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Thyristor choice?

Jadeit

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I need to control the power of the heating element 230V 15A.
Choice of triac, optotriac and MCU.
I will use either MOC3083 if I decide to control after half-waves, ie switching at zero or
MOC30452 .
Theoretically, a triac is enough BTA16, however, for almost the same money I can have
BTA26800B or even BTA40-800B in RD91.
Is it important to use a more powerful triac, thus reducing the losses on the triac, or is it necessary to switch more triacs to increase power and is it not worth it?
Is a snubber required to switch the resistance heating element?
 

KlausST

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Hi,

don´t half wave control, do full wave.

See the ON-State characteristics diagram: At about 15V the voltage drop is:
BTA16: 1.4V
BTA26800B: 1.25V
BTA40-800B: 1.20V

so the power dissipation is just reduced by 14%
Paralleling will spread the power dissipation to the triacs only if silicon is at equal temperature.
In reality I expect that one triac carries most of the current and the others almost nothing.

But don´t go close to the limit. I´d use at least a 20A rated one.
Mind to keep temperature within specified range.

***
If you want clean regulation, then use several loads: 1A / 2A / 4A / 8A and switch them individually. Binary style.

Klaus
 

Jadeit

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Thank you for the information. I will use BTA40, the case comes best for my cooling and allows direct power supply without PCB.
It is a muffle furnace, so I can only switch on the side and especially the rear heating.
Each winding approx. 15A.
Control to the required temperature and especially dT / dt (rate of temperature rise over time).
 

KlausST

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Hi,

One maybe useful point:
There are triacs with isolated package, so isolated mounting in a heatsink is easy.

Klaus
 

Jadeit

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If I'm not mistaken and the documentation is not lying, then BTA are always isolated A means isolated non-isolated means B BTB
See page 10 datesheet BTA40 800B
 

KlausST

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Hi,

You are right.
I had the black plastics coated tab in mind. But these triacs have the isolation internally.

Klaus
 

Easy peasy

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any scr or triac has an on drop, 0.8 - 1.0v for an scr, higher for a triac, 15A rms x 1.25v for a triac = 19 watts, you need a decent heatsink for this.
--- Updated ---

ideally control with full 20mS cycles if you can, failing that symmetric half cycle control.
 

Jadeit

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OK thank you all.
I have ordered BTA40-800b in RD-91 case

I'll ask about Snubber again
So .
Load is 3,4kW heater (helix Kanthar wire ) max temp 1300C ,
Triac BTA40
Driver: optotriac MOC3083 with zerro cross detector.
Do you recommend using Snubber?
If Yes. What parameters?

For smal Triac BTA16 and general Load I use 10nF 630V PP + 33 Ohm resistor, but I'm not sure here?
Plus case RDS-91 The RC should probably come directly to the BTA terminals.
Does it possibly make sense to add RC Snubber to the MOV?
 

Easy peasy

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depends on inductance of load, 100nF & 33 ohm a good starting point, right across triac, mov needs none.
 

Jadeit

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If I apply to kanthal heating as an air coil parasitic induction can be expected 6,7 uH and parasitic capacitance 12pF.
 

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