How can I finer control over a Triac (BTA100-800A)

[sam_sam_sam]

The photos are below

I have a few of these TRIAC ( BTA100-800B )

I can control the transformer but I do not have the fine control over the transformer that would like to have

Does anyone have any idea how to have more control over the triac

Here is the problem on the low end it has more even control but when you get close to the maximum current it goes up to fast and there is not much control of it at that point

Here is the data sheet for this device

https://cdn.badcaps-static.com/pdfs/...980f798e70.pdf

[Curious.George]

Re: How can I finer control over a Triac (BTA100-800A)

Does anyone have any idea how to have more control over the triac

How are you presently controlling it? And, are you operating it in just 1 quadrant?

[sam_sam_sam]

Re: How can I finer control over a Triac (BTA100-800A)

operating it in just 1 quadrant ?

Can you please explain this in a little bit more in more detail

I will draw the control circuit a little bit later on today

Thanks

[sam_sam_sam]

Re: How can I finer control over a Triac (BTA100-800A)

Here is a circuit drawing of this circuit board for the BTA100-800B triac

The part of this circuit I do not understand is what role does the bridge rectifier plays in this circuit the way that it is wired and why the (+) and (-) terminals are wired two 33k ohm resistors that come together on the opposite side of the resistors then go to (DB3) with I think is a DIAC of some sort

AC (IN terminals) on the bridge rectifier one terminal goes (K) and the other terminal to the DIAC and the 4.7k ohm resistor

[Curious.George]

Re: How can I finer control over a Triac (BTA100-800A)

Can you please explain this in a little bit more in more detail

Essentially, a reflection of the relative polarities across the device as it is being operated.

E.g., an SCR would operate typically in quadrant 1 (anode positive wrt cathode; gate positive wrt cathode). A TRIAC would typically be operated in quadrants 1 and 3 (Q3 being the reversed polarities of each of these relative potentials) -- though you could choose to only operate it in Q1.

All of this depends on the way the gate is driven -- which is typically by deriving power from one/both anodes and routing it to the gate. If there is no lag in this control signal then it is always in phase with the potential across the device.

Throw in an inductive load and things get murky.

In either case, if you look at the AC mains waveform (sinusoidal), its easy to see how there is more sensitivity nearest the zero-crossings -- |dV/dt| is at it's maximum, there so any control signal derived from it will have maximum sensitivity.

Up near the peak of the waveform, dV/dt reaches its minimum -- '0' -- so the point at which the triac fires can move around (in time) and still be considered well-behaved.

[as the firing point (angle) moves, more or less energy is allowed through on that AC mains cycle]

For better control of the "energy" being gated, you want better control of the time (phase angle) at which the triac is triggered. Examine your trigger circuit and decide how it is failing in this regard (recall that the mains voltage can also vary but the device itself doesn't -- so, any ratiometric drive circuit has inherently variability)

[sam_sam_sam]

Re: How can I finer control over a Triac (BTA100-800A)

Is there a better driver circuit for this triac I have google search it but I have not found a circuit that comes even close to what they have used on this controller board

Can anyone explain the control circuit that was used on this triac

Thanks

[redwire]

Re: How can I finer control over a Triac (BTA100-800A)

Can you check your schematic, the 0.15uF firing capacitor is not in the right place.

[redwire]

Re: How can I finer control over a Triac (BTA100-800A)

The circuit is your generic chinese triac phase control off fleabay. Usually mixed up or the wrong parts on them.

500k potentiometer is for 220VAC. 200k-250k potentiometer for 120VAC.

So a large dead zone with the pot you have. You could try add a resistor in parallel with the pot, like 250k 1/4W , to make up for the dead zone.

The circuit is not your usual one. There is an added bridge rectifier to give "hysteresis free" or "no snapback" effect, like you see with lamp dimmers. It's also helps with inductive loads.
The extra diodes discharge (reset) the firing delay capacitor every cycle, to give consistent phase delay.
More can be found in figure AN1003.12 on Teccor App note AN1003

Note the potentiometer is hazardous live and should have a grounded case/shaft or a good knob.

[sam_sam_sam]

Re: How can I finer control over a Triac (BTA100-800A)

More can be found in figure AN1003.12 on Teccor App note AN1003

Thanks for the information

Note the potentiometer is hazardous live and should have a grounded case/shaft or a good knob.

Thanks for the warning I am going to ground the welder to the triac controller and the pot housing

The yellow cap is the one that is next to the two 33k ohm resistor