulation or the susceptibility of other devices, keeping AC line current transients within reasonable limits is a good idea.

 73,
Glenn AC7ZN

That doesn't make much sense to me.  For many years, computers have all used power factor corrected switchmode power supplies that have very little inrush current, and won't even meet international compatibility standards if they create a line transient.

Re huge inrush currents and line transients, I doubt anything is as bad as large electric motors are.  My central A/C system consumes 40A at 240V and uses a remote contactor to start the compressor and creates such a huge line sag that when it starts the lights in the house can "blink" and it's never damaged anything.  Nor have my 1-1/2 HP pool and spa pumps, or large Kirby vacuum cleaner, or...really anything.

[AC7ZN]

WB2WIK:>>That doesn't make much sense to me

I would agree had I not witnessed it.  But the schematics of most computer power supplies show a simple offline rectifier/capacitor scheme with a varistor inrush limiter, and a simple EMI filter consisting of a common mode choke and capacitor.  No power factor correction.  Having worked with the cheap power supply shops and agency approval, I can tell you that as soon as they get agency approval it is a constant fight to keep them to the approved design.  They will constantly remove or substitute parts and 'see if anyone notices'....

For whatever reason, this supply was nasty enough that I was already worrying about its effect on other equipment...thus I witnessed firsthand the TV failure.  Have not seen a computer supply that bad before or since.

73,
Glenn AC7ZN   

[WB2WIK]

Hi Glenn,

For the past several years (2004?), computer power supplies rated >70W output power have been required to have PFC, by EU (EC) Directive; so if you don't have PFC, you're out of the entire EU market, and lots of other places that go by the same standards and directives.

I've never seen a modern computer power supply that does not have active PFC circuitry, other than the little "brick" power supplies for laptops, which can be exempt due to their lower power rating.

They all must meet EN 55022 as well as EN 61000-3-2; -3-3; -4-2; -4-3; -4-4; -4-5; -4-6; -4-8 and -4-11 in order to be exported, imported or marketed, so the schematically simple design you describe would be completely illegal today for any kind of SMPS at the power levels typically used.

[AC7ZN]

Thank you, that is interesting.  It is obvious I have not been in the power supply 'loop' for a while.  The power supply I refer to predated the EU directive.

73,
AC7ZN

[ZL1BBW]

I just use a 40 watt lamp in series with one leg of the power  supply and a switch to short it out.  Turn on, watch the HT climb, then flick the switch and it climbs some more.

[WA7PRC]

I installed step-start in my SB-220 simply 'cuz it was easy to do and I was tired of hearing the plate xfmr go BUZzz at power-on.

vy 73,
Bryan WA7PRC