CONNECTING A SOLID STATE RELAY TO MSP430G2553 (ON MSP430G2 BOARD)

Debasish Banerjee said:

What preventive measurement/s is/are necessary in this case?

Common sense to NOT work with high voltage circuits having such a rudimentary knowledge about subject.

Ilmars said:

Common sense to NOT work with high voltage circuits having such a rudimentary knowledge about subject.

Debasish Banerjee said:

Thank you, but I didn't ask for an opinion

It was advise. 4000V isolation is specified for SSR, so you shall be safe as long as you don't make any mistakes or lightning does not directly hit mains leads. Look for LED specs to calculate i/o pin current-limiting resistor. Other option would be to drive SSR using transistor, with appropriate current limiting resistor.

Thank you so much, but can you tell me just two things more, i.e. what happens if I put the signal line directly into the vcc pin, where the pin has more than 500mA; for 240 volts, there are two terminals, namely L1 and T1, I am not sure on which one goes the phase and which one is for switching the phase to the appliance, it wasn't there in the datasheet :P, and lastly, is it necessary to have the appliance grounded? say if it is a ceiling fan, or a bulb, then? L is supply and T is load/Tap, am I right?

Debasish Banerjee said:

what happens if I put the signal line directly into the vcc pin, where the pin has more than 500mA; for 240 volts, there are two terminals

If I am getting your question right - you don't connect AC and control sides! They must be isolated. So your msp430 VCC shall be supplied from isolated 3.3VDC supply.

Debasish Banerjee said:

and lastly, is it necessary to have the appliance grounded?

Depends on appliance, mostly yes.

Debasish Banerjee said:

L is supply and T is load/Tap, am I right?

Usually T is connected to neutral, L - load. SSR is AC switch so it will work both ways.

Success! Connected the MCU with this relay on one side, though control current should be at max 14mA, and I was able to achieve that using multimeter (to verify) and 470 Ohms resistor (around 7mA), I found that the signal LED is too dim by that way, so I just connected the pins directly on the control side, and on the other side L refers to Load or the input phase of 240 Volts, and T is the terminal for switching the load from L (Certainly and is undisputed), and then its just fine, and as far the security concern goes...I already have a fuse  through which the supply phase comes in, hence sudden upsurge should be handled by that fuse in a neat manner, and I don't think that there is a need of diode on control side, after staying behind that 4000 volts opto-isolation! and as the amperage is way low (0.8-1) for this 10A relay, everything stays cool even without the heat sink, though i will certainly add one with proper dissipation capability within a few days! Thank You all. 

Ilmars said:

Usually T is connected to neutral, L - load. SSR is AC switch so it will work both ways.

Ilmars said:

Depends on appliance, mostly yes.

Debasish Banerjee said:

 

Usually T is connected to neutral, L - load. SSR is AC switch so it will work both ways.

This advice would make a straight short-circuit in no time![/quote]

This is actual purpose of relay - make [short] circuit so current can flow through it. I did not say L - to Live wire, but L- to Load (meaning that other terminal of the load is connected to Live AC wire).

Debasish Banerjee said:

don't think proper grounding of an Tungsten Incandescent bulb is either necessary or practical.

You don't ground bulb (because glass is quite good insulator), you ground conductive parts of enclosure, especially if accessible from outside. Electrical safety questions is quite heavy of-topic here.

Just one thing more, in case I intend to make a parallel connection using two relays and two MCU boards, both has one load, waiting to be shorted for the same appliance, say a bulb.. Now, if I make one short, then the  mains voltage also comes on the 2nd relay's to be shorted terminal, even without switching it on, as both of them goes to the same appliance, will that cause any harm to the relay which is switched off but still has load on both terminals because of this? Also, can I use a diode to aviod this?

Ilmars said:

You need to protect single solid state relay or more than one parallel solid relays only in case of inductive load (like motor).

Ilmars said:

To protect against transients AC motors shall be controlled using "zero voltage turn-on" and "zero voltage turn-off", also snubber shall be present.

Ilmars said:

AC motors shall be controlled using "zero voltage turn-on" and "zero voltage turn-off",

Thank you Jens, my Relay is a Potter & Brumfield Zero Output Switching Relay, can you tell me which one is better for inductive loads, Snubberless Triac Output or Paired SCR Output? 

Debasish Banerjee said:

can you tell me which one is better for inductive loads, Snubberless Triac Output or Paired SCR Output? 

ok.

Hello Debasish,

For your 2Amp application you can use a much smaller SSR of 4A, which fits direct on a circuit board.

Connect direct to the SSR outputs a capacitor or a RC network. For small load (2A) a R=100Ohm and a C=100nF will fit, for heavy loads a C=1uF no R.

A Triac or SCR must NOT be switched On while voltage over the Triac or SCR is less then the Gate voltage, otherwise the Gate will be blown-up. Normally a SSR have a network to avoid this. Switching Off is only possible when the voltage over the Triac or SCR reaches 0-volt, and goes also automatically.

In case of inductive loads switching On randomly can causes very high current and voltage spikes. Switching On must be done immediate after rising voltage. Probably the SSR can arrange this, I’m never lay on this and always detect the Sinus-zero crossing and switch the relay On at rising voltage.

