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#73770 by kevinl4000
Thu Jan 27, 2011 11:23 am
Now that I've ditched the phone company, I need an uninterruptible Power Supply with DC outputs for 1)Ooma and 2)Motorola Cable Modem/Router. Where can I find, and what is the power supply voltage for Ooma Telo?
#73774 by hpepper
Thu Jan 27, 2011 12:22 pm
kevinl4000 wrote:Now that I've ditched the phone company, I need an uninterruptible Power Supply with DC outputs for 1)Ooma and 2)Motorola Cable Modem/Router. Where can I find, and what is the power supply voltage for Ooma Telo?


I believe you were asking what amperage (not voltage) does the Telo draw... It's minimal. (The volatege is a standard 120 v

Also, not sure why you are looking for a UPS with DC outputs. The UPS that lbmofo is suggesting will work great.
#73775 by kevinl4000
Thu Jan 27, 2011 12:35 pm
A regular UPS with AC output first has to convert AC -->DC to charge the battery, then when the power goes out the UPS has to convert the DC battery power back to AC, then the Ooma transformer changes the AC back to DC to work with Ooma (or does it?). Seems silly. I'd rather have a UPS with DC outputs (at the correct voltage and plug type) kick in instantly when the power goes out. Same with the cable modem.

$75 UPS with AC output I can find at the store. UPS with 2 x DC outputs is proving to be trickier. I would think Ooma would have already thought about this.
#73784 by hpepper
Thu Jan 27, 2011 1:40 pm
kevinl4000 wrote:A regular UPS with AC output first has to convert AC -->DC to charge the battery, then when the power goes out the UPS has to convert the DC battery power back to AC, then the Ooma transformer changes the AC back to DC to work with Ooma (or does it?). Seems silly. I'd rather have a UPS with DC outputs (at the correct voltage and plug type) kick in instantly when the power goes out. Same with the cable modem.

$75 UPS with AC output I can find at the store. UPS with 2 x DC outputs is proving to be trickier. I would think Ooma would have already thought about this.


While what you said is true, I think you are adding a level of complexity (even though technically what you are saying seems simpler) At the very least, you would definitely add cost. We have a UPS at work with DC output for a Cisco router and it was quite expensive.

I have my cable modem, wireless router and Ooma Telo on a standard APC UPS and it never loses a beat when the electricity goes out. The UPS doesn't "kick in" it is always supplying voltage to the outlets - there is no interruption of power at all during a loss of home AC power.
#73907 by nn5i
Fri Jan 28, 2011 7:10 pm
According to the easy-to-find label on the Telo power supply, the Telo takes 5 volts DC. Let's take a little time to examine your intention. As a point of departure, let us seek to maximize efficiency when mains power is active. The time spent running on the UPS, with mains power failed, is negligible; so we won't worry about efficiency in that condition.

Option 1: the way normal people (or engineers like me) would do it. Small UPS providing AC, with the Telo and modem power supplies (wall warts) plugged into it. When mains power is active, the total load consists of: (1) the Telo, which is running from the mains because the UPS has connected it to the mains; (2) the modem, similarly running from the mains; and (3) a very small load from the battery charger in the UPS. Since the Telo's wall wart is optimized for 5vdc out, it's about as efficient as it can be; similarly the modem's power supply is optimized for the modem.

Option 2: supplying DC for the Telo and for the modem from the UPS, which implies they're running from the (probably 12v) storage cells in the UPS. The charger in the UPS has to be a little larger because it is now not just floating the batteries but also supplying the Telo and the modem. The battery voltage (probably 13.5v float voltage) now has to be regulated down to 5v for the Telo, and whatever the modem requires also. There's an additional regulator in there, with associated energy loss. Depending upon the level of sophistication of the regulators, you're wasting between about 5% and about 63% of the energy taken from the batteries. Not smart.

Remember that the Telo's own supplied wall wart is, with overwhelming probability, more efficient at providing 2a at 5vdc than a regulator on a 12v battery could possibly be. The same is also true for the modem's wall wart.

Too, with option 1, you can run other things from the UPS. Your PC, for example, and a router. Besides wasting less energy, it's also cheaper (likely MUCH cheaper) to purchase, and more reliable, because failure of the UPS doesn't kill your phones and other stuff as long as mains power is on -- while with option 2 a UPS failure is added to the list of things that kill your phones, even with mains power available.
#73922 by murphy
Sat Jan 29, 2011 3:20 am
I have two APC UPSs in my computer room. One is 1000 VA and the other is 1400 VA. The first one is newer and runs on 48 volts while the second one runs on 24 volts. Dropping 48 VDC to run a 5 vdc product would be very inefficient. The UPSs are there to run the computers to provide a controlled shutdown. Running the modem, router, switch, Hub, Scout, Telo, and the cordless phone base from the UPS is an insignificant load once the computers have shut down automatically.
#73924 by thunderbird
Sat Jan 29, 2011 3:54 am
No one has mentioned that using any other Ooma device power adapter, than the Ooma supplied 120 VAC to 5 VDC power adapter, will void the Ooma device warranty. Than there is strong possibility that there would probably be additional "Noise" introduced into the Ooma device from the uninterruptible Power Supply, bypassing the Ooma device power adapter. I have seen previous posts on this forum about complaints about Ooma device noise. In one post the fix was to unplug from the uninterruptible power supply, and plug the Ooma device back into the regular wall outlet. So care must be taken when purchasing the uninterruptible power supply, to purchase a power supply that produces a fairly “Clean” output signal.
#73931 by Bear207
Sat Jan 29, 2011 7:06 am
My arrangement is like murphy's; using an APC SmartUPS (1500VA? not readily accessible at the moment) for my primary pc and simply placed the cable modem, wireless routers (Y configuration for security) and ooma on the same UPS.

The pc will shut down as necessary but keep everything else running.
The last extended mains outage I was able to use the phone for nearly sixty minutes (helping a friend navigate Boston metro area) before battery failure.

Note - do not skimp on the VA rating and do not overload the UPS. As a rule of thumb I never load a UPS or any power supply for that matter over 60% of its rated value. Engineers (no offense to the great post above who appears to be an engineer) may say 80%, yet I find "manufacturers" tend to overstate the capabilities of their products in my opinion.

Stick with "stock", off the shelf, name brand products and life will be easier from my forty years experience as a serious tinkerer.

Have a great day.

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