Triacs in Parallel...

On Tue, 9 May 2023 14:04:22 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Tuesday, May 9, 2023 at 8:10:09?AM UTC-7, Ed Lee wrote:
On Tuesday, May 9, 2023 at 6:29:11?AM UTC-7, John Larkin wrote:
On Tue, 09 May 2023 09:57:37 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 8 May 2023 21:25:36 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:

... For paralleling diodes
(and preventing current-hog problems) it takes a bit of series inductance for
each diode. That should work for triacs, too (you don\'t get normal triggering
on slower device #2 if device #1 has acheved low-terminal-voltage already,
because triggering is less effective if main terminal voltage drop is low).

That\'s an interesting idea, using a bit of inductance to limit the
current through each triac to <8A. Damn sight more practical than
power resistors! Well done. I might just use that.
How many henries?
At what frequency?

There\'s reason to believe the current-hog positive feedback that happens
in diodes (and transistors) isn\'t present in thyristors, so my thought on the
matching was only to limit dI/dt during the (zero-voltage switch) trigger, which might last 100us,
not during the whole of an 8300us half-cycle. It\'s even OK if the inductor
saturates, the next half-cycle will see that sorted out.

5kHz, couple of volts, half amp: 100 uH should be enough.
Click to expand...

Not sure where you got those figures from. We\'re talking about 8 amps
@ 240V and 50Hz.
 
tirsdag den 9. maj 2023 kl. 23.04.26 UTC+2 skrev whit3rd:
On Tuesday, May 9, 2023 at 8:10:09 AM UTC-7, Ed Lee wrote:
On Tuesday, May 9, 2023 at 6:29:11 AM UTC-7, John Larkin wrote:
On Tue, 09 May 2023 09:57:37 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 8 May 2023 21:25:36 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:
... For paralleling diodes
(and preventing current-hog problems) it takes a bit of series inductance for
each diode. That should work for triacs, too (you don\'t get normal triggering
on slower device #2 if device #1 has acheved low-terminal-voltage already,
because triggering is less effective if main terminal voltage drop is low).

That\'s an interesting idea, using a bit of inductance to limit the
current through each triac to <8A. Damn sight more practical than
power resistors! Well done. I might just use that.
How many henries?
At what frequency?
There\'s reason to believe the current-hog positive feedback that happens
in diodes (and transistors) isn\'t present in thyristors, so my thought on the
matching was only to limit dI/dt during the (zero-voltage switch) trigger, which might last 100us,
not during the whole of an 8300us half-cycle. It\'s even OK if the inductor
saturates, the next half-cycle will see that sorted out.

5kHz, couple of volts, half amp: 100 uH should be enough.
Click to expand...

maybe magnetically coupled? i.e. a common mode choke with one winding flipped
 
On Tue, 9 May 2023 14:04:22 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Tuesday, May 9, 2023 at 8:10:09?AM UTC-7, Ed Lee wrote:
On Tuesday, May 9, 2023 at 6:29:11?AM UTC-7, John Larkin wrote:
On Tue, 09 May 2023 09:57:37 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 8 May 2023 21:25:36 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:

... For paralleling diodes
(and preventing current-hog problems) it takes a bit of series inductance for
each diode. That should work for triacs, too (you don\'t get normal triggering
on slower device #2 if device #1 has acheved low-terminal-voltage already,
because triggering is less effective if main terminal voltage drop is low).

That\'s an interesting idea, using a bit of inductance to limit the
current through each triac to <8A. Damn sight more practical than
power resistors! Well done. I might just use that.
How many henries?
At what frequency?

There\'s reason to believe the current-hog positive feedback that happens
in diodes (and transistors) isn\'t present in thyristors, so my thought on the
matching was only to limit dI/dt during the (zero-voltage switch) trigger, which might last 100us,
not during the whole of an 8300us half-cycle. It\'s even OK if the inductor
saturates, the next half-cycle will see that sorted out.

5kHz, couple of volts, half amp: 100 uH should be enough.
Click to expand...

In diodes, thermal current hogging happens at low current, where it
doesn\'t matter so much. At high currents, diodes become ohmic with a
positive TC, so start to share.
 
