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Thread: UPS Battery Time Question

  1. #1
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    UPS Battery Time Question

    I'm looking to run a wireless modem and a wireless router in my car...the easiest solution I have to keep them juiced after the key is out is to run them off a large UPS, like this APC model at compusa. I can't find any info on ther site about how long it will run for...the needs of the router can't be anything compaired to the full blown computers they base their numbers on, so can I expect some long battery life because of that? The model say 1000 VA and 600 W, and the router needs 12V @ 1.0A, and the modem is something like 12V @ 0.75A...what kinda formula do I need to calculate an average time? Do I just divide the 1.75 into 1000 and get 571 minutes? Would be nice if it was that simple!

    Well, just hoping to see if anyone knew, or had experience running a router strictly off a UPS. Thanx!

  2. #2
    Maximum Bitrate eCarô's Avatar
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    What about buying a cheaper model, and just changing to a bigger batt?

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    InTheWayBoy, you'll be using the AC to DC adapters to power the router and modem, correct?

    If yes, use the amperage rating on the AC side to do your calculation. Basically do this:
    110V * (amperage rating of router + amperage rating of modem) = A

    Amount of battery time available: (600W / A) hours.

    I assumed you lived in the US so I used 110V.

  4. #4
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    110 (1.75) = 192.5

    600 / 192.5 = 3.11

    So I'm looking at around three hours then?

    eCar...that was my original plan, but after seeing how much a nice Optima battery would cost it looks like this is the simpliest way...three hours, if that is right, is about what I was shooting for!

  5. #5
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    No, you were doing it on the DC side. Unless both the DC and AC side have the same ratings (which is UNLIKELY) then that calculation is wrong.

    Look at the adapters, the AC ratings should be printed on them.

    Also, have you thought about using a battery tank instead. Rather than a UPS you might be better off with a battery tank.

  6. #6
    Maximum Bitrate VanMan69's Avatar
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    Quote Originally Posted by InTheWayBoy
    I'm looking to run a wireless modem and a wireless router in my car...
    What kind of network are you trying to set up here? I'm trying to decide on a wireless setup, but the common options don't accomplish what I'm looking for. Just wondering what you're trying to do here. What kind of wireless modem is it?

    Why are you trying to calculate the time you can run just the router off the UPS? Won't the computer also be on?

    And if you're looking to keep things running with the key out, you could just hardwire your inverter to your battery, or to avoid a dead battery go with my favorite option, the auxiliary deep cycle. Did you check eBay for the Optimas? I got two off eBay for $109 each, I think they're regularly about $175. Add an isolator and you can run EVERYTHING (stereo too) for three hours without the key (and run the router alone for WAY longer).

    And if you wanna get crazy you could put the UPS between the battery and equipment, for even more time. But obviously that's extraneous cost you're not looking for. I'm just thinking out loud.
    95 Chevy G20 Vroom Boom Room
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    Maximum Bitrate eCarô's Avatar
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    Here is what I make of it:

    First of all, you can't just divide the max power rating (600W) by what you will be using, and end up with minutes.

    Anyway, you have 2 devices that both run at 12VDC for a total of 1.75A (21W).

    You are going to use AC-DC transformers to run the devices. Let's say they are 75% efficient. So, they will draw about 28W from your UPS.

    The UPS you linked to is 1000VA. According to this page, a similar UPS (BR1000) gets 1h36m runtime at 50W draw. Now notice that this UPS is most efficient at 100-200W draw. At the max power rating (600W), efficiency drops off. At the low end (50W) it drops off also. Based on this, I guess that you will get about 2h15m, or maybe 2h30m max.

  8. #8
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    I think he's trying to create some kind of Personal Area Network. So he can browse the internet with his PDA, for instance, while roaming outside of his car.

    Just a guess. If he is then I've been thinking about the same thing my self. Maybe we put our heads together.

