Exceeding the number of Watts an APC UPS can provide

[Toni2009_apc]

This was originally posted on APC forums on 12/8/2009

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Has any of you ever exceeded the number of watts the equipment is supposed to provide? And if so, by how much and how did it perform?

My situation is as follow. I bought a house last year and during thunderstorms, I may lose power for less than 2 seconds. Unfortunately, it is messing up the furnace as the time without electricity is so short that the furnace doesn't have time to reset.

I took measurements of the power drawn by the furnace when working at full speed (the furnace is a Lennox G60V variable speed gas furnace). At full speed, I'm drawing a maximum of 1160 VA and 918 Watts. I was wondering if a ups that can deliver 1500 VA but only 865 Watts might do the trick for the no more than 2 seconds I need power from the APC UPS?

Thanks for your help and assistance.

Toni

[Erasmus_apc]

This was originally posted on APC forums on 12/9/2009

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There is generally a very small amount of leniency for slight overloads if it is not a sudden spike of draw (i.e if the load creeps 5-10w over the limit over a course of 5 seconds and goes down) on most UPS systems...but in any over-current situation you run a risk of triggering an overload fault and dropping the load. APC can never suggest an undersized UPS out of concern for providing reliable power to the end user.

[Toni2009_apc]

This was originally posted on APC forums on 12/11/2009

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For those interested, I used a small UPS I have, a ES 550 rated at 550VA and 330Watts to do some tests. Using lamps, I was able to determine that the UPS was capable of providing 377 Watts for at least 2 seconds prior to shutting down.

IOW, I was 47 watts, or 14% over the watt rating of the unit. What I don't know is if APC UPS units have a tolerance of about 50 watts or 14% over their limits? If anyone out there could test a UPC more powerful than mine, I would greatly appreciate.

Btw, in order to properly measure the watts (as well as VA) consumptions, I used a Kill-A-Watt. For those interested, when I switched between a 40 watts light bult to a 60 watts, the consumption only increased by 12 watts to 389 and was enough to prevent the 330 watts UPS to handle it.

Thanks for reading.

[Toni2009_apc]

This was originally posted on APC forums on 12/15/2009

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Listen up boys and girls, I have the answer. But first, let me give you some background info; I came here and asked a question because an APC UPS that can deliver at least 918 Watts and at least 1160 VA would set me back close to $600. While an APC UPS that can deliver 865 W and 1500 VA would only cost me ~ $200.

I was at Costco last Friday and they had received a shipment of APC UPS 780Watts and 1300 VA, the XS serie.

So I decided to take my chance and bought one. To my great surprise, the APC was capable of providing the 850 Watts I needed. Earlier, I used a Kill-A-Watt to measure the VA and Watts needed by the furnace and got a reading of 918W, but on the LCD of the APC unit, it said that it only needed ~ 850 Watts.

I was greatly surprise that a box rated for 780W was capable of providing 850W. Power lasted for about 2 minutes. The only problem was that the unit was bitching because it was in overload (even with power from electrical outlet). The overload icon was lit and there was the alarm sound.

Since I'm not sure if it could cause any harm being in overload and since I actually needed 850 W and not the 918 W I got from the Kill-A-Watt, I decided to return the APC and buy another APC UPS rated at 1500VA and 865 Watts.

[upsguy_apc]

This was originally posted on APC forums on 12/16/2009

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In my opinion your asking for trouble using a UPS rated at 865w for a planned 850 watt load. I think you would but your self at risk of occasional overload as well as shortening your battery life. Plus the UPS will probably not last as long as a larger unit would, exp..1000W or so at your 850w load level would be better. What are you using that is taking up 850W?

A suggestion would be to make sure things like printers, speakers, and maybe even your monitor are plugged into the surge outlets and not the UPS outlets to lower the load on the protected outlets.

[Toni2009_apc]

This was originally posted on APC forums on 12/16/2009

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Like I wrote in my first post of this thread, I only need to bridge a less than 5 seconds power loss. During summer months, when there is a thunderstorm, we might lose power, but it is usually for something like a fraction of a second to 2 seconds.

What will be connected to the UPS is a furnace. And btw, this is a special furnace. When the electric motor starts to run, there is NO surge in power consumption. The Lennox G60MPV has a $1500 eletric motor/control which makes the motor starts very gently. There is no such thing as a ON/OFF stage. The motor starts from 0 W to about 87 W, then ramp up to 200 W and then 450 W and then 850 W. The whole process takes about 3-4 minutes and apparently, is very energy efficient. Same thing when it turns off, it is very gradual.

To me, what is the most fascinating is the fact that a UPS rated at 780 W is capable of handling an 850 W load for very short period of time. I'm aware that completely discharging the battery is really bad. But for all the < 5 seconds power failure, I'll be fine with no harm to the APC and its battery.

[upsguy_apc · Accepted solution]

This was originally posted on APC forums on 12/17/2009

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UPSs are designed to handle slight overloads without shedding the load for short durations along an algorithm for overload%/time overloaded. Some of APC's large 3 phase UPS can handle overloads to the order of 125% 10 mins, 150% 1 mins and 1000% for 1 full cycle.