Solar panel wiring ?

Discussion in 'Electric Bicycles' started by Minnesolar, Dec 31, 2008.

  1. Minnesolar

    Minnesolar New Member

    I'm building a solar-electric trike on the frame of a stretched adult trike.
    It has three 12-volt batteries wired in series. There's a 36-V hub motor on the front wheel. Another important fact: I'm not good at wiring.
    The trike has two 12-volt, 40-watt solar panels and a charge controller for each, that are wired together but still need to be wired to the batteries.
    How would you go about wiring the two solar panels to the three batteries?
    Would some sort of diodes be needed to prevent backflow or shorting of the electric current?

  2. lordoflightaz

    lordoflightaz Member

    I would love to see what you are building. I am envisioning solar wings LOL.

    You should just be able to hook the batteries up in parallel to maintain 12 volts. Each controller should prevent blackflow. I have 3 little arrays (each with its own controller) attached to 2 batteries for a project I have in my back yard. visit Northen Arizona Wind and Sun Forum to learn stuff like this.
  3. Minnesolar

    Minnesolar New Member

    Here's a photo from earlier this month, to show the panel locations:


    As you can see, at that time both panels were wired to one battery. Since then I unhooked both leads from the panels. Can I just leave that wiring as is, and hook those two leads to the three batteries in series; in other words the (+) lead would connect to each (+) post on each battery, and the (-) lead would connect to each (-) post on each battery, so six more wires needed?

    Since then two similar batteries, speed controller, and hub motor were added and wired up.
  4. lordoflightaz

    lordoflightaz Member

    All the positive together and all the negative together is a parallel circuit. The voltage will stay the same (12 volts) which will charge the batteries.

    Plus to minus is series, which would increase voltage, 3 x 12v, which will give you the 36 volts that you need for the motor side

    Looking at the panels, I bet you can hook both to a single controller, depending on what it is rated at and then connect that controller in parallel to one of the batteries. You will be charging at 12 volts and sucking juice at 36 volts.

    If that is a car battery you are going to have a lot of storage issues. I tried using a car battery with solar cells. You will happier, but broker, with deep discharge batteries.

    BE CAREFUL Electricity can KILL you

    Wha'ts that white stuff on the ground in the picture? Frozen water crystals?

    I guess this is why I am still doing another gas engine project. Batteries are going to set you back about $300 to last more than a VERY short while.

    Don't let me discourge you I love the concept. Living in Minnesota you might want to mount the cells over the bike to keep the rain and snow off of you.
  5. Minnesolar

    Minnesolar New Member

    Thanks for the info.

    Well I'm pretty sure they are. The first one was a gel type that came with the panels in a home lighting, starter kit. The other two are SLA that were called replacements for the first one.

    Well, I better not say on this forum but it's a 4-letter word that starts with 's'. ;)

    Yea, maybe later. Could put a basket or box there instead. OTOH if mounted too high the panels could make the trike top-heavy and serve as wind catchers. Just trying to keep it simple to start with.
  6. loquin

    loquin Active Member

    12+ volts out of the two panels if they're wired in parallel, or 24+ volts if they're wired in series. (the + is the extra volts needed to actually charge a 12V battery - about 2 volts extra for each panel. A battery charger has to 'push' the power into the battery, and it can only do that if it has a higher voltage than the battery - but, not TOO much higher...)

    Now, with 2 cells & 3 batteries, coupled with the fact that you need to keep the batteries wired up in series to generate 36 volts for the motor, you'll need to convert the 12 or 24 volts to about 42 volts to charge the three batteries. The commonest approach is to use a DC-DC converter. Essentially, it converts the DC power to AC Power, using a transformer to step up the voltage, and then converts the higher-voltage AC back to the DC power at the voltage you need.

    Keep in mind the the amount of power remains the same (actually, somewhat less because of efficiency losses in the DC-AC-DC conversions.) And, since Power = Voltage * Current, when you increase the voltage, the current will be reduced. If your two solar cells produced 14V at 2 Amps, the MOST they could produce after the conversion to 42 volts would be 1.33 Amps. Even with a 90% efficient DC-DC converter (pretty darn good, BTW,) you would be looking at 1.2A DC output to charge the batteries.
  7. HoughMade

    HoughMade Guest

    Wow- solar powered in Minnesota....God bless your optimism and I hope it works well.
  8. Fuzzo

    Fuzzo Member

    A thought on how you could get more power when parked. Use a windshield reflector, angled to catch some more rays. They're really light and cost a few dollars. Put it away when you're moving, obviously. It wouldn't be 100% efficient, but it's worth a try to see how much more charge you get that way. You would either readjust it periodically, or set it to be just right at about the middle of the time the vehicle was parked. Really cheap fold out solar panels :).