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  • #16
    Originally posted by Mike90250 View Post
    Inverters, even when idle, still present a sizeable load on a battery. And if the battery was "soft" to begin with, who knows what shape it was in.
    And as the battery capacity decreases with cycle use and time a constant watt-hour nightly drain becomes a deeper and deeper discharge, in terms of % DoD, and thus accelerates the battery decay.
    Ideally the OP would only turn on the inverter when actively charging Ryobi batteries.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #17
      Thanks. I didn't know inverters used energy when idle? There was no load on the inverter at night or in the day, for that matter, as the inverter always shuts off after one minute or sometimes one hour.The 12V car charger to the pv system would not work because at night we'd move the battery and inverter inside in order to run two a/c floor fans off the inverter. The fans are necessary to keep the noseeums off us in order to sleep.

      I didn't know solar was so complicated. I just want a simple system to charge a few small 18V batteries and run two floor fans at night. So far I've spent a thousand dollars trying to setup an emergency battery charger (a lot of that cost was from my mistakes).

      My next attempt is to buy another battery. Should I re-purchase the NAPA 8301 deep cycle battery? The fans draw 50-60W each X 2 fans = 960W needed for eight hours sleep. How can I find what size battery I will need? I'm really stupid when it comes to numbers and figuring.

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      • #18
        Originally posted by Mackey View Post
        Thanks. I didn't know inverters used energy when idle? There was no load on the inverter at night or in the day, for that matter, as the inverter always shuts off after one minute or sometimes one hour.The 12V car charger to the pv system would not work because at night we'd move the battery and inverter inside in order to run two a/c floor fans off the inverter. The fans are necessary to keep the noseeums off us in order to sleep.

        I didn't know solar was so complicated. I just want a simple system to charge a few small 18V batteries and run two floor fans at night. So far I've spent a thousand dollars trying to setup an emergency battery charger (a lot of that cost was from my mistakes).

        My next attempt is to buy another battery. Should I re-purchase the NAPA 8301 deep cycle battery? The fans draw 50-60W each X 2 fans = 960W needed for eight hours sleep. How can I find what size battery I will need? I'm really stupid when it comes to numbers and figuring.
        For a quick & rough calculation if you know the amount of watt hours you need per day you can divide that number by the battery voltage and divide that value by the percentage you can safely drain the battery each day.

        In your case an example would be (960wh / 12V / 25% = 320Ah). Or you would need a 12v battery system rated 320Ah or more.

        The % you use in the formula will depend on the battery specification cycle life. If you drain it more or use a larger % you will either need a bigger battery or expect it not to have as many cycles.

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        • #19
          Batteries that big just to run a fan might not be the best solution, but if the fans are the biggest load, what about looking at other options?

          I use a rechargeable bug light in my cabin to get the critters that slip through the screens. It only runs for a few hours per charge, but it's a much less energy intensive option. Perhaps some better screens would let you go with a smaller solar setup?

          Just food for thought. Sometimes it's worth looking at the root problem.

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          • #20
            Mackey,

            i will comment on this issue...first a marine/RV deep cycle is really a car battery, a very poor choice for solar system use. It's primary job is to start the car, it's job is done in 15 seconds or less, then it's going along for the ride, on the other hand a golf cart battery is way better suited for the job as it works all day pushing you around the course with no help unless you are pushing! Golf cart batteries are not expensive and can be had for less than $100 ea. Maybe cheap ones at Sam's club or Costco for $79. or so. These will work for 5-8 years with a bit of care. They are available in 6 volt or 8 volt as carts are 36 (older carts)or 48 volts for the newer carts. Use 2 of the GC-2 6 volt batteries in series to get your 12 volts. Second issue...10 ga. Wire is far too small to feed power to the inverter......I don't use smaller than 2 ga. wire for inverters. Third issue.......power tool chargers are switch mode devices and some want real clean power even though they should work ok, some do not. The 12 volt input chargers are a much better choice for your use as you will not have inverter losses. The Sure-Sine inverter from Mstar is by far the best small inverter, rock solid, it has very low idle power

            as Butchdeal said.....Simpler is allways better!

            david
            Last edited by Tecnodave; 05-23-2019, 02:35 PM. Reason: Edited to correct Apple iPad autobutcherspell

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            • #21
              Years ago I killed a bunch of Makita NiCad rechargeable batteries using a modified square wave inverter. Plus it doesn't make sense to take 12 volt dc, invert it to crummy ac power only to convert it back to dc. Costly mistake I never made again.
              2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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              • #22
                Littleharbor, and others

                that is exactly what charger that I had trouble with....Makita with NiCad or NiMh....does not like anything but pure sine wave....it trashed by batteries as well, I bought a Makita 12 volt DC charger and new NiMh batteries....well I'm on the road doing field service and needed the portability of the 12 volt units, won't buy new power tools unless they have a 12 charger as well..
                david
                Last edited by Tecnodave; 05-23-2019, 03:04 PM.

