EXT250 A/C questions

[Mike J]

Thanks for the picture!

In that picture, both sides are not aligned vertically, as well as the air gap between them. Is that deliberate?

And how exactly does this play a role? If the arc can span the air gap, then it can span the gap between the tungsten and the welding material?

Cheers,

Mike

[parkour]

Doubtful. The misalignment is not important, and likely just low cost production where precision is not important.

No, the gap is part of the high frequency (HF) arc starter.

[Rivets]

[QUOTE



QUOTE]

I like the adjustment features on the 250 EXT spark gap unit.
Can I purchase one to retrofit my PP 256 ?

Thanks,
Andy

[Mike J]

Hi Andy,

You got any details? (pictures?). I am curious because I have one on order...

Cheers,

Mike

[QUOTE



QUOTE]




I like the adjustment features on the 250 EXT spark gap unit.
Can I purchase one to retrofit my PP 256 ?

Thanks,
Andy

[performance]

No, currently they won't retrofit. Two completely different machines. One is digital, the other not, though this part obviously is old fashioned HF, the parts are not made to be compatable.

[Rivets]

Hi Andy,

You got any details? (pictures?). I am curious because I have one on order...

Cheers,

Mike

Hi Mike,

The unit you have on order is the 250 EXT ?

The unit I have is the PP 256, therefore not the same as yours ?

Cheers,
Andy

[Rivets]

No, currently they won't retrofit. Two completely different machines. One is digital, the other not, though this part obviously is old fashioned HF, the parts are not made to be compatable.

Thanks Mark.

I figured points are points, and spark gap is spark gap.
Did'nt think the circuitry would know the difference or care.

Regards,
Andy

[Mike J]

Not sure what is in the PP256, but the 250EXT is a totally new machine. They have only shipped the first shipment from the factory out, second shipment due sometime in January. Since the unit is totally new, so that is why I asked about your comment on the spark gap - I thought you might have some insight into how the new box worked since you stated you liked the adjustment features on the 250EXT.

[Tinker]

Wow, I just joined this group less than a week ago and I'm finding all these type of technical discussions and DIY type efforts (pedals, fan on demand, etc.) very interesting. I've been on many of the other welding forums that just don't get into the details of the equipment. Probably not every welders cup of tea but for an ex-computer peripheral designer and lifetime electronic/mechanical tinkerer I love it.

I'm more familiar with low voltage stuff but I'll hazard a somewhat educated guess about the spark gap. Without having a schematic of that HV circuit and just judging from the components I'm thinking the following:
- It's using a pulsating DC via the black coil to charge the large capacitor to a high voltage.
- When the voltage builds to the point where it can jump the gap the high voltage flows from the capacitor and out to eventually get to the tungsten and jump to the workpiece. When the welding arc is established then the HV circuit is turned off.
- The spark gap acts as a very high resistance part of the circuit until you get to a high enough voltage where it will jump the gap. Certainly the size of the gap and probably the shape of the points in the gap (sharp, flat, etc.) will help determine how high the voltage must be to jump the gap. I remember something about it taking 35,000 volts to jump a centimeter but don't quote me on that and it's going to depend on the shape of the gap electrode.
- The rate at which the circuit can produce these arc starter sparks and their voltage is going to be affected by the size of the spark gap.
- Look a lot like a Capacitive Discharge Ignition (CDI) system for an engine.

It would be interesting to see a schematic of a typical HV start circuit for these welders.

Gary

[Rivets]

Not sure what is in the PP256, but the 250EXT is a totally new machine. They have only shipped the first shipment from the factory out, second shipment due sometime in January. Since the unit is totally new, so that is why I asked about your comment on the spark gap - I thought you might have some insight into how the new box worked since you stated you liked the adjustment features on the 250EXT.

Mike,

The only "insight" I have concerning the 250 EXT points is what I see in the picture that I copied in my post.

On my unit, the points are at the ends of two metal strips that require bending with long nose pliers for adjustment.

Hence my liking for the points in the new unit.

Cheers,
Andy

[todmorg]

No time to tinker with the gaps today, but I am curious how different settings change the results at the torch.

Does a larger gap = stronger but slower hf?

Would I be looking for a smaller gap to keep the hf from cycling at extreme low amperages?

