Circuit help: switching a load only at peak of mains

"JB"

In the case of LED and CFL lamps, the high inrush surges commonly seen are reduced by a factor of at least 5 because voltage rise time is controlled at

The MOC3062, 240V zero crossing opto driver and a 16A triac ( possibly a snubberless type ) would be a good start.

... Phil

Den onsdag den 18. september 2013 10.39.26 UTC+2 skrev Phil Allison:

all in one:

-Lasse

"Lasse Langwadt Christensen"

Single source, relatively expensive and liable to become unavailable.

Suitable 6 pins optos and 3 pin triacs are not going away any time soon.

... Phil

Ahh very good point. Thanks Jim. I suppose you could put two low passes in the circuit (with some sort of tw eak) to get more or less than a 90 degree phase shift. But at that point y ou might as well add an opamp and make an all-pass.

You are absolutely correct! It's now become down right *rude* to use googl e groups for usenet. (Or a major pita to remove all the extra lines.) I'l l have to write them a note, and see if eternal september will take me back . (Maybe tomorrow :^)

George H.

This is sort of what I had in mind. It seems the simplest and we can implement this easily here. Thanks to all for suggestions.

JB

Any advance on 12.5?

who has 20Hz power?

The simple way using a bridge between AC and Load is to put a small series resistor on the ground side of a large cap with some load for small ripple . This ensures the cap current charges only for a short time before peak wh en you can use the cap current sense to drive a triac with ~1V just before peak voltage.

It is useful to know that random switches such as Relay contacts without ZC S rely on the random phase for calculating the cummulative aging effects of surges. to rate lifetime. This is how Omron, the experts in Relay, des ign factors lifetime vs load current and number of cycles. This means you don't need to design a tester for this and can calculate the worst case inr ush based on the ESR of the load cap.

Arc currents are worst for contacts on Caps loads when closing and on induc tive loads when opening.

Snubbers reduce the harmful effects of inductive loads and ICL or NTC inru sh current limiters reduce the harmful effects of low ESR capacitive loads when discharged and switched at peak voltage.

If need references search the Omron site or just ask me. This random pha se on AC loads are the soe reason why Relay contacts have higher current ra tings than DC loads as the AC switch current is less than peak worst case most of the time.

Whereas in DC it is always worst case with 0V for initial conditions.

"Anthony Stewart"

The simple way using a bridge between AC and Load is to put a small series resistor on the ground side of a large cap with some load for small ripple. This ensures the cap current charges only for a short time before peak when you can use the cap current sense to drive a triac with ~1V just before peak voltage.

" I have a series of measurements to make of the inrush current ... "

FYI: " inrush current " refers to the one time transient at initial switch on.

ZCS rely on the random phase for calculating the cummulative aging effects of surges. to rate lifetime. This is how Omron, the experts in Relay, design factors lifetime vs load current and number of cycles. This means you don't need to design a tester for this and can calculate the worst case inrush based on the ESR of the load cap.

" ....the inrush current of a range of LED drivers and electronic ballasts"

The OP is not designing the loads, they are out there in the market already.

The worst examples of which are yet to appear.

... Phil

Phil you failed to comprehend.

A peak crossing Triac is simple taking to 90 phase shift in a low pass filt er as I explained sensing cap current at peak.

Another way is to use a 5ms one shot after each zero crossing.

Use a small signal diode bridge to make a full wave rect signal. Use 100:1 resistor divider to get down to logic levels or use an opto coupler if uns ure. A full bridge is equal to an XOR gate that will give you a 100Hz rat e Zero Crossing Switch pulse from 50Hz in. Usinga 5 ms one shot delay to f ire another one shot to trigger the Triac will guarantee peak voltage switc hing.

Since Phil failed to comprehend the accumulated wear factor of a random swi tch on AC loads and how surge varies dependant on phase which affects surge , Relay engineers rely on this random nature to increase the rating lifetim e of a Relay. This would not apply to dimmer Triacs as the repetition ra te is at line frequency and non-dimmable reactive ballasts would fry the Tr iac in a few seconds hours or days depending on reactance of CFL or LED bal last.

In Omron's site they will specify conditions for reactive loads such as,

Note:If the L/R of an inductive load exceeds 7 ms with a Model for a DC Loa d, the arc interruption time must be less than approximately 50 ms to use t he Relay. Design the circuit so that the arc interruption time is 50 ms or less. *These values apply to a switching frequency of 30 times per minut e.

In Capactive loads, the critical factor is the current limiting resistance of the switch, diodes and the Cap ESR.

I stated if you know the reactance and the ESR, you can save the trouble of testing a product, with surge currents at peak voltage, just measure the i nput impedance . But if you don't know, then by all means test it.

"Anthony Stewart"

Listen pal - YOU are a raving nut case, obsessed with your mole hill of knowledge on an irrelevance to the OP's problem.

PLUS you are breaking all the rule of usenet posting.

Snipping the entire context and posting speeches is ABSURD !!

.... Phil

Phil,

TO be prudent, ethical, practical and rational please stick to the topic an d suppress your personal remarks. Use intelligent corrections if you disput e my assertions.

1. 90 Phase shifter to trigger Triac at peak voltage using RC current sense . Works.

1. Relays with AC contact ratings are rated higher than DC because DC has m ax surge each time, AC does not due to random phase and surge currents are thus averaged to extend peak current ratings.

2. AC also suppresses sustained arcs from zero cross on turn off, but ques tion here refers to turn on surge.

1. Zero crossing clock derived from Line AC sinewave with frequency doubler ( bridge or XOR gate followed by 5 ms one shot delay for 90 deg phase shif t at 50Hz will be provide trailing edge precision to trigger a 2nd one shot to fire and latch a Relay for RC time constant of one shot or simply fire a Triac for next cycle depending on desired component to be tested with des ired loads.

2. No one knows more about Relays than Omron

If you disagree be sure to back it up with facts and not weightless opinion s.

"John Fields"

... Phil

To back up my assertion that no one knows more about Relays than OMRON , I offer this to anyone who wants to learn more about Relays, drivers etc.

Example of a well written Relay Spec ,

Note it is limited by power dissipation for small size.

Vacuum-sealed Relays? Although air can sustain arc burning it cannot preve nt it. Vacuum sealed Relays are not used in small items due to poor heat transfer of contacts which is the limiting factor for contact ratings. But they make many Hermetic sealed Relays for explosion-prevention environments with UL safety rating.

Although this goes beyond, OP's question, it may shed light on proper use a nd how to choose and specify all aspects of Relays.

If you know how XOR gates work when output goes high if only one input is h igh, you will notice a Diode Bridge performs the same task, when the output DC goes high only if one or the other ~ input is higher than the other. t his fact allows both devices to be used for frequency doubling so that puls es can be created for + &- transitions to make a positive pulse out. With X OR you only need to delay a clock input with small RC delay to produce posi tive ZERO crosssing pulses. similar with Bridge and RC current sense I sugg ested, small delay will be 0 degree on leading edge , and max delay of RC f ilter is 90 deg on trailing edge of diode to cap charging current. If thres hold to Triac is chosen properly this can work well enough to trigger at ne ar peak of 90 shifted voltage.

A picture would be clearer. But my comments are only gobbly-gook to those w ho cannot understand.

I assume you are in the UK, but it would be 5 ms, no? 20 ms is a full cycle and the delay needs to be 1/4 cycle or 5 ms. 4.167 ms when the line frequency is 60 Hz.

On Thu, 19 Sep 2013 08:43:36 +0100, "JB" wrote:

--- Just for fun:

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-- JF