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Topic: Questions about Arduino spot welder controller (Read 30418 times) previous topic - next topic

avandalen

I mounted the electronics for the spot welder, I turned, but I always 220 V on output to the transformer. I checked and installed all components correctly.It has already happened a problem like this?
Thanks.
If you want to measure the output voltage, use a load.

avandalen

I mounted the electronics for the spot welder, I turned, but I always 220 V on output to the transformer. I checked and installed all components correctly.It has already happened a problem like this?
Thanks.
You must load the output with a MOT, lamp, resistor etc.

candido

Considering that each one of the two SCRs switch on for either the positive or negative mains half-waves which are 10ms long (assuming 50 Hz for the power mains) is there any reason why the minimum welding time cannot be set to 10 ms instead of 50 ms?

Maybe with a shorter welding time there will be no need for switching to the lower 400A current mode.

avandalen

Considering that each one of the two SCRs switch on for either the positive or negative mains half-waves which are 10ms long (assuming 50 Hz for the power mains) is there any reason why the minimum welding time cannot be set to 10 ms instead of 50 ms?

Maybe with a shorter welding time there will be no need for switching to the lower 400A current mode.
The first weld controller that I have built had no synchronisation and therefore the weld time was not very accurate (+/-20ms) and the minimum weld time was set to 50ms because of reproducibility. For me this was fine. But with the synchronisation, the weld time is more accurate and a shorter weld time is possible, but I have not tested this. The weld times can be changed in the software easily.

>>>Maybe with a shorter welding time there will be no need for switching to the lower 400A current mode.
I think that very short weld times are tricky, in some circumstances it may work, it should further be examined.

candido

The first weld controller that I have built had no synchronisation and therefore the weld time was not very accurate (+/-20ms) and the minimum weld time was set to 50ms because of reproducibility. For me this was fine. But with the synchronisation, the weld time is more accurate and a shorter weld time is possible, but I have not tested this. The weld times can be changed in the software easily.

>>>Maybe with a shorter welding time there will be no need for switching to the lower 400A current mode.
I think that very short weld times are tricky, in some circumstances it may work, it should further be examined.

OK, that makes sense, thanks.

Some capacitor discharge spot welders can use dual pulses where the first is a short pulse in the order of 10 ms and the second (after, say, a 10 ms pause) is a bit longer. It was in this context that I had asked the initial question.

As you say, this will require some investigation and testing. In theory the current from the capacitor discharge will be a decreasing exponential while the one from the transformer should be sinusoidal. These different waveforms will probably produce different welds.

BobEdge

If you detect the zero crossing point of the mains, you can use phase angle control to vary the current, and also vary the time of the weld.

You would need 2 thyristors, or a non zero crossing triac, to switch the AC. detect the zero cross point, for full power fire thyristors just after zero crossing, half power then wait 5mS.

Then to adjust the time repeat above for the required number of half cycles.


BobEdge

P.S. The current would be very spiky at lower currents.

You could rectify the output, then use a coil of welding cable as a choke, to get a more smooth DC output.

Or you could of course leave AC on, and use a 4 thyristor bridge to control the dc current. This is the way I would, and have done it, except using 6 thyristors for 3 phase welders.

Jane1

Why do you use Arduino  like controller? What is a reason for that? Would not it be  possible to
 just use ON/OFF switch? When the arms connect, the switch would make a
 circuit and current will flow. Can you please explain the advantages of
 using your controller?
 

candido

#23
Jan 14, 2016, 12:51 am Last Edit: Jan 14, 2016, 11:12 am by candido
Why do you use Arduino  like controller? What is a reason for that? Would not it be  possible to
 just use ON/OFF switch? When the arms connect, the switch would make a
 circuit and current will flow. Can you please explain the advantages of
 using your controller?
 
It surely is possible to use a mechanical switch like a push button to do some spot welding but if reproducibility, consistency, reliability and welding quality are important then a micro-controller and solid state switching is probably the best way to achieve that.

Additionally, if doing battery tab spot welding then it is important to have a precise control of the amount of current/energy/heat used for the weld to avoid damaging the battery. A good overview is given in here:

http://www.macgregorsystems.com/app_note7_battery_pack_manufacture.pdf

avandalen

Why do you use Arduino  like controller? What is a reason for that? Would not it be  possible to
 just use ON/OFF switch? When the arms connect, the switch would make a
 circuit and current will flow. Can you please explain the advantages of
 using your controller?
 
With a mechanical switch you can't create short weld times which are required, 50ms, 100ms etc.

avandalen

OK, that makes sense, thanks.

