Electronics explanation

[Drains]

Ok, a nice simple one for those who know, but way over my head...
The circuit diagram shows a remote controller for an inverter set. It sets the amps, only (I think). I want to use it as the basis for a foot pedal for tig. My question is, what does RV1 do, and what does P1 do. Is one a preset and one the adjustable, or what?, or is one a max amps, the other the pedal etc etc. I'm sure you understand my conundrum, if not my cluelessness

this is the relevant circuit in the machine, just in case it helps...

btw, if any of you want to build your own inverter, i've got the rest of the diagrams too!!!

 

[Welderpaul]

Quick one: The torch type with the roller on the handle; does this control the amps same as the foot pedal does? If so would it not make more sense to use this rather than a foot pedal?

 

[shenion]

DZ1 is a 5.6V zener. So it will set the wiper of RV1 to 5.6v. You would adjust RV1 so the upper end of P1 is 5.0V. The whole purpose of R1/ZD1/RV1 is to get 5V on P1 from the unregulated 10-15V input.

P1 is the potentiometer to set the current.

Do you already have a torch with a pot in the handle or are you asking if that would be better?

I would use one in the torch if possible.

 

[Drains]

DZ1 is a 5.6V zener. So it will set the wiper of RV1 to 5.6v. You would adjust RV1 so the upper end of P1 is 5.0V. The whole purpose of R1/ZD1/RV1 is to get 5V on P1 from the unregulated 10-15V input.

P1 is the potentiometer to set the current.

Do you already have a torch with a pot in the handle or are you asking if that would be better?

I would use one in the torch if possible.

Ah...Thanks Shenion. Ok, so rv1 is a preset then(?). Stick the voltmeter on it to adjust the volts down to max 5v (yes?)

Re torch - no, it's just a gas valve job. I want to put the pot on a foot pedal. Better control than on the torch I reckon - it's difficult enough holding the torch comfortably, feeding the wire, keeping the weldpool nice, without having to manipulate a roller with a gloved hand... know what I mean?

Any clues as to how I would put in an extra pot to set maximum amps? (too easy to overstep the pedal, blast out 200A and burn a hole in everythin/ blow the fuse...)

 

[Drains]

Quick one: The torch type with the roller on the handle; does this control the amps same as the foot pedal does? If so would it not make more sense to use this rather than a foot pedal?

I refer the member to my previous answer. lol

And to add to that answer - I can play a drum kit, but I can't roll a ciggy in one hand!

 

[snowcat]

Yep footpedal is the only way to go anything on the torch is just hard work to use, Glad you understand RV 1 and P1 etc, I have to pay a man called richard when my machines go down, I always end up pokeing something i shouldnt with a screwdriver followed by a flash, I hate buying pcb,s lol.

 

[shenion]

Yes, use two pots replace P1 with:

The pot on the left sets the max, the one on the right sets current 0-max.

 

[Drains]

Ah Shenion, you star

. Do I make both pots 2k2's?

No no, sorry, not paying attention AGAIN. They are 2k's right?

Does it matter?

 

[shenion]

2.2K. Was not paying attention to the Asian notation 2K2 vs 2.2K.

Will change foot pedal to be a bit non linear, especially when MAX is set to 1/2.

Personally, I would add a 0.1uf cap to the V_reg line and 0V at the connector (ould also add one across DZ1). But that is just me, designing to filter out noise and clamp any spikes. Probably there is already filters in the machine.

 

[Drains]

Now Shenion, you're losing me again. Re the non linear pedal... can you explain further? I'm going to be knocking this up myself, it'll be a mechanical action to the pot so I can organise the mechanics to be non linear if i'm smart enough.... - what curve am I working with here?

And the caps - just in line?

Interesting re what you call Asian notation. It's standard European too. (You Americans have to be different! )

Sorry I have to keep asking questions, but I'm really out of my depth.

