Pure Sine Wave UPSes for New Dell PCs
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From: William R. Walsh on 8 Apr 2010 12:31 Hi! > And it's not only Dell's problem...any new PC with an active > PFC power supply is going to need an expensive UPS. No. A *properly designed* power supply will work with a UPS that has a stepped approximation to a sinewave output. I've done this often enough with various power supplies that have active PFC circuits to say with reasonable assurance that it will work. I maintain that Dell is cheapskating on the quality of their power supplies, and they may have a nasty backlash from doing so. (But then again, I'm a pretty big believer in "do it right the first time" for stuff like this.) There's also the PS/2s...I have a herd of those and some are hooked up to UPS units with stepped approximation to a sinewave output. Sometimes the power supply harmonizes a little bit when on battery power, but they work. The late model 400 (actually 399.1!) watt power supply has an active PFC circuit and it seems to get along fine on power from the average UPS. (Some people do report power ups and power downs, but I have never been able to duplicate this.) > I can buy a new PC for the price of a properly-sized UPS for > my system. It's not cheap or particularly easy to design a UPS with true sine wave output. What an AC generator does just by virtue of its mechanical design a UPS must do electronically. The complexity of the circuit is much greater--if you ever get a chance, compare the two designs sometime. I couldn't think of the term last night, but a lot of really old UPS designs put out a simple squarewave and don't even bother trying to make it look like a sinewave in any way. There were some exceptions--I had a very nice (and old!) APC 1200VA UPS with true sine wave output. A lot of BIG UPS units have true sine wave outputs. Here comes your money saving tip--even today you can find these and they are typically priced on a "if you can carry it you can have it basis". That is because the batteries in them will be totally dead. Good quality car batteries or deep cycle marine batteries can usually serve as replacements, although you may have to buy a battery box and wire up external cables. That was exactly what I did with that APC unit. It took 48 volts worth of input power to its inverter, so I wired up four big car batteries in series. The thing would run a moderately sized 120 volt room air conditioner or washing machine, although it had a hard time starting either one. The same thing works with many smaller UPS units as well, although sometimes the charging circuit flips out and won't do its job. The older APC UPS units sold from the mid to early 90s handle a battery retrofit perfectly. I'm using several that have been converted to operate from a lawn tractor battery. One of them is at the heart of a backup lighting system--it is connected to several CFLs. These sit idle until the power goes out--at which point the UPS goes to battery, a contactor with a normally closed contact goes closed and the backup lights come on. With a few 60W equivalent CFLs, the whole shebang runs for at least two hours with ease. Of course, if you do this you have to be wary of the fact that you're dealing with high current circuitry that really won't understand how you were just curious and wouldn't touch THAT again! Even one car battery contains enough stored energy to weld, cauterize, start big fires, etc. You must be sure that any wiring you do is safe and will stand the load placed on it. Oh, and charge sealed lead acid batteries in a decently ventilated area only. Otherwise explosive hydrogen gas would build up. William
From: Daddy on 8 Apr 2010 12:44 William R. Walsh wrote: > Hi! > >> And it's not only Dell's problem...any new PC with an active >> PFC power supply is going to need an expensive UPS. > > No. A *properly designed* power supply will work with a UPS that has a > stepped approximation to a sinewave output. I've done this often > enough with various power supplies that have active PFC circuits to > say with reasonable assurance that it will work. > > I maintain that Dell is cheapskating on the quality of their power > supplies, and they may have a nasty backlash from doing so. (But then > again, I'm a pretty big believer in "do it right the first time" for > stuff like this.) > > There's also the PS/2s...I have a herd of those and some are hooked up > to UPS units with stepped approximation to a sinewave output. > Sometimes the power supply harmonizes a little bit when on battery > power, but they work. The late model 400 (actually 399.1!) watt power > supply has an active PFC circuit and it seems to get along fine on > power from the average UPS. (Some people do report power ups and power > downs, but I have never been able to duplicate this.) > >> I can buy a new PC for the price of a properly-sized UPS for >> my system. > > It's not cheap or particularly easy to design a UPS with true sine > wave output. What an AC generator does just by virtue of its > mechanical design a UPS must do electronically. The complexity of the > circuit is much greater--if you ever