[Mike J]

No, currently they won't retrofit. Two completely different machines. One is digital, the other not, though this part obviously is old fashioned HF, the parts are not made to be compatable.

I think it would be cool to have a short discussion on the EXT - for example, how "digital" is it really, and what does that really mean? i am an old fashioned computer engineer, and that term is very overused and subject to all sorts of interpretation.

I assume that the control portion of the welder is software based, including the control of the welder output (waveforms, amperage and voltage control, frequency and high freq arc control, etc). What I do not know is how digital is the waveform creation, i.e. there is likely some analogue circuitry somewhere before the final output, since many power circuits remain analogue.

Being "digital" also add new aspects to the support side - for example, is the welder flash-enabled for software updates?

I am not anticipating deep details here, but just enough to appreciate how the machine overall works. I find that if i understand how the machine works, I seem to use the equipment better...! :-)

Cheers,

Mike

[performance]

Wow, I just joined this group less than a week ago and I'm finding all these type of technical discussions and DIY type efforts (pedals, fan on demand, etc.) very interesting. I've been on many of the other welding forums that just don't get into the details of the equipment. Probably not every welders cup of tea but for an ex-computer peripheral designer and lifetime electronic/mechanical tinkerer I love it.

I'm more familiar with low voltage stuff but I'll hazard a somewhat educated guess about the spark gap. Without having a schematic of that HV circuit and just judging from the components I'm thinking the following:
- It's using a pulsating DC via the black coil to charge the large capacitor to a high voltage.
- When the voltage builds to the point where it can jump the gap the high voltage flows from the capacitor and out to eventually get to the tungsten and jump to the workpiece. When the welding arc is established then the HV circuit is turned off.
- The spark gap acts as a very high resistance part of the circuit until you get to a high enough voltage where it will jump the gap. Certainly the size of the gap and probably the shape of the points in the gap (sharp, flat, etc.) will help determine how high the voltage must be to jump the gap. I remember something about it taking 35,000 volts to jump a centimeter but don't quote me on that and it's going to depend on the shape of the gap electrode.
- The rate at which the circuit can produce these arc starter sparks and their voltage is going to be affected by the size of the spark gap.
- Look a lot like a Capacitive Discharge Ignition (CDI) system for an engine.

It would be interesting to see a schematic of a typical HV start circuit for these welders.

Gary

Gary,
Typically its referred to as High Frequency, though High voltage is a part of it. We do have a High voltage start in our CNC plasmas that is not HF.

[performance]

Mike,
Perhaps it would be better to download the manual and look at the unit wiring schematics. Its not detailed circuit board schematics, but it covers the basics. The features and functions are microprocessor controlled largely and the inputs and panel are digital... No analog rheostats except on the foot pedal.

[Mike J]

Mike,
Perhaps it would be better to download the manual and look at the unit wiring schematics. Its not detailed circuit board schematics, but it covers the basics. The features and functions are microprocessor controlled largely and the inputs and panel are digital... No analog rheostats except on the foot pedal.

Oh man, now I feel like a dummy! You mean RTFM, right?

That is the beauty of these forums, thanks!

Cheers

Mike

[everlastsupport]

The unit is a digitally controlled solid state (inverter) welder. But it still uses a lot of analog on the welding side. But has a digital is the front end/control.

On the HF board. It is a flyback transformer, like a 15KHz Hosc circuit in a TV. It is a lot higher freq than the welding features/frequencies, so it is HF compared to most (excluding the ATMEL mega's internal or external osc in the digital control). To an EE it would be a HV board not a HF board. In a welding circuit it is the HF spark gap to jump and start the arc transfer.

Hope that helps.

[jakeru]

Here is a post I made a while back regarding my Super200P's high frequency circuit design (turns out it was on another forum, but relevant to what we're discussing here):
http://weldingweb.com/showpost.php?p=342080&postcount=3

In summary, it's a "tesla coil" circuit.

As for the 250EXT, I would guess based on the picture in this thread, that it may use a similar "tesla coil" circuit as well. (Those two blue, cylindrical capacitors look just like the ones in my Super200P.) The EXT's spark gap conductors are dramatically different (possibly improved durability tungsten?) compared to the copper material spark gap found on nearly all other imported inverter machines with high frequency arc starting.