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Flashing bulb — Parallax Forums

Flashing bulb

LightfootLightfoot Posts: 228
edited 2006-11-12 14:09 in General Discussion
I have a flashing light bulb in parallel with a steady burning one powered by a regulated DC power supply. How come when the flashing light turns on the steady one dims slightly? I tried several capacitor values but they seem to make no noticable difference. Without the regulator the problem is worse.

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Well well, I'm seeing things, three of them.

-Stanley Blystone

Comments

  • stamptrolstamptrol Posts: 1,731
    edited 2006-11-12 01:34
    Assuming the regulator is working OK, the only thing that can affect the two lamps in parallel is the voltage drop in the wires feeding them. When both are on, the current drawn is at maximum and any IR drop in the wires is highest. When the flasher turns off, the current drops, the IR drop becomes less and the remaining bulb brightens slightly.

    You can confirm this by using a meter or 'scope across the bulbs.

    Similarly, if each bulb had its own set of wires running back to the regulator, the only change in voltage that would be observed would be that of the regulator.

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    Tom Sisk

    http://www.siskconsult.com
    ·
  • LightfootLightfoot Posts: 228
    edited 2006-11-12 02:48
    The regulator is rated at 5 amps and the power supply is 3 amps. The wires that supply the current are 22 gauge. I do know the voltage is dropping because of the flasher, what should I do to fix the problem?

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Well well, I'm seeing things, three of them.

    -Stanley Blystone

    Post Edited (Three of Them) : 11/12/2006 2:56:13 AM GMT
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  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-11-12 04:14
    Like stamptrol wrote, you could wire each back to the source with a pair of wires each its own.· The resistance of a filament increases as current through it increases.· The current isn't a constant, when you turn it on there is an initial surge (or "in-rush".)· Using a "stand-up cap" to buttress the non-blinker presents problems of its own: the in-rush to charge a capacitor of sufficient capacity to do the job here (a "computer-grade" sort,·several thousand uF. )

    Post Edited (PJ Allen) : 11/12/2006 4:21:17 AM GMT
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  • LightfootLightfoot Posts: 228
    edited 2006-11-12 05:58
    That flasher thing I have is kind of cheap anyways, a more expensive device should have that resistor/diode/capacitor built in (in my opinion). You also don't need the resistor, the diode and cap got rid of it.

    Thanks guys.

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    Well well, I'm seeing things, three of them.

    -Stanley Blystone
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-11-12 13:47
    Three of Them said...
    The flasher thing I have is kind of cheap anyways, a more expensive device would have that resistor/diode/capacitor built in...
    The diode and cap wouldn't be a part of the flashing bulb as it is, afterall, shoring up the non-flasher's situation.
    Three of Them said...
    You also don't need the resistor...
    Actually, the resistor is needed, because it softens the in-rush to the cap when it's discharged and practically a short-circuit, however briefly.
  • John R.John R. Posts: 1,376
    edited 2006-11-12 14:09
    Three of Them said...
    The regulator is rated at 5 amps and the power supply is 3 amps. The wires that supply the current are 22 gauge. I do know the voltage is dropping because of the flasher, what should I do to fix the problem?

    How about increasing the wire size in order to reduce the resistance? While 22 Ga is probably fine for the 3 Amps, it will have some resistance, especially if there is any meaningful length involved. How about replacing with 16 Ga?

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    John R.

    8 + 8 = 10
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