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  • Noob here, checking in.

    Interested in building a solar charger for my 18v power tool batteries as a learning experience before moving on to bigger and better at the cottage someday.

  • #2
    Hope you are an electrical engineer with Switch Mode design background.

    The easy way is get a 240 watt Solar Panel, 15 amp MPPT Charge Controller, 24 volt 100 AH battery, and a Hobby Charger. You can charge any battery type of today and tomorrow up to 36 volts up to 40 amps. They are so smart you can use your power tool battery to charge your solar battery. They are bi-directional.
    Last edited by Sunking; 07-17-2017, 10:42 PM.
    MSEE, PE

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    • #3
      Originally posted by ggorveatte View Post
      Interested in building a solar charger for my 18v power tool batteries as a learning experience before moving on to bigger and better at the cottage someday.
      Welcome but your goal will require expertise in multiple areas at the same time:
      - PV MPPT implementation
      - your tool battery charging characteristics
      - switching power supply design experience
      - overall circuit design experience

      if it was me I'd buy few standard components and call it a day and this comes from a guy who replaced lead battery in Home Depot lawn mower with lithium one and custom motor controller. Even for that project I used standard balancing charger to charge the battery, it seemed too involved to come up with one on my own.

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      • #4
        While I am a Mechanical Engineer, my intent wasn't to design a charger; nope going the simple route and going to buy a 12v vehicle charger, LOL. I was going to use a 12v battery to regulate the current drawn by the charger thou. My thoughts were PV to Charge Controller to Smallish (?) 12v AGM to my tool charger.

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        • #5
          Originally posted by ggorveatte View Post
          While I am a Mechanical Engineer, my intent wasn't to design a charger; nope going the simple route and going to buy a 12v vehicle charger, LOL. I was going to use a 12v battery to regulate the current drawn by the charger thou. My thoughts were PV to Charge Controller to Smallish (?) 12v AGM to my tool charger.
          makes sense I guess if I understood you correctly: PV -> MPPT Charger -> 12V AGM -> Tool Battery Charger -> Tool Battery. Just curious what is the point of the whole thing- to charge AGM battery during day so you can work at night? You'd need to estimate how much capacity you need and then select battery/PV/CC accordingly. Not sure why you chose AGM for this application but I'm not a battery expert so others might chime in.

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          • #6
            Originally posted by max2k View Post

            makes sense I guess if I understood you correctly: PV -> MPPT Charger -> 12V AGM -> Tool Battery Charger -> Tool Battery. Just curious what is the point of the whole thing- to charge AGM battery during day so you can work at night? You'd need to estimate how much capacity you need and then select battery/PV/CC accordingly. Not sure why you chose AGM for this application but I'm not a battery expert so others might chime in.
            Yes that was the basic plan. I figured I needed a battery help regulate voltage going into the 12v charger, but maybe I don't need it at all???? As for AGM, well that was because there wold be long periods of no use and i planned, and i wanted low maintenance.

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            • #7
              Almost EVERY charge controller needs a battery to keep it's electronics alive. The PV panel is not a reliable source of power and the battery is needed to provide the controller electronics stable power/
              Powerfab top of pole PV mount (2) | 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 ||
              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
              || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

              solar: http://tinyurl.com/LMR-Solar
              gen: http://tinyurl.com/LMR-Lister

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              • #8
                Originally posted by Mike90250 View Post
                Almost EVERY charge controller needs a battery to keep it's electronics alive. The PV panel is not a reliable source of power and the battery is needed to provide the controller electronics stable power/
                This i did not realize but it makes sense. Since I'm not really looking to store energy in this battery, or not much anyways, how would i size it?

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                • #9
                  Use a separate LVD=low voltage disconnect, with a high disconnect voltage. 12.8 to 13.1 volts. This will prevent the load from draining your battery, but still offer stability for your power source. You can purchase an inexpensive LVD on e-bay and or add a relay for a higher amp load. This set up, designed correctly would not cycle your battery and extend the life of both the load device ie:motor or electronics as well as the battery bank.

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                  • #10
                    Originally posted by ggorveatte View Post
                    This i did not realize but it makes sense. Since I'm not really looking to store energy in this battery, or not much anyways, how would i size it?
                    That is what we have been trying to tell you from your very first reply when I told you to get a panel, controller, battery, and a hobby charger. The hobby charger is not an AC powered charger, they are made to work with 12 to 36 volts or whatever you got.

                    Not only would a Hobby Charger charge your power tools, but any battery made today and in the future of all most any size or at least larger than anything you will ever have. They are multi-taskers. What you want to do can only do one thing, and you would have to design it.

                    So again about as small as you can get away with is a 100 to 200 watt panel, a good 15-amp MPPT Charge Controller, 12 volt 80 to 120 AH battery, and a smallish inexpensive Hobby Charger like an iCharger 106B+. This iCharger takes anything from 10 to 18 DC Volts Input, and will charge any 1S to 6S Lithium batteries (all of the lithium variants), 1S to 17S NiMh/NiCd, and 2 to 24 volt lead acid batteries. It will charge any of those with a programmable current of 0.5 to 10 amps. These are real SMART CHARGERS because you can fully program any charging algorithm you want to charge with. That means any battery type anyway you want. Its power limit is 250 watts, which means charging current is limited depending on battery voltage to be charged. Not only would it charge your power tools, but anything you have like your car and boat batteries.

                    Now if you want something cheaper like Chi-Com junk Hobby King has a lot of offerings, But none will be as robust as the iCharrger. You get what you pay for. Case in point Hobby King has a Chi-Com knock-off copy of the iCharger 106B+ as seen below.

                    You are not going to get any better advice.


                    Last edited by Sunking; 07-23-2017, 11:35 AM.
                    MSEE, PE

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                    • #11
                      I'll look into them, but why wouldn't I just buy the in vehicle charger which also is not an ac charger, it's battery specific and has a 12v plug on it already. I use it to charge my ryobi 18v batteries in my truck?

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