After printing a part last week I noticed a line about a millimeter or so high running through my part that had occurred about 2/3 rd’s of the way through the print run. I sometimes have to think about what causes printing issues but not this time, I immediately thought voltage drop (sag). Consumer DLP projectors have reasonably good voltage regulation but they were not built for 3d printing, outside of a particular input voltage range to the projector, I suspect, the bulb can dim or brighten enough to alter layer exposures. This is not a problem if you are watching a movie because you probably wouldn’t notice the projected images change in brightness but for 3d printing it can be an issue. My neighborhood is not exactly known for rock steady line voltage (I monitor line voltage with a Kill A Watt meter/monitor. If the line voltage is consistently out of range I let the power company know, they can’t fix a problem they don’t know about). The power has been pretty good lately but in the past I have seen it drop lower than 105 volts and if the furnace or air conditioner comes on while the line voltage is on the low side all bets are off if you are printing.
I didn’t have to think of a solution to a low voltage problem I already knew of one, something I had used in the past when I needed stable voltage it’s called a constant voltage transformer. What a constant voltage transformer does is for a pretty wide range of input voltage the output voltage will remain stable within a few percent of the transformers specified output voltage. You may think a battery backup (UPS) serves the same purpose but they do not and they cannot be used as a source of constant voltage, most ups’s will let the voltage drop to 100 volts or lower before kicking in, they will maintain a minimum voltage (until the battery runs out) but do not provide a constant voltage. See updates below
I decided to hop online (ok, ebay) and see what was available (just looking, not going to buy anything). After searching on “constant voltage transformer” for about 5 minutes I ran across a Sola (check), 500va constant voltage transformer (check), 60hz (check), 120vac +-3% output for input voltages 10% above to 20% below 120vac, continuous, +20% to -35% surge/sag (check), legit vendor 99% plus rating for tens of thousands of sales (check), new (check), $125.00 (reflexively click buy now). Constant voltage transformers are expensive, very expensive and I know a major score when I see it. The transformer will be in this week and I will probably set it up this weekend. I am going to use the transformer for the projector only, my projector uses about 300 watts running, 500 va will handle that just fine.
Some notes on constant voltage transformers. : They are power HOGS, a 500va cvt uses a considerable amount of power (70 – 90 watts) even if you don’t plug anything into it. They get HOT, one of the transformer spec’s is btu’s at the rated va’s (they don’t get hot enough to burn you but you wouldn’t want hug one after it’s been on for a while either). They take 60 hz hum to the next level (my phones sound level app showed 58db at roughly 1 meter but they do quiet down under load). For a dlp projector you need at least 500va, there are a lot of 250va units out there, they will not work, they do not have sufficient power output, more than 750va is probably too much, these transformers like to run at 60 to 100 percent of the va rating for the most efficient operation (my projector draws about 260 VA and about 250 watts , only a bit under the efficiency sweet spot). The transformer should match your countries line frequency, in the US it’s 60hz in other counrties the line frequency is 50hz. Sola, I’m sure there are other quality manufacturers of these transformers but I know Sola and I stick to what I know if I can. Many of this type of transformer are configured for hard wiring, that is, you have to wire a power cable and receptacles to them. Wiring a CVT is pretty simple but people who are not VERY comfortable wiring for line voltages are better off trying to find a cvt that has a plug and recepticals or an electrician.
This post is informational only and describes work I am doing on my own equipment.
I got the CVT set up and plugged my projector ( acer 6500) in to it and let it run for a couple of hours with a voltage monitor connected to the output of the transformer. The voltage stayed between 119. 6 and 120.1 volts consistently and only dropped to 119.3 volts for about a second when I plugged a shopvac into the same outlet and turned it on (looks like no more waiting for the 3d printer to finish before turning on the compressor, vacuum etc.). The projector was drawing about 260 VA and about 250 watts at the transformer output. Also, the transformer “core” temperature was reading about 130F after a few hours.
Since writing this post I have become aware that certain AVR “Automatic Voltage Regulating” UPS’s may work in this application also certain line conditioners (google “tripp lite avr” for a overview of what you can expect from these type of devices). If you consider an AVR UPS or line conditioner pay careful attention to the regulation values while on ac, the range over which the regulation operates and the type of output sine wave if these specs are available, the higher the va/watt rating the better, and read reviews on the product if available. In my opinion an AVR line conditioner would probably be the best option for providing stable voltage to a dlp projector (the projector only), the ability to keep your projector on during a power failure for another few minutes isn’t going to help you that much. However, if you find an avr ups at a good price with good specs clearly stated, good user reviews and made by a solid company, that automatically becomes the best option. Whatever the device the bottom line here is good regulation of the line voltage to your projector. For me, I will stick with the cvt because nothing I’ve seen has such bullet proof regulation specs.