Hybrid Relay- reverse Engineering

Question

I want to design a hybrid relay for a three phase motor. The rating is 230VAC L-N @20A. In order to get a better idea, I ordered this hybrid motor starter.

It is also a 3 phase hybrid motor starter with used two TRIACs and 4 × DPDT relays. It has left and right motor rotation option and needs external 24 VDC to operate.

What I want to ask is if someone can help me reverse engineer this a bit.

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The above image is of the PCB board of the relay which I ordered, basically the inner circuitry of Phoenix Contact hybrid motor starter.

Let us just focus on the power part and not the logic.

As you can see in the image attached the the right most part has two pairs of 3-pin connectors used for L1; L2 and L3 and U; V and W. The white parts are the relays which are by Phoenix Contact and two black T2550-12G TRIACs.

Red components are MOVs and blue ones are the Y safety capacitors.

The two black-yellow components must be transformers. (I am not sure because the part number mentioned has no information available on the Internet, maybe they are Phoenix Connect internal numbers and the parts are not for sale.) Same also goes for the part 9159523 AC-098 ACUWA 2218.

Now can someone help understand how this circuit works?

My questions are:

1. Why only two TRIACS are present and not three for each phase?
2. Why there are four relays?
3. Are the transformers used as gate drivers here because I see no optocoupler?
4. How is zero cross detected for TRIACS and how do we turn them on and off on the right time without driver/optocoupler?

Thank you in advance for your time and help.

Answer 1

These are my interpretations of the datasheet db_en_elr_h5_ies_pt_p_107917_en_03.pdf (618 kB) on the download page and your photograph. The answers are only possibilities that occur to me and may be wrong!:

1. Why only two TRIACS are present and not three for each phase?

You can control a single-phase (2-wire) circuit with only one switch. You can control a three-phase (3-wire) circuit with only two switches. This will simplify the circuit, reduce cost and improve reliability.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Opening SW1 and SW2 will de-energise the motor (although it will remain live).

2. Why there are four relays?

One of them is for the error output signal.

Figure 2. Block diagram showing error relay.

Only three more to figure out! I suspect that they may be safety related. See if they follow the pattern outlined in my answer to https://electronics.stackexchange.com/a/240352/73158.

3. Are the transformers used as gate drivers here because I see no optocoupler?

It seems unlikely to me. (a) They're too big for a pulse transformer. (b) There seems to be a single-turn winding on them which suggests something more like a current transformer. Again, only two phases would need to be monitored to get the complete picture.

Post a photo of the back of the board but mirror it horizontally to make it easy for us to correlate stuff on the front and back.

4. How is zero cross detected for TRIACS and how do we turn them on and off on the right time without driver/optocoupler?

Figure 3. (1) to (4) may be what you're looking for as these 4-terminal devices straddle the no-man's-land isolation barrier (marked in light green). Optos (5) to (7) don't.

I can't make out from the photo which direction they're feeding. You might be able to determine by inspection.