Laser power consumption

[James Terry]

I am curious about the power consumption on my 25 watt Laser. I have one of those portable power meters and I also have a whole house digital power meter so I can see levels change when things power on and off and I have gotten to know the power consumption of various devices and my house very well. I religiously watch the power meter.

So I hooked up the portable to the laser today and ran it on 100% power and measured. I also looked at the whole house meter to verify the same numbers. The machine operating at 100% is measuring at 300 watts. This cant be true. The docs read that it needs a 20amp circuit just for the table itself.

Am I getting incorrect readings, ie: RMS reader is not taking into account the transient high power surging or something? The billing meter here is mechanical still and if my laser is actually drawing larger amounts of transient power, then it must end up being unbilled power.

Or does this thing just draw 300 watts?

[Ross Moshinsky]

I am curious about the power consumption on my 25 watt Laser. I have one of those portable power meters and I also have a whole house digital power meter so I can see levels change when things power on and off and I have gotten to know the power consumption of various devices and my house very well. I religiously watch the power meter.

So I hooked up the portable to the laser today and ran it on 100% power and measured. I also looked at the whole house meter to verify the same numbers. The machine operating at 100% is measuring at 300 watts. This cant be true. The docs read that it needs a 20amp circuit just for the table itself.

Am I getting incorrect readings, ie: RMS reader is not taking into account the transient high power surging or something? The billing meter here is mechanical still and if my laser is actually drawing larger amounts of transient power, then it must end up being unbilled power.

Or does this thing just draw 300 watts?

I wouldn't be surprised about that power consumption. It is essentially 5 light bulbs of power.

[James Terry]

Well the specs on the L25 say 1100 watts. If it is really only drawing 300 watts then I might as well have the blower and pump running on the same circuit. I was going to wire up something fancy but perhaps I dont need to.

[Richard Rumancik]

Its unlikely that a 25 watt would need 1100 watts input. You can look at the rating on the switching power supply and see what it is rated for. That would give you an upper limit for the draw of the laser tube. (Actual will be less, as there should be some margin in the design but also the power supplies are only avail in certain increments. And sometime they have margin to allow for an upgraded tube.)

There is probably a second power supply for the mainboard but this is likely only 50-100 watts or so.

The manufacturers often have a habit of putting a nameplate or spec sheet rating on equipment which is much higher than actual. I'm not sure the reason for this. The 25 watt machine will not need 10 amps at 120V. (Are you sure it said 20 amps?)

Another point is that specs are often sloppily written as they sometimes will say "100~240V, 10 amp". But this is improper as the current draw at 240VAC will be much less than the current draw at 100VAC.

4-5 amps is probably right; I think GCC told me to use 5 amps (120VAC) on my 30 watt machine when selecting a UPS but I don't have the memo in front of me. Just as a reference point, the Synrad 25 watt tube is rated 30V/14A = 420 watts input. So you would probably need a 500+ watt power supply to run that tube and maybe 500-600 watts for the entire laser.

I'm not sure how accurate that type of meter is for determining power draw of switching power supplies, expecially for older supplies that don't have power factor correction (where current and voltage are out of phase.) So you might not have a totally accurate measurement. But it is still in the ballpark. I expect that you are likely being billed correctly; you are not getting any free energy.

When you do the 100% power test, I would cut at slow speed and make sure you the tube is lasing "continuous". With the GCC lasers, I believe this requires setting the speed below 2.9%. Not sure how to do it with other machines. If you are pulsing, you are setting a duty cycle which reduces average power output of the laser tube.

[Tim Bateson]

At the risk of repeating myself; It would REALLY help if new users - all users added a sig line to identify their equipment.

For example if you have a 25watt Epilog machine, I could tell you they can use larger tubes up to something like 40watts. That would explain a higher wattage rating. Other brands may have similar options.

[Michael Hunter]

I think that the laser manufacturers over-rate the supply requirements because the load changes so much. Not only the laser turning on and off, but also the X motor which takes significant power to accelerate the optics.

Measured with a cheapo plug-in domestic power meter, my 60W Epilog draws about 400W when idle, going up to a maximum of 750 to 950W when operating. Occasionally the meter will show as much as 1200W momentarily.
The cheapo meter is clearly not up to the job, but since everything works it isn't worth hiring a mains analyser to find out what is really happening.

My laser is in a purpose-built workshop, with about 75 yards of wiring from the main fusebox. The cable is 6mm2 and the voltage 230, with a 40A main breaker and a 16A sub-breaker in the workshop.
When the laser is operating, the flourescent lights in the workshop flicker in synchrony with the laser.

[Lee DeRaud]

Well the specs on the L25 say 1100 watts.

Random data point: the specs on a 30W ULS VL call for "up to 5A" at 110, i.e. about half that much. Your measured 300W number certainly sounds reasonable for steady-state, maybe half-again that much worst-case.

[John Noell]

My 45 watt peaked at less than 4 amps on 230VAC (at 100% power etc. to maximize draw). What the label on the power supply and the manual say imply something higher. (What tech support said was ridiculously off-scale.) We used a high-end Fluke meter (RMS) so I am pretty confident about our measurements.

[Richard Rumancik]

. . . We used a high-end Fluke meter (RMS) so I am pretty confident about our measurements.

John, if you have a "true-RMS" Fluke multi-meter, you probably have made an accurate measurement, but a regular RMS meter can give a bad reading. It depends on how the RMS value is calculated internally. Some RMS meters will assume voltage and current are in phase and that they are sinusoidal (and the portable watt-meter probably does this as well).

For a switching power supply, you need to use a meter that is labeled "true-RMS" or sometimes called an Integrating RMS meter. The watt-meter probably works fine on resistance-type appliances but not so well on electronics.

Here are some words from the Astro-Med site that explains it more if anyone is interested:

"All electrical loads draw some type of current in response to applied voltage. The most simple being the load that acts like a resistor. This type of device simply draws current in a linear fashion. In this case conventional meters measure RMS values appropriately. However, any device that draws current in a non-linear or non-sinusoidal fashion, such as a switching power supply, can trick the conventional meter. A conventional volt meter simply calculates the RMS value as A x 0.7071, where A is the peak voltage. Most conventional volt meters assume the input is sinusoidal and may introduce an error if the waveform is distorted or non-linear."

[James Terry]

I connected all of my equipment to a single power source which includes the laser, exhaust, assist and a laptop. While operating the meter read 1100 watts and then 1400 while cutting. It's nice to not need the dual circuits like I was expecting. Perhaps the 25 watt wasnt a bad choice for starting out with.


I did my very first ornament tonight on my very own laser using the only stock I have available which is some leftover 1/4" plywood veener kind of thing from Depot. It is a terribly wrong substrate to use but all I have in hand. It was a bit messy when the laser burned through the layers of glue and alternating patten wood. Took me a little bit to get a feel for color mapping, power and speed settings and then cutting, but I got it all figured out with a few runs on just one piece of test material. A nice 3/16" alder wood will make this thing look nice.

I set four layers of data, the final being a cut. I cant wait to see what creative things I can come up with now that I can test things immediately in house for a change. Happy me!




For comparison, here's the 2009 ornament on alderwood from my local production guy.

[James Rambo]

James, You said you ran the laser at 100% and measures 300 watt. Was that rastering 300 watts or vectoring at 100%. my 60 watt measures at 1400 watt vectoring 100%. Jaime