Is a useful UPS possible?

I run an HP server with two parallel power supplies. One is plugged in via a UPS (HP) and the other is direct to the wall.

Since the most common UPS failure is from the loss of battery capacity due to aging, the only valid test is to pull the plug, as most self-tests don't load the UPS batteries long enough. The optimum solution here is to replace the batteries every 18-24 months. If the equipment truly is critical, the expense of replacing the batteries is not an issue. This does require that the UPS be designed for battery replacement without being removed from service - unfortunately, very few have that much forethought put into their design. I have some APC UPS units (two 250VA, one 1000VA) whose instructions say to disconnect power before doing any maintenance - but the batteries *can* be replaced without disconnecting the power cord or the protected equipment.

One possible alternative is to have the UPS batteries mounted outside the UPS case so they can easily be changed. This may also allow using higher capacity batteries for longer UPS run time. Obviously this is dependent on the UPS case design, the location in which it's used, and the type of use intended. I have a 350VA Energizer UPS that powers part of a home network (5 port switch and wireless access point). This equipment requires low power, but the UPS should power it for as long as the battery in a laptop computer (2.5 - 3 hours). The internal 12 V 4AH battery was replaced by a pair of 6V 8AH batteries mounted outside the case. This was feasible because this UPS is mounted on a high shelf in the basement.

The solution here is to have two power outlets that are fed from the same phase of the power line and dual power cords on the equipment to be protected. The second cord would be plugged in the second power outlet (or a second UPS, fed by that outlet) and the first power cord can be unplugged from the UPS that is to be checked/repaired. This wiring requires a qualified electrician or a very knowledgeable maintenance person.

I'm not a licensed electrician, but I have extensive knowledge of electrical wiring and electronic equipment. One city I lived in allowed you to do your own home wiring, subject to getting a permit and having the same inspection that any other electrical work would get. The inspector had one question about my work: "Are you an electrician?"

If you're close to Atlanta, GA, you can pick my brain for the price of a lunch ;-)

John

A comment; we have a couple of personal UPS at home here. In at least one of them the internal battery is connected, somehow to one side of either the live AC input or the live AC output. We out boarded some batteries and found out the hard way that the battery was AC live! At least one would have thought it would AC neutral!

Tom Horsley wrote: IN PART.

................................................................................. Reminds of an incident some 15 to 20 years ago. There was rare summer time power failure (a forest fire burnt down a HVoltage pole line). The very modern five storey main office building of the telecommunications utility where I worked had two massive diesel generators. One was down for maintenance and the other wouldn't start! We all went home early!

Real industrial UPSs have static switches that connect the power line to the output, and allow the entire rest of the system to be isolated and tested, repaired, or replaced. But this is solved by having two units that are synced, and you connect the spare before disconnecting the main. The main risk is that there will be a power failure while the unit is isolated and that there is a wiring error in the replacement unit that has reversed the output phase. This last one happened, recently at the plant where I work. Somewhere between when the first unit was made and the second one was made, the company reversed two of the three phases on the output terminals. Kaboom!

Such units are a lot more expensive than the household toys you get at Circuit City.

Ask NASA, they would have some notion how to design, build and budget hardware that IS 101% reliable at any possible time and circumstances. And how much it cost to put in a crew that keeps it in this condition for years.

Good luck!

Stanislaw.

In message , John writes

Depends on the number and length of outages, if critical equipment is on them, every 12 months and replace the whole unit after 36.

I would also add, replace the batteries after a major outage as most UPS manufacturers seem to punish the batteries with a very fast charge which leads to early death IME

A *lot* of the APC units I see have a grey high current connector for the batteries which makes it possible to replace them hot, it's supported but you need to let the new batteries charge and run a test on some if not all afterwards.

You can also buy UPS bypass devices which will allow you to switch out the UPS for service but of course this leaves you without protection whilst in bypass, not too expensive, I'll find and post details if I remember. Bigger UPSs often have this built in or wired to an external switch.

Umm, I service equipment at a company that has IBM servers with 3 parallel PSUs installed, each one is fed from a different phase and each phase has it's own UPS (20,000VA). I'm not saying do it, I'm not saying it's safe, I'm not saying it's right, just that I've seen it and no, I can't say who it is, but I'd expect them to know not too if it was unsafe.

Be careful sizing an UPS for redundant PSU machines as well, one company had two 10KVA UPS feeds to their server racks running a fairly large number of servers with two redundant PSUs each, all well within spec or so they thought. One UPS went bang and *ALL* the servers immediately went dead as the remaining UPS went into overload and shut down. The load was 50% over the rated output of the remaining UPS.

Stanislaw Flatto wrote in news: snipped-for-privacy@news.comindico.com.au:

You mean something like a touch sensitive Abacus so you can compute in the dark? ;-)

Puckdropper