# Soft starter AC help

Hello, I have a site here that explains an Ac soft starter circuit with a schematic I will post below. The article explains very well what components do what, But i am trying to get an overall explanation of what happens as soon as you turn on AC load and most importantly is what order everything happens is.

The instant power is applied at P1 it is applied to the load through R7 a 22 Ohm 5 Watt resistor so the load at P2 really does not see the full applied voltage. How much it sees depends on the load but it will not see full power since there will be a voltage drop across R7. That's all that is going on at the instantaneous moment power is applied. Keep in mind circuits like this have their limitations.

From there the circuit works as it was explained. The key players are R5, R6 and C3. C3 begins charging till it turns on Q1 at which point K1 relay is energized and all that happens is R7 is now bypassed by the K1 contacts. I assume the relay coil is 12 volts and the contacts rated for 10 amps. With R7 bypassed full power is applied to the load.

Ron

Ron_Blain:
The instant power is applied at P1 it is applied to the load through R7 a 22 Ohm 5 Watt resistor so the load at P2 really does not see the full applied voltage. How much it sees depends on the load but it will not see full power since there will be a voltage drop across R7. That's all that is going on at the instantaneous moment power is applied. Keep in mind circuits like this have their limitations.

From there the circuit works as it was explained. The key players are R5, R6 and C3. C3 begins charging till it turns on Q1 at which point K1 relay is energized and all that happens is R7 is now bypassed by the K1 contacts. I assume the relay coil is 12 volts and the contacts rated for 10 amps. With R7 bypassed full power is applied to the load.

Ron

perfect explanation, i also just had someone explain it also and it totally makes sense.
One thing that i still dont get is are (4 and 1) on P1 both hot terminals. I get that normal 120v AC the current switches with one leg acting as the hot and the other as the nuetral-return. But how does it work with the 220? wouildt there need to be another leg so that it is 3-phase 220v? and what are (3 and 2) on P1 and why are they bridged?

If the relay fails to operate the current limiting resistor R7 will burn out as its only rated for 5W continuous,
and may be seeing several 100W during the soft-start sequence. Its effectively a fuse in this situation.

Home designed transformerless power supplies always make me nervous. The ground shown on that schematic must be completely isolated and is not, for example, to be confused with the power supply earth connection.
The ones in consumer devices, such as time switches etc., usually use a 24 volt relay to reduce the current requirements.

I get that normal 120v AC the current switches with one leg acting as the hot and the other as the nuetral-return. But how does it work with the 220? wouildt there need to be another leg so that it is 3-phase 220v? and what are (3 and 2) on P1 and why are they bridged?

I am not sure about that or why it was drawn that way. Here in the US, Canada and N. America in general Residential power distribution consist of 240 VAC 60 Hz. "Split Phase". So we have 240 VAC we can call L1 and L3. Either L1 or L2 to Neutral Ground is 120 VAC. Neutral and earth ground are bonded at the entry point or in my case circuit breaker panel. L1 and L2 are 180 degrees phase shifted from the transformer out on the pole. The pole transformers where I am take single phase 13.3 KV and deliver 240 VAC Split Phase to the residences.

My guess is most of Europe uses 230 VAC 50Hz with a Hot and Neutral ground. Lived in Italy for three years and that is how I remember it but been a long time. I am sure any other members could fill you in.

While I am not fond of transformerless power designs as used in this case they do work.

Ron

When I had to have a soft start on a reverse wired huge transformer, I found a SSR with a built-in time delay circuit on Ebay. I used it to short out a 1 Ohm, 100 watt resistor after it's time delay. I was never able to find out what it's delay was, but it works fine.

Paul

and what are (3 and 2) on P1 and why are they bridged?

What is connected to the left side of P1?

JCA34F:
What is connected to the left side of P1?

Infinity? The article makes no mention of that which I saw. Could be infinity, maybe endless space or just 230 VAC 50 Hz. Seriously I haven't a clue. No clue why the jumper is in there either. However, it looks nice on paper. I guess someone could leave a question for the author if they were curious enough. I'm not.

Ron

JCA34F:
What is connected to the left side of P1?

Just guessing by the name 220V-IN/SW

1: AC Neutral
2: AC Phase
3: Switch
4: Switch