dual dc motor control

Discussion in 'General Electronics Chat' started by nimrod, Oct 24, 2008.

  1. nimrod

    Thread Starter New Member

    Oct 24, 2008
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    To begin, I know just enough to be dangerous. That said, I will go forward with this repair project I took on that clearly is over my head. It's a powered three wheeled radio controlled golf bag cart. Two motors. The motor control looks proprietary (chinese). Board has one IC, four relays, 6 mosfets, 1 cap (50v-1000mfd) and a sub circuit board that appears to be a receiver that operates on 430 something mgz freq. Uses a small lead acid 12v battery similar to those used on lawn mowers (50amp) maybe? The thing is also controled manually with a switched Pot that has an LED in the power line. The thing will do nothing now. The LED will not light when the pot is switched on. When I check the voltage at the power input points on the circuit board I get .57 volts with a charged battery. I have removed the wires from the board and get the full 12 volt reading. What's going on here?
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Iy seems that you have a short circuit in your circuit. What is the switched Pot?
     
  3. hgmjr

    Moderator

    Jan 28, 2005
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    Can you post a few digital pics of the control box?

    hgmjr
     
  4. nimrod

    Thread Starter New Member

    Oct 24, 2008
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    I put it back together, so I don't know for sure, but I think it was around 10k.
     
  5. nimrod

    Thread Starter New Member

    Oct 24, 2008
    8
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    yes, give me a few minutes
     
  6. nimrod

    Thread Starter New Member

    Oct 24, 2008
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    My cam bateries are down, I thought I had some saved on the computer but I don't. I'll have to get back to you later, sorry
     
  7. nimrod

    Thread Starter New Member

    Oct 24, 2008
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    OK, here are some pics of the device.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    Nothing looks like a crispy critter. Do you have a meter? Can you check for continuity in the supply lines from the battery to the circuit? There might be a fuse open in the positive (red) lead.
     
  9. nimrod

    Thread Starter New Member

    Oct 24, 2008
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    Yes, I replaced the wire to the battery due to lousy connectors, thinking along the same lines, so I know the integerty of the supply line. The device lititure claims to have had automatic overload control. There is no schematic. I traced the origin to a web site in china that had to be googled for translation. Needless to say it is of no help. Can the so called protection be a function of one of the relays? and; can the relay be stuck? Or, is this 'protection' in the circuitry?
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    There's a bank of six TO-220 devices behind the relays. Looks like the center four could be the same type; the outer two have differently shaped tabs.

    It may be worthwhile to remove the bar that holds the devices against the heatsink to determine what they are. Additionally, that will allow visual inspection for possible "smoke damage"

    The STC12C4052AD (20 pin IC perpendicular to the wall) is an 8-bit 8051-compatible microcontroller. Unfortunately, the datasheet is written mostly in Chinese.

    D1 through D4 are likely transient suppression diodes for the relays.

    It might be helpful to know how much current is going to the controller. Use a high-wattage 1 Ohm resistor in series with the power wire, and measure the voltage across it. Since I=E/R, the voltage you measure across the resistor will be the amperage flowing through the controller.
     
  11. nimrod

    Thread Starter New Member

    Oct 24, 2008
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    Thanks, I've had the board out of the box and inspected all the parts for obvious damage and the thing is as clean as a whistle. To give you a little history, I've been into this thing before and rewired the hard wire control to the led and the pot (located on the handle). It traveled up through the tubing you see in the photo and was routed with solid wire. The antenna was also routed up this chase also. How anyone could expect the remote to work is beyond me. After the rewire and antenna replacement (routed outside with wire ties) the thing worked fine and the distance was increased several hundred feet. I put the shielded cable on the receiver that you see in the photo and striped the other end to the 430 mhz wavelength. The guy that owns it used it for nine holes and it worked perfectly. Then down it went with it's present condition. The only portion of the original wiring I kept is from the board to a connector, about a nine inch pigtail, this passes the continuity check.

    Thanks for the tip regarding the resistor, I will try that next and let you know the results.
     
  12. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    I think that your battery is in a bad condition. With no load you measure a full voltage but with a load on it, the voltages drops because its bad. Disconnect the battery from the circuit and take a 12 volt car bulb and connect it on the battery. See if the bulb illuminates and measure the voltage across it.
     
  13. nimrod

    Thread Starter New Member

    Oct 24, 2008
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    I think I found it, thanks for you input, as it turns out, the main battery conector has faulty solder connections, I havn't repaired it yet, however, it seems the only plausable cause at this time. The battery was up, I used your suggestions to test that. Thanks again.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    OK, good to go.

    However, any solid wire connections to off-board need to be replaced with stranded wire connections, with the exception of the RF cable.

    Finely stranded wire is best for applications like that; it will survive far more flexings than solid wire will. However, stranded wire may interfere with RF.

    Let us know how this project goes.
     
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