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Arlec BC58112 v battery charger

Discussion in 'Electronic Basics' started by Roger Dewhurst, Feb 25, 2007.

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  1. I have an Arlec 12 volt battery charger which I accidentally blew up when
    the 3 pin plug touched the chassis of my truck while the leads were clipped
    to the battery. The circuit contains three resistors, what I think is a
    small Zener diode, two large diodes and a peculiar elongated glass tube with
    two wires leading in at one end. It has been glued in place between the two
    diodes and connects to the input from the transformer. The glass tube is
    about 30mm long and 5mm in diameter, It appears to be either gas filled or
    evacuated. It reminds me slightly of a diode valve. Could it be some form
    of capacitative device to smooth the waveform? Since the transformer
    appears to be OK I suspect that it is either this tube device or the Zener
    diode that has blown. Can anyone offer any suggestions? The Zener, if that
    is what it is would be about 12.5 volts, would it not? The charger cost
    less than $20 and a technician would charge twice that just to open the box!

    R
     
  2. Phil Allison

    Phil Allison Guest

    "Roger Dewhurst"

    ** That should not happen !

    The DC output terminal of a car battery charger should have NO connection
    to the AC supply ground conductor.

    You just found out the reason.

    Sure that Arlec charge was built like that or was it modified by some zealot
    to make it "safer" ??



    ** Sounds like a fuse that has blown.



    ........ Phil
     
  3. That makes sense. I should have written 2 pin, not 3 pin plug.
    No. I bought in new and can see no signs of modification. I had only used
    it two or three times.

    There is a two wire power supply to the primary of the transformer but a
    three wire output, two blue and one black. The two wire supply should be
    safe enough because the only metal parts that can be touched are the output
    clips. Everthing else touchable is plastic.

    When the power is on and the clips are on the battery none of the lights go
    on, but two should. Whe a clip is pulled off the battery, with the power
    still on, all the lights go on! That suggests to me that transformer is OK
    and the fault lies elsewhere. The LEDs are OK, the resistors appear to be
    OK and there is no reason for them not to be. The big diodes should be as
    tough as old boots. That just leaves the Zener (?) and the glass tube
    device.
    It does not look like any fuse that I have ever seen! It is a fixture and
    obviously not intended to be changed. It seems to be part of the rectifier
    section of the circuit. That there are only two diodes instead of four
    seems a little odd. It would have been easy enough to put in a four diode
    rectifier.

    R
     
  4. Phil Allison

    Phil Allison Guest

    "Roger Dewhurst"

    ** What crazy drivel is this ???

    There is no circuit between those pins and anything else.

    You need to work out what actually happened - cos your explanation is not
    right.



    ** Shame if the insulation in the tranny ever fails.....

    The unit is Double Insulated - right ?

    Has the double square symbol on it.



    ** A "last line of defence " fuse would NOT be fitted to allow user
    replacement.

    One often sees a bi-metal over current trip in the same spot.


    ** That is how nearly all battery chargers are made - makes for lower cost
    and less diode voltage and heat loss.

    Shame the AC tranny is under utilised.



    ........ Phil
     
  5. But it did. A bunch of sparks and now a dud charger.
    I should have put a couple of lines between the two statements above.

    *******************************************
    Thus:

    You: The DC output terminal of a car battery charger should have NO
    connection to the AC supply ground conductor.

    Me: That makes sense.
    *******************************************
    Indeed the resistance between the power supply plug pins and the secondary
    coil outputs appear infinite i.e there appears to be no connection between
    the primary circuit and the secondary and thus no connection between the
    power plug and the output clips.
    not right.

    I do not have an explanation merely a bunch of symptoms of the thing blowing
    up!
    It does carry the double square symbol.
    Is this a glass tube with both wires going at one end?

    If it is a 'last line of defence' fuse and the output is rated at 2.5 amps
    should I try replacing it with a 3.0 amp fuse?

    What are the chances that it is the Zener that has blown?
    El cheapo came to mind!

    Roger
     
  6. Can you post a picture on ABSE?
    Do you own a multimeter?
     
  7. Phil Allison

    Phil Allison Guest

    "Roger Dewhurst"
    "Phil Allison"

    ** So no current can flow and no damage can happen that way.


    ** Then your first para is pure fantasy.


    BTW

    Try replacing that glass tube thing with a 5 amp thermal cut out.



    ......... Phil
     
  8. A three wire output sounds strange - is it intended to charge two
    batteries with a common ground? How are you supposed to connect the
    three leads to the battery?
    Is this glass device 1.25 inches long by .25 inch diameter - if so, it
    sounds like a common North American fuse. The appearance of the thing
    inside the glass can vary depending on whether it is a fast-blow or
    slow-blow fuse.

    Two diodes sounds like a full-wave rectifier - a perfectly reasonable
    and common design. Four diodes are required for a bridge rectifier
    (also reasonable and common).
    --
    Peter Bennett, VE7CEI
    peterbb4 (at) interchange.ubc.ca
    new newsgroup users info : http://vancouver-webpages.com/nnq
    GPS and NMEA info: http://vancouver-webpages.com/peter
    Vancouver Power Squadron: http://vancouver.powersquadron.ca
     
  9. Phil Allison

    Phil Allison Guest

    "Peter Bennett"

    ** Err - the AC tranny has three output wires.

    The third ( black) one is the centre tap of the winding - allowing use of a
    two diode, full wave rectifier.



