Newb AC frequency range

[moleb]

Hello,

I'm choosing between 2 AC TIG machines and was wondering how important the frequency adjustment range is. One of the welders goes from .5hz to 5hz and the other from .5hz to 500hz. I prefer the one with the smaller range but not sure if I need the 500hz maximum on the other one. I understand the theory but no idea yet if I'll need it.
I do a lot of small beads in DC on motorcycle parts and will need to continue that on aluminium.

Thanks,

Brian

 

[Jim Davey]

Don't get confused between +/-AC frequency, and pulse frequency, the two are separate entities and easily confused.

 

[Jim Davey]

Most AC sets with frequency adjust go from 50-200Hz or 50-150Hz.
Pulse frequency could be anything within reason up to KHz.
If sacrifice some pulse frequency for better HF start and a really nice stable arc in AC mode.
It may help if we know the two machines on your shortlist. People might be able to offer first hand experience.

 

[moleb]

Thanks for the reply. You are correct that I've mixed up pulse and AC frequency. The 2 machines in question are:-

Stamos S-ALU 220

http://www.ebay.co.uk/itm/262252072795?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

Apex Tig 200

http://www.ebay.co.uk/itm/371421168740?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

The Stamos quotes 'Impulse Frequency' .5-5hz

The Apex quotes 'Pulse Frequency' at .5-500hz and 'AC Frequency' at 15-200hz.

The Stamos does not appear to quote AC frequency.

I've been getting on well with a Rotenbach Chinese/German affair for DC only and both of these fit the bill I can't quite stretch the budget to an R-tech...

 

[Jim Davey]

That Apex machine is an R-Tech, what is the warranty like?

 

[moleb]

That Apex machine is an R-Tech, what is the warranty like?

They are quoting 2 years for domestic use and 1 year for professional use.

I like the loook of it and have had good results with a German/Chinese Rotenbach thing. The reason I like the other one is that the optional foot pedal is better than the one for the Apex which looks like the rubbish one I have for the Rotenbach. It also looks like the Eastwood chassis which gets good reviews (not that this guarantees the contents are the same).

 

[hotrodder]

Pulse is more useful on heat sensitive materials like stainless or Ti than it is on materials like aluminium which need a higher heat input due to thermal conductivity. Even then pulse is mainly useful on thin stuff only. For welding properly thin (under 0.5mm) stuff high a frequency pulse (hundreds of Hz and up) is waaaaaaay more useful than slow on/off pulse. Less annoying/likely to cause eye strain/headaches/fits either as the flickering is too fast for the eye to register

Higher frequencies, pulse and/or AC frequency, constrict and stiffen the arc improving the weldpools depth to width ratio. For example using a slow on/off pulse on say some thin stainless and the weld width will increase slightly compared to just welding it. The same weld pulsed at >100Hz will be narrower everything else being equal i.e. in all 3 cases the average amperage, travel speed etc is the same. With ally AC frequency has a similar effect while pulse is just annoying IMO

Doesn't matter given the above but bare in mind that in lots of spec lists they 'forget' to mention that the advertised pulse frequency sometimes only applies to DC and in AC the max pulse frequency is a chunk lower. If the Apex box is the same as one with Rtech painted on the side i'd expect in AC the pulse range is 0.1 - 250Hz versus 500Hz in DCEN
I'd also take many (most) reviews with a pinch of salt too, fairly common for them to be written by someone that has just bought their first TIG to learn to weld and has never used let alone owned anything else. I've never used anything that looked like the Eastwood box but on paper it's a properly mickey mouse POS that i wouldn't touch with a bargepole. AC frequency and pulse are luxuries rather than necessities really but that said an inverter that doesn't offer both these days is a bit backwards and of the two AC frequency is waaaaay more useful

 

[moleb]

Excellent, thanks for the advise everyone. Given the price differential, I took a punt as the Apex has a 'Make Offer' feature. They accepted at £500 which makes me wonder if they'd take less than that even...
Anyway, I'm happy with that as it leaves me some room for a decent pedal.

 

[Jim Davey]

Try and get hold of an SSC pedal, they work great.

 

[hotrodder]

+1 for SSC pedals, top quality and very reasonably priced compared to most, if not all, other pedals too

 

[Richard.]

Better quality than most top line OEM pedals let alone the cheap s##t throw ins.
The SSC pedals are simply excellent tools.

 

[moleb]

Yes, those look good. I like any manufacturer that freely gives pin-outs so I get an idea of what is going to work. I couldn't get on with the 'throw-in' that came with the Rotenbach and used the torch instead but I feel like I'm missing something there.
On the other hand, persevering with a truly crap SIP 130 Mig welder that wouldn't feed wire turned me into a decent welder in the end. When I finally tried a proper rig (Portamig) I couldn't believe it...Not that I'd recommend that as a means of training but there you go.

 

[spixycat]

Note on frequencies in AC and DC:

DC: switching frequency in DCEN means that the machine switches between two selected current setting at the desired frequency while the current direction remains the same

AC: switching frequency when reversing the welding polarity and therefore welding current. The tricky part is welding on high AC frequencies: the welding machine has a so called H bridge to switch currents and due to bad timing or non matching MOSFETS or IGBT a short can be unintentional created (may be by aging and temp) that can blow up suddenly your machine. I am not sure but it seems logical that when the current stops that the arc will also stop which means that the arc must be HF ignited to allow the reverse polarity current to start flowing. This sounds way more complicated than just changing the current between two presets as described above in DC mode. Last but not least you need to select the AC balance: the percentage of time that de machine is DCEN and DCEP: normally this is 50/50% but if you use only 10% in DCEP than the above proces in terms of timing gets even more complicated when welding on the max AC frequencies.

What a really really perfect foot pedal is is this one

Works perfectly and can handle the load of a truck. Quite (read really) expensive but you might find a bargain if you do a proper search

 

[Jim Davey]

Nice pedal, not nice price when you want parts.

 

[spixycat]

or the pedal itself : they are around €500 or so which is lot of money to manipulate a single Potentiometer and a single microswitch ....

 

[Jim Davey]

Cheaper here in the UK. £430 is list price. Can go to about £350+VAT with a bit of determined negotiating.

 

[spixycat]

It's steap price is it really worth if this is your bread and butter

 

[Jim Davey]

I'd say no having been on the SSC pedals for a few years now.

 

[Richard.]

Id agree. I've owned and still own top line OEM pedals. And while they are simply fantastic the SSC pedals are a cut above (slightly) it's the low and wide centre of gravity that really makes them. OEM pedals are too well fitting with your foot which is fine if your foot is perfectly on them (hardly the case ever) the SSC you can control it from any obscure angle and it just works. Not to mention it's as smooth and robust as any £400-500 pedal ive used.

 

[spixycat]

indeed: footpedals are ment to be used when you are working at a welding table which isn't always the case. In such situations I have used my elbow as an artificial foot