Custom charger and results…

Viewing 12 reply threads
  • Author
    • #10809
      • Posts: 2088

      I’ve been building a custom charger over the last month and I thought I’d share it with you all. Like most Bit freaks I’ve been looking for ways to get the longest runtime possible for the shortest charge. Since there is only 24 hours in a day and the human body needs sleep it’s taken me a while to get all my sh1t together. I’d like to thank micro_amps for all his help with this since a lot of the success of this project has been to do with his advice, anyways enough of the award ceremony speech, lol!

      The charger is based on two major parts, the timing circuit and the current/voltage limiting circuit. My goal for this project was to be able to have a fully custom charger for my cars that had variable time, current and voltage selection. From this I can charge singe/dual batt cars from a low 14H standard charge (5-15mA) to a more intense 45Sec 1.6A charge!

      Before I go any further, here is a graph I generated from MS Excel outlining the THEORETICAL values of current and time required to charge various capacity batteries to 100% charge. Keep in mind that using most of these values in the real world will prolly blow up your car, doh! I used it as a guide only.


      Here’s a picture of the prototype. Once I’m happy I will build it into a nice little jiffy box with charge clip, push buttons and pretty lights.


      As you can see in the diagram above the charger is currently charging my MS 49Mhz Skyline at 0.59A or 590mA. I used the multimeter to be able to measure the current I was sinking into this poor little guinea pig battery. With various testing I’ve been able to put as much as 1.6A into the car’s battery for a VERY short period. I don’t know about the long term wisdom of this though, will prolly end up killing a few batts this way….

      The strengh in having a custom charger is the ability to be able to increase the charge time and current. You can get some really amazing results from doing this. Below is a table of my results so far.


      As you can see the run time varies incredibly depending on the load. Charging at 1.1A for 54Secs gives me 21 minutes of runtime, for 5 minutes charge I get 50min!!! No load is the car upside down on my test bench. Fwd load is the car running fwd only with no steering, Fwd + Steering load is the car going fwd and turning to the left all the time.

      How did I do this? I put the car on the end of some sewing thread and wound the string around a center pole. Check the video here of how I did this test.


      The car appears to run slow because in this particular video the steering is set to left, causing a lot of resistance to the motor. I did this because to gain an accurate runtime I needed to be able to simulate a normal play session as much as possible. Given the figures I’ve attained you will probably find that the realistic runtime of a car is 15%-30% greater given that you don’t always have fwd+steering on all the time.

      To keep the car going I butchered a controller and shorted the Fwd and Left terminals as shown below.


      Keep in mind all the figures above are based on the stock 50mAh TOMY battery. Once I get it all in a neat little case I’ll post some more pics. I might even start selling them if the interest is there, lol!



    • #28361
      • Posts: 1290

      Good stuff Ph2t, its coming along nicely.
      And thanks for the acknowledgement.:D


    • #28363
      • Posts: 1124

      Nice as always ph2t:) Nice work on the vid as well. How did you cut and paste a spreadsheet in your post??

    • #28367
      • Posts: 2088

      Prez, I did a PrntScreen and copied it into paint. Then I cropped off the excess crap and saved it as a JPG.

    • #28372
      • Posts: 1321

      damn ph2t, you always seem to surprise me.

    • #26245
      • Posts: 80

      Hi Ph2t,

      you sound like the man for my question :D. Or anyone else who would like to answer :smiley2: I bought a k-2808 regulated power supply from dick smith. 1.2V To 37.5V and max 1.5A

      excuse my ignorance, :blush: as I though these kits where made for little kiddies and it would take me like two seconds to put it together. Even with my lack of electronic knowledge.

      I bought it so I can vary voltage and current, so I can charge my bits depending on dual, tri cell, single cell modded cars, and also choose between a slam charge or a more gentle one. From the description on the pack, this kit is meant to do that as it states it on the front page quote “combined voltage/current limiting” anyhows that is what made me buy it :p

      But now that I have opened the kit and there is only one varaible resistor :sad:. And after reading the 6 page essay they supply with the kit. I think I have figured out the following. . . excuse my lack of elecrical terms etc. first time tech building hee hee

      Number One:

      I can vary the voltage by varying the resistor that sits between the “adj.” terminal of Volt reg LM317 and “voltage out”(which is ground on the load side).

      Number two:

      I can vary the current by varing the resistor that sits between the “Out” terminal of the Volt reg. LM317 and the DC out terminal(which is the + terminal on the load side)

      I know there is a alot of other components in the circuits which manage to link up the out terminal with the adj. etc. etc. but I thought that was the easiest way to put it.

      I Think those two statements are true obviously it would help you a lot to answer my question if I posted a schematic but I can’t :sad:.

