High efficiency solar charger circuit tops off those lead-acid batteries

Make your next project solar-powered with this charging circuit. It’s completely through-hole, and there are no microcontrollers that need to be flashed. If you can source parts and are handy with a soldering iron building this will be a breeze.

Both the maximum system voltage and the low voltage drop out are configurable. After assembly, you just need to attach a regulated power supply to the load terminals. Tune the power supply to the max voltage and turn a potentiometer until an LED comes on, then repeat the process for the drop out voltage. Board artwork for the two-sided PCB and a schematic are available from the page linked at the top. If you’re not into etching your own circuit boards you can buy one for around $10.

[Thanks Murray]

21 thoughts on “High efficiency solar charger circuit tops off those lead-acid batteries

    1. RTFA :)

      The SCC3 kit is just using a conventional 18TQ045 18A Schottky diode, dissipating a lot of heat.

      The 200ds230 on the other hand uses a MOSFET instead of the usual diode, thus dissipating far less heat.

      It can even be scaled to whatever current you want by putting MOSFETs in parallel.

  1. Has anyone seen a DC to DC converter for wheelchairs?

    I have a Quantum 6000Z that has dual 24v batteries and I’d like to pull some of that through the charging port to power my laptop when I’m not near an outlet at school. It has a 3 Pin XLR connector, two pins for +/- and a third to lock out the control when charging.

    1. More info, it needs to to go an Apple Macbook. In theory it says 18v at the magsafe connector, but I’m not sure about that and I don’t know enough about electronics not to pooch my chair =p.

      1. i’d look at car usb-adapters for parts. i got a 12v to 5v usb-adapter from the dollar store, but the chip inside is a it34063, which handles up to 40v input and provides 1 amp output at any voltage you want (below input of course). but maybe not enough amp for a laptop.
        the other route would be to look at car to 120v adapters. some should handle 24v. (especially if sold as car+airplane adapters). check truck, military surplus, solar for a suitable adapter.

      2. Modify an Apple Magsafe Airline Adaptor to do the job. It’s Apple original, has the Magsafe connector you need and is powered by 15-24V DC. No other solution will be as efficient or as reliable.

        Be aware that for aviation-industry-paranoia reasons the adaptor may not provide the power needed to charge your laptop at an acceptable rate, but it should at least power it for use.

        Good luck, and please make sure to send in your hack when it’s done!

    2. A laptop is gonna whack your battery really fast. I would say you are better off utilizing the ability to carry an extra battery, maybe a solar panel to trickle charge it and a DC to DC convertor running off of the extra battery. I say have an extra bat so you can isolate the whole set up and make it so you will never get stuck because your MacBook ate your wheelchairs battery. Trust me, don’t even try and hook that up to your chair unless you have a spare set of batteries laying around…

    3. You would need a lot more info before developing something.

      I hate to post this on a hardware tinkering site, but wouldn’t it be a lot easier to buy a higher capacity laptop battery off ebay instead of messing with the power supply for your mode of conveyance?

  2. As somebody who is currently working on a large-ish solar project, I can attest for the rather high price of commercially available charge controllers.

    Especially since, if I am reading this correctly, it looks like the MOSFET he is using here is capable of handling 50A. We paid something like $70 for a 30A controller…

  3. $10 for a controller that can be tuned very efficient and handles 50A…assembled. It’s a rare thing..

    Chip tuning would be better IMO

  4. The FETs are rated at 50A, but for that kind of current you will have to mount them on heatsinks. Also, PCBs are bare. ie unassembled.
    The nice thing, is that the circuit is scalable, more fets in parallel, more current.
    Murray.

  5. Hi guys, this seems like a really good well explained project, I’m a beginner but I think I’d like to try a thing like that, but have some questions. He does not seem to mention any solar panel apparel, what would be a good choice for that? And while checking for parts, the webstore mentioned about the IRFZ44N mosfets that NTE2395 would be a “suggested replacement”, is that bogus?

    1. As is, I use this circuit on 10W..50W installations. It should be able handle more with an uprated fuse but I have not tested it on larger installations. The IRFZ series are good FETs for this application. Low on resistance, cheap and available. The circuit is pretty forgiving but note the mosfets on resistance The IRFZ48 is about 16m Ohm while the NTE2395 is 28m Ohm That would mean at 4A (50W) the IRFZ48 dissipates 0,256W while the NTE dissipates 0,448W.
      At 1A the difference becomes almost insignificant
      0,016W and 0,028W.
      Murray.

  6. Couple comments,

    Paralleling MOSFETs only leads to lower total power losses when you include rdson increasing with MOSFET junction temperature, the PTC effect. If you were to exclude this effect, the total power losses would be the same with 1 MOSFET or 100 paralleled MOSFETs. You did elude to that in your write up, but it is the reason why IGBTs, bipolar transistors and diodes are practically impossible to parallel and why MOSFETs are so easy to parallel.

    For people who are experimenters, ON Semi makes self-protected mosfets and so does ST. ST calls them OMNIFETs. These devices include thermal cutout, over voltage protection, and built in current limiting. They are MUCH more expensive than IRFZ44s, but are also alot more forgiving as they can handle essentially a continuous dead short.

    That said, I’m having a tough time understanding how this works exactly…

    If “solar” is the input power from the solar panels, and my battery is connected to terminals ST3 then don’t I have a permanent current path from the “solar” terminals, through Q2′s body diode, through D2, through Q4′s body diode out to my battery? Is the only thing that limits the current the maximum Iout of the solar panel or the fuse?

    1. Yes, this is a simple charge controller, the current limit is provided by the capacity of the solar panel.

      During charge time, Q4 and Q2 are on and current flows through the FETs in reverse. Losses are purely resistive thats why more mosfets mean less losses and no diode volt drop. The regulation is provided by Q1 in a shunt format. So the diodes on the mosfets provide no problem as the maximum panel is limited to about 13,8V.
      Murray.

  7. I’m curious why this guy chose not to design an MPPT (Maximum Power Point Tracking) charging controller.

    As an FYI, if your charge controller can vary its input resistance to track the output resistance of the PV panel, you’ll get maximum power transfer and higher efficiency. Doing this in practice is more difficult of course, but the idea is that the equivalent output resistance of the panel will change with light intensity, such that the charging controller must also track this to get the most out of the panels.

    Or, put shortly, your 100 watt panel isn’t going to provide what you’re expecting without an MPPT charger.

    1. MPPT does gives better efficiency, but the cost is accessibility. MPPT invariably requires a microprocessor, this is a single source item and requires the maker / repairman to have a programmer a PC and the confidence and experience to use both. This charger only requires solder, a soldering iron and a variable supply for calibration. In the 3rd world things are repaired not replaced and microprocessors can be an obstacle. There is a gap for an open source MPPT and “this guy” is working on it.
      Murray.

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