On Tue, 9 May 2023 14:19:30 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

tirsdag den 9. maj 2023 kl. 23.04.26 UTC+2 skrev whit3rd:
On Tuesday, May 9, 2023 at 8:10:09?AM UTC-7, Ed Lee wrote:
On Tuesday, May 9, 2023 at 6:29:11?AM UTC-7, John Larkin wrote:
On Tue, 09 May 2023 09:57:37 +0100, Cursitor Doom <c...@notformail.com
wrote:
On Mon, 8 May 2023 21:25:36 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:
... For paralleling diodes
(and preventing current-hog problems) it takes a bit of series inductance for
each diode. That should work for triacs, too (you don\'t get normal triggering
on slower device #2 if device #1 has acheved low-terminal-voltage already,
because triggering is less effective if main terminal voltage drop is low).

That\'s an interesting idea, using a bit of inductance to limit the
current through each triac to <8A. Damn sight more practical than
power resistors! Well done. I might just use that.
How many henries?
At what frequency?
There\'s reason to believe the current-hog positive feedback that happens
in diodes (and transistors) isn\'t present in thyristors, so my thought on the
matching was only to limit dI/dt during the (zero-voltage switch) trigger, which might last 100us,
not during the whole of an 8300us half-cycle. It\'s even OK if the inductor
saturates, the next half-cycle will see that sorted out.

5kHz, couple of volts, half amp: 100 uH should be enough.

maybe magnetically coupled? i.e. a common mode choke with one winding flipped
Click to expand...

CM chokes are deceptive. They are spec\'d for current at, basically,
zero net flux. If you flip one winding and use them as a 2-terminal
inductor, or run current the same way through both windings, they
usually saturate at very low current.
 
On Monday, May 8, 2023 at 2:38:14 PM UTC-4, Cursitor Doom wrote:
Gentlemen,

I guess this is going to be a non-starter, but here goes:
Can I put two BT137 8 Amp triacs in parallel and get a 16 Amp
capability from them?

CD
Click to expand...

You can alternate the TRIACS with 16A every other cycle. That looks like 8A per each to me.
 
On Tuesday, May 9, 2023 at 2:11:32 PM UTC-7, Cursitor Doom wrote:
On Tue, 9 May 2023 14:04:22 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:

There\'s reason to believe the current-hog positive feedback that happens
in diodes (and transistors) isn\'t present in thyristors, so my thought on the
matching was only to limit dI/dt during the (zero-voltage switch) trigger, which might last 100us,
not during the whole of an 8300us half-cycle. It\'s even OK if the inductor
saturates, the next half-cycle will see that sorted out.

5kHz, couple of volts, half amp: 100 uH should be enough.

Not sure where you got those figures from. We\'re talking about 8 amps
@ 240V and 50Hz.
Click to expand...

It\'s 8 amps RMS, or peak, but this is only during the low (zero-voltage-switch)
voltages at which the trigger is applied. The 240V is RMS as well. 50 Hz
or 60 Hz are likewise full-cycle measures, not directly related to the
instantaneous behavior at trigger time.
 
On 2023-05-09, Cursitor Doom <cd@notformail.com> wrote:
On Mon, 8 May 2023 21:25:36 -0700 (PDT), whit3rd <whit3rd@gmail.com
wrote:

On Monday, May 8, 2023 at 11:38:14?AM UTC-7, Cursitor Doom wrote:
Gentlemen,

I guess this is going to be a non-starter, but here goes:
Can I put two BT137 8 Amp triacs in parallel and get a 16 Amp
capability from them?

Yeah, with a tiny bit of isolation, that\'ll work. For paralleling diodes
(and preventing current-hog problems) it takes a bit of series inductance for
each diode. That should work for triacs, too (you don\'t get normal triggering
on slower device #2 if device #1 has acheved low-terminal-voltage already,
because triggering is less effective if main terminal voltage drop is low).

That\'s an interesting idea, using a bit of inductance to limit the
current through each triac to <8A. Damn sight more practical than
power resistors! Well done. I might just use that.
Click to expand...

Not really. triacs don\'t like inductive loads

Use a common mode choke instead. (in a crossed over configuration).

