Author Topic: Arc welder triac controler  (Read 60367 times)

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Offline rodrigopiresTopic starter

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Arc welder triac controler
« on: August 23, 2015, 09:51:49 pm »
Hi, i have made this triac power controller for my homemade MOT arc welder, but the first time i plugged it in on mains, 230VAC, with no load, one of the 27K resistors (R6 / R7) blow up. What could be the problem?

Thanks!
 

Online IconicPCB

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Re: Arc welder triac controler
« Reply #1 on: August 23, 2015, 10:21:58 pm »
what is the purpose of the two resistors in the circuit?
 

Offline rodrigopiresTopic starter

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Re: Arc welder triac controler
« Reply #2 on: August 23, 2015, 10:57:34 pm »
what is the purpose of the two resistors in the circuit?

DB1 diode bridge and R6-R7 resistors are used to discharge C1 at each line zero voltage. This resets the voltage charge at each new half line cycle, and keeps the same turn-on delay.
 

Offline rodrigopiresTopic starter

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Re: Arc welder triac controler
« Reply #3 on: August 25, 2015, 09:04:35 pm »
Help? I really want to finish this project and i don't want to blow more parts, so if someone could help, i would appreciate it. Thanks!
 

Offline TheElectricChicken

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Re: Arc welder triac controler
« Reply #4 on: August 25, 2015, 09:34:37 pm »
are photos of the board possible, to check for mistakes, just in case the circuit is not consistent from paper to real world.
 

Offline TheElectricChicken

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Re: Arc welder triac controler
« Reply #5 on: August 25, 2015, 09:37:38 pm »
it is difficult to understand the function of the first rectifier, it is a strange configuration for a rectifier. It doesn't turn AC into DC as most rectifiers do.

I think this one is beyond me.
« Last Edit: August 25, 2015, 09:40:07 pm by TheElectricChicken »
 

Offline TheElectricChicken

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Re: Arc welder triac controler
« Reply #6 on: August 25, 2015, 09:52:25 pm »
this one has a more conventional easy to understand cct, might be a backup as you'd have the parts already.



https://sites.google.com/site/jfpayeur/welder
 

Offline eneuro

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Re: Arc welder triac controler
« Reply #7 on: August 25, 2015, 10:15:55 pm »
What could be the problem?
I do not like this design at all, while you have potentiometers P1, P2 (I guess) NOT galvanic insulated from AC mains  ???

Anyway, In spot welder I've used two thyristors in anti-parallel configuration and they can be easy trigered using optotriac from small MPU powered from 12V battery or low power small trafo <$2  8)
AC mains zero crossing can be detected using two PC817 in anti-parallel.
I see no reason to use oldschool analog dimmers those days, since small 8 pin MPU <$1 can be easy programmed to do this job in more sophisticated way.

I think, galvanic insualtion from AC mains of anything used to controll arc welder is a must, especially in DIY home made projects....while so many things can go wrong and it is better have a few kV insulation, not only for human safety, but also to limit possible circuit failure to power triacs/thyristors and make it easier to debug and test, while we have optoisolated subcircuits and we can test them alone to ensure they works as expected  :popcorn:
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Offline TheElectricChicken

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Re: Arc welder triac controler
« Reply #8 on: August 25, 2015, 10:21:05 pm »
I expect it is possible however, to bury the potentiometer deep inside the case and glue an insulator to the shaft. The insulator can run to the outside as the knob.... ?
 

Online IconicPCB

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Re: Arc welder triac controler
« Reply #9 on: August 25, 2015, 10:26:13 pm »
1W rating of the resistors is on the low side.

Resistors are not the most expensive components. Buildup a 27K resistor from four 27K 1w resistors by runing them in aeries parallel combination ( two series groups of two parallel resistors).

Presently the resistor are operating close to their upper dissipation rating.
 

Offline rodrigopiresTopic starter

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Re: Arc welder triac controler
« Reply #10 on: August 25, 2015, 11:34:47 pm »
Thanks for the help, here are some photos of the circuit.
this one has a more conventional easy to understand cct, might be a backup as you'd have the parts already.



https://sites.google.com/site/jfpayeur/welder

I have seen this circuit but Q1 is too expensive for me, so i tried this one instead.

1W rating of the resistors is on the low side.

I was just testing for the first time, with no load, is t normal to pop 1W resistor with no load, and also my 16A circuit breaker shuts off.
 

Offline TheElectricChicken

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Re: Arc welder triac controler
« Reply #11 on: August 25, 2015, 11:39:50 pm »
when you say no load, do you mean no transformer connected ?

is it possible to get a closer-up view from direct above the components and a view of the underside. People could use the two to check the wiring I think..

