Solar Charging a 48V go kart

Functional_ArtistFunctional_Artist Posts: 5Registered Users ✭✭

Hello all,

I build electric go karts.  Here is one of them. 

I am interested in setting up a solar battery charger for them.

The batteries I am using are (4) 12V 12AH SLA's. I would like info on how to properly set up a 48V solar battery charger.

I have looked @ these "cheap" 100W panels from Harbor Freighthttps://www.harborfreight.com/100-watt-solar-panel-kit-63585.html but, as I understand they are for or to charge @ 12V.

Would I need (4) of them ($600.00-$800.00), wired in series, to charge my 48V battery packs?  

Any suggestions on "better" alternatives?

Location: Toledo, Ohio USA

Thanks in advance

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Comments

  • BB.BB. Posts: 27,566Super Moderators admin
    Don't get those Harbor Freight panels... They are not very good.

    The only off the shelf 48 volt battery "boost" controller that I know of is this guy "GVB-8" 8 amp charger:

    https://genasun.com/all-products/solar-charge-controllers/for-lead/gvb-8a-pb-solar-boost-controller/

    You will probably have to contact Genasun directly to confirm what the input voltage range is... I believe it can take Vmp~30-36 volt panels... I am not sure it can take a 12 volt panel for 48 volt battery charging directly.

    One charge controller and one ~200-350 watt panel and it could give you an alternative to 4x 140 Watt "12 volt" (Vmp~18 volts) set of panels.

    Normally, >200 Watt Vmp>=30 volt panels are 1/2 the cost ($$$/Watt) of 140 Watt Vmp=18 volt panels.

    The other question is how much current do you need to recharge your batteries... Normally, 10% to 13% rate of charge would be the nominal charging current (1.2 amps to 1.6 amps for a 12 AH battery bank). Higher than that could start to give you battery bank overheating issues. For example:
    • 12 AH battery * 58 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 90 Watt nominal solar array
    I don't know if the GVB-8 can recharge a 48 volt battery bank from a single ~90-140 Watt Vmp~18 volt panel.

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

    Thanks for the reply & the link to the "boost" controller.

    I mentioned the Harbor Freight panels, just as an example, to help begin the conversation.

    The  battery chargers that I, usually, use to charge these 48V battery packs (4-12V 12AH batteries) have an output current of 1.5A - 2.5A

    The Genasun specs says

    ...that it should work with almost any panel that is below your battery's voltage

    …& that it puts out 8A @ 12V so, would that be ~2A @ 48V?


    So, it looks like it would cost

    …~$100.00 for boost controller + ~$300.00 (+) for solar panels & mounting, cables etc.

    Total ~$500.00


    Man, that kinda blows this DIY solar charging of small Ev's idea "out of the water"

    (go karts, golf carts, boats, jet skis, snowmobiles ect.)

    How can I employ/promote, solar charging of go karts, if a standard (plug in) 48V 2A battery charger costs ~$20.00

    ...& if (lets say) it costs $1.00 per charge cycle

    It would take like ~500 charge cycles just to "break even"

    ...if the system gets set it up right, no complications arise & the components perform/last as long as their advertised too

    What is the average life of solar panels? 5 years? 500 cycles?




  • BB.BB. Posts: 27,566Super Moderators admin
    Fun_Artist,

    You got it... 4x higher voltage, 1/4 current equals the same amount of power... (Power=Voltage*Current)--Ignoring losses for the moment.

    In general, the least expensive (in volume) is to have a solar panel whose output voltage is appropreate for charging the attached battery bank (for a 48 volt lead acid battery, that is around Vmp-panel/array ~ 70-76 volts--Or 140 to 152 solar cells in series). Then you can use a simple PWM charge controller to charge the device(s) in question.

    Vmp~70-76 volts are not a common value these days--But given enough demand, I am sure you can find multiple solar panel vendors willing to build something like this for you.

    There are downsides with "high(er)" voltage DC systems... Basically they make great arc welders. If you have a failed connection or short somewhere, there will be a very nice arc (aka fire starter):



    These days, it it getting pretty cheap to do things in electronics... An MPPT boost controller is not that difficult or expensive these days--You are looking at $100 retail, or probably $40 or so wholesale.

    In general, good quality glass + crystalline panels should last 20-40 years--Assuming nothing damages the glass (hail, rocks, dropped, etc.) or rips the rear membrane. And for panels over ~200 watts, you can get them at $0.50 a Watt--A steal compared to 20 years ago when panels cost ~$10 a Watt.

    Another issue that we have seen here is that many people want to run the carts/etc. during the day, and recharge at night... Now you are looking at another battery (or set of batteries) that charge during the day and are used to charge the cart battery set at night--Another expense (or have 2 battery banks for the cart, one in cart, second in charging station).

    Add that solar charging is dependent on weather/seasonal sun/shade (solar electric panels do not work in full or partial shade).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Posts: 2,444Registered Users ✭✭✭✭
    I'm assuming the carts are individually owned (not part of a track/park multi-cart type of thing)? You want a sort of individual "docking station" so an individual owner can dock the cart and have it charged with solar?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • cow_ranchercow_rancher Posts: 96Solar Expert ✭✭✭
    You need a speed control on that go-cart... Also if you have access to an electrical outlet, then Solar is going to be way more expensive to charge your batteries.  Now if you are out in the Sand Dunes of Ohio, then it might make sense to use Solar.