  9. #9
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    Since it looks like I've got some people attention with this, I'll explain more!

    I live in Jacksonville, FL and we're are one of the first markets to get ClearWire, which is essentially wireless internet...they accomplish this by using their own towers to distribute the signal, which is picked up by their proprietary modem. Each tower covers something like seven miles, so it's not all it's cracked up to be, but better than nothing! Thankfully they haven't screwed it up by requiring tons of software to run the thing...in fact, there is none! All you do is plug in a CAT5 cable and you're done!

    I run a small on-site repair company, and lots of times our customers don't have broadband. This gets to be really annoying when I have done everything but still need to download a 40MB+ driver file. So what I was thinking is run the modem and a wireless router in my car, which would distribute the wireless internet connection via the router...then all I would have to do is install a wireless adapter if they don't already have one and then I would be online!

    Most service calls last between two to three hours, so I would like to find something along that level. I'm not really interested in a big production, cause that just means I'll never get it done. I've looking into some of the previously mentioned ideas, and just never go a good enough explanation. The vehicle is a Honda Element, which comes with a pretty week stock battery. Also, there is no power to the ports when the key is out. I would prefer to do something modular like the UPS, or something that I can at least install and remove easily for when I don't need it.

    If what eCar is saying is true, then I think I might just stick with the UPS...I like the idea of the Optima and an isolator, but how would I hook all that up? My understanding would be that I would hook the batter up to the isolator, and the what? Does that have to hook back up to the car's electrical system somehow?

    The only thing running off the UPS while the car is off would be the modem and the router...sometimes I might plugin in my laptop if I'm just chillin somewhere, but not very often.

    I appreciate all the help fellas, and I would be glad to help with anything if possible. I don't think ClearWire is going anywhere else soon, and truthfully the coverage isn't all it's cracked up to be...but what else is new right? And just so you know, it's 1.5MB for $35 a month with a free modem when you sign up for twelve months. The modem is simple...power and ethernet. No config, no software...sadly no external antenna port either. Since I get pretty spotty signal I'm gonna call them and see if they offer something more powerful, but I doubt that they do. Of course, a mobile hot spot is not really their intended use.

  10. #10
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    Quote Originally Posted by InTheWayBoy
    So what I was thinking is run the modem and a wireless router in my car, which would distribute the wireless internet connection via the router...then all I would have to do is install a wireless adapter if they don't already have one and then I would be online!
    Ah, I knew you were trying to create something like this. I've been thinking to do kinda the same thing. What I envision is to have my carputer to serve as an internet gateway to my wireless devices, either PDA or notebook pc. My carputer needs to be connected to the internet first, of course. I'll do this through the cellular network. See the problem yet? Yup, internet service through cellular network is still quite expensive. For the city I live in to get something like ClearWire is like hoping for the winter to bring some snow. It's just not going to happen in Central California. Although we are getting the 10th Campus of Univ. of CA. So we'll see. It might snow after all. Anyway, that's why my vision is still.., well, a vision.

    If what eCar is saying is true, then I think I might just stick with the UPS...
    I don't think the calculation will ever be accurate enough if it's done using the rating on the DC side. You're planning on using a UPS, that tells me that you will be powering the modem and router through the AC adapters. Then it's the rating on the AC side that needs to be used in the calculation.

    I like the idea of the Optima and an isolator, but how would I hook all that up? My understanding would be that I would hook the batter up to the isolator, and the what? Does that have to hook back up to the car's electrical system somehow?
    Yup, the idea is your car's battery charger will charge both the car's battery and the Optima. The isolator governs the charging current. The positive poles of the batteries individually hook to the isolator and the isolator hooks to the battery charger.

    sadly no external antenna port either.
    Most modems/routers are hackable. Some of their PCB even already have predrilled holes for antenna hook ups. Of course, hacking will always be equal to warranty voidance by the manufacturer. Maybe you can find a way to acquire a hackable second unit.

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