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Running 10.5 volt modem on 12 volt system

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  • Running 10.5 volt modem on 12 volt system

    Hi,

    My ISP sent me a broad-band modem to upgrade my service. However, it includes an AC adapter (117AC to 10.5 volt DC/900ma). Since my home is a 12 volt stand alone operation I can't see using an inverter to run this little modem. But I do have a 12 volt power converter with following step-down settings:

    Input: nominal 12 volt
    Stated output: "9 volt (900ma)"
    (meter on it reads 10.3 volts)

    And:

    Stated output: "12 volts (3 amps)"
    (meter on it reads 13.6 volts)

    Question: Can I run the modem off the power converter at the 9 volt setting without damaging it? (again, a voltage meter on it reads 10.3 volts -- darn close to 10.5 volts). Or would I do better using the 12 volt setting? (meter on it reads 13.6 volts). Or is that too high voltage for it to handle? My system voltage gets up to 14.01 volts when the batteries are fully charged. Why they just didn't make this modem 12 volt is beyond me.

    Thanks!

  • #2

    Re: Running 10.5 volt modem on 12 volt system

    Re: Running 10.5 volt modem on 12 volt system

    that is an odd voltage. i say try the 9v. it's the higher voltages that would be likely to blow things out and not usually the lower voltages that when they don't work mostly just sit there. out of curiosity, is the voltage the same on it with a load as without if it's possible for you to measure it? i ask this because wall warts usually aren't big on regulation, but some are now the better switching supplies.
    NIEL

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    • #3

      Re: Running 10.5 volt modem on 12 volt system

      Re: Running 10.5 volt modem on 12 volt system

      Originally posted by niel View Post
      that is an odd voltage. i say try the 9v. it's the higher voltages that would be likely to blow things out and not usually the lower voltages that when they don't work mostly just sit there. out of curiosity, is the voltage the same on it with a load as without if it's possible for you to measure it? i ask this because wall warts usually aren't big on regulation, but some are now the better switching supplies.
      Do you mean the voltage of the wall power supply unit that came with the modem or the modem itself?

      I'm not sure how to test them under load except that I do have a small digital voltmeter.

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      • #4

        Re: Running 10.5 volt modem on 12 volt system

        Re: Running 10.5 volt modem on 12 volt system

        You have to be able to somehow connect the DVM to the modem's power supply while the unit is hooked up and running. That's a bit difficult of course, as the connection between the two is no doubt some type of sealed mini-jack. Can you measure the power supply's open circuit voltage first? It's bound to be higher than the 10.5. And yeah, that's an odd voltage all right!

        But yes; start low.
        1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

        Ohm's Law: Amps = Volts / Ohms
        Power Formula: Watts = Volts * Amps

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        • #5

          Re: Running 10.5 volt modem on 12 volt system

          Re: Running 10.5 volt modem on 12 volt system

          Originally posted by Cariboocoot View Post
          You have to be able to somehow connect the DVM to the modem's power supply while the unit is hooked up and running. That's a bit difficult of course, as the connection between the two is no doubt some type of sealed mini-jack. Can you measure the power supply's open circuit voltage first? It's bound to be higher than the 10.5. And yeah, that's an odd voltage all right!

          But yes; start low.
          I'll check the power supply's open circuit voltage. That's easy enough.

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          • #6

            Re: Running 10.5 volt modem on 12 volt system

            Re: Running 10.5 volt modem on 12 volt system

            Originally posted by paulstamser View Post
            I'll check the power supply's open circuit voltage. That's easy enough.
            that'll be good as it will show the unloaded voltage. if it's high like 13-14v then it is either not regulated or regulated well and putting 12vdc on it with a few series diodes (i'm guessing greater than or equal to 3-4 diodes @ 1 amp or greater) would suffice to run it. each diode will drop the voltage by about .6v give or take and you would not want the voltage configuration you are working on to ever exceed that of your supply voltage as you measured it.
            NIEL

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            • #7

              Re: Running 10.5 volt modem on 12 volt system

              Re: Running 10.5 volt modem on 12 volt system

              Ya, I bet it's 9vdc running under load, or darn close to it.

              I agree they should make a standard for all external equipment being 12v or 5v or something standard anyway. It would be nice in a computer room if there were a standard and you could have one 100w power supply feeding a bus that all the peripherals in to. Just think of all the wall warts that could replace and wasted idling transformers... Anyway...
              XW6048, 4 KC 120's, 4 KC 130's and 4 Evergreen 200's totaling 1800w of PV, MX-60 charge controller, Trimetric meter and eight AGM 8A8D's or 490 amps at 48v. 4 tons of geothermal and 3 tons of air source.

