UPS for Entertainment Center

[silver-eagle]

How best to estimate size of a UPS for the entertainment center? Not to keep them running while power is out but to save the programming loaded in it. Small draw to keep clock and program alive, off chance it might be recording when power is out. I'd think a small 350VA would be good.
And to make it a math problem... how would I figure it out?

 

[bbchien]

I've got an electronic control on the water softenerin the basement. Water was always hard and we were alway resetting and waiting for the hard water in the 80 gal heater to cycle through and get soft again.

We put a UPS on it and it hasn't blinked since.

 

[jesse]

I would just measure how much power they consume and then it's just simple math.

 

[Steve]

I use a couple units for computer from APC.

http://www.apc.com/solutions/index.cfm?segmentID=1

They have home theater applications, too.

 

[mantakos]

I'd probably use it as an excuse to pick up a gadget like this:

http://www.amazon.com/P3-Internatio...Monitor/dp/tech-data/B00009MDBU/ref=de_a_smtd
​

You can use it to measure the power consumption (both in watts and VA) of the system in "typical use". That allows you to size the UPS you'll need.
-harry

 

[gismo]

How best to estimate size of a UPS for the entertainment center? Not to keep them running while power is out but to save the programming loaded in it. Small draw to keep clock and program alive, off chance it might be recording when power is out. I'd think a small 350VA would be good.
And to make it a math problem... how would I figure it out?

First, are you certain that power is required to retain the "programming" and time? Many recent designs use non volatile memory for the program and can automatically set the clock from a local TV station. If your system has those features a UPS would be redundant.

Second, assuming you aren't needing the ability to actually record when the power is out and your equipment needs a UPS for that, I'd only power the programmable recording device (TiVo?) from it and insure the device was in it's lowest power state when I left it set up for unattended recording. Chances are the idle power is in the 35-50w range although you should probably confirm this with a measurement or check of the equipment specs in a manual. To measure the power consumption will require either an AC ammeter or one of those power measurement devices mentioned earlier. With an AC ammeter you would also need a way to insert the meter in series with the device(s) which could be as simple as a hacked extension cord or something more sophisticated like a plug to socket current loop combined with a clamp on meter. To get watts from a current measurement in amps multiply by 120 (then divide by 1000 if the current was milliamps)." Once you have determined the power consumption in watts you must multiply that by the number of hours you want the UPS to be able to operate the equipment. I'd then double that for a "safety margin" to allow for the eventual loss of capacity over time.

Now comes the tricky part. The power (watt or VA) ratings of a UPS have little to do with their energy capacity (watt hours), they simply indicate the maximum load the internal inverter can deliver. The energy capacity is a function of the battery's capacity and the efficiency of the inverter and both vary considerably with the load. For instance the capacity at full load is likely about half what it is at half load and even greater at a quarter of the max load but as you decrease the load further the capacity will actually begin to decrease at some point because the inverter is likely to be very inefficient with a light load. None of the consumer UPS's I've ever seen come with much information about this, some don't provide any. The most I've seen is the number of minutes the UPS can deliver full load and half load power. It's not difficult to actually measure the efficiency of the inverter in a UPS but you typically have to purchase the unit before you can make any such measurements. And buying the one with the biggest wattage rating would probably be counterproductive because such a unit is likely to have an inverter that's designed to be most efficient at high power and may be horribly inefficient at the low power you will be needing.

Another option would be to purchase a fairly low power (and low cost) UPS and connect an external battery to it that's much larger than the one inside. As long as the battery voltage and the chemistry are the same it's OK to just parallel them. Use a separate fuse at the external battery end of the connection and tie it into the UPS on the LOAD side of the UPS's internal overcurrent protection to prevent a fire hazard.