      Don’t be two fussed if you don’t understand I have some people I can ask, just that there not here right now :smiley2:

      Also read in some forum, that using linear variable resistors are not so good as when you want to change current/voltage by a small notch at the lower and upper range of the resistor it becomes touchy. Is there such thing as a non-linear resistor?? did you have this problem?

      Ultimately I would like 2 dials one to turn up or down the voltage and the other for current.

      Clear as Mud??? :p

      thanks in advance:D

    • #39076
      • Posts: 1290

      Charger theory 101…..I can feel a long post coming on.

      Perri, let me try and make a start on an answer for you, ph2t will probably hit you with schematics, graphs and a video at 1.00am (lol :), just kiddin’ ph), but maybe I can provide some preliminary explanation here.
      Firstly, do you have a multimeter, because you are going to need one. Even just a $10 digital multimeter will do fine. Two of them would be ideal.

      Unfortunately you cannot simply adjust the current with a variable resistor, its not that easy, the current will be determined by the voltage supplied to the battery. More on that in a minute.

      Just to clarify a few things, on an LM317t the variable resistor between the ADJ terminal (pin 1) and ground will adjust the output voltage. The resistor between Vout and ADJ is a feedback resistor (of about 200 to 400 ohms), its fixed and it makes the output more stable, you cannot change the curent by varying this resistor. These are all the lm317 needs to operate as a voltage regulator.

      Build the power supply as per the instructions and then put your multimeter accross the output to test that you do indeed have a variable output voltage that you can control.
      Then put your mulitmeter (or the other multimeter) in series with the positive output terminal and connect a single cell to the power supply. (positive output to positive on the cell, negative out to negative on the cell) The minimum output of a LM317 is 1.27 volts, this isnt enough to charge a cell, so you should see almost no current going to the cell. Turn the variable resistor VERY slowly to increase the voltage accross the cell and you should see the current into the cell increases rapidly. It doesnt take much to get 1 amp running into the cell. Be careful though, your 317 is only rated at 1.5 amps and will shutdown when it gets too hot.
      When you see 1 amp running into the battery, check the voltage accross the power supply, you will probably find that you need as little as 1.4 or 1.5 volts accross the cell to push an amp into the cell. This can be your first setting for charging a single cell car. 1 amp for about 90 seconds makes for a reasonable amount of charge and a decent run time.
      You need to adjust the voltage and check the current and write them down and this will form a list of steps, that you can go back to if you want to charge the same type of cell. eg single cell 1.5v charge for 90 secs @ 1amp, dual cell 3.0v charge for 90 secs @ 1.2 amps, etc etc.
      For a full charge, charge at about 5mA for 12 hours, this will fill a standard cell overnight. Quick charge at just under 1.5amps for 1 to 2 minutes, but keep an eye on how warm the cell is getting. Heat whilst charging will prematurely kill the cell
      You are right about the adjustment being touchy. Try putting a 2 ohm 5 watt resistor in series with the cell. The reason for this is a long story, but it will help moderate the current that flows into the cell as it is charging.
      I hope this is of some help, well done on taking on a project like this. Charging BCGs with an LM317 power supply is not the easiest way, but it is effective. Good luck with the project, let us know how you go.

    • #26121
      • Posts: 80

      Thanks Micro Amps that helps,

      I will take baby steps, There still seems to be alot more learning for me to do, So i will build it and experiement as your description.

      I hope ph2t and your self will rest easy tonight I am not in a hurry to complete this project:smiley2:. I figured it was about time I took on something a little challengeing. My father is an electrician I’m sure he can help me but he happens to be on the other side of the world(literatley!!) at the moment and won’t be back for a few weeks yet. Thought I might impress him If I got it done before hand though :shy: . . I certaintly will keep you posted thanks again:D

    • #26111
      • Posts: 80

      ohh yes I have multi meter :smiley2:

    • #24888
      • Posts: 400

      if you make a few let me know right now im just useing a novak rihno charger with 2 wires soldered to the bcg charger dock. “really dont like pumpin that meny volts throught my bcg”

    • #24606
      • Posts: 2563

      VR-4, i found that method didnt work, my charger would detect that the rx was ‘on’ in the car and would refuse to charge it.

    • #24658
      • Posts: 1038

      I had planned to try and design a charger like this, only mine was not a variable time unit, so you have outdone me there.

      I did however plan to have 4 car terminals on it, so I could sync charges for 4 cars before a race. This would give everyone equal footing, and roughly an equal run time, so no one dies after 2 laps, ending the race early.

      ToyEast sell the charger terminals seperately, but setting up 2 screws per car to poke through the plastic jiffy case, set at the right height and distance apart would work just as well. Al lthat would be needed then is something to hold the car to those terminal points, like an elastic band, or butcherred bulldog clip, clothes peg, etc.

    • #23016
      • Posts: 143

      Hey Ph2t,

      You wouldn’t mind giving us a schematic of your charger would ya? 😀

Viewing 12 reply threads
  • You must be logged in to reply to this topic.