    ....... Phil
     
  10. Three wires from the secondary coil to the electronics but two wires from
    the electronics to the battery clips.

    My estimate was a bit on the low side! It is 40mm x 9mm exactly. That is
    a bit bigger. The white glue smeared over the glass makes it difficult to
    see what is inside. The tube is pointed at the end with no wires and
    flattened at the end with the wire inputs. Just inside the tube there is a
    dark coloured bead which appears to keep the wires separate. The battery
    charger is almost certainly made in China.
    A diode rectifier would only need a two wire input. What is the third
    (black) wire from the secondary coil doing? It does connect to one side of
    the tube device. The other side of the tube connects to the negative output
    and to one of the LEDs.
     
  11. My wife has the camera at the moment! And what is ABSE?
    Yes, and a soldering iron but I am not ready to start de-soldering wires
    until I have a better clue about what I am doing!

    R
     
  12. Phil Allison

    Phil Allison Guest

    "Roger Dewhurst"


    ** Ok - now it sounds like a PTC = positive tempco thermistor.

    Also known as Polyswitches.

    Jaycar sell them.



    ** Oh dear.

    Look up " full wave rectifier " on Google.




    ......... Phil
     
  13. Phil Allison

    Phil Allison Guest

    "Roger Dewhurst"

    ** " alt.binaries.schematics.electronic "

    Most news servers have it in their list.

    Great for schems, JPEGs etc.




    ...... Phil
     
  14. Subscribed to that but I have to wait for the camera.

    R
     
  15. Ross Herbert

    Ross Herbert Guest

    The Arlec BC581 is a current model
    http://www.arlec.com.au/pdfs/battery_chargers.pdf

    With these cheap and nasty chargers a common method of charge control
    is to use a thermal current switch, which is what I suspect the
    elongated glass tube is. Does it appear to have a metallic contact in
    it?

    To avoid any fancy regulation circuitry the idea was that the
    transformer operated at maximum voltage output up to its VA rating at
    all times and when the current exceeded a set value the thermal switch
    operated to cut off the charge current. After many successive cycles
    the battery voltage would gradually rise to the rectified output
    voltage of the transformer (which hopefully would be in the region of
    14V) thus the charge current would no longer be sufficient to operate
    the thermal switch. This is where the danger of these cheap chargers
    lies - they keep charging as long as the battery is connected and if
    not disconnected after a full charge is reached they will lead to the
    demise of the battery.
     
  16. Phil Allison

    Phil Allison Guest

    "Roger Dewhurst"

    ** What you did was this:

    The AC plug was resting on the car body with the two pins in contact with
    bare metal - no conduction until YOU connected the leads to the car
    battery IN REVERSE !!

    Large current pulses flowed in the secondary winding as you attached the
    battery clips generating large primary voltage spikes and hence the visible
    sparks at the AC plug pins.

    Then the glass tube thermistor device failed from the over current
    ituation - it is the only protection the charger has from reversed leads.




    ...... Phil
     
  17. It's a center tapped transformer with two diodes for full wave output. Quite
    normal.


    --
    ..

    --
    ..
    ..
    ..
    ..
    ..
    ..
    ..
    ..

    --
     
  18. jasen

    jasen Guest

    sounds like a self-resetting thermal, fuse. it's unlikely to be the
    problem if the cause was as you describe, if it works it shouls read
    as a low resistance (less than 0.1 ohm)
    does it hum when you plug it in? can you light up a small 12V lamp by
    connecting it to the output side of the transformer?

    Bye.
    Jasen
     
  19. There appear to be two parallel strips of metal terminating in something
    looking a bit like the points in an ignition system. The two strips of
    metal are separated by a bead at the input end. The 'points' appear to be
    fully closed.
    I see now that the two main outputs from the secondaty coil supply the two
    diodes and the centre tap supplies one side of this thermal current switch.
    The other side of the TCW is connected to the negative battery clip. The
    outputs from the two diodes are connected together and to the positive
    battery clip. The rest of the circuit, which is hard to follow, is in the
    middle somewhere. If the TCW is closed the charger should work as long as
    the secondary coil is OK? But the secondary should be protected against
    reverse current by the diodes and against excessive forward current by the
    TCW? That seems to leave the thing which looks like a Zener. Would that be
    a 12.5 volt Zener? On reading all the comments and thinking about it some
    more I think that I may have just connected the clips to the battery the
    wrong way round! I have been using a battery charger for years and have
    never made this mistake before, but I suppose that there is always a first
    time. Assuming that is what I have done which elements in the circuit would
    you expect to be destroyed?

    Roger
     
  20. Oops - I somehow read that as three wires out of the charger. Three
    wires from the transformer to the full-wave rectifier makes sense...



    --
    Peter Bennett, VE7CEI Vancouver BC, Canada
    peterbb4 (at) interchange.ubc.ca
    new newsgroup users info : http://vancouver-webpages.com/nnq
    GPS and NMEA info: http://vancouver-webpages.com/peter
    Vancouver Power Squadron: http://vancouver.powersquadron.ca
     
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