tbonz
Full Member
Posts: 162
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Post by tbonz on Sept 23, 2006 18:25:07 GMT -5
I am installing one of the mini speedos that Mike's sells. The neutral lamp doesn't want to light. I regular 12 v bulb ill light right up, so the switch is sending power, but the speedo neutral won't unluss I jiggle the key. I tried wiring the oil lamp instead to the neutral wires, and same thing, doesn't want to light unless you turn the ignition a little past its proper point.
Are these know to be fussy about the power they get?
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Göran Persson
Full Member
Senior Technical Advisor
Wellington - New Zealand
Posts: 183
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Post by Göran Persson on Sept 24, 2006 3:59:40 GMT -5
Hello tbonz,
The lights inside some of the new meters are LED's
and are therefore polarity sensitive.
Have you checked that the polarity is correct?
Best Regards
Göran Persson
New Zealand
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tbonz
Full Member
Posts: 162
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Post by tbonz on Sept 24, 2006 22:07:39 GMT -5
I will check. The wiring is a disaster of tape wads and shortcuts, so who knows. Thanks.
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tbonz
Full Member
Posts: 162
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Post by tbonz on Sept 26, 2006 0:13:40 GMT -5
Oh, man. I am a dope. I assumed the brown lead, since it had a fork and some other indicators on it, was a ground. Didn't know the neutral switch was a single wire switch on the ground side of the light. So I ran current through the LED backwards for long enough that it doesn't light anymore. If I were less honest, I'd send it back. Any way to replace an LED? Superficially the unit looks sealed.
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tbonz
Full Member
Posts: 162
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Post by tbonz on Sept 26, 2006 11:43:30 GMT -5
"Because the voltage versus current characteristics of an LED are much like any diode (that is approximately exponential), a small voltage change results in a huge change in current. Added to deviations in the process this means that a voltage source may barely make one LED light while taking another of the same type beyond its maximum ratings and potentially destroying it.
Since the voltage is logarithmically related to the current it can be considered to remain largely constant over the LEDs operating range. Thus the power can be considered to be almost proportional to the current. To try and keep power close to constant across variations in supply and LED characteristics the power supply should be a current source. If high efficiency is not required (e.g. in most indicator applications), an approximation to a current source made by connecting the LED in series with a current limiting resistor to a voltage source is generally used.
Most LEDs have low reverse breakdown voltage ratings, so they will also be damaged by an applied reverse voltage of more than a few volts. Since some manufacturers don't follow the indicator standards above, if possible the data sheet should be consulted before hooking up an LED, or the LED may be tested in series with a resistor on a sufficiently low voltage supply to avoid the reverse breakdown. If it is desired to drive an LED direct from an AC supply of more than the reverse breakdown voltage then it may be protected by placing a diode (or another LED) in inverse parallel."
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