Golf Cart Battery Chargers

Discussion in 'The Projects Forum' started by BReeves, Nov 6, 2015.

  1. BReeves

    Thread Starter Member

    Nov 24, 2012
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    I have two 60's vintage Cushman electric carts used to run around the property with. One is 36 volts (6 - 6 volt L/A batteries) and the other is 24 volts (4 - 6 volt batteries). The chargers I have are also 60's vintage with the charge cycle set with elec/mech timers. The chargers aren't at all automatic and if I don't keep an eye on the charge state it's very easy to over charge the batteries. I would really like something I could plug in and leave (forget about) anytime the carts are parked that would keep the batteries charged.

    I ran across this and am thinking about building one for each cart.
    Looks pretty straight forward and easy to build and I probably already have most of the components.
    http://www.electroschematics.com/7687/24-to-36v-battery-charger-circuit/

    Would like to get the forum's opinion of the circuit and views on if you think it would do what I need.
    Thanks..
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Looks ok, better to use a full wave bridge instead of a voltage doubler, there are better designs with precision using regulator ICs like L200C, with variable voltage and current limit,with a pass power transistor for current over 2amps.

    Datasheet figs 21,24

    https://www.google.co.uk/url?sa=t&s...dTyCz8&usg=AFQjCNG-wm7DceyUyi1ZHHQn3IwpaEDQaQ

    there is still the problem of connecting a 24v battery set to 36v output, by mistake.
     
  3. BReeves

    Thread Starter Member

    Nov 24, 2012
    412
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    Thanks for the tips..

    I would be building two and probably use different connectors on the carts to make sure the chargers don't get switched.
    Understand about the full wave bridge, will have to see what I have in the transformer junk box. 24volt version shouldn't be a problem but may not have a 48+ volt transformer.
    I already have most of the components in my parts stash and it would actually be easier for me to build the discreet version if it looks like it will do the job.

    Just had a thought.. May build them into the existing chargers, add a mode switch to bypass the timer and connect the output to the batteries. This would solve the transformer and mixing up charger issues.

    On another subject.. Both chargers still have selenium rectifiers which I probably should replace with silicon diodes simply due to age. They still seem to work OK but haven't done any real testing to see if the output is clean DC or not. They are ferroresonant chargers and depend on a capacitor tied across a transformer winding for regulation. The caps are also original and probably should also be replaced.
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Yes replace the rectifier with a modern silicon one, 25 to 35 amp, and capacitors also, discrete components are ok, mount the 2n3055 on an heatsink.
     
  5. BReeves

    Thread Starter Member

    Nov 24, 2012
    412
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    After spending a week thinking, analyzing, laying out a circuit board, looking up components and calculating costs for stuff I didn't have decided to just buy the durn things.
    Found this and decided I can't build it for what it costs plus it's a true 3 stage charger.
    http://www.cloudelectric.com/product-p/sch-jac0436.htm

    The 24 volt version is a little more expensive but still under what I can build it for.
    http://www.cloudelectric.com/product-p/sch-jac0524.htm

    Oh well it was a fun exercise...
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    @BReeves ,

    My 86yo neighbor has an old Westinghouse cart that she runs around in. She forgets to charge it, and I have to tow it home...

    I built a circuit into her Lester charger (the buzz box) where I bypassed the time clock, and replaced it with a voltage detector that turns at on at ~37V (adjustable), and turns off at ~43.5V (separately adjustable).

    It controls a 30A SSR which is wired in the primary of the big transformer inside the Lester charger. I used a small wall-wart that I put inside the Lester box to power the voltage detector. The voltage detector stays on as long as the AC cord of the charger is plugged in, and does not contribute to discharging the batteries.

    The operation is now fully automatic just like the charger that came with my newer style EzGo. You can just leave the charger plugged into the AC, and the charger plugged into the cart 24/7. If the cart is sitting unused, the charger comes on once about each month as the batteries self-discharge.

    The instructions to my neighbor is to just always plug in the charging cord whenever she parks the cart in the garage. After most short trips, the charger does not come on because the batteries haven't discharged all the way down to 37V...

    The schematic for the voltage detector is on another computer (not here), so if you want it, I can get it later....
     
    Last edited: Nov 15, 2015
  7. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    Selenium rectifiers cannot be replaced with a silicon counterpart. A series resistor must be added. Usually, it's guessed and checked when doing valve (tube) sets. Measuring the current and the voltage drop would give you a BIG hint.
     
  8. BReeves

    Thread Starter Member

    Nov 24, 2012
    412
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    Hi Mike,
    Sure I would like to see the schematic, whenever you have time.
    Thanks.
     
