firing angles

Discussion in 'General Electronics Chat' started by gyamfi, Dec 2, 2011.

1. gyamfi Thread Starter New Member

Dec 2, 2011
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The effect of firing angles?

2. Wendy Moderator

Mar 24, 2008
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Insufficient information.

Need input.

3. SgtWookie Expert

Jul 17, 2007
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Are you talking about "firing angles" in regards to ignition spark advance in gasoline powered engines? Or perhaps firing angles in regards to thyristors (SCRs, TRIACs, DIACs, etc)

4. bountyhunter Well-Known Member

Sep 7, 2009
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It refers to the gate triggers on SCR's and I recall it used in power AC-DC converters

5. joeyd999 AAC Fanatic!

Jun 6, 2011
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I was going to give him a tutorial in ballistics!

6. DerStrom8 Well-Known Member

Feb 20, 2011
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As was I! This is what first came into my mind:

7. SgtWookie Expert

Jul 17, 2007
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I'd considered that too, but this would not really be the forum to ask that kind of question in.

8. bountyhunter Well-Known Member

Sep 7, 2009
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here's what I was talking about:

9. thatoneguy AAC Fanatic!

Feb 19, 2009
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I want a Triac that will let me chop a full 120VAC cycle into a few hundred PWM pseudo-squarewave "slices". Just for kicks.

10. MrChips Moderator

Oct 2, 2009
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Different ways of disposing of a bad employee?

11. joeyd999 AAC Fanatic!

Jun 6, 2011
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You can't do that with a Triac.

A triac turns on with the gate trigger, and turns off at the zero current crossing. Therefore, you can only control the position in each 1/2 wave where the triac turns on (or, as you originally stated, the firing angle). Turn-off will always occur at the same position in each 1/2 wave (which may or may not be the zero *voltage* crossing if you have a reactive load).

12. jimkeith Active Member

Oct 26, 2011
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@ bountyhunter

This is the phase control circuit that Lambda uses--old brute force, but very reliable technique--uses expensive 60HZ transformers, but provides DC with very low ripple and a 360HZ ripple component.

I have applied this technique with good success in NEMA D high slip motors for variable speed pump applications.

The SCR anti-parallel current is 58% of the line current--substantial thermal advantage.

Line synchronization is also immune to phase rotation.

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Last edited: Dec 3, 2011
13. BillB3857 Senior Member

Feb 28, 2009
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Can you expand on this? Any drive I worked with required phase synchronization with the trigger circuitry. If the phasing on only the line feeds to the SCRs was rotated without rotating the trigger sync lines, we got a lot of smoke. Is this what you meant?

14. jimkeith Active Member

Oct 26, 2011
539
99
You got it--the phase control ramp generators (whether linear or digital) are reset at line voltage zero crossing--generally the synchronization voltage is taken phase to phase, but this does not exactly work out so the signal must be delayed 30 or 60° (do not remember which) to make it work properly--then when the phase rotation is reversed, the timing is really out of whack and the SCRs will snap on at quite a high voltage.

The best design creates an artificial neutral and synchronizes the ramp control circuits in respect to line to neutral voltage--this technique is immune to phase rotation.