Power Supply Protection - Inrush (very nerdy)

[MEXICOWANDERER]

Adequate protection means a two-step process. Limitation ramping of AC inrush current in conjunction with a delay-on-make DC relay load isolator. Starts off with load isolation, when softened inrush is complete, switching of DC output.

Objective: Significant increase in circuit board component lifespan.

https://www.ebay.com/itm/110V-Class-A-High-Power-Amplifier-Temperature-Protection-Board-Soft-Start-/...

https://www.waytekwire.com/item/75580/White-Rodgers-DC-Power-Relay-Contactor-/

https://www.ebay.com/itm/H3Y-4-4PDT-Power-On-Time-Delay-Relay-Timer-w-Socket-3-5-10-30-60S-3-5-10-30...

(choose the 1-30 second module)

Note. The timer has built-in hysteresis which limits upramp problems


Analysis: This is a "project board" job. (2) modules. The first being the device being controlled, the 2nd being the components listed above. The DC power relay is deliberate megaton overkill rated because of limiting vulnerability of power supply DC output arcing damage.

Is it worth it? For Junk Store grade converters...no. Justification comes from cost of control accessories versus what it is protecting and what early power supply (converter) failure means to the individual consumer.

This is intended to be a discussion and specifically not a recommendation...

[MEXICOWANDERER]

50 amperes inrush impressed me. The circuit board does have a 10 amp axial glass-tube fuse. The two largest capacitors 200v 680uf are of most concern. I could downgrade to a 100-ampere White Rogers relay which chops about thirty eight dollars off the price. Dang! I need my oscilloscope and 4" analog 10 ampere Simpson panel meter and pickup. Switch on power supply and 40 amps DC output appears "in the blink of an eye". Yes, this is an exercise of picking nits. The thermistor issue is that I am working with 90F ambient temperatures down here. I would need a high capacity thermally "compensated" thermistor. My circuit does not care about that. The audio amplifier ramp looks like it would live for a long time, I am unsure of the projected Lifespan of the time delay relay for the White Rogers power Relay.

Jeezo, Brenda and Jesus, auntie Andrea, they ALL are addicted to Mexican soap operas. The women sneered when I labelled them "The Idiot's Guide to Marital Problems".

[westend]

Well, that relay is beyond MY lab budget. If I wanted to protect a lower amperage DC circuit against inrush, especially one with a transformer or inductor based power supply, I might choose an Omron relay and a couple of thermistors. A lot depends on how much current is being passed along.

[MrWizard]

especailly when the tube is showing "tele Novelas" instead of good SciFi

[MEXICOWANDERER]

Yup. And thermistors get tired and they are "difficult" to select for profiling the inrush. Not only does softening the current peak help borderline charging sources (generators) but shocking large electrolytic capacitors is bad juju for them getting gray hair prematurely.

I would love to see a full five seconds elapse for capacitors to charge then engage the output. Wouldn't it be nice to ramp the output as well? That is beyond my pay grade. Ramping the voltage divider 10-turn pot would be the way to do it but end resistance would have to be precision controlled and dead-on repeatable.

When I engage my massive 400+ lb ferroresonant charger* it actually bangs hard enough to feel it in my feet. I was fortunate enough in 1987 to bid on a partial box of 480uf 1240vdc capacitors (17). The first set lasted 24 years and a week before the NYC attack I found my trusted #13 transformer tap had shifted almost .40 volts higher. The caps were dying. Curious? How big are these puppies? Roughly the size of a 64 oz can of tomato juice only about three inches taller. Manufactured by "Linol" in Illinois. I am afraid to start pricing a soft start and delay contactor setup for the Big Belden. The 180 ampere ATS was bad enough.

*The charger is as big as an old timey Wells Fargo safe. It has a 3' tall full width hinged door. I got cute and installed a 30 watt LED lamp and "inside" voltage and amp meters. A massive 10-watt 3000 ohm 5-turn Ohmite pot (also NASA) controls an H1 and H2 tickler transformer. An 80 watt 240vac ball bearing squirrel cage fan blasts the inside with "cooler" air.

Setting the generator, and chargers and wiring everything, took 3-months of 7-day workweeks. Jesus and crew helped under supervision. They had to have days off. I worked like a dawg.

The power supply soft-start is a hobby make-work exercise. But a time is coming when I will not be around, and I want to leave the kids set up with stuff that will endure.

Beats vegetating in front of the boob-tube.

[pianotuna]

Hi Mex,

Would it not be possible to just use a thermistor?