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  • Solar panels/Battery charging???'s

    Home Power mag had an excellent article about a gentlemen in San Diego who did a "perfect situation" install. Took advantage of Energy Subsidies, sold power back to the utility during peak, and bought during off peak. Perfect, I think.

    For shop use, you really have to look at what he did - and bend it to heat/cool/power a shop. Home use is more picky, I think.

    I can undestand not liking to use a Diode. A good Schottky is a reasonable choice. You can also add "the right kind" of MOSFET in parallel, to get the benefits of low resistance. Same trick is used on high efficiency switchers for PCs.

    --jerry
    dvideo

  • #2
    This is a test
    Free software for calculating bolt circles and similar: Click Here

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    • #3
      Solar panels/Battery charging???'s

      I have the oppurtunity to purchase a Siemens solar panel, model SM50H, for $50. These are upwards of $300, new, so it looks like a good deal. What I don't know, is if it will work for my specific application.
      Tis is the panel/specs:
      http://www.fords-mtm.com/solar/sm50.htm

      What I want to do is set up a CB base station, running from a deep cycle battery, at my hunting cabin. I want to be able to recharge the battery with solar power. Typically, I will use the CB on a weekend, and during the week or two that I am at home, the battery recharges. I have searched the net, and it seems that there are solar charge maintainers, but no actual chargers.My ??'s:

      Can I use the panel to charge the battery?
      What kind of monitoring device(s)/circuitry will I need?
      How much CB usage can I expect per battery amp/hour?

      I am an electrician, so circuits and wiring are no problem, once I have a schematic, or at least a good idea of how everything is supposed to work together.

      ------------------

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      • #4
        I used a small 12volt cooler(refridgerator?) in my T/T when I was running over the road. When I would get home, I would leave it on, which would drain the batteries after the 3rd day. I bought a battery charger/solar panel that put out .53watts and laid it on the skylight cover which kept it charging all the time. Plugged it into a cigerette lighter and left it. It would drain down all night, but charge back up during the day. That was just enough to allow me to leave it plugged in all the time, so I didn't have to unload it every time I came home.
        Price was around $50. years ago. They offer larger units. This one is flexible, and will withstand water.
        BoatsUSa or something like that.
        David from jax
        A serious accident is one that money can't fix.

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        • #5
          Wow, that's one high powered solor cell. 3amps will maintain a battery and charge it if you have a way to limit the current. A group 24 "dead" battery (less than 11.3v) will draw over 12 amps at the start of charging. Sooooooo... you'll need a control circuit for it.

          Put an AMP meter between your CB +lead and the battery. On standby, I don't think it will draw more than 1/4 - 1/2 amp depending on volume. On transmit, it may hit 4 amps. Use the Ah rating on your battery (not CCA) and divide that by your amp reading. That will get you close to the hours of use. Just a guess but I bet you'll get 20 hours on transmit and a week of just listening.

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          • #6
            <font face="Verdana, Arial" size="2">Originally posted by mofugly13:

            Can I use the panel to charge the battery?
            </font>
            Yes, it will charge (maintain and/or re-charge) a 12V lead-acid battery.


            <font face="Verdana, Arial" size="2">
            What kind of monitoring device(s)/circuitry will I need?
            </font>
            Depending on the battery, nothing, maybe.
            If you have a battery set of 200-300AH, that panel won't hurt it if it continuously charges. You will need to add water.

            A charge controller may help somewhat, especially if
            1) You discharge deeply (more than 20% of capacity on a larger battery)
            2) Controller is one that incorporates a switchmode regulator which can increase the current into a discharged (and thus lower voltage) battery.

            <font face="Verdana, Arial" size="2">
            How much CB usage can I expect per battery amp/hour?
            </font>
            An Ampere-hour is just that, one ampere for an hour. If you have a 100 AH true deep-cycle battery, you can feasibly discharge about 10A for 7-8 hours regularly without damage (Capacity/10 rate).
            Other lower currents for proportionately longer, higher currents for shorter times, but not proportionately.
            That means 1A for 80 hours, but not 80A for 1 hour, more like 40A for 1 hour due to increased losses.