    Rancher
  • Functional_ArtistFunctional_Artist Posts: 5Registered Users ✭✭

    Thanks for NOT taking (the end) of my last post, the wrong way ...sometimes I'm way too blunt.

    300W x $0.50 = $150.00 for panels plus $50.00 - $100.00 for controller & accessories

    ...plus a 10 - 20 yr. panel life is "more doable".

    Yes, exactly a "Solar Docking Station" (I like that term, sounds kool)

    The solar charging go kart idea (I have in mind) is for individuals, who mostly work all day. (the kids are in school) 

    Here is an example:

    a100 lb. kart with a 100 - 150 lb. rider & a 48V 1,000W propulsion system with a 48V 12AH (SLA) battery pack

    The battery pack (in this situation) usually lasts ~30 - 60 min (depending on driving style & terrain)

    You come home, have supper, get their kart (snowmobile, jet ski etc.) out, have some fun

    ...then put 'er away (plug it in to the (solar) charger/maintainer) till next time.  ...Clean & Green

    Yes, I use speed controllers, that was a "Hold on to your Hat" test (part of a series of tests)

    I was testing to see if there were any performance differences in a couple different speed controllers

    ...& also without a speed controller (off of the line was a "hoot" but, in the end the top speed was the exact same)



  • EstragonEstragon Posts: 2,444Registered Users ✭✭✭✭
    Have you considered a lithium based battery? They have the advantage of being able to use more of the overall capacity, have a better power to weight ratio, and are happy sitting partially charged.

    If a lead acid battery is run down to a low state of charge and left sitting for long it can permanently impair capacity. This seems likely with a solar docking station if there was a run of gloomy weather. A 48v nominal 12ah battery has about 500 watt-hours of total capacity. With 1000w motor load varying with terrain etc for 30-60 mins, I assume the battery would be at a pretty low state of charge. Being cycled that deeply will be hard on a lead acid battery, and left in that state until solar is available to recharge even more so.

    Lithium would be more expensive, but longevity may more than make up for this. Safety could be a concern, with some lithium chemistries more so than others.

    Maybe some of those with more lithium knowledge could chime in.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • Functional_ArtistFunctional_Artist Posts: 5Registered Users ✭✭

    Very good points, I hadn't thought about the SLA's sitting partially charged overnight. (over & over again)

    I'm glad you brought Lithium up. Yes, I have done tons of research on Lithium batteries.

    I have just purchased a 2kWh section of a 2015 Chevrolet Volt battery pack for a motorcycle that I converted over to an 8 kW electric motor.

    but, it's nominal voltage is ~45V not 48V so it needs a "special" charger.

    From what I understand,
    These 2kWh sections are 45V with a capacity of ~47AH
    ...they were made by LG Chemical
    ...chemistry is Lithium Maganese Oxide (LiMg204)
    ...they have 3 pouches in parallel & then 12 cells in series (3P12S)
    ...basically, 12 cells in series

    Special requirements

    Since these battery packs nominal voltage is 45V (3.75V per cell nominal)
    The "safe" voltage range of this battery pack is 3.0V per cell (low) to 4.1V (36V low & 49.2 high)
    It can only be "safely" charged to ~49V NOT 51V+ like most common 48V chargers will do.
    So, it needs to have the top charge (cut-off) set at ~49V

    Any info or help on "safely" charging this battery pack will be greatly appreciated

  • EstragonEstragon Posts: 2,444Registered Users ✭✭✭✭
    A solar charge controller (eg Midnight "Kid") should be settable to a 49v limit. Not sure about AC options. Does the pack include a BMS?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • Functional_ArtistFunctional_Artist Posts: 5Registered Users ✭✭

    Kool, I'll do some research on the "Kid", thanks

    As far as a BMS, the Chevy Volt uses an entire 370V pack BMS & their very proprietary & not really hackable (to use on individual sections)

    There are many kinds of "aftermarket" BMS's available with many different features.

    But, many of them are kinda "experimental" or cost "way more" than the battery pack their protecting is worth

    ...& their are a lot of other variables too (# of cells, chemistry, configuration, installation etc.)

    After ~6-8 months of research on lithium batteries/BMS's/monitoring & charging, I have found that their seem to be about just as many situations/stories where a BMS was overly relied upon

    ...or failed (component failure or just failed to do its job) & "actually" killed the battery pack instead of protecting it. 


    Another reason that I went with the "Volt battery" was, I wanted to stay away from trying to build DIY (home made) battery packs

    ...again, because their are so many variables from different cell, material & connection resistances,  amperage discharge rates etc. 

    From all of my research, these "Volt batteries" are professionally designed & manufactured & the quality control was set at a such high standard, that could never be duplicated in a home workshop (probably, due to a Zillion dollar contract with GM) 

    From what I've read, that these batteries are & stay so "balanced" that there are many folks using them on golf carts, motorcycles & lawn mowers (without a BMS) & having great success.

    The (2) main parameters are

    1.) don't discharge them below ~3.2V per cell (36V)

    2.) don't charge them up beyond ~4.0V per cell (48V)

    Some have instead used a "Batt-Bridge" to monitor cell balance within the battery

    ...but, I have not had any success with it

    I am instead plan to monitor the battery pack using digital monitors (1) that monitors/displays the entire pack voltage

    ...& (2) others that will monitor/display each 1/2 of the packs voltage (to monitor balance)

    So, to answer your question,  no it does not include a BMS

  • EstragonEstragon Posts: 2,444Registered Users ✭✭✭✭
    With the displays, I guess that makes you the BMS :wink:
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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