Running 10.5 volt modem on 12 volt system

paulstamserpaulstamser Posts: 85Solar Expert ✭✭✭✭
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!

Comments

  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    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.
  • paulstamserpaulstamser Posts: 85Solar Expert ✭✭✭✭
    Re: Running 10.5 volt modem on 12 volt system
    niel wrote: »
    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.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    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! :roll:

    But yes; start low.
  • paulstamserpaulstamser Posts: 85Solar Expert ✭✭✭✭
    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! :roll:

    But yes; start low.

    I'll check the power supply's open circuit voltage. That's easy enough.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    Re: Running 10.5 volt modem on 12 volt system
    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.
  • BrockBrock Posts: 628Solar Expert ✭✭✭
    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...
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • paulstamserpaulstamser Posts: 85Solar Expert ✭✭✭✭
    Re: Running 10.5 volt modem on 12 volt system
    niel wrote: »
    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.
  • mike95490mike95490 Posts: 6,523Solar Expert ✭✭✭✭
    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.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • PhotowhitPhotowhit Posts: 3,400Solar Expert ✭✭✭✭
    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 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    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.
  • icarusicarus Posts: 5,070Solar Expert
    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
  • nielniel Posts: 10,311Solar Expert ✭✭✭✭
    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.
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