Strong light may help make the picture clear too...
 

Offline rodrigopiresTopic starter

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Re: Arc welder triac controler
« Reply #12 on: August 25, 2015, 11:52:29 pm »
yes, with nothing on the output wires.
 

Offline Andy Watson

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Re: Arc welder triac controler
« Reply #13 on: August 26, 2015, 12:07:04 am »
I was just testing for the first time, with no load, is t normal to pop 1W resistor with no load, and also my 16A circuit breaker shuts off.
I would guess that either you've not wired the circuit as per your diagram and/or there is a short on the board.

Either way: 27k at 1W rating is pushing it. Are the resistors rated for 325V operation? Are you sure it was a 27k - looks like it popped with some violence.

In the last picture you posted they look like 27 Ohm resistors.
 

Offline TheElectricChicken

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Re: Arc welder triac controler
« Reply #14 on: August 26, 2015, 12:13:48 am »
In the last picture you posted they look like 27 Ohm resistors.

I agree. 27k off the top of my head has a orange stripe rather than black. Those resistors are not 27k they are 27 Ohms

0 = black
3 = orange

27 x zero tens = 27 ohms
 

Offline rodrigopiresTopic starter

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Re: Arc welder triac controler
« Reply #15 on: August 26, 2015, 12:18:41 am »
I was just testing for the first time, with no load, is t normal to pop 1W resistor with no load, and also my 16A circuit breaker shuts off.
I would guess that either you've not wired the circuit as per your diagram and/or there is a short on the board.

Either way: 27k at 1W rating is pushing it. Are the resistors rated for 325V operation? Are you sure it was a 27k - looks like it popped with some violence.

In the last picture you posted they look like 27 Ohm resistors.

OMG  :scared:, they are actually 27 Ohms, not 27K, the must have been a mistake in the shipping when i bought them, because i ordered 27K. Thank you so much! i will replace the resistors, and next time check every component!

Thank you all for the help, i really appreciate it!  :D
 

Offline TheElectricChicken

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Re: Arc welder triac controler
« Reply #16 on: August 26, 2015, 12:49:50 am »
 

Offline oldway

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Re: Arc welder triac controler
« Reply #17 on: August 26, 2015, 06:06:36 am »
I know well this circuit because I use it in a battery charger project.
The circuit is very simple and works well.

It must however comply with certain precautions.
1)For safety,  the potentiometer must have a plastic shaft and be mounted on an epoxy insulating plate.
2) the circuit generates a pulse train, which is correct for an inductive load.
But pulses are very short (2 to 3 microseconds) and are insufficient to ensure that the current reaches the holding/latching current with highly inductive load.
For proper and safe operation, add an incandescent lamp 100W 220V in parallel with the transformer.
3) I replaced the MOV by a bridge rectifier and 4 zener diodes in serie of 15V 1,3W.

Choose 3 quadrants snuberless triac (with snubber added for more reliability).

To test the circuit, use only the 100W lamp as load, without the transformer.

Nb: for auxiliary triac, be sure to use the Z0103, not the Z0107, nor Z0109, nor Z0110 because it will not generate pulse train with lower sensitivity auxiliary triacs. (higher gate current)
With transformer, you must have a symetrical triggering of the triac to avoid create a DC voltage on the primary of the transformer.
If this occur, transformer will saturate and a very high current will blow your mains fuse and perhaps also your triac.
With a 100W  incandescent lamp in parallel with the primary of the transformer (resistive load low enough to reach the latching current), you are sure that no false triggering can occur and it will works with reliability.
« Last Edit: August 26, 2015, 09:24:09 am by oldway »
 

Offline rodrigopiresTopic starter

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Re: Arc welder triac controler
« Reply #18 on: August 26, 2015, 05:59:47 pm »
I know well this circuit because I use it in a battery charger project.
The circuit is very simple and works well.

It must however comply with certain precautions.
1)For safety,  the potentiometer must have a plastic shaft and be mounted on an epoxy insulating plate.
2) the circuit generates a pulse train, which is correct for an inductive load.
But pulses are very short (2 to 3 microseconds) and are insufficient to ensure that the current reaches the holding/latching current with highly inductive load.
For proper and safe operation, add an incandescent lamp 100W 220V in parallel with the transformer.
3) I replaced the MOV by a bridge rectifier and 4 zener diodes in serie of 15V 1,3W.

Choose 3 quadrants snuberless triac (with snubber added for more reliability).

To test the circuit, use only the 100W lamp as load, without the transformer.

