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AC Active Soft Starter for Inductive Load with less energy dissipation

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BravoV:
Aware of various AC soft starter designs, but most are using resistance at the initial inrush moment and then later by passed by relay switch, or even much more simpler design using NTC to limit the inrush.

Discovered this design -> Active Softstart for Welders



The designer claimed its suitable for inductive load, in this case it was designed for welder.

Quote :

Working principle
It exploits the fact that current in transformer is 90° out of phase of the voltage, which leads to conclusion that best time to switch on the transformer is in voltage peak of mains power line (which was quite counter-intuitive for me at the first time). This circuit detects the peak using 300V bi-directional transil (TVS diode) which is then used to trigger snubberless TRIAC which switches on the power transformer of welder. Once this happens, there is normally open relay with AC coil connected in parallel to transformer which shorts out whole active circuit and therefore prevents any excesive heating caused by high currents through semiconductor components (= No heatsinking needed!). To make circuit more robust and endurable there are two more components to prevent possible damage to semiconductor elements. In series with TVS there is resistor to limit current through TVS and to TRIAC's gate. Also there is 390V varistor across the whole switching circuit which prevents voltage spikes from transformer to kill the TRIAC and partially helps to supress arcing in relay contacts.


What interest me are these features :

- Much less dissipation, especially for load that getting turned on an off often in short period like a drill.
- Less delay or instantaneous power delivery at power on, cmiiw.


Question, is this design decent ?

- Do I need to adjust the 300V TVS (Bi-Diretional) for the triggering, to somewhat lower abit as my mains is 220V while its designed for 230V ?
- What is a good enough wattage for the R1 resistor ?

Appreciate any comment or feedback regarding this circuit.

TIA

coppercone2:
Are you sure this makes sense with using on a power tool? It's not like you turn it off every second.

What I do for my soft start high dissipation designs is solder the resistor upside down on some wires over a little catch net so if it melts itself it breaks the circuit and falls onto a cooling mesh.

I think its safer at high currents because there is nothing to explode, at most a relay won't short it out and the resistor will melt itself free and break the circuit. Just make sure the cooling mesh is low enough that the resistor can't melt on one side, and short out the mesh. it has to be able to fall freely. and the wiring around it must be secure. And out of paranoia i recommend single strand wire.

also fuse and stuff is missing

coppercone2:
in terms of shop tools and a delay, I think the most beneficial candidate for a circuit like this would be a chop saw since that is often used fairly rapidly. A table saw or drill press don't really get turned on that much IMO.

coppercone2:
http://class.ece.iastate.edu/ee330/miscHandouts/AN_GOLDEN_RULES.pdf

there is also this beast,

http://www.icbase.com/File/News/download/ON_Reference_1.PDF

I tried to read it before but I got unethused as it made more sense to learn about drives and tubes (for fast switching) then this component (SCR and derivatives) in great detail, because I felt for physics stuff and experiments it would make more  sense to use the tube and for mechanical drives and precision process control you would want to use a drive anyway if you can (even for heaters they have special multi kW drive type circuits), which kinda made me feel like the SCR/TRIAC etc is supposed to be a circuit more for 'economic' use which is not that interesting to me in the home laboratory.

The exception to this that I found is for protection circuits, even for advanced electronics (because of devices like bourns makes, i.e. TSP), due to its speed, but if I was going to do that I would do it to protect the drive not run the saw. The case made for the welder is good though. I also wonder what other electromechanical devices it makes sense to run with.

coppercone2:
and I suspect you will thank yourself in the long run if you put a drive on your drill press so you can properly regulate drill speed. Its been on my list for a while. You really are supposed to do it and its too frustrating to mess with the belts IMO. That would be the best mod to go for with the drill.

And I never saw noise analysis done with those types of circuits on the VARIAC. Not sure if you want that in your lab if its going to make some kind of noise (i even put a disable switch on my variac digital display so its lab worthy).

a chop saw however.. i am not sure if regulating speed on a wood cutting saw for metal cutting is a good hack, I don't think its built right for metal cutting even if you slow it down to the 200 surface feet per minute or whatever it needs  (those cold cut metal saws look more robust, i suspect it might vibrate alot), so the (appropriate single material chop saw) might be a good candidate for this project other then old welders.

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