Duty cycle on tb302

admin

Just out of curiosity, normally when i weld i have my bosses tb set about 23.5-24 volts cv. Thats at idle. When i start welding the welder and my suitcase read about 17-19 volts. On the tb 302 that is well within the duty cycle which claims i can weld at 25 volts with 100% duty cycle. Occasionally when im welding thicker material i set the machine about 27-29 volts. Now is the duty cycle being exceeded even though the actual weld voltage may be about 23-24 volts?Sent from my DROID RAZR using Tapatalk 2
Reply:The power source setting is what the TB is putting out, the drop in voltage to the suitcase is line loss, how much of what gauge cable are you running?  What's the suitcase rated for?From Miller:  "Duty cycle is the amount of time a voltage-sensing wire feeder or welding power source can weld out of a 10-minute period before needing to cool. A 60 percent duty cycle means that the SuitCase X-TREME 12VS can weld at 425 amps for six minutes, and then needs to cool for four minutes. At outputs of 300 amps or less, it can weld continuously."SqWave 200Millermatic 190Airco 200 ACHypertherm PM45Boice-Crane Band SawVictor O/A
Reply:Amazing.
Reply:If you were drawing 10Amps, the equation for power is I^2R so 100*.1 = 10 Watts.  So that cable will get as warm as a 10 Watt light bulb.   And you would loose 1 Volt.First, there isn't a welder around that when you set it at X volts while you are not welding (0 Amps) will actually put out X volts at say 200 Amps welding.  They all have a curve.  Miller does publish this curve (at least for non-engine welders).As for power (and this means power loss as well): Power = Voltage * CurrentPower = Current * Resistance * Current or rather Current^2 * Resistance.The biggest factor in duty cycle is current (Amps).  Big Amps require bigger wires, transformers, diodes etc. etc.  The smaller the components the hotter they get (and the less room they have to dissipate the heat).For example. say you had a piece of cable that worked out to about .1 Ohm (point 1 Ohm).  You might thing that its a pretty good connection.Now, say it was 100Amps.   Now the math is 100*100 *.1 or 1000Watts.  So that cable is now as warm as a 1000 watt light bulb and you are loosing 10V on the cable.Now if that cable was the transformer inside your welder... or the diodes in your inverter, they would be getting plenty warm.High current generates heat.In your case, assuming all the voltage meters are correct - you are loosing 4 to 5 volts at probably 200+ amps.   That means your are loosing (and by loosing I mean 'heating up') 1000 Watts or so.I don't have any evidence for this, but I would double check all the connections - including the ground/work cables first.   Nice tight corrosion free fittings.  Next, get a volt meter and see if either gauge is lying.So voltage drop should not in itself indicate a problem, its the current flow + voltage drop that would ultimately dictate duty cycle.Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX