Project

Hertzfish
Hertzfish Registered Users Posts: 5 ✭
in Solar Beginners Corner #1
I am a senior engineering student taking senior design. My project is to build a golf cart that uses the batteries more efficiently. Now i believe we are using a 36 V golf cart motor with 6x 6V deep cycle lead acid batteries and a LCD moniter system to be used as a HUD to control the motor and show all the data from sensors.

Now I am building a solar panel roof for the golf cart. I know it wont be the most efficient to fully recharge the batteries. I am using either 1 or 2 polycrystalline solar panel, mainly the GEPV-185 MCB-001 from GE http://sunelec.com/index.php?main_page=product_info&cPath=5&products_id=1003. Now I was thinking of using a MPPT controller. any help will greatly appericiate.

This is my first time dealing with solar panels. Also if you have some points or websites in dealing with the design of the system is appreciated.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #2
    Re: Project

    you may also want to look at the motor controller for regenerative braking.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,622 admin
    #3
    Re: Project

    Make sure your controller (and other components) can work with a 36 volt battery bank. It is not a very standard voltage for off-grid systems.

    Keep the solar charge controller to battery bank connections short and use heavy gauge wire (read the manuals). It is critical that there be little voltage drop between the controller and the battery bank.

    Also, use fusing/breakers between the major components (charge controller to battery bank, battery bank to any of your test/monitoring equipment, etc.).

    Batteries can source huge amounts of current (1,000's of amps or more) into dead shorts. Always very careful with your tools and wiring (place fuses/breakers near battery bus and size fuses/breakers for maximum current rating of wire connected). Batteries do generate hydrogen gas when charging which is easily ignited with a random spark.

    Always wear safety goggles when working near the batteries themselves.

    Another issue is the output voltage of your solar panels vs battery bank voltage. Few (if any) charge controllers can "up convert" Vmp from solar panels to battery bank voltage. They normally require Vmp>Vbatt-charging+voltage-drops.

    For a 36 volt battery bank with an MPPT charge controller, your Vmp should be >51 VDC. You will need at least two of those 185 watt panels in series to charge your golf cart. One panel will not be sufficient (Vmp=25.6 volts at STC). Remember that Vmp is measured at 70F solar panel temperature--in full sun the panels will usually be much hotter and Vmp will be, roughly 80% of the STC rating in full sun on a hot day.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Project

    Believe it or not, this issue has come up before on this forum! :D

    You can search for "golf cart" related threads - there are many and most just refer to the use of the standard 6V battery. But a couple actually deal with the 36 Volt golf cart set-up.

    The short version is that there isn't enough room on top of a cart to put enough panel to make any significant contribution to charging. Something like this:

    11.5 Amps (5% of a 225 Amp hour bank) @ 42.6 Volts (approximate charging Voltage for a 36 Volt system) = 489.9 Watts. Factor in the inefficiency of a panel (especially sitting in the sun at Palm Springs) and you get about 650 Watts.

    So the best you could hope for is to mitigate some of the use loss. As most panels are either "12 Volt" or "24 Volt" there's some difficulty in fitting enough PV to achieve the necessary Voltage (unless you can up-convert as Bill mentioned). A full size panel is about 2.5' x 5', so you'll have to look at a lot of specs to see how much Wattage you can actually fit above the cart (all about the same in terms of Watts per sq. ft.).

    And watch out for flexing. Golf carts don't have great suspension, and the panels aren't going to like being jostled.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,622 admin
    #5
    Re: Project

    Also, to add to Marc's comment about durability of panel... If this is a "real" golf cart--Panels can be holed by golf balls (expensive mistake).

    Also, tempered glass is very sensitive to forces/notches/scratches at the edge of the glass. Be very careful on mounting/protecting the panels.

    Tempered glass pretty tough--but this is still single weight window glass and if the glass is overstressed--the whole panel will shatter and be virtually useless.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Hertzfish
    Hertzfish Registered Users Posts: 5 ✭
    #6
    Re: Project

    Thanks for all the helpful info. Yeah i was figuring I would need 2 panels. If they cant fit on the roof. I probably rig something so it will. And this is most likely be given to the school, so I doubt that there will be golf balls hitting it lol. I will keep that in mind when I mount the panels though and make sure they are kept in a secure environment. Sorry i didn't search for this topic. Any additional information is well appreciated. This should help my group when building the golf cart.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,622 admin
    #7
    Re: Project

    Golf Cart projects are hard to search for when we talk about golf cart batteries. :roll:

    Try this Google Search and see if this helps.
    • golf cart project site:wind-sun.com

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Slappy
    Slappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    #8
    Re: Project

    http://www.youtube.com/watch?v=zFYpNrbyKCA jump to 3:35 that is when the golf cart starts, it can give ya visual idea on how 2 panels can fit, worth a watch ;)
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  • Hertzfish
    Hertzfish Registered Users Posts: 5 ✭
    #9
    Re: Project

    Sorry to bring this thread up again. Finally got all the pieces and had to kind of rebuild the golf cart. Now i am about to hook up the panels to the battery bank. And i was curious about something. I tried to read some things however, I couldnt get the straight answers I was looking for. I have a DC motor and a PWD controller for that motor.

    NOw I was wondering if I can hook up the panels and the charge controller to the batteries in a series or in parallel. Everywhere I have looked have said you can do both, but didn't really explain why. I am worried that it will over load the controller and the motor.

    I have switched out parts and now using a http://sunelec.com/index.php?main_page=product_info&cPath=22&products_id=39 and 2 http://sunelec.com/index.php?main_page=product_info&cPath=5&products_id=750. Also I was curious where you can get some good wiring for the products.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Project

    I think you've made a mistake with the charge controller. The Tristar comes in two versions: PWM and MPPT. You want the MPPT one: http://www.solar-electric.com/motr45ampmps.html

    Its output would connect in parallel with the batteries. The panels would be wired in series and connected to the controller's input.

    Oh and please try to refrain from linking to competitors' web sites; this forum is hosted be Northern Arizona Wind and Solar and it's not fair to them. Just the product make & model would suffice, okay?
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  • Hertzfish
    Hertzfish Registered Users Posts: 5 ✭
    #11
    Re: Project
    Cariboocoot wrote: »
    I think you've made a mistake with the charge controller. The Tristar comes in two versions: PWM and MPPT. You want the MPPT one: http://www.solar-electric.com/motr45ampmps.html

    Its output would connect in parallel with the batteries. The panels would be wired in series and connected to the controller's input.

    Oh and please try to refrain from linking to competitors' web sites; this forum is hosted be Northern Arizona Wind and Solar and it's not fair to them. Just the product make & model would suffice, okay?
    Sorry about that.

    And I decided to go with PWM since it was cheaper by half the price and this is for a budget senior design project. I checked on the website and the TS-45 can be used in a 36 volt system. So the charge controller more than likely will be hooked up in parallel. I am connecting the 2 panels in series with each other then to the charge controller. And I believe that it will work the same way

    I also was wondering. I have already purchased the parts. Now I was curious the panels came with plugs instead of wires that you can just connect to the charge controller. any way or part i need to do/get to make those work.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: Project

    Yes the PWM controller can be used, but it functions basically as a switch. So the output Voltage corresponds directly with the input Voltage. Under normal circumstances this isn't a problem: a "12 Volt" panel has a Vmp of 17.5 Volts which is just right to provide the 14-15 Volts for charging the battery.
    In this case you have a bit of a mismatch. The Vmp of the two panels in series will be 58 Volts, whereas the "ideal" Vmp for the 36 Volt batteries would be less than that. Not sure what's just right for the 36 V system - 52 ish. So you'll be losing about 10% of the panels' power, possibly more. It will work, but it's not as efficient as possible. Darn MPPT's are expensive!

    You can only hook the controller output in parallel with the batteries; there is no other way to do it.

    You need an MC4 (possibly MC3?) connector cable to tie the panels to the controller: http://www.solar-electric.com/incaforsoelp.html Basically you buy one of these extensions; it has a (+) connector on one end and a (-) on the other. Cut it in half and you have the connector ends for the panels and wire ends for the controller.
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  • Hertzfish
    Hertzfish Registered Users Posts: 5 ✭
    #13
    Re: Project

    Thanks yeah I know that it is the better idea to go with the MPPT, but the budget just wasn't going to let that happen. And the reason why I went with the stronger panels is so that we can always have the sufficent charge even on the less desirable days. NOw I am a bit curious if it will actually limit the amount of current so they motor will get over the maximum voltage allowed.

    I wasn't 100% sure about the parallel and that is what I was intially going to go with. I will be looking into those MC4 or MC3 cable today or tomorrow to figure out which ones I need, which i probably need about 10 to 15 feet to ensure i can make it look nice and reach the charge controller. Then I have to get cables to connect to the batteries.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: Project

    I shouldn't worry about excess current pushing the Voltage too high. 430 Watts of panel will produce about 6 Amps peak at charging Voltage. That's roughly 2.5% of the batteries' capacity. Hardly more than a trickle. The 45 Amp controller is over-kill, but most controllers aren't designed to work in the Voltage ranges necessary (either input or output) for this project.
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