            I dunno how much your CB draws on standby vs in use, so I can't comment on actual times.


            Your issue is battery type and how much power you need, vs your recharge rate.

            I would avoid the "marine deep cycle" because they aren't either one. They are trolling motor batteries, and are built like car batteries. They will crap out on deep discharges if repeated often. If you don't draw much, you could even use a car battery.

            For deep discharge use, I would recommend Trojan T-105 Mileage-master golf cart batteries, a pair of 6V ones. More money, but worth it. They should last 10 years.

            They are 220 AH, and will not be hurt by continuous charging at 3A if kept watered. I will assume use of these just for argument.

            But, if you deeply discharge, you will be sitting partly discharged for a long while as that little panel charges it back up. That can allow capacity loss due to what is usually termed "sulphation". It happens when the battery sits discharged for a long time, the lead sulphate becomes difficult to convert back to acid.

            Your panel will recharge at a basic rate of 3 AH per hour of full sunlight exposure.

            It will take about 90 hours of good light to recharge from zero (which you wouldn't want to have to do). Figure a 60% discharge max, which needs then about 60 hours of light to recharge (including charge losses of about 20%).

            You get about 6 hours good light in the best location with a fixed panel (no sun-tracker) so that's 10 days of varying partial charge state for a 60% discharge. But then, that's for about 130 AH usage in one weekend, not accounting for recharge during daylight.

            If you use less you would have excess capacity and no problem. One day you might need that, you can get light from it too, etc.

            A smaller battery will need a charge controller to kep from boiling dry, but will charge up faster. In fact, the current-boost types mentioned above will charge any battery faster, as at low states and voltage you might get 5A charge (same power, lower voltage, = more possible current). That will cut re-charge times maybe 20%, and spend less time deeply discharged.

            if you don't pull 100+ AH in a weekend, you won't take so long to charge back up.

            I have a shed/garage with 440AH of batteries and a 6A panel setup. I pull large currents, but not for that long. Sometimes up to 100A for a few minutes, because out there I have a 2500W DC to 120AC inverter and various electric tools including air compressor. (lights are DC)

            The setup has been running 10 years and is going strong. Usually 90+% charged. I do have a simple-minded charge limiter on them, left over from when I had smaller batteries. The panels were 10 years old when I got them (from the Carrizo solar power test plant).
            1601

            Keep eye on ball.
            Hashim Khan

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            • #7
              <font face="Verdana, Arial" size="2">Originally posted by J Tiers:
              I would avoid the "marine deep cycle" because they aren't either one.</font>
              Ditto there. I found out the hard way trying to cheat and use them 3x3 in a golf cart. Lasted one week. Fortunately, the store took them all back.

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              • #8
                The standard 5 watt CB draws around an amp on transmit and maybe 100ma on listen. I have one I put a 4 amp hour nicad pack on and it can be used all day.

                One thing about solar panels is that if any part of the panel is shadowed the output falls to near zero. Also, you can't "overload" a solar panel. Shorting the output doesn't hurt it at all.
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                • #9
                  Thank for all the good info, guys. I am leaving in about 10 min. to go up to my cabin, where I have the battery. It's a trojan, and quite large. I'll get a model# from it this weekend. Again, thanks to all who replied.

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                  • #10
                    Good point Evan,I have several "top off"chargers on various vehicles around here,they output 14.7 volts in full sun and drop off to 10 or 11 with clouds.Never had one dry a cell,not enough output for that.

                    Be aware thou not all solar chargers include one crucial part,a back up diode,without them I found out the solar panel will back radiate at night(drain battery).Found this to be the case on the top offs,$30.00 model has them and they work like a champ.$19.99 HF model doesn't,and boy do they suck till you add one.
                    I just need one more tool,just one!

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                    • #11
                      Evan, I wasn't aware that the panels could be shorted. That was the only reason I mentioned using a controler. I wouldn't want to fry a $300 cell. Good to know though. Thanks!

