Forum Discussion

BStrummin's avatar
BStrummin
Explorer
Apr 21, 2015

12v Electrical Issues

Last fall I replaced the crappy loud exhaust fan in the bathroom of my trailer with a heng fan, and added one of the cheap PWM controllers. I also added a switch on the wall(converted from single to double) so that you could operate the fan while seated. It worked great for awhile, but now the whole circuit is doing something odd, and I've checked all the wiring in the bathroom backwards and forwards to make sure I haven't cross wired anything. The circuit itself will test at 13.5 volts. Both wall switches work. But neither the dual lamp nor the fan will power on. I can get a small LED to power on but it is dim. I've bench tested both the fan and the lamp assembly with a 12v power supply and they are fine, and pull very little power. I tried just bare wiring the fan from the negative block to where the positive feed leaves the circuit board, and when I do it on that circuit the red light comes on and there is nothing. Trying it on any other circuit and it works.

What's going on here? Is there something wrong with the circuit board? The fuse is fine. It's a WFCO-8935 in a circa 2008 trailer. Maybe I should try moving the feed to the bathroom to another block on the circuit board?
  • BStrummin's avatar
    BStrummin
    Explorer
    Apr 22, 2015
    Well the 12v fuse panel was the problem. I moved the positive feed from the existing bank to an unused one and everything is fine. I even reused the fuse. I wish I had an actual explanation but maybe a component on the board failed. I don't see anything obvious.

    Thanks for all the help.
  • scrubjaysnest's avatar
    scrubjaysnest
    Explorer
    Apr 21, 2015
    Sounds like a high Resistance connection some where, corrosion or loose connection. Both the fan and light want more current then the led and you said it was dim. Problem could be in either pos or neg side.
  • consumeratlarge's avatar
    consumeratlarge
    Explorer
    Apr 21, 2015
    Not familiar with the PWM controller for fans, but 2 observations:
    1. LED's used for lights actually will act as diodes, or one way valves for dc circuits, since they are light emitting diodes. So, they are polarity sensitive, somebody commented above about that.
    2. According to my old school lessons, PWM circuits need to be on an oscilloscope to see the 'on-off' cycle, and the voltage 'on' is always the full amount, or 12v in this case. That's my experience with those things, that you can't check them for function with a voltmeter.
    Just adding to the discussion with a couple of things to maybe consider.
  • RoyB's avatar
    RoyB
    Explorer II
    Apr 21, 2015
    I also fought a LED BOARD PROBLEM once where the fix was to just REVERSE THE TWO WIRES feeding the LED LIGHT. They were same color wires. This one was polarity conscious...
  • neschultz's avatar
    neschultz
    Explorer
    Apr 21, 2015
    From your descriptions I don't think this is it but I thought I would mention it anyway.

    I bought a few cheap PWM controllers and use them to control the brightness of our LEDs. Mine don't control the positive voltage.....they control the negative output voltage. Could this be tied into your problem?

    Norman
  • BStrummin's avatar
    BStrummin
    Explorer
    Apr 21, 2015
    Yup. Mine uses solid white for neg and this leg uses white with purp stripe for pos.
  • RoyB's avatar
    RoyB
    Explorer II
    Apr 21, 2015
    Just checking that you did follow house wiring rules when taping into the trailer wiring. A SOLID WHITE wire is always -12VDC or NEGATIVE GROUND. any other wire color including white wires with color stripes are +12VDC or POSITIVE.

    My trailer wiring from the 12VDC Power Distribution uses two wire conductors sometimes called BOAT WIRING with one BLACK wire for +12VDC and one WHIRE wire for NEGATIVE FRAME GROUND polarity...

    Roy Ken
  • BStrummin's avatar
    BStrummin
    Explorer
    Apr 21, 2015
    I don't think so because I've bench tested the fan by itself and the fan with the PWM with a separate power supply. They both work fine and only pull 1.8A at full speed. Also just wiring the fan directly in without it doesn't work either. I don't know enough about how the distribution center works but at this point I think I've tested everything else.
  • SoundGuy's avatar
    SoundGuy
    Explorer
    Apr 21, 2015
    If I'm understanding your description correctly does this not all point to that PWM being faulty? :h Perhaps you've exceeded it's ratings ... when I wanted to install one in the vent fan over the stove I made sure to buy one rated at 10 amps, not 5 amps.

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