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Parts, Plans and Petitions

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Posted 02-03-2009 at 01:00 PM by mattW
Tags schematics

It's been a while between posts, life's been busy and I've been waiting for parts, but here's where I'm up to now. I've bought a bunch of gear- Motor assemblies, batteries, charging kits, throttle, soldering station, fuses, an LED headlight kit and an Amp Meter, most of it came on Thursday and I bought some today. I built the first battery charger kit today, it testing my soldering skills, but it seems to charge the battery which is a good sign. I need to work out a more permanent plug system for between the charger and the batteries (any suggestions?). I also have a key ignition and 24V controller in the mail. I've revised the wiring diagram making it cleaner and with more features, take a look:

I was hoping to ask some questions of some more experienced electrical types, like I have said in previous posts I haven't ever done anything like this. The first question is should I have a fuse on the battery side of the controller (if so would I make it 20A or something different)? Also how can I limit the current coming out of the controller through the motors? It can put out 20A but I only want 10, 5A in each motor max. Finally is there anything noticeably wrong and/or missing from the diagram? I'm included an amp meter cause there was a cheap one left at the electronics shop I went to, now my driver will be able to tell if he is about to blow a fuse (I bought slow blow fuses). I've made a couple of changes to the mechanical design of the car as well but I'll talk about that in another post. Its funny how my feelings about this project swing so easily from a confident "this isn't too hard" to a "I am so over my head here" and back again. The joys and terrors of the unknown!

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Total Comments 9


  1. Old Comment
    One thing I note is that the amp meter is only going to show the draw on 1 motor.

    It should be placed in line with the neg cable from the battery pack.

    It must be a shuntless, direct reading meter, or it will fry on the first run.

    Your ignition switch won't carry the load for long. You will need a contactor (relay) rated @ 24 volts.

    Your fuse should be on the pos cable going to the controller and it should be 50+ amp.

    Others will check it out also....
    Posted 11-03-2007 at 11:15 PM by Coley Coley is offline
  2. Old Comment
    mattW's Avatar
    Thanks for your feedback, I've made a revised drawing with your suggestions. I've also taken out one of the LED headlights because they have 18 LED's each and I'm just going to have 9 on each side instead. The key I was intending to use looks like this (still in the mail):

    It is built for scooters so I'm pretty sure it can take 24V or will I still need a contactor? I think I am planning to limit the current to the motors by adding a variable resistor in series with the throttle to adjust the signal to the controller. Would that work?
    Posted 11-05-2007 at 06:11 AM by mattW mattW is offline
  3. Old Comment
    mattW's Avatar
    OK i have done some more reading and i think i understand. The switch will work fine for turning the car on and off while stationary but when the car is moving the current will arc across the switch and fry it, is that right? So i need a contactor for if the throttle stays on and the car needs to be turned off while moving. How do you work out what the maximum current will be out of the batteries in order to choose what rating the contactor needs to be? Can anyone else see anything wrong with my new diagram?
    Posted 11-07-2007 at 09:22 PM by mattW mattW is offline
  4. Old Comment
    Yay I can post!

    Ok, I've added the wiring diagram on the Big Red Car page on my site if it helps


    Posted 11-12-2007 at 06:22 AM by BjBlaster BjBlaster is offline
  5. Old Comment
    mattW's Avatar
    Ok third time lucky, here is another more revised diagram, now that I have the controller and know how it works. There are currently three ways to switch off the controller. The first is by letting go of the throttle, if that fails you can also hit the brakes or finally turning off the ignition key. Each of the above has its own input into the controller which assumable has its own relays within it. Do you think this three level safety system is enough or do you think I need another relay to cut the power independent of the controller? Also Bj has a couple of diodes in his circuit, do I need any in mine? Thanks heaps for all your help everyone .
    Posted 11-13-2007 at 06:38 AM by mattW mattW is offline
  6. Old Comment
    The diodes in my circuit are just for the tail lights / brake lights so they don't come on when it's "docked" and so it has two levels of brightness, on dull with the ignition and bright when brakes are applied.

    I also forgot to add my brake dummy load. My second relay for the brake actually dumps the motors into a 25Watt 0.5 ohm resistor as an electric brake. It's very effective in slowing the whole thing down and the cable brake just stops it from rolling down the hill. I've updated my schematic to reflect this.

    You circuit looks good, it will work fine, the only thing is the voltmeter will be on all the time (not that that is a problem it's just cosmetic) and if you want to add other accessories later like a horn or whatever you won't be able to switch them with the key because the key input on the controller is a low current signal (+5V) and is just for the controller enable.

    Hopefully the power indicator output on the speed controller has enough current to run the relay coil and the headlights as shown in your diagram. Personally I'd use the key to handle this load and feed the controller enable signal (usually 24V but can be 5V) from the key using a regulator if required to get a 5V enable signal.


    Posted 11-13-2007 at 05:03 PM by BjBlaster BjBlaster is offline
  7. Old Comment
    BJB! I just checked out your site. You are a very Busy guy. I am in awe.
    I fear I've waited too late in life to ever be able to learn and apply electronic skills like yours to the constant stream of ideas that run through my head. Man, if I only knew what you know.
    Posted 12-10-2007 at 06:22 AM by eRubicon eRubicon is offline
  8. Old Comment
    rbgrn's Avatar
    We all started from not knowing anything! Put your mind to it, rubi!
    Posted 12-10-2007 at 01:33 PM by rbgrn rbgrn is offline
  9. Old Comment
    Originally Posted by eRubicon View Post
    BJB! I just checked out your site. You are a very Busy guy. I am in awe.
    I fear I've waited too late in life to ever be able to learn and apply electronic skills like yours to the constant stream of ideas that run through my head. Man, if I only knew what you know.
    I've glad you've been inspired I've got a few more things to throw up on the site, but I'll wait until after christmas as it's a bit hectic right now... stay tuned!

    Posted 12-10-2007 at 07:14 PM by BjBlaster BjBlaster is offline
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