Nb: for auxiliary triac, be sure to use the Z0103, not the Z0107, nor Z0109, nor Z0110 because it will not generate pulse train with lower sensitivity auxiliary triacs. (higher gate current)
With transformer, you must have a symetrical triggering of the triac to avoid create a DC voltage on the primary of the transformer.
If this occur, transformer will saturate and a very high current will blow your mains fuse and perhaps also your triac.
With a 100W  incandescent lamp in parallel with the primary of the transformer (resistive load low enough to reach the latching current), you are sure that no false triggering can occur and it will works with reliability.

Hi, thank you for the information, i will use the 100W bulb in parallel with the transformers, my pots have long plastic knobs, and i used the Z0103 that is on the circuit.

Once again, thanks for all the help  :D
 

Offline TheElectricChicken

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Re: Arc welder triac controler
« Reply #19 on: August 26, 2015, 06:06:57 pm »
Please do let us know if it works !!!!!

all the best.
 

Offline rodrigopiresTopic starter

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Re: Arc welder triac controler
« Reply #20 on: August 26, 2015, 06:50:00 pm »
yah, just have to wait for my new resistors and probably will post a video on yt to show the project, and also leave a link in this post.
 

Offline TheElectricChicken

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Re: Arc welder triac controler
« Reply #21 on: August 26, 2015, 06:58:39 pm »
SWEET! Thanks, can't wait  :popcorn:
 

Offline eneuro

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Re: Arc welder triac controler
« Reply #22 on: August 29, 2015, 07:35:53 pm »
Please do let us know if it works !!!!!
It will be interesting to see, but it lacks a lot of things like overcurrent detection and protection to do not triger home mains fuse when it wil draw too high current for longer period of time, so that is why I've also Hall current sensor and MPU which averages input current (10000 samples per second) and when it is above preset limit than adjusts phase to be able lower it down to safe levels  8)



Anyway, I've also reinforced 5mm mains PCB SCRs tracks with two copper wires 1.5mm2 each in parallel, so it is 3mm2 + solder per PCB power track, so now I think that in the case of disaster high current those SCRs will explode first and this PCB should survive-just replace them with brand new SCRs and weld again ;)



Working now on synchronous rectification on secondary side, to be able get high DC current with low power losses on transformer secondary (classic bulky 230VAC -> 24VAC ).

Another story is HV arc ignition pulses and this is in my interest too and looking for good ways to do it. I consider also preheating welded parts with spot welder high current, while higher metal temperature shoould also help get stable arc easy, while air will break at lower voltage when it is hot  :-/O
« Last Edit: August 29, 2015, 07:38:10 pm by eneuro »
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Offline oldway

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Re: Arc welder triac controler
« Reply #23 on: August 29, 2015, 09:26:28 pm »
Quote
Hi, i have made this triac power controller for my homemade MOT arc welder, ...
Rodrigopires did not explain what transformer he is using.
I hope he knows that the welding transformer must have a high short circuit voltage (20%) to limit short circuit current and an open voltage above 40V to work correctly.
« Last Edit: August 29, 2015, 09:28:00 pm by oldway »
 

Offline eneuro

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Re: Arc welder triac controler
« Reply #24 on: August 29, 2015, 10:30:38 pm »
I hope he knows that the welding transformer must have a high short circuit voltage (20%) to limit short circuit current and an open voltage above 40V to work correctly.
What do you mean work correctly?
For me this means for example limit input power to be below 5kVA.

This bulky 10kVA 200AC/DC Inverter Operating Manual by WELDSKILL has 76V open circuit voltage.

I can build up such voltage even from 24VAC but what short circuit current is required at this voltage above 40V-to ignite arc I guess, while later welding  closed circuit voltages are <=~24V in the case of this welder shown above  ::)

Update, As always patents can explain many things-sounds good  :D
Patent US 6156999 A: Method and device for welding arc ignition for arc welding apparatus

Anyway, from this linked manual:
Quote
Suppose a Welding Power Source is designed to operate at a 20% duty cycle, 200 amperes at 18.0 volts.
they says about 18V*200A=3.6kVA , so when we assume 70% efficiency we get ~5kVA input power, which means 5kVA/230V~22A (for 240VAC it is ~20A), but they says about 15A effective input current which means 3.6kVA @ 240VAC they specified in their datasheet, but when we take 170A*25.8V~4.4kVA and it is higher than their effective current..  ???  :-//
100A*24V~2.4kVA, so it could be ~67% efficiency when we take 3.6kVA input power...



The first thing when looking for welder probably should be home grid power capabilities in the case of single phase, so sensing input power (current) was a must in my design to leave some power for other home equipment and avoid blackout while welding  :-D


« Last Edit: August 29, 2015, 10:44:26 pm by eneuro »
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