Heavy loads such as power-supply transformers needs to be started-up and current needs to be limited, this can be simply done with an NTC in series of about 33Ohm depend on current.

Driving the SSR with a low voltage as 3V can give a instable switching result. Better use a voltage between 8-20V. A 24VDC and a series resistor of 330Ohm works perfect.

I don’t know if there is a difference between Triac and SCR in use. Firing yes but this is done internally in the SSR.

-Leo

A silicon-controlled rectifier (or semiconductor-controlled rectifier) is a four-layer solid state currentcontrolling device. The name "silicon controlled rectifier" or SCR is General Electric's trade name for a type of thyristor. The SCR was developed by a team of power engineers led by Robert N. Hall and commercialized by Frank W. "Bill" Gutzwiller in 1957.

Leo Bosch said:

I don’t know if there is a difference between Triac and SCR in use. Firing yes but this is done internally in the SSR

SCRs are mainly used in devices where the control of high power, possibly coupled with high voltage, is demanded. Their operation makes them suitable for use in medium to high-voltage AC power control applications, such as lamp dimming, regulators and motor control.

SCRs and similar devices are used for rectification of high power AC in high-voltage direct current power transmission. They are also used in the control of welding machines, mainly MTAW and GTAW processes. All are from wiki, hence it seems that it is better when the load is inductive and relatively heavy in nature, especially when both types has zero voltage switching (on and off) as well as more than enough amperage for the load. Isn't it ?

What I mend is I don’t know if there is a different in ‘use’ of load between Triac and SCR.

Triac’s are mostly (especially) build for 50 or 60 cycles only, SCR’s can be much faster. The good advantage of SCR (and Triac) was the very short switching ON time, but today I think FET’s are more common to use now. It’s long time ago I designed SCR circuits and don’t remember all detail’s, but important is to keep track of the Gate current/energy. If the SCR is not starting, no cathode anode current, all current goes through the Gate and will blow-up (the Gate himself is like a small SCR), and therefore you need a minimum load/current and adjust the size of the SCR to what Amps you need (not too big SCR).

Different SCR’s needs different trigger parameters. At the time SSR came’s it was more easy and cheaper to buy the complete part.

In your discussion you are talking about zero-voltage switch On/Off as if you need to switch the SCR On or Off at zero-voltage, that’s wrong. The Gate must be triggered with a relative high current for a very short time (maximum amount of energy), and only if the SCR can start (cathode to anode current).

-Leo

Leo Bosch said:

In your discussion you are talking about zero-voltage switch On/Off

In my opinion there is no difference.

Leo Bosch said:

In my opinion there is no difference.

Don’t trust too much on this;

Debasish Banerjee said:

I don't bother about arc flash or blowing the gate ,as long as there are working opto isolation ,ground and in line fuse.

Inductive loads (also long wires) can generate very high voltage spikes, even in an overload condition and the fuse is blowing (disconnecting the load). If you don’t use an adequate fuse the fuse and holder can explode.

Leo Bosch said:

If you don’t use an adequate fuse the fuse and holder can explode.

I just wants to warn you, you sounds a little bit naïve like ‘as long there is ‘a’ fuse nothing can happen’ and I would blame me when something badly happens.

It happens me a few times, little bit more current about 8Amps and a large transformer and wrong timing. I never found the fuse and holder back, not even a little piece.

A little Fan or Pump will not give a big problem (start-up current can be limited with a NTC), but you are talking about Fridge which has a very high start-up current and may not be limited.

BUSS has very good fuses for this purpose but even they are able to get-up in flames unless you use a big ceramic one.

These fuses are quiet expensive and I give up to use them and use for 4Amp SSR regular 5x20mm Fast ones till 3.15A and case them in, and bigger loads like big Fridge a PKZM switch.

But I take good care about I already earlier told; Capacitor, Timing and Power-Up (false)pulses, that’s prime.

And another thing is which I can’t explain, I stopped using 10A versions they gets very easy broken, 4A (PCB version) and 25A perfect.

since i have seen from the childhood, that a fridge connected to a main line with a normal socket and switch, operates fine, infact ths main line comes through the same fuse i was talking about, a ceramic fuse which is usually used in household electrical connections of ~240v pressure, and I have got both, a 10A snubberless triac SSR and a 50A paired SCB type SSR, both are panel mount big relays, which is better to handle the fridge? do I really need an additional fuse?

There is a nice FAQ on SSRs : http://www.crouzet-ssr.com/english/faq.shtml

Peter

The link from Peter gives a good explanation of some of your questions.

A fuse can do at least two things; Protect your SCR and protect against fire (cut power at overload of wires etc). Protecting SCR’s needs Ultra Fast fuses, but in most cases fuse and SCR blows together. To protect against fire one fuse (at main) is enough.

With a 50Amp SSR you can switch your complete household power.

For a fridge a few items needs attention (maybe you already know). After switching Off (and also at power-up) wait a couple of minutes (5-10) before switching On. Liquid pressure needs to fall down first otherwise the motor can’t start and switches Off thermally. The thermal fuse (Clixon) is intend to use for protection and lifetime is short, about 100 times switching Off, after this the motor will blown.