How Long Connection Cable Can Be Extended

[ashish jain]

Dear Sir,
1 I Have A Mig Inverter Of 250 A.with Interconnecting Cable Length Of 5 Mt Bet Power Sourc And Wire Feeder..i Want To Extend It To 15 Mt.whethere It Is Possible Or Not?or Up To What Extent I Can Increase The Cable Length?what Are The Parameters To Be Kept In Mind Before Extending The Length.

 

[Hitch]

I cant see a problem with 15metres to be honest.
You will probably need to up the gas pressure a little.
What length torch have you got on it? You could extend the torch to give you a bit more range, (depending on quality of machine) and possibly the mains cable. If its an inverter, it shouldnt take much to move the base unit.


We run a few of ours with only a few metres of umbilical, a 5m torch and a 10m of mains cable.

 

[Archie]

Well since MIG is constant voltage there will be a drop in current between the feeder and power source which will increase with distance (since the longer the wire the greater the resistance). I would have thought you'd be OK with 15 meters but I'm only hazarding a guess. If in doubt, upping the cable thickness would reduce the resistance.

 

[Drains]

Ashish, I have a 20m cable, power source (300A) to feeder. It's fine, no problems at all.

As Hitch says, watch your gas pressure, but if you use a pea shooter flow valve, it won't be a problem.

Archie, there won't be a drop in current, there will be a drop in voltage, because that's what happens in wires over distance. The machine will raise the current to suit, adapting to the usual factors - wire speed, stickout, etc.

The important thing is to make sure the power and earth leads are chunky enough to take the current and not impose too high a voltage drop (and get hot!)

 

[Archie]

Ah! Looks like I got that one wrong then! But please do explain where I went wrong. I thought MIGs supplied a constant voltage and that the current fluctuated with respect to the load conditions. Surely then (or at least by my reasoning!) if V=IR and voltage is constant, if R increases (which we know it does because R = (Rho L)/A so as L gets bigger so does R), I must decrease? I suppose I must be wrong to have thought the voltage remained constant? Hehe. Good little physics lesson coming up, Mr Drains!

 

[shenion]

The voltage would decrease due to the drop in the wires, but you would just set a higher voltage in the machine. As long as the weld cable is large enough, it will be a very small drop.

Mine has 10M and I can extend it to 20M (plus a 5M torch.) I spent more in #1/0 cable than I did for the welder (also has some #2/0.)

Si, only if your machine has 2 additional wires that run to the ground clamp and torch can the machine sense the drop in the lines. Otherwise it will not automatically adjust for the drop.

 

[Drains]

There you go Archie, Shenion has explained. There's a v drop cos of wire resistance. Only a machine that could sense the voltage drop at the torch would adjust to suit. It's still a constant voltage machine, but AT the machine, not anywhere else (Migs are good, but not quite clever enough to notice 20M of cable hanging oot their erse).

 

[Archie]

Ah ha. Ok, I'm happy now. My physics wasn't so wide of the mark, I just didn't think about the practicalities! I remember now, the bumpf for my welder said the voltage at the torch could be up to two volts different from that displayed on the readout. Cheers, Si and Shenion.

 

[shenion]

I might also add higher-end MIGs are not constant voltage, but close to it. They have a designed-in drop with current (current slope or droop.) My Miller has 9-different drop settings. You could adjust it for a drop in the cable. There is also a drop with current across the reactor. This is one place where cheap MIGs have small transformer and reactor windings (hence poor duty cycle) and don't maintain a good constant voltage.

Spray-transfer usually wants a small drop with current, short-arc a larger one. Getting the slope right can make a difference in production/robotic welds and arc consistency.

Archie, 2V is a lot, I bet a considerable amount of the 2V is inaccuracies in the meter.

 

[Archie]

I can't remember exactly what it said but yeah, 2V does seem like a lot over a total of about 10m of wire. I suspect you're right.