cycle limiting after zero crossing max voltage device? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: March 08, 2021, 08:15:10 am
content: is there a commercially available device that does cycle counting after a zero cross on AC, so it starts at full voltage, so you can set it up so that when it has a input you can adjust how many half-cycles of AC go through before it turns off? For an inductive load so there is no surge current but you deliver a set amount of energy into a transformer before it turns off. there is something about highly inductive loads and remanesence that makes normal zero crossing a problem for them, so its better for a peak start 0 turn off, I think.Something like a drive/control box.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 08, 2021, 09:50:16 am
content: Turning of a transformer at the right moment to keep the remanence small is tricky - it could work with no load, but with a load to the transformer it is not very practical (about the voltage peak would be right, but hard to control. An SCR switches off near zero current, but this is only good for an unloaded transformer.There are special modules for controlled turn on, so they can live with the remanence in the transformer. AFAIK some module also monitor on how the transformer was switched off and this way can better start.

author: coppercone2
author_rank: Super Contributor
timestamp: March 08, 2021, 09:56:30 am
content: damnit, sounds difficult

author: David Hess
author_rank: Super Contributor
timestamp: March 10, 2021, 02:25:26 am
content: I have seen it done but am not aware of anything you can buy which specifically implements it.

author: coppercone2
author_rank: Super Contributor
timestamp: March 10, 2021, 02:39:42 am
content: the idea was to turn my resistance brazing transformer (output 2000A max) into a spot welder by finding the right taps + tuning it with a variac then firing the whole assembly through a big SSR.I am not even sure if the correct settings exist on the equipment I have, but I thought if the controller did exist then I could find out if my setpoint does exist or if it has merit, but right now its a problem with 2 unknowns.looks like its not easy compared to the normal methods that are popular, the amount of work required is equal or greater to then 'modern' method of using super capacitors, even if the equipment is on hand.I have super capacitors on hand also, but I thought this might have merit as a shorter path in time to garage, the design of proper operating mains electronics is similar in difficulty to the high current switch (or buying a kweld), at least for me.

author: BrianHG
author_rank: Super Contributor
timestamp: March 10, 2021, 02:46:11 am
content: Though different than your appp, I've used a heavy duty 10 ohm resistor across a normal zero crossing SSR (parallel). The SSR would turn on a second after the main power was fed and it would open 1 second before the main power was turned off. The 2kw transformer powered on and off silently, many 100s of times a day. No tripped breakers, no surges, no kick noise.Maybe this can give you ideas.

author: coppercone2
author_rank: Super Contributor
timestamp: March 10, 2021, 02:47:58 am
content: Hmm, right so if you are using it for intermittent pulse operation you don't care about the efficiency,the problem is though I guess is timing it for turn off.Is there a SSR that can give a indicator of its zero crossing, that is after its triggered it gives an indicator that it has fired so then it can maybe trigger a function generator to give it a timing pulse to turn it off at the correct time so I an adjust it easily on a work bench?So when I trigger the SSR I believe it will wait for the first zero crossing. But I have no idea where in the cycle it was, so its a problem on short cycles (i am not sure how much time spot welding will take). What would be nice is a easy TTL indicator of actual conduction so then I can put it into the trigger of a pulse generator and have it turn it off exactly as to my setting so I know how much energy went into the weld. So pushbutton start, then the off time is decided by the pulse generator.I expect ALOT of work to go into figuring out if its doing a good job welding, so I wanted as simple a control system as possible for timing. I have alot of function/pulse generators laying around. It might be a good reason to fix my 3310B, small and compact and I can take it to the garage easily and its pretty cuteNot sure if there is another way to sync up a typical function generator with mains. This one does have a phase adjust so I suppose I can monitor both signals with a scope then set it up on a one shot.. maybe a good use for my scope meter here.I have higher confidence then a hacked up MOT with this setup at least.I bought a desoldering iron specifically for the 3310B so I don't feel as much frustration trying to fix it.Perhaps if someone figures this is a good method I can switch from repairing my sorsensen 33A and work on the scopemeter (huge mechanical problems) and 3310b (huge electrical and mechanical problems).This defiantly would be good equipment to fix up for working on this.. probobly should not take my DSO into the garage.. ever.. thought I would never find a use for that scope meter