  9. BReeves

    Thread Starter Member

    Nov 24, 2012
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    Understand in a circuit where the voltage drop across the diodes would be critical but doubt that would be the case in a brute force battery charger. Hard for me to believe 1/2 volt would make much difference on a 36 volt charger. I ordered 40 amp diodes and will check when I get around to installing them.
     
  10. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    Read this article: http://w3hwj.com/index_files/RBSelenium2.pdf You decide. I have no experience with high current Selenium rectifiers.

    All I can suggest is to measure the drop across the rectifier and to measure the current through it, but at least measure the drop. 10 V vs 1/2 is a BIG difference , IF it turns out to be that much.
     
  11. BReeves

    Thread Starter Member

    Nov 24, 2012
    412
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    Thanks for the link. It's been a long time and the older I get the more my memory gets fuzzy.
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    An expensive - but very good solution would be individual smart 6V chargers that automatically throttle back to float charge when they sense full charge. The 6V ones were offered by a Honda motorcycle parts distributor.

    Maybe a little cheaper; 12V smart chargers and charge pairs of identical 6V batteries.

    In the UK we have stores like Lidl and Aldi that sometimes have automatic chargers that are fine for overnight charging and can be left unattended.

    There's charger/conditioners like the Optimate that can be left float charging for months, even years - but they take several days to charge a fully flat battery.
     
  13. BReeves

    Thread Starter Member

    Nov 24, 2012
    412
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    I have several 6/12 volt chargers and have at times over the winter charged the batteries independently but it's a real pain.
     
  14. Colin55

    Member

    Aug 27, 2015
    191
    19
    Here is a simple circuit to turn off your charger when the voltage reaches a maximum.
    Use your charger in the normal way and connect a second set of contacts to the relay in this circuit and adjust the voltage to activate the relay when the voltage rises. This will turn off the charger.
    If the battery voltage drops appreciably, the circuit will turn on the charger again.
    If you don't understand this, email me.


    Colin Mitchell talking@tpg.com.au


    TALKING ELECTRONICS.com

    AutoBatteryCharger-1.gif
     
  15. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    As promised, here is the circuit I put in Betty's 36V Golf Cart. This circuit is much more precise than Colin's circuit. It also has separately adjustable CutIn and CutOut adjustments.

    I had on-hand a surplus, regulated, switch-mode Wall-Wart, whose output voltage is nominally 12Vdc, but it actually measured 11.75Vdc. It is the reference voltage to which the battery voltage is compared, and it powers the detector circuit. I mounted it inside the Lester charger, such that it is switched by a toggle switch which replaced the timer. If you dont have such a WallWart, you can replace it with an unregulated one, followed by a ~12V voltage regulator chip.

    I use a NE555 as the window comparator. The CutOut voltage (~42.5V) is set by U1. Since the 555 is powered with 11.75V, the Threshold voltage is 2/3*11.75V = 7.83V (green trace). The voltage divider consisting of R1, U2, R2 converts the rising battery voltage of 42.5V to 7.83V at the Threshold pin of the 555 (yellow trace), turning off the Solid State Relay, which cuts off the 120Vac to the charger's big transformer.

    The CutOut voltage is trimmable over a range of about +-3V. If your Wall-Wart had a slightly different voltage, adjust U1 to get your desired CutOut voltage. I set Betty's CutOut to 42.5V (2.36V/cell).

    The CutIn voltage is set by the voltage divider R3, U2, R4, and the 555 Triggers when that pin (red trace) reaches 3.92V (blue trace). I set Betty's CutIn to 37.5V (2.08V/cell).

    The final output switching is done by a Crydom TD1210 Solid State Relay I already had in my parts stock. You could use the 555 to switch a conventional 12Vdc relay instead. Write back if you want to do this.

    Here is the circuit and its simulation: The orange trace is the simulated battery bank voltage.

    Betty.gif

    ps, if your oem charger works, why screw with the selenium rectifier? The transformer turns ratio is specific to the forword voltage drop of the selenium rectifier. If you substitute Silicon, you will screw-up the charging rates.
     
    Last edited: Nov 17, 2015
  16. BReeves

    Thread Starter Member

    Nov 24, 2012
    412
    64
    Hi Mike,

    Just happens that I have a couple solid state relays that would do the job. Can't remember the ratings but know they are at least 10 amp.
    Would you mind sending me that .asc file? bob somethinxtra com. add the usual characters between the words and watch the spelling of somethinxtra, only natural to try and spell it correctly.

    Have always heard selenium rectifiers degrade with age and concerned the chargers may have (or develop) an AC component on the output which can't be good for the batteries. My chargers are at least 40 years old maybe older, haven't put a scope on the output yet, planning on doing that when I get them on the bench.

    Thanks
    Bob
     
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