How to determine which UPS Battery Backup to get?

[Larry Browning]

I want to add a UPS Battery Backup to my wifi and Satellite equipment and I really can't figure out how big of a unit to get. I have been doing some internet research and since I have a very limited knowledge of power terminology I am lost even when I see some sort of formula to calculate the load requirements. My instinct tells me that the load requirement is pretty low but I still want to figure out how much I will need.

I should have 4 devices to connect to the UPS battery. An Asus wireless router, an 8 port network switch, the cable modem, and the Direct TV satellite stuff (not the receiver at the tv, I think this is the stuff that connects to the dish itself). I have another UPS that is connected to my PC and Monitor, I just want to add UPS backup in my communications closet. My thinking that the power requirements for this stuff is pretty low. The pricing on these thinks start at about $40 for low load ones that look like a fancy surge protector and go way on up to over $1000 for the higher end units. I'd like to stay toward the lower end.

Thanks,

[Wade Lippman]

You find how many amps you need and multiply by the time you want it to last. It couldn't be much simpler, no formulas. If need be, put an ammeter over the lines involved and add up.

Unless you have a generator you will need a pretty big UPS to survive an outage.

[John Lanciani]

The real question is how long do you want them to run for? A few minutes to ride through a momentary outage is cheap and easy, a few hours not so much.

[Eric DeSilva]

Larry, I don't know about the DirecTV gear, but the rest probably totals under 50W--the Wifi router is probably 3-10W, the switch 5W, and the cable modem 30-40W (google for manuals for your gear and look up the draw, or just measure it like Wade said). That's a pretty small load for most UPSes. The UPS mfrs use "volt amps" (VA) to rate their devices, but it is a little silly because 1W = 1A x 1V, so 1W is 1VA. The key is that the "safe" draw from a UPS seems to be about 60% of the VA rating--so if the UPS was 100VA, it could safely supply 60W continuously. That's a pretty small UPS. They next key is how long it will last. Batteries are rated in Amp-Hours, so a 2AH battery will supply 0.5A for four hours, 1A for two hours, or 2A for one hour. Based on that, overbuying VA for your gear will probably get you (more or less) a linear increase in the time specified. So, for example, if you bought a 200VA UPS that give you 10 minutes of runtime, and you only hook up 50W of gear to it... The VA requirement for 50W is 83VA, so 200VA is about 250% of what you need, so you probably get 250% of the 10 minutes of run time, or about 25 minutes. This is all back of the envelope, but given how the SLA batteries in UPS degrade over time, it is all a bit of a crapshoot anyway. If you aren't connected to your WiFi, it is probably drawing less current, etc. So if you just want something that will hold you for the normal short summer brown-out so you don't have to run around and reset things, you are probably pretty safe with a lower end UPS--something in the 300-500 VA range seems like the low end of what mfrs produce. If you are looking for something that will last over a 24 hour outage, you are in different territory.

[Larry Browning]

I mostly want to have it keep power for those short hiccups that we get so often around here. They can sometimes last 5 minutes or so. It sounds to me like one of the low end units will work fine for me.
Thanks so much for the input. That is really what I thought, but I just wanted to hear from some more knowledgeable folks than me.

[Curt Harms]

I think you're right about the lower end units being adequate for 5-10 minutes. IMO it's hard to beat measuring the actual draw the equipment you want to power if you have an ammeter.

[Ole Anderson]

Always wondered if you can get just the electronics of a good UPS (not pieces, one made to do this) and add your own battery or batteries, big honking 12 volt or 6 volt golf cart batteries if you want long run time. Batteries go bad, just swap them out from your local auto parts dealer. Not so much to get more power, just longer run time.

[Rich Engelhardt]

Always wondered if you can get just the electronics of a good UPS (not pieces, one made to do this) and add your own battery or batteries, big honking 12 volt or 6 volt golf cart batteries if you want long run time.

Probably. but, why? The right battery for the job is a deep cycle & those cost as much (or more) than a sealed UPS battery.

If you need longer run times, you can buy a UPS that has the ability to add extra batteries.

As mentioned above though, the function of a UPS isn't to run the equipment for any length of time - a UPS is only used to run the equipment long enough for the standby generator to kick in - - or - - in the case of computers - long enough to gracefully down the system.

[Wes Thom]

Always wondered if you can get just the electronics of a good UPS (not pieces, one made to do this) and add your own battery or batteries, big honking 12 volt or 6 volt golf cart batteries ...

Never locate those batteries in an unventilated area (ie in a communication closet). Those batteries must be well ventilated to avert an explosion created by outgassing.

[Larry Frank]

Just a suggestion, I use a Kill-a-watt device to tell me how much it cost to run various 110 appliances. It would also tell you how watts your various electronic things would use. It will display volts, amps, watts, and VA.

[Wade Lippman]

Always wondered if you can get just the electronics of a good UPS (not pieces, one made to do this) and add your own battery or batteries, big honking 12 volt or 6 volt golf cart batteries if you want long run time. Batteries go bad, just swap them out from your local auto parts dealer. Not so much to get more power, just longer run time.

Sure, the USP only knows it has a 12v battery hooked up to it; it doesn't know the amp-hours of it. I once ran a battery powered backup sumppump off my car when its battery ran down. You wouldn't get more power, as that is a function of the USP, just longer power.

If you do it, let us know what happens to the functions that tell how much time is left on the system; presumable that is a function of voltage.

[Jim Becker]

Larry, given that the cost of these things has come down substantially over the past few years...make your life simple and just buy a "big" one.

[Matt Meiser]

Agreed. Assuming you don't have a standby generator, just buy the biggest one you can within the budget you want to allot. You aren't talking about much load and the bigger it is the longer your internet will work (assuming the provider stays up.) You don't need shutdown capabilities for that gear so inexpensive would be fine. If you've got a generator, you probably can't even buy too small a UPS for what you want to power.

I have everything in cabinet with a 700VA rack-mount UPS. Even my access points are powered from there now via PoE. Everything in the cabinet, including 2 small servers, two switches, modem, 2 routers, and a NAS is on it and it reports >15 minutes of available power, way more than I need for the generator to start and transfer.

[Larry Browning]

Larry, given that the cost of these things has come down substantially over the past few years...make your life simple and just buy a "big" one.

Honestly, I can think of many many ways to spend the kind of money it would take to get a big one and they all seem more fun than a great big battery. I will probably go for one in the 350-500VA range. (If I even do it at all) All of which are way less than $100.

[Matt Meiser]

Honestly, I can think of many many ways to spend the kind of money it would take to get a big one and they all seem more fun than a great big battery. I will probably go for one in the 350-500VA range. (If I even do it at all) All of which are way less than $100.

One way to get a bigger one for less (with a little risk) is to buy a used one that needs a battery. Many people throw them away but the batteries are in the $20-30 range if you don't buy them from the UPS manufacturer. Last one I replaced cost me $30 locally. I've bought them for $15 new on Ebay. I bought 5 UPSs on ebay once for something like $40 total, added $15 batteries and ended up with 4 nice 350VA UPSs (one was actually bad) for about $100.