car battery charger not working

Discussion in 'General Electronics Chat' started by bear1, Jan 6, 2013.

  1. bear1

    Thread Starter New Member

    Jan 6, 2013
    1
    0
    I have a Mac Tools brand battery charger model BCH066. the charger reads voltage but not amperage and does not charge the battery. you can hear it running but when I put a volt meter to the leads it shows barely 12 volts,even on the volt meter on the machine. the amp meter does not move at all. looking inside I do not see anything out of order like frayed wires. what should I be looking for?
    any ideas before I venture any further?

    Thanks
    Vinnie
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,057
    3,819
    Get a 4.7 ohm, 10 watt resistor (big white ceramic type) and connect that to the charger leads. Then measure the voltage when it has this load connected to make sure it is really broken. Current will only flow when a load is connected.

    If you confirm it is really broken, then you should look for the two big parts (transformer and rectifier). Unfortunately, the fact that it is able to output 12 volts means both are working and some control circuitry is then messed up. Look for a schematic on the inside back cover. More troubleshooting info may be there.

    My guess is that your battery is bad and the unit works OR you are trying to test the unit when a load (battery or low value resistor) is not connected.
     
  3. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Connecting a 4.7 ohm resistor to 12V will result in over 30 Watts. The resistor will disappear in a puff of smoke.
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    It may be better to test it with a cars headlight (12 Volts 55 Watt).
    (if it is a halogen lamp. Do not touch the glass).
    If it turns on, it will get warm pretty soon.

    Bertus
     
  5. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Make sure it's a 'dumb' charger. Mine is so smart, it won't put anything out unless it detects a connected battery. If you have a smart charger, you'll need to connnect a battery and measure the rise in voltage when connecting your charger.
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,057
    3,819
    I just looked to see if this might be a smart unit or an old school box. It is actually a MAC model, not SnapOn, and it looks very old school, and industrial sized capable of jump starting cars with dead batteries (charge, boost and test features).

    The switch or relay that allows you to switch from test to charge and boost mode may be damaged (arc welded into place), corroded, or otherwise scortched. If it is a relay instead of a switch, look for something that looks like a small transformer (relay). It may also be referred to as a "contactor" in the schematic. It may just look like a plastic box (1 to 4 inches per side). If you find a relay box, listen for a click when you turn from test to boost or charge, the relay should magnetically switch the circuit on and off.

    Good luck
     
Loading...