When you're feeling bored...

[Torchhead]

Originally Posted by thkoutsidthebox You can us a Phase converter to get 3 Phase power on your single phase mains. This is what I'm intending to do if/when I ever get around to buying and building a plasma cnc. Here's one link from google, but a search for 'Phase Converter' throws up lots of links. They can be quite expensive though. http://www.phase-a-matic.com/?gclid=...FRHgXgodgg4kdw Torchead, the mechanism you referred to about the air pushing the tip away from the sheet, whats this called and is it standard on most new machines now (Thermal Dynamics or Hypertherm) ? i.e:Should I ask for it when buying?

It's pretty much how all the plasma torches work that are not specifically HF istart. I have heard of some really cheap imports that require you to tap the tip and do your own arc start (like a stick welder). Those would definitely NOT work for CNC cutting!

There is a lot of confusion about HF start and it not working with PC's or CNC electronics. Anything below 100A in HF can be made to work if proper grounding for noise is applied. When you get over 100A the problem intensifys to the point you have to mount logic level componets inside sheilded enclosures and be very careful with cables and ground loops.

I started cutting using an old Miller 500 50A unit that was HF. I ran my table with the PC 4 ft from the table and the Miller on the opposite side. I did have a good ground (metal pole in earth a few feet from the plasma) and made sure that the palsma machine chassis, the table and the moving componets on the table all were grounded to a central plate on the side of the table. The PCside was isolated and not grounded to the same plate and gets it's ground back through the AC ground. I made sure the only place the PC side and table side meet up is at the breaker box.

Tom Caudle
www.CandCNC.com

[Robin Hewitt]

I just had a word with our friendly neigbourhood electrician.

Apparently we do have a 3 phase 400V supply to the house, but I can't use it because of building regs.

The Cutmaster 81 will run on 230V 50/60Hz, but 52A probably means a new connection and digging up the road.

The Cutmaster 51 will accept 230V but not 50Hz

Y'all reckon the Cutmaster 38 hasn't got enough welly

That R-TECH 40A is starting to look really good, even if it does have the less desireable arc initiation circuit

[Torchhead]

I'm not sure outside of I^r losses in the Plasma unit where the efficiency of using the three phase will workout. You have an inherent loss of power in the conversion process. So you take single phase, convert it to three phase then rectify it (inside the plasma) change it to pulsed DC and use it at up to 80 Amps. The three phase rectification process is more efficient that single phase but you won't gain back what you lose in the first conversion process.

Power is sold in kilowatts (yes I know power companies sell three phase at a different rate) but we are starting out in single phase watts here. In the end you have to ask: Are you drawing less watts than you would being directly connected and if so how? Since there is no such thing as a 100% efficient conversion process you have to account for the inherent loses there. How much electricity will you have to save to pay for an 800.00 (or more) rotary phase converter?

At the very most you might break even and have a lot of equipment involved. In my engineer's sense of thinking the only reason to use phase converters is to:

A: run equipment that won't/can't run on single phase
or
B: Run a motor that you need frequency speed control on.

The latter can be done with a VFD from single phase.

Tom Caudle
www.CandCNC.com

[thkoutsidthebox]

Originally Posted by Robin Hewitt I just had a word with our friendly neigbourhood electrician.

I'd check that again if I were you, just to be sure to be sure. I know that the UK is different to Ireland, even though we both use a 3 wire mains system countrywide unlike the USA. But last year I checked about the possibility of getting 3 phase power hooked up in the garage behind the house. There was no problem, simply an €800 connection charge, and I'm in a housing estate. I suppose it depends where your located though. Also, I didn't ask what the usage charges are after connection.....

Torchead, the major reason as I see it for the rotary converter and 3 ph power is not to have a cost saving in the long run, its to have more powerful machinery. 6HP 440V motor instead of 3.5HP 220V ..... 350Amp Mig 80% Duty Cycle, instead of 200Amp Mig 60% Duty Cycle etc .... I didn't think about the cost savings directly from more efficient use of electrical power, as you said, I don't think you'd save much ..... although over twenty years you might .... .... speaking of which, what's the typical life of a TD or Hypertherm plasma cutter run on cnc with a machine torch? Would it be 10,000hrs, or is that way too high?

[Robin Hewitt]

Originally Posted by thkoutsidthebox I'd check that again if I were you, just to be sure to be sure.

He said we weren't allowed to fit both 3 phase and single phase in a dwelling because someone might plug in to the wrong one. We only got the 3 phase connection because a previous owner had plans to put a heated swimming pool at the bottom of the garden and the utility company were leery of having that many amps on a single phase in case it threw their transformer out of kilter