get a chance, compare the two > designs sometime. > > I couldn't think of the term last night, but a lot of really old UPS > designs put out a simple squarewave and don't even bother trying to > make it look like a sinewave in any way. > > There were some exceptions--I had a very nice (and old!) APC 1200VA > UPS with true sine wave output. A lot of BIG UPS units have true sine > wave outputs. Here comes your money saving tip--even today you can > find these and they are typically priced on a "if you can carry it you > can have it basis". That is because the batteries in them will be > totally dead. Good quality car batteries or deep cycle marine > batteries can usually serve as replacements, although you may have to > buy a battery box and wire up external cables. > > That was exactly what I did with that APC unit. It took 48 volts worth > of input power to its inverter, so I wired up four big car batteries > in series. The thing would run a moderately sized 120 volt room air > conditioner or washing machine, although it had a hard time starting > either one. > > The same thing works with many smaller UPS units as well, although > sometimes the charging circuit flips out and won't do its job. The > older APC UPS units sold from the mid to early 90s handle a battery > retrofit perfectly. I'm using several that have been converted to > operate from a lawn tractor battery. One of them is at the heart of a > backup lighting system--it is connected to several CFLs. These sit > idle until the power goes out--at which point the UPS goes to battery, > a contactor with a normally closed contact goes closed and the backup > lights come on. With a few 60W equivalent CFLs, the whole shebang runs > for at least two hours with ease. > > Of course, if you do this you have to be wary of the fact that you're > dealing with high current circuitry that really won't understand how > you were just curious and wouldn't touch THAT again! Even one car > battery contains enough stored energy to weld, cauterize, start big > fires, etc. You must be sure that any wiring you do is safe and will > stand the load placed on it. > > Oh, and charge sealed lead acid batteries in a decently ventilated > area only. Otherwise explosive hydrogen gas would build up. > > William Very interesting, William, as usual. But a lawn tractor battery is not an option for me. Nor can I imagine how I would explain it to my wife. Daddy
From: Daddy on 8 Apr 2010 16:43 Daddy wrote: > 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 I have made my decision, based on further research. The issue concerning a UPS and a power factor corrected power supply arises when the power supply recovers from a temporary power shortage. A PFC power supply can have a high "inrush current" -- the amount of current it draws when first switched on. A highly efficient power supply (with apparent power approx. equal to actual power) can draw as much as 100% of its full power for an extended period of time (approx. 50 ms.) A UPS that delivers its output power in a sine waveform is more likely to provide power for long enough vs. a UPS with a stepped approximation of a sine wave. Another factor in UPS selection is the transfer time. A PFC power supply can request power from the UPS in as little as 4 milliseconds. If the UPS has a transfer time longer than 4 ms, it may not be able to provide the power supply with power in time. (This entire discussions does not apply to an "online" UPS.) It's probably impossible to come up with accurate measurements for the actual inrush current and minimum transfer time of a given power supply. So, practically speaking, the only way to know for sure whether your computer is adequately protected is to 'pull the plug' from the wall socket. That's what I plan to do tonight. Daddy
From: Tom Lake on 8 Apr 2010 22:36 > I maintain that Dell is cheapskating on the quality of their power > supplies, and they may have a nasty backlash from doing so. (But then > again, I'm a pretty big believer in "do it right the first time" for > stuff like this.) Not necessarily. The PS in the 9000 is rated for 475 Watts and puts out a true 475 Watts. I've seen some name brand supplies put out less than their rating. Tom L
From: Daddy on 9 Apr 2010 00:31
Tom Lake wrote: >> I maintain that Dell is cheapskating on the quality of their power >> supplies, and they may have a nasty backlash from doing so. (But then >> again, I'm a pretty big believer in "do it right the first time" for >> stuff like this.) > > Not necessarily. The PS in the 9000 is rated for 475 Watts and puts out > a true 475 Watts. I've seen some name brand supplies put out less than > their rating. > > Tom L Well, I conducted my little experiment...pressed the power button on my UPS to turn it off, and...my computer and monitor immediately shut off. That's not necessarily because my UPS doesn't produce a sine waveform. For one thing, at 550 VA, my UPS is way under-powered. For another, this sissy little UPS probably doesn't have a fast enough transfer time. By the way, don't waste your time asking Dell technical support about power supplies or UPSes. They don't have a clue. Daddy |