Voltage vs. Current
08-02-2007, 08:27 AM,
 powerman Active Member Posts: 40 Threads: 12 Joined: Jul 2007 Reputation: 2
Voltage vs. Current
My electrical knowledge is poor. What is the difference/functions of current and voltage in plasma spray system and arc spray system?

Why when spraying, voltage stable but current unstable?

Voltage difference is use to create arc. Then current ? In arc spray system, increase current, then wire speed increase, why? Current is to supply thermal energy to heat the coating materials?

08-03-2007, 12:56 AM,
RE: Voltage vs. Current
Hi Powerman

We could consider the analogy with water flowing through a pipe: current is similar to water flow, voltage is similar to pressure. This link may help further http://www.4qdtec.com/water.html

It is normal with plasma spray to set your current at a constant value, say 500A. The voltage you get then depends on the electrical resistance across the gap between electrode and nozzle (effected by plasma gas, flow, turbulence and nozzle/electrode geometries). The higher the electrical resistance across the plasma, the higher the voltage needs to be to maintain the current flow. Argon plasma alone tends to give relatively low resistance, while nitrogen only or adding secondary hydrogen increases resistance. So argon only plasma will run stable at quite a low voltage, while nitrogen and hydrogen will run at a much higher voltage (see here for more info on plasma theory https://www.gordonengland.co.uk/pft.htm . Voltage, V x current, A = Power, W. This is basically how we control power output (adjusting current and or plasma gas mix/flow settings).

Arc spray is similar, but we set the voltage constant (rather than current), generally at a value that gives us a stable arc. The current is dependent purely on the wire speed/spray rate that we select. Again voltage x current = power. Increase spray rate gives increased current (voltage constant) gives increased power.

Hope that helps
08-03-2007, 04:24 AM,
 chy0495 Member Posts: 7 Threads: 2 Joined: Jul 2007 Reputation: 0
RE: Voltage vs. Current
I have a question about that in our plasma parameter we can see voltage ,current and power .

We fixed the current and let the vlotage free ,but most of time the voltage can not reach the value in the parameter paper,is it possible need to use H2 increase to reach the voltage value?

We use Sulzer MultiCoat? system.In this system we can see two types of power value ,one is called power and another is called net power.

Do any one know that is the differents about them?
08-03-2007, 03:36 PM,
RE: Voltage vs. Current
Hi chy0495

Quote:I have a question about that in our plasma parameter we can see voltage ,current and power .

We fixed the current and let the vlotage free ,but most of time the voltage can not reach the value in the parameter paper,is it possible need to use H2 increase to reach the voltage value?

To some extent and within a limited range, yes. You do need to be careful though, the important parameters for controlling effective plasma power is current and plasma gas composition/flow. Voltage indications are really just to confirm the system is working as it should. If the voltage reading is falling outside the recommended range for your specific parameters, then it indicates something is not right. This could be worn hardware (nozzle/electrode) or the equipment needs calibration (voltmeters, ammeters, gas flow meters etc.). See my post in another thread http://www.gordonengland.co.uk/sef/colou...tml#pid817. We also need to be careful and know where the voltage is actually measured. If the voltage is measured at the plasma controller console (as in Metco 3/7M systems) rather than at the gun, the condition and length of the water cooled power cables/hoses will cause a voltage drop. So the voltage reading is higher than what the gun actually sees. A typical 15 foot cables give about 3-4 V drop, longer cables will give more. This one of the reasons setting flows is better than setting by voltage. Important to bear in mind when using parameters developed on say a 7M system on a more recent system that measures voltage at the gun.

Quote:We use Sulzer MultiCoat? system.In this system we can see two types of power value ,one is called power and another is called net power.

Do any one know that is the differents about them?

I'm not too familiar with the MultiCoat system, but to be honest power values are a bit academic really, as the business end of actually spraying the materials, only use a fraction of this power. Net power I would assume is at the gun (gun voltage x current) while the other power reading is from a point nearer the point of input and will be higher as it does not account for power loss in the system prior to the gun.
08-03-2007, 07:53 PM,
 Diucky Member Posts: 9 Threads: 1 Joined: Aug 2007 Reputation: 0
RE: Voltage vs. Current
Hi chy0495

Quote:We use Sulzer MultiCoat? system.In this system we can see two types of power value ,one is called power and another is called net power.

Do any one know that is the differents about them?

Power value is given by tension mesured at the power supply (PTpower supply or Tristar?)

Net power is given by tension mesured in Jambox? (closer to the gun).
It's the one witch is monitored in repporting system ( if my memory is good ).

My advice if you cannot reach the setvalue give in your recepy : check gun cable and the gun itself

For example simply clean the gun ; as an F4 gun (water/ scotch-brite) will improve conductivity in the gun and you will have maybe 2 or 3 volts more...

Hope it helps you...
09-19-2007, 12:39 AM, (This post was last modified: 09-19-2007, 10:24 AM by powerman.)
 powerman Active Member Posts: 40 Threads: 12 Joined: Jul 2007 Reputation: 2
RE: Voltage vs. Current
Hi Gordon,

Why cant use hydrogen as primary gas?

According to the catalogue, the Metco F4 gun's performance is 55KW, while 9MB gun's is 80KW, and the latest one is TriplexPro-200. Which one is better for use in spraying TBC? Is power one of the main characteristics to compare two guns? I heard F4 gun is good for TBC while 9MB is good for general powders. However, the deposit efficiency of 101NS for 9MB is 80% while F4 is 60% (from parameter book), DE of 205 for 9MB is 50% while F4 is 54%, DE of 350NS for 9MB is 60% while F4 is 56%. Which one is better?
09-19-2007, 01:40 PM,
RE: Voltage vs. Current
Hi Powerman
Quote:Why cant use hydrogen as primary gas?
Basically, it is really only a limitation of the equipment.

Of all the commonly used plasma gases; argon, helium, nitrogen and hydrogen, hydrogen is by far the most aggressive towards hardware. Most equipment just can't tolerate high hydrogen levels or achieve the power/cooling requirements necessary to get a stable hydrogen rich plasma. I have used helium only as a plasma gas, which proved to be good, but very expensive

Quote:According to the catalogue, the Metco F4 gun's performance is 55KW, while 9MB gun's is 80KW, and the latest one is TriplexPro-200. Which one is better for use in spraying TBC? Is power one of the main characteristics to compare two guns? I heard F4 gun is good for TBC while 9MB is good for general powders. However, the deposit efficiency of 101NS for 9MB is 80% while F4 is 60% (from parameter book), DE of 205 for 9MB is 50% while F4 is 54%, DE of 350NS for 9MB is 60% while F4 is 56%. Which one is better?

Its all swings and roundabouts Rating equipment performance on power output alone is not really useful, most coatings are applied quite happily at less than 40KW anyway. I won't get into what equipment is best, only to say it is important to optimise what you have. Your example of 101NS, originally sold by Metco for use in it's plasma equipment. At the time Plasma Technik F4 was a competitor and 101NS was not specifically design for that equipment. An alternative alumina powder maybe graded slightly differently to better suit the F4 may reverse those comparative deposit efficiencies.
09-20-2007, 12:01 AM,
 powerman Active Member Posts: 40 Threads: 12 Joined: Jul 2007 Reputation: 2
RE: Voltage vs. Current
Hi Gordon,