                      By the way, your CB must be one of those teeny-weennies. Or.... I think I "tweeked" mine a number of years ago. (Before adding the linear)

                      Oh yea, did you know they dropped the output from 5 to 4 watts a number of years ago? At least in the US.

                      [This message has been edited by CCWKen (edited 04-16-2004).]

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                      • #12
                        <font face="Verdana, Arial" size="2">Originally posted by wierdscience:
                        .

                        Be aware thou not all solar chargers include one crucial part,a back up diode,without them I found out the solar panel will back radiate at night(drain battery).Found this to be the case on the top offs,$30.00 model has them and they work like a champ.$19.99 HF model doesn't,and boy do they suck till you add one.
                        </font>

                        A silicon solar panel WILL NOT allow back current. Most of them do include a diode in them. But even if they did not, the array is made up of 30+ silicon diodes, all oriented so as to block reverse current. Any current will be negligible.

                        They will NOT "re-radiate" in any case. They are not "reversible".

                        If you get into high voltage arrays, diodes make sense
                        But at low voltages, they are pretty much a net loss of power.

                        An "amorphous" array may have reverse current, its cells are not very good diodes. With them, a diode is a necessary evil. I suspect the "top-offs" are amorphous, as they are quite cheap. I have a couple of them.

                        All arrays are current limited by the amount of light hitting them, and their maximum efficiency. So shorting causes no damage at all.
                        Current is quite constant from the "peak power point" normally around 16 to 18 volts, to zero volts, as load resistance is reduced.

                        [This message has been edited by J Tiers (edited 04-17-2004).]
                        1601

                        Keep eye on ball.
                        Hashim Khan

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                        • #13
                          A little mental exercise- if the battery's capacity is 90 ah, and the charge current from the solar array is 3 amps max, it will take 30 hrs of full sun to charge it from dead. Not from shorted, but from fully depleted. Add to that a factor of about 30% for losses in charging, that becomes 40 hrs or so. That charge rate also is less than the maximum continuous trickle charge rate, but it will use up some water. Other than that, no regulator should be needed, nor should a diode be needed. If anything, I would use a simple current cutoff set for 13.6 volts. That charge rate is so low that the battery will just slowly build in voltage until that supposed full charge level is achieved, which that voltage is supposed to represent. It's not like an alternator is driving it, where the voltage will rise to maybe 15 or 16 volts during the charge, which is a requirement for a fast charge. You can't fast charge a battery by feeding it from a 13.6 volt power source, even if the current capacity of the source is huge. So a simple current cutoff based on a voltage reading is all that's needed to reduce or prevent the slow water loss that you would have with a continued trickle charge. I figure that with a charge rate less than 1% of ah capacity, no regulation circuitry is needed, and for a rate of 1% to 5%, use the cutoff regulator set at 13.6 volts. For a faster charge rate, you'll have to set the limit higher, at 14.5 or so, but don't make it continuous.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                          • #14
                            JT,

                            Even monocrystalline cells will allow a significant reverse current when not illuminated. Since most panels are composed of cells in parallel as well as series the reverse resistance is reduced. Polycrystalline cells are much worse and a blocking diode is mandatory. Amorphous cells are even worse. Solars cells as diodes have low reverse resistance.

                            I didn't mention it as most panels include a blocking diode. For maximum efficiency a shottky diode can be used, only around .3 volt forward drop.

                            Darryl, look up solar panels on the net, diodes are mandatory.

                            [This message has been edited by Evan (edited 04-17-2004).]
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                            • #15
                              Yep,thats right,they do need diodes,I didn't believe it until a buddy mentioned it to me and I also saw the same thing in a West Marine catalog,solar top off's are popular on boats.West had several large panels and all the descriptions said that they included backup diodes.

                              I still didn't believe it until my buddy said to look at the HF model after dark,sure enough it looked radioactive,had kind of a yellowish glow,not real bright,but you could tell it was there.
                              I just need one more tool,just one!

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