HF 91811, the $200 wonder

[MrWild]

I bit the bullet and bought one. After playing with it over the last few weeks, my impression is, "They got all of that for just $200?" Although it doesn't state this in the ads, It does have pre and post gas flow. The start isn't done with striking the surface to innitiate an arc. There is some sort of low voltage/amperage prestart. You touch the tip to the work, and lift it off the surface. The pre-gas flow starts and then the main amps kick in starting the arc. Soft start?

Something interesting is that the weld power can be controlled by twisting the power control knob during a weld. I've been brain storming with another HF owner and we seem to have found a sort of holy grail. Foot control. Someone said it couldn't be done. Others said the electronics were proprietary. Smarter men have failed, it is time for a stone axe approach. My friend got his together before me, but here is a good idea of what we are doing.

A delrin pulley is made with two shoulders. These act as bearing surfaces for the mounting plates. Concern about pot life was raised if the pot had to take the entire pulley force. The cable is a bicycle shift cable. The interesting return spring is from a broken motorcycle kickstarter. Mine is getting a standard coil spring. Only one hole gets drilled in the case foir the cable end.

The torch head is a bit cheesy, but seems to do the job fairly well. Is it on par with a $1,600 Miller? Nope, but it is very capable for what it does cost. If you have a budget and want to get into TIG welding without the big outlay of cash, here you go. You will also need a flowmeter/regulator as the unit doesn't include one. Found one on eBay for $35 delivered

[MrWild]

Addendum

The problem with cratering at the end of the weld has been solved with this adaptation. Let up on the pedal and draw back slightly to extingiush the arc, and the post flow stays on the weld.

[mlaws1172]

Glad you posted this, I have been looking at them too and wondering if it would be any good.

I just wanted a tig to play with at home, now I will get one

Thanks
mike

[mixdenny]

I had one for awhile but ended up selling it. It does work pretty well for a $200 tig. I easily made a real foot control. I got a guitar foot pedal on eBay for less than $20. I swapped out the pot for the correct range, I think it uses a 10K ohm. It is a bit tricky to setup, as the amp control use both halves of the pot at the same time, ie, one side decreasing and one increasing, just be methodical when doing the wiring.

Another aspect on mine was the pot I got had a 270 degree sweep, but the foot pedal was a bit shy of that. So I could set it up to give amperage all the way up, or all the way down, but not both at once. A better fit for the pot to the foot pedal would solve that problem.

I sold it because the unit does not come down to low enough amps for the light sheet metal work I wanted to do. I have heard a good review of Grizzly's $500 tig with pulse control, and I am going to that next. The poster previously had the HF tig, and found the Grizzly to be superior in starting and had a more stable, less agressive arc.

Dennis

[uhmgawa]

I think it uses a 10K ohm. It is a bit tricky to setup, as the amp control use both halves of the pot at the same time, ie, one side decreasing and one increasing, just be methodical when doing the wiring.

It is a 10K linear taper pot. You could substitute another pot for an external control.
For a foot control I might consider using a slide pot.

Another aspect on mine was the pot I got had a 270 degree sweep, but the foot pedal was a bit shy of that. So I could set it up to give amperage all the way up, or all the way down, but not both at once. A better fit for the pot to the foot pedal would solve that problem.

That could be addressed electrically or mechanically. The 10K pot is part of a simple voltage
divider spanning between 19%..60% of the internal PWM controller's 5V reference.

I sold it because the unit does not come down to low enough amps for the light sheet metal work I wanted to do.

There is also an internal 50K trimpot used to set the heat range which could be adjusted to
increase the low end range. In any case the PWM controller is an SG3525 which is pretty
simple to massage to get what you're after.

[uhmgawa]

I bit the bullet and bought one. After playing with it over the last few weeks, my impression is, "They got all of that for just $200?" Although it doesn't state this in the ads, It does have pre and post gas flow. The start isn't done with striking the surface to innitiate an arc. There is some sort of low voltage/amperage prestart. You touch the tip to the work, and lift it off the surface. The pre-gas flow starts and then the main amps kick in starting the arc. Soft start?

Well sort of. The pre flow actually depends on the user to keep the electrode in
contact with the work long enough to effect "pre flow". When the electrode is
lifted off the work the PWM starts and initiates the arc. For the first second +/- the
heat is fixed to insure an easier start when the running current is low. After this initial
fixed heat the PWM will be driven at the running heat selected via the front panel
pot.

Something interesting is that the weld power can be controlled by twisting the power control knob during a weld.

Yes, it is just applying a voltage to the PWM error amp which except for the start
current above is variable during the weld operation.

I've been brain storming with another HF owner and we seem to have found a sort of holy grail. Foot control. Someone said it couldn't be done. Others said the electronics were proprietary.

Ha. That's the one thing this welder's electronics are not -- which IMHO is a huge benefit
for those who would like to conduct some experimentation. The design is fairly vanilla
and associated components are industry standard. On more mainstream equipment
you're going to be looking at reverse engineering a microcontroller based approach vs
the Kende discrete design. Although a microcontroller design is going to provide far
more features than are available in this controller.

Smarter men have failed, it is time for a stone axe approach. My friend got
his together before me, but here is a good idea of what we are doing.

I'd opt for the external pot solution. There is an internal transformer which isolates
the control circuitry from the mains so that shouldn't be a concern.

The actual control circuitry resides on a small PCB which contains the PWM controller
and start/timing logic. One could remove the existing board and substitute a more
comprehensive microcontroller based solution to provide additional heat control
features found in substantially more expensive equipment. The logic which implements
the post purge "feature" would be one of the first things I'd toss out in favor of a
more general approach.

Another possibility is a slight modification to the output transformer to furnish
AC current. This is a bit of a hassle as you'd need a means to switch the high
current secondary winding between the existing center tapped configuration
and that of two separate but parallel windings.

[mixdenny]

It is a 10K linear taper pot. You could substitute another pot for an external control.
For a foot control I might consider using a slide pot.

Thanks for the insights on the electronics. A slide pot would be a good choice if you are building a foot control from scratch. The guitar foot pedals are already set up with standard rotary pots. They use a gear track attached to the pedal to spin the pot. Very easy to change out the pot, and my foot control cost less than $25 total.