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                • #23
                  Thank you to SunEagle (and to everyone else who's been trying to help) for calculating the battery I need based on the figures I presented. It seems my problem is the battery. The biggest deep cycle battery I found at NAPA only has the part number and the cold cranking amps of 1720, but there's no easy way to find how many amp hours that converts too. I welcome the suggestion of two 6V gulf cart batteries, but will that power my AC needs?

                  I'm so disgusted with my efforts I don't know what to do. I'm perplexed by everyone telling me to use DC. I thought the convenience of solar is you can use it to power AC devices. How in the world can I charge 5-6 Ryobi batteries during the day and then use the battery (disconnected from the panels and brought inside) to power two 60W floor fans by our bed at night?

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                  • #24
                    Mackey,

                    Any battery that a cold cranking amps rating is a starting battery primarily. A marine/RV "deep cycle" may be a bit better than an auto starting battery but it is not a true deep cycle battery. Real deep cycle batteries do not have a "cold cranking amps rating" . Starting batteries have very thin plates and lots of them to accommodate starting surge. True deep cycle batteries have much thicker plates and are not designed for starting the auto but can supply power for a much longer time. The only rating that really counts is the 20 hour amp/hour rating. Really good ones like the Rolls-Surette batteries also have a 100 hour amp/hour rating. You should be using true deep cycle for your use. Starting batteries can be run flat about three or four times before they are toast!

                    I would suggest using an extension cord to power the fans and keep the batteries outside. Non sealed Flooded Lead Batteries do emit hydrogen gas mixed with oxygen and acid fumes mostly when charging and do not ever belong in a living space. Hydrogen gas mixed with with Oxygen burns at 6600 feet per second......that's more than a mile...a second! ...more correctly termed as an explosion.
                    david
                    Last edited by Tecnodave; 05-23-2019, 05:31 PM.

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                    • #25
                      One other potential misunderstanding, based on the OP's response about bringing the charger inside at night, is that a "car charger" for power tool batteries would not have to be installed in a car or even connected to a car. With a suitable socket or wire connection it can be installed directly to any 12V nominal battery bank. If you have a 24V or 48V battery bank, then additional equipment would still be needed.
                      SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                      • #26
                        And on the issue of energy effeciency, DC powered fans are far more efficient than AC powered fans. A 20 watt DC fan will move more air than most 50-60 watt AC powered ones. Reason is simple, AC motors lose their magnetism when rotating and are recharged by power input as the motor turns. DC fans do not lose the magnetism. A 12 volt DC fan would be better, no inverter loss and better effenicy. I tested the run time draw of a cheep Harbor Freight inverter lightening a 13 watt lamp and it was over 200 watts, idle draw of 42 watts and an effeciency of 25-30 percent at a very small load on a 2500 watt inverter. Off grid is all about energy effeciency....
                        Last edited by Tecnodave; 05-23-2019, 07:42 PM.

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                        • #27
                          Originally posted by Tecnodave View Post
                          And on the issue of energy effeciency, DC powered fans are far more efficient than AC powered fans. A 20 watt DC fan will move more air than most 50-60 watt AC powered ones. Reason is simple, AC motors lose their magnetism when rotating and are recharged by power input as the motor turns. DC fans do not lose the magnetism. A 12 volt DC fan would be better, no inverter loss and better effenicy. I tested the run time draw of a cheep Harbor Freight inverter lightening a 13 watt lamp and it was over 200 watts, idle draw of 42 watts and an effeciency of 25-30 percent at a very small load on a 2500 watt inverter. Off grid is all about energy effeciency....
                          There is a big difference between efficiency and power factor (PF). An AC induction motor will draw some current which establishes the stator field but does not directly contribute to the operating torque of the motor. This causes the product of the RMS amps and RMS volts to be greater than the actual Watts consumed by the motor. This can require an inverter to deliver more current than the wattage of the fan would indicate, but in a good inverter that extra current does not actually require power from the batteries. This difference between apparent power and real power is called the Power Factor or PF, and in a resistive load it is 1.0. As the load becomes more reactive or the current waveform more distorted the PF decreases toward zero. A typical AC motor, fully loaded, has a PF in the range of .6 to .9.

                          The efficiency number is the ratio of the output mechanical power, in watts, over the input electrical power, also in watts. Inefficiency in a motor corresponds directly to heat being generated in the motor itself, both in the stator windings and in the rotor.
                          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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