Please help me spot the issue...

Discussion in 'The Projects Forum' started by jwilli, Jul 1, 2009.

  1. jwilli

    Thread Starter Active Member

    Apr 21, 2009
    42
    0
    The circuit below is for a solar panel charge controller. It monitors the battery voltage and once the battery is fully charged, a relay activates a dummy load to drain the battery down to a safe level.

    The battery status LED's are working correctly and everything seems great except that the relay is not activating. Only the red LED is being lit. When the red LED is lit, the relay should activate, kicking over power to the dummy load.

    Could someone suggest to me why the relay is not activating?? Any help is MUCH appreciated!!!

    [​IMG]
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The Mosfet is a P-channel. But the circuit needs an N-channel Mosfet for it to turn on.
     
  3. jwilli

    Thread Starter Active Member

    Apr 21, 2009
    42
    0
    I just found the issue. I left out the stupid 560ohm resistor (R4). I just added it and now it works fine. I've been driving myself crazy on this for 3 days now!
     
  4. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    Audioguru,

    It is an N-channel MOSFET. Contrary to BJT, the arrow should point inside for an N-channel, and outside for a P-channel.
     
  5. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Its your own words against you. :confused:

    The R4 is in series with the RED led. How can the LED being lit without a series resistor?

    In addition, the stupid R4 would not prevent the relay from operating. :confused:
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Our OP meant that they didn't connect R5 to the gate of the MOSFET. If you look closely at the schematic, you'll see that they are close together, but there is no actual connection.
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    You have good eyes :D
    I could not see it :(

    Rifaa
     
  8. pilko

    Senior Member

    Dec 8, 2008
    213
    20
    I notice you are using a PICAXE 08M microchip. Do you have the code?
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    When I searched for the datasheet of an IRF610, the first one on the list was an IRF6100 which is a P-channel Mosfet.

    I hate to see parts drawn upside-down. Positive is supposed to be upwards.
     
  10. pilko

    Senior Member

    Dec 8, 2008
    213
    20
    I notice you are using a PICAXE 08M microchip. Can you supply the code?
     
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