View Full Version : UPS on laser system

Richard Rumancik
10-16-2006, 12:50 AM
There has been some discussion in other threads about using Uninterruptible Power Supplies on laser systems. As a few people seemed interested, I will describe my own experience with using a UPS. You can use this information as a starting point but please do your own investigations to ensure that the equipment you select is appropriate for your situation.

I was concerned that a surge suppressor alone would not be adequate to protect my laser (Mercury 30w). After some research I decided on a UPS. The UPS is not intended to run the laser during a power outage but to protect the laser from power line transients. Although I could run for many minutes on battery power, I would probably just pause the system and wait for power to return. On standby, the UPS can keep the laser system alive for a long time.

Ultimately I opted for a rack-mount style UPS. It is a BestPower Fortress 2250 running on 240VAC. Originally I had the laser running on 120VAC but since I was able to purchase the UPS at low cost, and since I have 240VAC available, I decided to run the laser on 240V. If I had a choice I would probably use a 120V unit.

The rack-mounted UPS units are often used in server environments (large banks of processors, storage units, etc.) These units are designed for computer-type loads, but my laser uses a switching power supply which is the same type of supply as used in PCs, monitors, and most modern "electronic boxes". So as far as the load on the UPS is concerned, it probably wouldn't see the laser as a much different load than a bank of PCs. Someone mentioned that you can't run motors on a UPS this is normally true of AC motors and power tools, but the motors in the laser are not directly connected to the UPS and so are not feeding back directly into the UPS itself.

The Fortress 2250 model is now obsolete but there are many similar ones out there. A suitable rack mount is usually about 19" wide and will likely be just short of 6" high (3U size) in this power rating. There may be some smaller ones that are 2U high. Because of the batteries it will be very heavy.

One problem you will have is figuring out the ACTUAL power draw of your equipment. The rating plates and specification sheets for the laser and power supplies are often misleading. For example, my Mercury says 100V-250V 8 AMPS on the rating plate. But it can't draw 8A at both 120 and at 240. If you look at the LaserPro spec sheet it may say something like 15A. This is for configuring the breaker and wall outlet, but the laser does not actually draw anywhere near 15A. The bottom line is that you have to figure out the actual load, and it might not be simple. You can try going back to the manufacturer but it may still be difficult to get the answer.

The Mercury 30w has a 500 watt power supply installed for the laser tube (there is another small supply for the mainboard and motors which is unmarked). The Synrad tube can draw 400 500 watts. The total AC load with efficiency factored in is likely less than 750 watts. A 1200 VA UPS would probably do with a little margin. (Note that a 1200 VA UPS would probably be marked something like 1200VA/850 watts). It is better to have 50%-100% margin if you can get it (and afford it.)

If you know a friendly electrician you might be able to get some help. One option is to do a physical measurement of power draw when the equipment is running.

As I had extra capacity on my UPS I also connected my PC and monitor. (Many monitors and PC's can be run at 240V as they are designed for International use. Some have switches and some switch automatically to the applied voltage. Use caution.) I have been running the UPS for a couple years and although I have not had a power failure in the middle of a job, the power has gone out, and I have had flickers and brown-outs, and the laser system has never been affected by a disturbance. My model also acts as a sophisticated regulator, constantly monitoring line voltage and adjusting the output up or down. There is also a monitoring program installed on my PC (the PC and UPS are connected by a USB cable.) It tells me exactly what line voltage is coming in and how the UPS is reacting to it. Also indicates expected operating time available if it were running on batteries.

I have been satisfied with the operation of my system. Your situation may be different so be sure to consult with the appropriate technical people including your laser manufacturer before you try to set up a UPS. To learn more about types of UPS systems try Wikapedia and Google. On eBay search for "UPS" and "rack". I bought a new UPS surplus for $150. There are often units that sell for less than $250. Try to find a new or almost-new unit, as batteries are expensive to replace.