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— | howto:electro:active_softstart [2016/10/29 23:05] (aktuální) – vytvořeno - upraveno mimo DokuWiki 127.0.0.1 | ||
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+ | ====== Active Softstart for Welders ====== | ||
+ | This covers softstart circuit designed especially for upgrade of cheap MIG/MAG transformer welder. | ||
+ | |||
+ | ===== Problem ===== | ||
+ | * Welder triggers the 16A/B circuit breaker during switch-on phase (when the torch trigger is pressed) | ||
+ | * This is caused by inrush current spike before transformer core get magnetized | ||
+ | * MIG/MAG welder usage means frequent switching of primary and has to respond immediately | ||
+ | * Can't use NTC termistor because it works only when it has enough time to cool down before repeated power on. | ||
+ | * Can't use delayed switching relay circuit for premagnetization circuit because it would not switch fast enough for short welds. | ||
+ | * Can use peak-switching SSR (solid state relay) with proper rating. These are designed to fit this use, but they are rather expensive and hard to find. This makes them impractical for using with cheap hobby-grade or old welders (which are probably only ones that need this as inverter based welders do not need softstart) | ||
+ | |||
+ | ===== Schematic ===== | ||
+ | |||
+ | {{: | ||
+ | |||
+ | ==== 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' | ||
+ | |||
+ | ==== Notes ==== | ||
+ | |||
+ | * You can probably try it without varistor (however blown varistor is cheaper to replace than blown triac) | ||
+ | * You can probably try it without current limiting resistor (haven' | ||
+ | * You should use snubberless triac, i haven' | ||
+ | * You can experiment with transil values from 280V to 315V | ||
+ | * higher value = more precise peak detection, but don't overdo it. otherwise line will not have sufficient peak voltage to trigger the switch. | ||
+ | * 230VAC line has peaks of approx. 320V but there can be some fluctuation, | ||
+ | * I did not managed to get 300V bi-transil (TVS), so i've used two 150V ones in series. | ||
+ | * It's designed for 230V~ grid, if you live in 120V~ country then you should make these (obvious) changes: | ||
+ | * use relay/ | ||
+ | * use 150-160V bi-transil to trigger the triac instead of 300-310V (otherwise the transformer will not start) | ||
+ | * use 190V varistor instead of 390V (used for 230V~). This is not needed, however it should make circuit more endurable | ||
+ | * maximal voltage of triac doesn' | ||
+ | * Circuit will probably need complex review before using with 3-phase appliances/ | ||
+ | |||
+ | ==== Testing ==== | ||
+ | As i currently lack proper testing equipment i can't give you precise numbers. I've measured maximum current in primary winding of welder transformer (without load) using "HIOKI 3291 clamp on HiTESTER", | ||
+ | |||
+ | ==== Photos ==== | ||
+ | |||
+ | Deadbug style softstart circuit: | ||
+ | {{.: | ||
+ | |||
+ | Softstart built into the welder (black plastic box): | ||
+ | {{.: | ||
+ | |||
+ | ===== Passive version ===== | ||
+ | However the active version using TRIAC is superior, there is also other possibility which doesn' | ||
+ | |||
+ | http:// | ||
+ | |||
+ | {{http:// | ||
+ | |||
+ | Problem is that it relies on mechanical delay of relay contacts. I've tried with small 230VAC relay and it did not prevented circuit breakers from being triggered by welder completely. (probably you should use big contactor for better performance). | ||
+ | |||
+ | ===== Links ===== | ||
+ | |||
+ | * http:// | ||
+ | * http:// | ||
+ | * http:// |