Pure Sine Wave UPSes for New Dell PCs
in [Dell]
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From: Daddy on 7 Apr 2010 22:00 I had to give myself a basic education on alternating current, output waveforms and active PFC power supplies just to be able to ask this question. It all started because I heard that new Dell PCs need a new kind of UPS (uninterruptible power supply.) It's a fact: To comply with regulations, Dell now includes something called an active-PFC power supply with their PCs. I also understand that users and power companies benefit from PFC, as does the environment. The problem is, active PFC power supplies supposedly need current with a pure sine wave output - and a Dell technical rep told me that all new Dell computers need this - but virtually all UPSes for home use have a stepped approximation of a sine wave. Has anybody priced a UPS with pure sine wave output? Those buggers are expensive! On the other hand, according to APC: Starting in mid-2008, all APC Back-UPS (home and small office) products were revised to better handle load requirements for PFC devices...allowing the majority of Back-UPS being manufactured now to handle most (not all) PFC loads within their wattage range much better than older units. Their output is still step-approximated, however, and APC still finds the occasional PFC device that they have trouble with. Here's where I throw up my hands. Do I really need to pay an arm-and-a-leg for a pure sine UPS, or is most any properly sized UPS 'good enough'? Daddy
From: William R. Walsh on 8 Apr 2010 01:59 Hi! > It all started because I heard that new Dell PCs need a new kind of UPS > (uninterruptible power supply.) > It's a fact: To comply with regulations, Dell now includes something > called an active-PFC power supply with their PCs. I also understand that > users and power companies benefit from PFC, as does the environment. Active PFC is not a new idea. Many power supplies have had it for a long time. The IBM PS/2 Model 95 had it in the early 90s. It makes no big difference to most computer users, as most are not billed by the power company based on how much they may be messing up the relationship of voltage and current in each AC power cycle. Some industrial customers are--and for them it is a good idea to try and clean up the mess they're making with power factor correction circuits, because doing so will save them money. I think the truth is that Dell is cheap-skating on their power supplies. The output of a UPS with a stepped approximation to a sinewave could conceivably trip up a power factor correction circuit, but I'm unclear as to why this might cause power cycling from the power supply. I think it more likely that the amount of input filtering on the supply has been reduced to reduce costs, exposing the power supply to more of the "nastiness" of the input waveform when it's a stepped approximation to a sinewave. To my way of thinking, that could trip things up. A half-decent switchmode power supply really should not care too much about this. Some electrical motors and simple transformers can "care" a great deal more about this--and they may burn up or operate incorrectly when run from a device that doesn't provide true sine wave output. This is why some UPS units are made with a true sine wave output. I would still recommend buying the best UPS you can afford. Get one that offers more capacity than you need at the very least--it'll run cooler, longer, give you room for future upgrades and in general be a better value for the money than a unit just big enough to scrape by. In particular, I do not recommend the APC "plugstrip" or similar units for computers. They are the cheapest of the cheap, and the quality is just good enough. (They do seem to work well with network switches, routers and such, however.) If you can afford one with true sine wave output, so much the better--but I don't think you *have* to for computer loads. William
From: Tom Lake on 8 Apr 2010 03:14 > Here's where I throw up my hands. Do I really need to pay an > arm-and-a-leg for a pure sine UPS, or is most any properly sized UPS > 'good enough'? Not good enough. For the XPS 435T/9000, at least, it absolutely won't work with a stepped approximation. You really do need a true sine wave. Tom Lake
From: Daddy on 8 Apr 2010 11:24 Tom Lake wrote: > >> Here's where I throw up my hands. Do I really need to pay an >> arm-and-a-leg for a pure sine UPS, or is most any properly sized UPS >> 'good enough'? > > Not good enough. For the XPS 435T/9000, at least, it absolutely won't > work with a stepped approximation. You really do need a true sine wave. > > Tom Lake > In fact, I just finished a 'chat' with a tech from APC. They recommend a pure sine wave UPS for the Studio XPS 9000, and I think my 8100 is similar enough for the same recommendation. Even APC's least expensive sine wave UPS (from their Smart UPS line) is more than a third of what I paid for my PC in the first place! And although I haven't looked at other makers, I can't imagine that their sine wave UPSes are so much less expensive. This sounds to me like a big consumer backlash that is waiting to explode. Dell does not warn potential customers: "Attention - If you buy this PC you will also need an expensive UPS to protect it." And it's not only Dell's problem...any new PC with an active PFC power supply is going to need an expensive UPS. I can buy a new PC for the price of a properly-sized UPS for my system. This whole thing is just too surreal. The UPS makers must be drooling. Daddy
From: Daddy on 8 Apr 2010 11:27
William R. Walsh wrote: > Hi! > >> It all started because I heard that new Dell PCs need a new kind of UPS >> (uninterruptible power supply.) > >> It's a fact: To comply with regulations, Dell now includes something >> called an active-PFC power supply with their PCs. I also understand that >> users and power companies benefit from PFC, as does the environment. > > Active PFC is not a new idea. Many power supplies have had it for a long > time. The IBM PS/2 Model 95 had it in the early 90s. > > It makes no big difference to most computer users, as most are not billed by > the power company based on how much they may be messing up the relationship > of voltage and current in each AC power cycle. Some industrial customers > are--and for them it is a good idea to try and clean up the mess they're > making with power factor correction circuits, because doing so will save > them money. > > I think the truth is that Dell is cheap-skating on their power supplies. The > output of a UPS with a stepped approximation to a sinewave could conceivably > trip up a power factor correction circuit, but I'm unclear as to why this > might cause power cycling from the power supply. I think it more likely that > the amount of input filtering on the supply has been reduced to reduce > costs, exposing the power supply to more of the "nastiness" of the input > waveform when it's a stepped approximation to a sinewave. To my way of > thinking, that could trip things up. A half-decent switchmode power supply > really should not care too much about this. > > Some electrical motors and simple transformers can "care" a great deal more > about this--and they may burn up or operate incorrectly when run from a > device that doesn't provide true sine wave output. This is why some UPS > units are made with a true sine wave output. > > I would still recommend buying the best UPS you can afford. Get one that > offers more capacity than you need at the very least--it'll run cooler, > longer, give you room for future upgrades and in general be a better value > for the money than a unit just big enough to scrape by. In particular, I do > not recommend the APC "plugstrip" or similar units for computers. They are > the cheapest of the cheap, and the quality is just good enough. (They do > seem to work well with network switches, routers and such, however.) If you > can afford one with true sine wave output, so much the better--but I don't > think you *have* to for computer loads. > > William > > Thank you once again, William, for your comprehensive and informative reply. Please see my reply to Tom Lake. Like you, I find it hard to swallow that new PCs *need* this expensive type of UPS. Daddy |