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  •  You should write up a description of the small (15+ / 0-)

    scale systems you have for you boat, as I'm certain folks would be fascinated.

    I'm looking into getting a small system for my BiPap machine. I have severe sleep apnea so when central PA was warned about the possibility of extended power outages from Hurricane Sandy, I went to buy an emergency portable generator of the sort I used in Massachusetts last year when the power went out for a week, but they were sold out.

    With the benefit of extra time I've discovered that a solar system may be safer, quiter, and not dependent on refilling the fuel tank every  7 hours.

    But. there are still things about the inverters and battery connections I do not completely understand. Apparently, some of the older model inverters use only square waves instead of pure sinusoids which might be an issues for medical equipment.  

    Also, the battery systems sold by ResMed for my specific BiPap machine bypasses the 120 volt transformer and plugs directly into a 24 volt input, which is more efficient, but I don't know exactly how to connect a solar panel to the battery.

    The complete battery system sold by a leading global producer of camping equipment looks very attractive but I'm still waiting for the supplier to respond to my question about the inverter and its use for medical equipment.

    The means is the ends in the process of becoming. - Mahatma Gandhi

    by HoundDog on Sat Dec 15, 2012 at 05:32:44 PM PST

    [ Parent ]

    •  question about the inverter (5+ / 0-)
      Recommended by:
      HoundDog, reflectionsv37, wader, elwior, nzanne

      Good call.
      Most modern inverters now are true sinewave. Setting up 24V is doable, but you might need an electrical engineer or contractor to set you up right. If that machine runs on 24V DC, you don't have to worry about an inverter, just line up two 12V batteries in series and you've got 24V You'd have to make sure the panel could provide at least 25V to charges them. As I said, it is doable, if not already made.

      If I ran this circus, things would be DIFFERENT!

      by CwV on Sat Dec 15, 2012 at 06:34:08 PM PST

      [ Parent ]

      •  Thanks CwV. I've also learned that there are (9+ / 0-)

        several kinds of batteries, and I would need a deep cycle marine battery or a later style hybrid, instead of the standard car battery, which is optimized for very large charges of short duration to start cars, while marine deep-cycle are optimized for delivering steady lower currents over a sustained period of time.

        I also read some interesting articles about battery systems in RVs which suggest that putting two six volt batteries in series is better than a single 12 volt.

        I need study some texts on electrical engineering to better understand the details.

        The means is the ends in the process of becoming. - Mahatma Gandhi

        by HoundDog on Sat Dec 15, 2012 at 06:44:39 PM PST

        [ Parent ]

        •  Pretty much everything in the above posts are... (5+ / 0-)
          Recommended by:
          KenBee, HoundDog, wader, Zinman, elwior

          correct. I use 4 6-volt golf cart batteries, each pair is wired in series to produce 12 volts and the 2 pairs are wired in parallel to provide more battery capacity in amp hours. This is a common setup on boats and, as you can probably imagine, golf cart batteries can take some real abuse.

          A 24 volt system is no problem to set up with solar panels. Many foreign boat manufactures wire boats with 24 volt systems but pretty much everything in the US is 12 volt. To get 24 volts out of a solar system, you just wire 2 12 volt panels in series as you would batteries. The only problem with this is if you want to use the battery bank and solar system for another purpose, you'll have trouble finding things that run on 24 volts. Another option is to set everything up as 12 volt and then search for a 24 volt regulated power supply to convert the 12 volt to 24 volt. Off hand, I don't know where to source on of those, but a quick search with Google should come up with some results. If you are going to use this for critical medical equipment, make sure it is a "regulated" power supply. That means it will always put out a true 24 volts and compensate for the batteries being significantly above or below 12 volts.

          It is easy to find sine wave inverters these days. In the past they were much more expensive, but now they don't really cost much more. I have an old modified sine wave version and it runs most things, power tools, microwave and other 120 volt items very well. This time on our cruising adventures we decided to bring along a bread maker. I never bothered to test the bread maker running on the inventor and much to my surprise, it will only work with a true sine wave inverter. From what I read, bread machines are notorious for not working with old inverters. Same thing with our fancy rechargeable electric tooth brushes. I suspect your medical equipment might have similar problems, but the manufacturer should be able to answer those questions.