Si

 

[shenion]

Non linear as in (approximate, too lazy to calc the numbers) :

MAX pot set to 50% full position. Current at full pedal would actually be 33%.
Max pot set to 75% full position, Current at full pedal would be 70%

So the MAX pot is not center position=50% max. The pedal will be linear.

I could make the max pot linear and also get rid of the trim pot, but that would involve adding a transistor. Don't know if you want to go there.

Well, Asian parts are nKn notation. I don't buy many parts from europe.

Don't worry about the caps.

 

[mishka]

The 'nKn' notation is a European thing, as an aid to clarity on schematics. In the days of blueprints it was quite easy to lose the '.' in the reproduction process, turning '2.2k' into '22k' ... with potentially disastrous results. The solution devised was to use the multiplier letter in place of the '.', so that '2k2' would always come out correctly. Oh, and for resistors 'R' is used when there is no multiplier, like '2R2' for 2-point-2 ohms.

I guess it also works for marking components, where the '.' might not be embossed sufficiently to be visible.

 

[Drains]

Non linear as in (approximate, too lazy to calc the numbers) :

MAX pot set to 50% full position. Current at full pedal would actually be 33%.
Max pot set to 75% full position, Current at full pedal would be 70%

So the MAX pot is not center position=50% max. The pedal will be linear.

Do you mean if I just wire up as is, I will get the above? How do I arrange the max pot to give 50% at 50%, or do I just calibrate it/ work it out from your figures above and mark on appropriately? (seems the thing to do to me).Can you explain why Max pot at 50% gives 33% power? I'm sure you wern't intending to give a lesson in basic electronics, but I was rather hoping you would!

Shen, You have to treat me as an ignoramus and make no assumptions about my electronic ability, other than a basic skill with iron and solder.... sorry (I'm quite good at hitting things with hammers though!)

Si

 

[shenion]

The pot has an output impedence that varies. At each end it is a dead short. At mid point it has an effective resistance of 550 ohms (1/4th value)

That drives the second pot that is a 2.2K load. So at mid point you 550 driving 2.2K. So you get 80% out of 50% or 40%.

Setup:

1. Turn MAX and foot control to full.
2. Adjust RV1 to get 5V out.
3. Vary MAX control with footpedal at full and measure voltage. Mark each 0.5V step. That will give you 0-10 scale for 0-100%.

I have a version with no trim adjustment and is more linear on the output here: http://shdesigns.org/Welding/footctl.pdf

Note: even with the change, the inverter has a resistive divider on the pot output that will make it slightly non-linear (50% pos=45%). I also bet there is a "dead-zone" for near 0% so it may not turn on until 10% current (by design)

Edit

 

[Drains]

You beauty, I understand!
Thanks Shenion, you've come up trumps again!

(sorry you had to spell it out for me, but there you go...).

Si


Edit
Got the pdf. I reckon I can manage that. Thanks mate.

 

[Drains]

I'm finally getting round to building this pedal.... but would like to be able to pick up the electronic bits from Maplins, for convenience but they don't supply 2K2 pots, only 1K, 4K7, 10K. How can I use one of those instead of 2k2?

Any suggestions? I'm following Shenions design linked above.

Thanks
Si

 

[shenion]

1K will work. 4.7k would be my second choice.

 

[Drains]

1K will work. 4.7k would be my second choice.

Cheers mate

Si

 

[Drains]

Well folks, a big box (about the size of my head) containing a very little connector (about half the size of my thumb), arrived via TNT from Lincoln Electric, Italy, this morning (Lincoln have never sold this part in the UK before!), so I hastened to the yard to wire up connector and homemade tig pedal, electronically engineered by Shenion, and...... It Works!!

So, many thanks to Shen for his circuit diagram, and I must say the control over the arc is fantastic! I'm a happy bunny.

All I need now is something to do with the machine.

Anyone want any Tig work done?

Si

 

[Welderpaul]

Great stuff mate. Good when summat works out innit.