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              • #8

                Re: Running 10.5 volt modem on 12 volt system

                Re: Running 10.5 volt modem on 12 volt system

                Originally posted by niel View Post
                that'll be good as it will show the unloaded voltage. if it's high like 13-14v then it is either not regulated or regulated well and putting 12vdc on it with a few series diodes (i'm guessing greater than or equal to 3-4 diodes @ 1 amp or greater) would suffice to run it. each diode will drop the voltage by about .6v give or take and you would not want the voltage configuration you are working on to ever exceed that of your supply voltage as you measured it.
                I tried to measure the wall wart power supply output but it's DOA. That is, no juice is coming out of it when plugged into my inverter. I know the inverter and voltmeter are good because two other wall wart power supplies give an output reading just fine (one 12 volt unit reads a whopping 19 volts).

                So I called and they are sending a replacement, whenever that arrives.

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                • #9

                  Re: Running 10.5 volt modem on 12 volt system

                  Re: Running 10.5 volt modem on 12 volt system

                  This is how I deal with trying to see what the supply voltage actually is.
                  Get 2 straight sewing pins, piece the power cable cord, about 2" apart, one pin on each side, turn unit on, and measure voltage at the pins ! Power off, and remove pins. The pinholes are far enough apart, and so tiny, only imersion in water will be a problem.

                  I think the straight battery voltage, when charging, will be too high, and cook something eventually. You can get a 7412 regulator, and set up a trim adjustment to get your 10.5V or , use several 2 or 3 amp diodes in series, you get a bit of voltage drop for each diode, but it will still fluctuate, but it wont be 14.8V anymore.
                  http://tinyurl.com/LMR-Solar
                  http://tinyurl.com/LMR-BigLug
                  http://tinyurl.com/LMR-NiFe

                  Grundfos 10 SO5-9 with 3 wire Franklin motor (1/2hp 240V 1ph # 214505 ) on a timer for 3 hr noontime run - Runs off PV
                  Powerfab poletop PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe battery | 15, Evergreen 205w "12V" PV | Midnight ePanel || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT

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                  • #10

                    Re: Running 10.5 volt modem on 12 volt system

                    Re: Running 10.5 volt modem on 12 volt system

                    I'd go to Ebay and search for; 10.5v car adapter

                    and change the end to what I need if It needed changing...
                    Home system- 20 - 200W Evergreen blems, 2 Classic Lites, E-Panel, 2 Prosine 1800 watt inverters, 800AH 24V forklift Batt, up and running 1 Classic Lite and 14 Suntech 185W in spare room.
                    Experience with Pulse/Trace PC250 Power Center, Original Rouge CC, 80-4/5watt 6v panels, Odds and extras,

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                    • #11

                      Re: Running 10.5 volt modem on 12 volt system

                      Re: Running 10.5 volt modem on 12 volt system

                      some adapters, or wal worts as we sometimes call them, are prone to blowing out on modsine inverters. you may need to take it someplace when the new one arrives that you can plug into utility ac power to measure the output or risk blowing out the 2nd one.
                      NIEL

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                      • #12

                        Re: Running 10.5 volt modem on 12 volt system

                        Re: Running 10.5 volt modem on 12 volt system

                        Let me preface this by saying I am, categorically NOT an electronic expert and in fact I know less than nothing about such but,,,

                        My neighbour IS an electronic expert who designs and builds all kinds of test equipment for scientific applications. He has suggested to me in the past that MOST electronics really don't care if they have exact voltage, as long as they are with in some range. For (simple) example, your car radio will work just fine as low as ~9 vdc, and as high as ~15 vdc. Too some extent it depends on the roubustness of the circuit, but none the less there is often significant tolerance range.

                        Having said this, I would certainly CONSIDER wiring it direct to 12vdc to see what happens. The risk is that it will go poof. Question is, how hard it it to get a replacement installed and at what cost? Can you get a spare modem for next to nothing from the ISP or Ebay or Craigslist and try it on a test modem?

                        I personally have run my satellite modem off of all kinds of weird off spec voltages now and again with no ill effect. I am not suggesting you try it lightly, but sometimes it is better to ask forgiveness than permission.

                        Good luck,

                        Tony
                        Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!

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                        • #13

                          Re: Running 10.5 volt modem on 12 volt system

                          Re: Running 10.5 volt modem on 12 volt system

                          doing what tony said is a risk as something that specs 10.5v would need lower voltage otherwise they be using the more common 12v adapters. some things can vary their input voltage and some cannot and many spec the variance they can typical take while some stuff, especially the cheap stuff, makes you guess. my guess would be a good pwm adapter regulated at 12v might work if the other is a non-regulated type adapter. the adaptor would show a higher open circuit dc voltage when not plugged into its load. like 14v for example, but it could be more or less in the unregulated example's voltage. point is if the unregulated supply voltage is equal to or higher than the well regulated pwm supply then you can use the well regulated pwm supply.
                          if it blows out because it's on a cheap msw inverter it is moot on doing it at all.
                          NIEL

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