--
Jasen.
🇺🇦 Слава Україні
 
Jasen Betts <usenet@revmaps.no-ip.org> wrote:
On 2023-05-09, Cursitor Doom <cd@notformail.com> wrote:
On Mon, 8 May 2023 21:25:36 -0700 (PDT), whit3rd <whit3rd@gmail.com
wrote:

On Monday, May 8, 2023 at 11:38:14?AM UTC-7, Cursitor Doom wrote:
Gentlemen,

I guess this is going to be a non-starter, but here goes:
Can I put two BT137 8 Amp triacs in parallel and get a 16 Amp
capability from them?

Yeah, with a tiny bit of isolation, that\'ll work. For paralleling diodes
(and preventing current-hog problems) it takes a bit of series inductance for
each diode. That should work for triacs, too (you don\'t get normal triggering
on slower device #2 if device #1 has acheved low-terminal-voltage already,
because triggering is less effective if main terminal voltage drop is low).

That\'s an interesting idea, using a bit of inductance to limit the
current through each triac to <8A. Damn sight more practical than
power resistors! Well done. I might just use that.

Not really. triacs don\'t like inductive loads

Use a common mode choke instead. (in a crossed over configuration).
Click to expand...

With enough iron, that could work. However, your usual little CM choke
doesn’t have too many voltseconds available to enforce good sharing,
especially when the trigger occurs near a voltage peak. Even small timing
errors add up fast with 240V applied!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC /
Hobbs ElectroOptics
Optics, Electro-optics, Photonics,
Analog Electronics
 
On 2023-05-10, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Jasen Betts <usenet@revmaps.no-ip.org> wrote:
On 2023-05-09, Cursitor Doom <cd@notformail.com> wrote:
On Mon, 8 May 2023 21:25:36 -0700 (PDT), whit3rd <whit3rd@gmail.com
wrote:

On Monday, May 8, 2023 at 11:38:14?AM UTC-7, Cursitor Doom wrote:
Gentlemen,

I guess this is going to be a non-starter, but here goes:
Can I put two BT137 8 Amp triacs in parallel and get a 16 Amp
capability from them?

Yeah, with a tiny bit of isolation, that\'ll work. For paralleling diodes
(and preventing current-hog problems) it takes a bit of series inductance for
each diode. That should work for triacs, too (you don\'t get normal triggering
on slower device #2 if device #1 has acheved low-terminal-voltage already,
because triggering is less effective if main terminal voltage drop is low).

That\'s an interesting idea, using a bit of inductance to limit the
current through each triac to <8A. Damn sight more practical than
power resistors! Well done. I might just use that.

Not really. triacs don\'t like inductive loads

Use a common mode choke instead. (in a crossed over configuration).


With enough iron, that could work. However, your usual little CM choke
doesn’t have too many voltseconds available to enforce good sharing,
especially when the trigger occurs near a voltage peak. Even small timing
errors add up fast with 240V applied!
Click to expand...

Perhaps put the choke on the MT1 side so that a misbalance increases the trigger
signal to the slower triac .

It won\'t give you perfect balanace but it will mitigate trigger
threshold issues somewhat, as long as the gate drive is in the
odd quadrants.

--
Jasen.
🇺🇦 Слава Україні
 
Jasen Betts <usenet@revmaps.no-ip.org> wrote:
On 2023-05-10, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
Jasen Betts <usenet@revmaps.no-ip.org> wrote:
On 2023-05-09, Cursitor Doom <cd@notformail.com> wrote:
On Mon, 8 May 2023 21:25:36 -0700 (PDT), whit3rd <whit3rd@gmail.com
wrote:

On Monday, May 8, 2023 at 11:38:14?AM UTC-7, Cursitor Doom wrote:
Gentlemen,

I guess this is going to be a non-starter, but here goes:
Can I put two BT137 8 Amp triacs in parallel and get a 16 Amp
capability from them?

Yeah, with a tiny bit of isolation, that\'ll work. For paralleling diodes
(and preventing current-hog problems) it takes a bit of series inductance for
each diode. That should work for triacs, too (you don\'t get normal triggering
on slower device #2 if device #1 has acheved low-terminal-voltage already,
because triggering is less effective if main terminal voltage drop is low).

