Fundamental Question about Input Power
04-11-2019, 02:32 AM,
 ThermalSprayingPhysicist Member Posts: 9 Threads: 3 Joined: Jun 2015 Reputation: 0
Fundamental Question about Input Power
Hi all,

I am an academic researcher who is trying to use thermal spray to develop new low density coatings for optics.

One way that I have been pushing the density down is by varying the following parameters: spray distance, powder feed rate, and secondary gas (He) pressure.

I have been reading literature that shows input power of the plasma. The literature says that they hold plasma current and voltage constant while they vary input power. The plasma spray technician has noted to me that input power is simply plasma current x voltage.

Who is right here? I am very confused. Thanks in advance for any help!

P.S. I've attached a screen shot of the paper.

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04-11-2019, 01:03 PM,
 Lemster68 Senior Member Posts: 56 Threads: 2 Joined: Jul 2018 Reputation: 1
RE: Fundamental Question about Input Power
Volts x amps = wattage: power. 600A x 50v =30000w -- 30kw.
04-11-2019, 01:06 PM,
 Gordon Administrator Posts: 1,794 Threads: 70 Joined: Jun 2006 Reputation: 9
RE: Fundamental Question about Input Power
Hi ThermalSprayingPhysicist

I would say your plasma spray technician is correct. Holding current, voltage and plasma gas flows constant will make power constant, unless they are measuring power in a different way

By having He secondary plasma gas as a variable, changing this value will change the power (the voltage will change assuming constant current). Changing spray distance and powder feed rate only should have no effect on power.

Hope that helps.

04-11-2019, 07:30 PM,
 ThermalSprayingPhysicist Member Posts: 9 Threads: 3 Joined: Jun 2015 Reputation: 0
RE: Fundamental Question about Input Power
(04-11-2019, 01:06 PM)Gordon Wrote: Hi ThermalSprayingPhysicist

I would say your plasma spray technician is correct. Holding current, voltage and plasma gas flows constant will make power constant, unless they are measuring power in a different way

By having He secondary plasma gas as a variable, changing this value will change the power (the voltage will change assuming constant current). Changing spray distance and powder feed rate only should have no effect on power.

Hope that helps.

Thanks for your reply!
So just to get the details correct, voltage (measured number like 50V) is determined by He secondary gas pressure? While current is not. So what are the independent variables: He gas pressure and current?

If this is true, I should be lowering both gas pressure + current.

Thanks in advance!
04-11-2019, 08:23 PM,
 Lemster68 Senior Member Posts: 56 Threads: 2 Joined: Jul 2018 Reputation: 1
RE: Fundamental Question about Input Power
(04-11-2019, 07:30 PM)ThermalSprayingPhysicist Wrote:
(04-11-2019, 01:06 PM)Gordon Wrote: Hi ThermalSprayingPhysicist

I would say your plasma spray technician is correct. Holding current, voltage and plasma gas flows constant will make power constant, unless they are measuring power in a different way

By having He secondary plasma gas as a variable, changing this value will change the power (the voltage will change assuming constant current). Changing spray distance and powder feed rate only should have no effect on power.

Hope that helps.

Thanks for your reply!
So just to get the details correct, voltage (measured number like 50V) is determined by He secondary gas pressure? While current is not. So what are the independent variables: He gas pressure and current?

If this is true, I should be lowering both gas pressure + current.

Thanks in advance!

The voltage is influenced by the secondary gas, AND is usually adjusted by increasing the FLOW with a pressure that remains constant. After arc ignition, you bring your current up to the desired level and then introduce your secondary gas, thus raising the volts. As a result, your current may drop, but you adjust it back to the desired level. Depending on the level of automation of your spray controls, that last part may be transparent to you.

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