Some capacitor discharge spot welders can use dual pulses where the first is a short pulse in the order of 10 ms and the second (after, say, a 10 ms pause) is a bit longer. It was in this context that I had asked the initial question.

As you say, this will require some investigation and testing. In theory the current from the capacitor discharge will be a decreasing exponential while the one from the transformer should be sinusoidal. These different waveforms will probably produce different welds.

The weld-controller software creates a short pre-weld time of 50ms (see http://www.avdweb.nl/tech-tips/spot-welder.html). I will this info the the PCB site too.

Jane1

Thank you for the link
Does it mean with your controller you can control current as you need?

I need to heat up a large soldering tip of size 45x20x1mm (lengthxheightxwidth).For this reason I also modified a micro oven transformer( to use a resistive heating).The secondary gives about 600A /2V. But when I shorted it , in a very few seconds, winding was very hot, so not possible to use. I need the soldering tip to be heated up so that it reaches a temperature about 200C, then I need to allow the temperature to drop to about 170C and after a minute or two, I need to increase the temperature to 200C again, wait about 15 sec then drop to those 170C ad so on.
It is not a problem to control the temperature, but my problem is the current that causes big heating of the secondary of the transformer.

Would be possible to use your controller for this project or how  I should modified it?

avandalen

Thank you for the link
Does it mean with your controller you can control current as you need?

I need to heat up a large soldering tip of size 45x20x1mm (lengthxheightxwidth).For this reason I also modified a micro oven transformer( to use a resistive heating).The secondary gives about 600A /2V. But when I shorted it , in a very few seconds, winding was very hot, so not possible to use. I need the soldering tip to be heated up so that it reaches a temperature about 200C, then I need to allow the temperature to drop to about 170C and after a minute or two, I need to increase the temperature to 200C again, wait about 15 sec then drop to those 170C ad so on.
It is not a problem to control the temperature, but my problem is the current that causes big heating of the secondary of the transformer.

Would be possible to use your controller for this project or how  I should modified it?
My spot welder controller board can be used for all kinds of 230V / 120V power control but you need to find out yourselve and write the software yourselve, I can't help you with this.

Jane1

#28
Jan 15, 2016, 07:18 pm Last Edit: Jan 15, 2016, 07:36 pm by Jane1
@avandalen 
Thank you for reply.
I can rewrite the software and buy the hardware from you but will it help to reduce the heating if I send pulses to the secondary? The secondary of my modified MOT gives about 600A /2V. But when I make it short  , in a very few seconds, the secondary winding is  very hot, so not possible to use( it could burn out).
Any spot welder is shorted for a very short time, but I need much longer time to be shorted.
So my question is: will pulses cut down the heating? Or how  could I reduce  heating and prevent transformer from burning?

P.S. I read about Pulsed Heat Soldering Power Supplies,( http://www.amadamiyachi.com/products/hot-bar/hot-bar-power-supplies)  does it mean that it uses pulses and not continuous current?( You have a link on your website to that amadamiyachi company too

candido

@avandalen  
Thank you for reply.
I can rewrite the software and buy the hardware from you but will it help to reduce the heating if I send pulses to the secondary? The secondary of my modified MOT gives about 600A /2V. But when I make it short  , in a very few seconds, the secondary winding is  very hot, so not possible to use( it could burn out).
Any spot welder is shorted for a very short time, but I need much longer time to be shorted.
So my question is: will pulses cut down the heating? Or how  could I reduce  heating and prevent transformer from burning?

P.S. I read about Pulsed Heat Soldering Power Supplies,( http://www.amadamiyachi.com/products/hot-bar/hot-bar-power-supplies)  does it mean that it uses pulses and not continuous current?( You have a link on your website to that amadamiyachi company too
On the ex-MOT I've rewound the maximum current I get (with secondary short circuited) is about the same as shown in Albert van Dalen's website, i.e. 1200A. If I use a 80mm x 4mm nail made of steel to short-circuit the secondary it melts in about 3 secs. In 3 secs there are 100 power mains half-waves (assuming 50 Hz).

Doing some quick calculations, the melting point of steel is about 1500C, so to achieve instead 200C in the same time we need 100/7.5 ~ 13 half-waves or about 4 or 5 half-waves/sec. This can easily be implemented using Albert's "Arduino spot welder controller", just needs some reprogramming of the C code shown in there.

To guarantee a more precise temperature control a thermocouple sensor can be used and interfaced into the Atmega MCU. The advantage of Pulse Heat Soldering is that  the soldering tip heats up and cools down very fast, compared to a soldering iron, hence not much energy is wasted. A good description can be seen here:

http://www.avio.co.jp/english/products/assem/principle/phu/index.html

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