That\'s an interesting idea, using a bit of inductance to limit the
current through each triac to <8A. Damn sight more practical than
power resistors! Well done. I might just use that.

Not really. triacs don\'t like inductive loads

Use a common mode choke instead. (in a crossed over configuration).


With enough iron, that could work. However, your usual little CM choke
doesn’t have too many voltseconds available to enforce good sharing,
especially when the trigger occurs near a voltage peak. Even small timing
errors add up fast with 240V applied!

Perhaps put the choke on the MT1 side so that a misbalance increases the trigger
signal to the slower triac .

It won\'t give you perfect balanace but it will mitigate trigger
threshold issues somewhat, as long as the gate drive is in the
odd quadrants.
Click to expand...

Okay, you’re putting them in the gates. That would probably help with the
triggering, I agree.

It’s fairly far from a complete solution, because it doesn’t enforce
current sharing.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC /
Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
 
On Monday, May 8, 2023 at 2:38:14 PM UTC-4, Cursitor Doom wrote:
Gentlemen,

I guess this is going to be a non-starter, but here goes:
Can I put two BT137 8 Amp triacs in parallel and get a 16 Amp
capability from them?

CD
Click to expand...

Just buy a 16A triac, they\'re only a few dollars.

https://www.mouser.com/datasheet/2/240/Littelfuse-3011227.pdf

The dv/dt of 1000V/us is phenomenal compared to the older parts I\'ve known way down at 30!

I^2t seems a bit low, but the 100A/us critical rate of di/dt is exceptional..

This part is virtually indestructible in the hands of all but the most reckless.
 
On 2023-05-12 14:31, Fred Bloggs wrote:
On Monday, May 8, 2023 at 2:38:14 PM UTC-4, Cursitor Doom wrote:
Gentlemen,

I guess this is going to be a non-starter, but here goes:
Can I put two BT137 8 Amp triacs in parallel and get a 16 Amp
capability from them?

CD

Just buy a 16A triac, they\'re only a few dollars.

https://www.mouser.com/datasheet/2/240/Littelfuse-3011227.pdf
Click to expand...

You\'re no fun anymore. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Friday, May 12, 2023 at 8:09:31 PM UTC-4, Phil Hobbs wrote:
On 2023-05-12 14:31, Fred Bloggs wrote:
On Monday, May 8, 2023 at 2:38:14 PM UTC-4, Cursitor Doom wrote:
Gentlemen,

I guess this is going to be a non-starter, but here goes:
Can I put two BT137 8 Amp triacs in parallel and get a 16 Amp
capability from them?

CD

Just buy a 16A triac, they\'re only a few dollars.

https://www.mouser.com/datasheet/2/240/Littelfuse-3011227.pdf
You\'re no fun anymore. ;)
Click to expand...

He means to take it apart and see how they make it work. A 16A triac is two 8A triacs in one package, right? Or maybe it\'s 16 - 1A triacs... Just sayin\'

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209
 
Jasen Betts wrote:
================
Not really. triacs don\'t like inductive loads

** Not if you avoid pulse firing.
Click to expand...

Use one of the opto triac drive chips ( MOCxx etc) OR a continuous stream of high frequency pulses transformer coupled to the gate.
In both cases, keep the drive ON whenever you need the triac conducting.
Driving transformer coupled ( ie 12V lamp) loads is a trap, as phase controlled the triacs may wind up conducing mostly in one polarity, burning the tranny out with DC.
The idea of paralleling two triacs is very optimistic. One my latch ON first, preventing the other from doing so due to the low voltage ( under <1v) available from MT1 to MT2 at the time.

..... Phil
 
On 12/05/2023 6:57 pm, Phil Hobbs wrote:

Okay, you’re putting them in the gates. That would probably help with the
triggering, I agree.

It’s fairly far from a complete solution, because it doesn’t enforce
current sharing.

Cheers

Phil Hobbs
Click to expand...

Any realistic inductor in series with the MT1 terminals is probably
going to have at least 20-30 milliohms series resistance anyhow which
should help share the current?

piglet
 
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