          If you decide to go solar, make sure you know how many watts your medical device draws and how long it runs, before you determine how many amps of battery power you need. And remember this important equation Amps x Volts = Watts. Batteries can only be discharged to about 50% of their capacity. So, if you have a 200 amp battery bank, you actually only have 100 amps you can use before the battery needs to be recharged. If your medical device needs 150 amps to run for 8 hours, 200 amps of batteries would not be enough to get you through the night. It's also important to know how many amps your solar panels will deliver on a typical day. Once the solar power and battery banks are setup for your needs, it can run for years without you having to do anything!

          Never attribute to malice that which can be adequately explained by stupidity.

          by reflectionsv37 on Sat Dec 15, 2012 at 07:18:01 PM PST

          [ Parent ]

          •  amp - hours you mean? (4+ / 0-)
            Recommended by:
            reflectionsv37, HoundDog, wader, elwior

            I think I know what you meant, but for those who don't here's a link that describes it better than I could
            Amp-hour

            good advice on the regulated power supply a google search and downnnn the rabbit hole....

            This machine kills Fascists.

            by KenBee on Sat Dec 15, 2012 at 07:47:07 PM PST

            [ Parent ]

            •  Good post! (4+ / 0-)
              Recommended by:
              KenBee, wader, elwior, HoundDog

              Things get even more confusing when your trying to figure out how many amps you will draw out of your 12 volt battery system when running an 120 volt AC device through your invertor.

              For some reason, that I've yet to understand, AC devices are rated in watts and DC devices are by how many amps(amp hours) will be consumed by the device in one hour.

              For example, I want to run a 1000 watt microwave on my inverter and my 12 volt battery supply. How many amp hours will be used from my battery bank while it is running.

              Using the equation Amps x Volts = Watts, we can determine how many amps of 110 volts will be consumed by the device.

              Amps(?) x Volts(110) = Watts(1000) At 110 volts the microwave draws about 9 amps (1000 / 110)

              At 12 volts we have
              Amps(?) x Volts(12) = Watts(1000) From a 12 volt battery bank we would be using about 83 amps (1000 / 12)

              It would take one big battery bank if you wanted to run a device like that for more than a short period of time, but since it only typically runs for a few minutes at a time, it's not that big a problem for a 400 amp battery bank.

              Never attribute to malice that which can be adequately explained by stupidity.

              by reflectionsv37 on Sat Dec 15, 2012 at 08:47:35 PM PST

              [ Parent ]

              •  check it out, found by my seekrit little fren' (4+ / 0-)
                Recommended by:
                reflectionsv37, wader, elwior, HoundDog

                hyar

                or worser, how much solar panel and time to charge and discharge to 50% a 12 volt battery and run a 110 v microwave with it..with the conversion efficiencies and all...people do those calculations, but geez..

                that link can run at either 110vac or 12vdc...they say, and double as a cooler.

                This machine kills Fascists.

                by KenBee on Sat Dec 15, 2012 at 08:53:42 PM PST

                [ Parent ]

                •  Once you throw in the time required... (4+ / 0-)
                  Recommended by:
                  KenBee, wader, elwior, HoundDog

                  to recharge the battery with solar power, it becomes almost a wild ass guess unless you live in some place like the Sahara Desert where you never see a cloud. I use my simple method and it seems to work fairly well...

                  If your battery is still not charged at the end of a sunny day, you need more solar panels!!! I'm not sure you can ever go wrong having more panels than you need!

                  Never attribute to malice that which can be adequately explained by stupidity.

                  by reflectionsv37 on Sat Dec 15, 2012 at 09:05:50 PM PST

                  [ Parent ]

        •  One more thought... (5+ / 0-)
          Recommended by:
          KenBee, HoundDog, wader, elwior, nzanne

          If you decided to go with a 24 volt solar/battery system, you should still purchase a regulated power supply to supply the current for your medical device. Although the system is 24 volts, the actual voltage can/will vary considerably. When the batteries are partially discharged, you may only be getting 22.5 volts and when the batteries are being charged by the panels the voltage may reach 26 volts or even higher. The regulated power supply will take those different voltages and continue to output a clean 24 current regardless of the voltage of the batteries.

          I use a desktop computer on the boat as opposed to a laptop. They now make 12 volt regulated power supplies for desktop computers, available for car computers, and those power supplies ensure my computer always sees clean 12 volt power.

          Never attribute to malice that which can be adequately explained by stupidity.

          by reflectionsv37 on Sat Dec 15, 2012 at 07:25:48 PM PST

          [ Parent ]

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