Hypertherm PM65 cut height/volt

[MorastCNC]

I have bought a Proma THC and after a little testing it works great
However it seems that the volt output from PM65 not follow the cutting table in the manual
Cutting 6mm mild steel with 45A says 137V in the table, proma shows 97 V at 1.5 mm.
I thought it was something wrong with the Proma which according to the manual would have
input from 50:1 divider
I checked with a multimeter and it shows 1.94V , 1.94 x 50 = 97

I know the height is 1.5 and the consumables is new
If follow the cutting table it should show 2.74V

Anywone know what causing this?

Bj?rn

[jimcolt]

The arc voltage specs in the Hypertherm manual are correct when you have a new set of consumables, and when you are following the specs in the manual exactly. amperage , thickness, cut height (within .005" of .060"), cut speed, cut air pressure all have to be exactly as the manual suggests. These specs are developed in laboratory conditions using laboratory grade machines and instrumentation.The voltage is read right at the raw arc voltage output of the plasma system, not through the divided voltage output. I will stand behind their accuracy.

There are a lot of things that affect the relationship between height and voltage:
-Air pressure at the torch
-air purity (water or oil) will change arc resistance value and voltage
-Cut speed, faster equals lower voltage
-material allow has a slight effect
-electrode and nozzle wear can change arc voltage as much as 25 volts near the end of their usable life
-any use of aftermarket (non genuine) consumables will alter voltage / height relationship.


If you are concerned with this you can put on meter on the raw arc voltage output (up to 300 volts DC) and another on the divided voltage output. Level a plate perfectly (within .001") and cut a part with the heigh control "off" and a fixed height at the torch. The meter on the divided voltage should track at the proper ratio of the raw arc voltage under these conditions.

If the ratio is off dramatically as you mention, then I would suggest replacing the voltage divider circuit. Keep in mind that arc voltage is just a reference voltage that is proportional to height. The settings in our operators manual are correct with new consumables (Hypertherm genuine consumables only...aftermarket consumables will always read differently)....but will vary with each of the above parameters.
On the latest technology height controls....you never set the arc voltage, the height control samples the arc voltage at the beginning of each cut (at an accurate, fixed height) then locks on that voltage until the next cut cycle. This auto calibrates the height control and compensates for consumable wear, air pressure/purity changes, etc. With these systems if the divided voltage ratio is off slightly...the height is still correct, and the operator never needs to make adjustments!

Best regards, jim Colt

[MorastCNC]

Thank's for your quick reply

I will thank you for sharing your knowledge and always
do your best to help all in their plasma cutting issues.

In the beginning of my plasma table build I did the mistake and bought a china
Plasma and of course nothing worked as I wanted

After a lot of reading in different forums I decided to buy a Hypertherm PM65 and
suddently all worked well, your help and the documentaion from Hypertherm is very helpful.

However the output volt is not a big issue, but it had be nice if I could look in the cutting table and
not have to cut a reference before each job

The consumables is new Hypertherm original and the cuts looks good, even small holes
The attached picture is 6mm sheetmetal

So I'm very happy with my Hypertherm

Best regards
Bj?rn Holmqvist

[jimcolt]

On my machine with a Powermax85....with new consumables, the arc voltage follows the cut charts within a volt or two. As I said...the cut charts are correct. If you want to use them....follow the procedure I outlined in the earlier post to determine why the voltage you are reading is way off from the specs in the chart. If the problem is in the voltage divider ratio, then replace the part (it is under warranty).

If the divided voltage ratio is off..it will be off by the same voltage on every cut. If your arc voltage reading is off by 20 volts....then all of your settings will be off the same amount so you can easily compensate without doing a smaple cut before each part.

Your cuts look pretty nice!

Jim Colt