triac selection and implementation for heating application

Other Hardware General Electronics
1

hello!

i am looking to do a project using triacs to control a JBC soldering iron. i am new to using triacs, having never done a project with them. i'm basing my design (picture below) on an existing schematic (from great scott), which uses a BTB26-600 triac. LINK: click here. however, the vast majority of the components i'm using are SMD in nature, and the maximum current of this triac is 25A, but the supply for this project has a maximum current of 7.5A @24vac, so its much bigger than i need. also using a smd package would make fitting it to an enclosure easyer.

my question is: could i replace the afformentioned triac with a T2535-800G? LINK: click here. this one is still rated for 25A (i only need ~8A, but a little overkill never hurt), and is snubberless. are there any differences between the two that i'm overlooking, or could i just drop it in as a direct replacement? am i overlooking something obvious?

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the T+/- nets go to a mx6675 thermocouple IC, and the D+/- nets go to ACS712ELCTR-20A-T current sensor. the two other nets go-to a atmega 2560-16AU. if anyone wants to see my full schematic, i can post it.

please disregard all resistance/ capacitance values. i am yet to-do the math to get them fine tuned. suggestions for things wrong with the "bones" are appreciated.

the system is a 7.5A @ 24vac, and max amperage will be limited via software to 7A.

i'm not using mosfets. i know they are more efficient. perhaps you can convince me otherwise.

any help/suggestions/experience with similar projects are greatly appreciated. thanks!

2

The other TRIAC will probably work, but you might need a heatsink with either one.

It's "not standard" to use a zero-crossing "dimming" circuit for a heater since heat can't change instantly.

Usually there is a temperature sensor. The heat comes-on until the temperature is reached then it's turned off, and then on-again when the temperature drops. etc... (with some hysteresis). The furnace in your house works like that, as does your refrigerator.

Or if there is no feedback, the heat can be turned on & off at a predetermined duty cycle.

i'm not using mosfets. i know they are more efficient. perhaps you can convince me otherwise.

A single MOSFET won't work with AC.

3

I 100% agree its nonstandard. However the heater cartrage is 100% nonstandard too. It has 3 pins for the heater and thermocouple.

The zero crossing is used to determine a time where tempetures can be read.

Yes I would either need two mosfets or a big ol rectifier.

The second triac is smd. The heatsinks would be integrated onto the pcb pad.

Thanks!