lm3914 and PWM?

Discussion in 'The Projects Forum' started by bjhbjh, Sep 24, 2008.

  1. bjhbjh

    Thread Starter New Member

    Jan 4, 2007
    3
    0
    Hi,

    I am running some heated gloves and sox while riding my motorcycle. Flat out each glove / sock draws 1 amp. 48 watts total for all garments, thats a lot for a m/c to power!

    I have a pair of variable pwm controllers to regulate the power/heat to the sox and the gloves independantly of one another, in pairs.

    I am concerned though about the total draw from the vehicle's electrical system and I'd like to keep it to 1 amp max total for gloves and sox. I'd like to have a simple no fuss indication of the total current draw from the bike. A green light for <1amp and a red light for >1 amp.

    I'm thinking of putting a current shunt, of say 1 ohms, in the garment ground circuit so that I can use an LM3914 to give me the indication. I am unsure however how the LM3914 will react to the pwm nature of the current through the shunt and what kind of filtering to apply to its input signal ?

    Google and I, cannot seem to find any references to 3914's in pwm environments, try as I might.

    Advice?

    The other way to do this of course is to use ganged pots on the pwm controllers so that c/w is say more heat to gloves less to sox and cc/w is the other way around. Then I'd limit the max duty cycle with fixed resistors so neither could go more than 50% dutycycle. Lights are cooler though and the 3914 method gives more flexibility.

    Thanks,

    Brian H.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    You could try a capacitor in parallel with the 1 ohm resistor. Otherwise, you would be PW modulating the LEDs along with your heaters.
     
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