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MEXICOWANDERER's avatar
MEXICOWANDERER
Explorer
Jun 09, 2016

Turn Side Lights Capacitor Sizing Formula

I have to be careful because the following is a description of a proposed capacitor charging cycle timing circuit.

OBJECTIVE: Convert flashing turn signal to continuous signal for side illumination lighting.

DESCRIPTION: There will be one circuit for each side

SIGNAL: 12 volts. Duty cycle one second 50/50

LOAD 18 watt each side LED

Signal from turn signal switch will pass through a diode to prevent feedback. The pulse will charge an (?) rated electrolytic capacitor.

The capacitor charge will feed an 88 ohm coil Tyco battery fed relay, rendering a continuous signal as long as the signal pulse exits.

SENSITIVITY: I do not want an "overly" long time to elapse between initiation of trigger and lighting of load. Nor do I wish to have an excessively large capacitor capacity which will keep the side load lamp lit "too long" after the trigger pulse is removed.

Triggering pulse (for capacitor charging) can supply up to 10-amperes st one second intervals.

Remember the triggering pulse feeds the relay coil not the load.

I have today only to order the caps and intend to order 3 different uf just in case. I am going to choose 56 volt rated for longevity.

Too many years since college and sundial response internet has failed to download R/C and L/R/C charts.

Thanks

11 Replies

  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jun 10, 2016
    18 watt LED lamp. Washing machine size electrolytic...

    I'll go the Delay Off timer route. 5-seconds otter do it.

    Why 18 watts? I'm going to lay prismatic lens diffuser plastic sheet. it's going to light up the entire side. Ooooooooo hard on other driver's eyes, you say? Not when the top inch of the 4-inch lens is blacked out with reflect one side tape.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Jun 10, 2016
    With LED lighting why not just put the cap across the socket and put the diode feeding it.. Radio shack has 5 volt caps at 1 farad as I recall, 3 of those in series (15 volt should do it.. or a decent 20 volt rated electrolytic.. The LEd's only draw about 0.2 amps so given the one second flash rate that should do it, Wire resistance should be enough to protect the fuse but you can add say half an ohm to one ohm if you need to.
  • Beverley_Ken's avatar
    Beverley_Ken
    Explorer
    Jun 10, 2016
    How about just picking up the power for light from the tail/marker light circuit and cutoff/cap the wire from the turn signal circuit.
    Or add a dual filament bulb light fixture and have both.

    Ken
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jun 09, 2016
    Yeah I agree. I have been dosing myself with pure start-from-scratch do it myself for too long.

    A delay off timer could care less about repetitious input pulses.

    I already ordered a pair of 10-amp adjustable timers from Amazon. Enclosed, a better package.

    Re-inventing the wheel is embarrassing.
  • BB_TX's avatar
    BB_TX
    Nomad
    Jun 09, 2016
    Why not a simple adjustable 12 volt off-delay time delay relay. Energizes immediately upon power application and de-energizes after set time. Time set slightly longer than flasher half cycle time.
  • DrewE's avatar
    DrewE
    Explorer II
    Jun 09, 2016
    I think a more reliable solution would be to use some sort of a proper timer circuit. Something like the ubiquitous 555 timer feeding a solid state relay or a traditional relay via a driver transistor would give a more reliable timing, have a much lower initial current when switched on, and use a much smaller and less costly capacitor. Putting in a trimpot would allow the time delay to be adjustable. The data sheet has lots of nice charts giving the timing for various timing capacitor and resistor combinations.

    (Actually, if I were doing this, I would rig up a little microcontroller to do the timing because I like little microcontrollers, but there's no real objective reason why it's inherently a whole bunch superior to a simple timer.)
  • boogie_4wheel's avatar
    boogie_4wheel
    Explorer
    Jun 09, 2016
    BB_TX wrote:
    Just curious. Side lights would already be on after dark with headlights on. What benefit comes from turning the side lights on steady during the day time? Apparently I am missing something.

    Think side/turn flood lights for illumination.


    Be patient with me, it has been awhile since I've worked with SS relays. I remember the 'coil' having next to no load.
    Would/could you parallel the coil with a resistor to pull down the voltage (bleed the capacitor) to de-energize the relay? If so, you could run a smaller cap and a higher ohm resistor, and adjust the resistor size to control the delay time until the light is shut off. Do you have any components now (a known capacitor size and a few resistors) to establish a baseline for what the SS relay load is?

    The 88 ohm coil is confusing me; I looked at it as an 88 ohm load on the cap and my cap size was determined based on that...
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jun 09, 2016
    TURN SIGNAL ON Means turning

    "Sidelights" are for marking not for driver visibility

    Once a turn is committed, it can become quite dicey if a deep dip is encountered.

    Some folks have 20/10 eyesight and can read the Wall Street Journal by the light of a full moon.

    I am not in that category.
  • BB_TX's avatar
    BB_TX
    Nomad
    Jun 09, 2016
    Just curious. Side lights would already be on after dark with headlights on. What benefit comes from turning the side lights on steady during the day time? Apparently I am missing something.

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