UPDATE:
For grins, I had the LEDs from a second bulb. It fully illuminated at the
same 80 volts over 14 LEDs at 60 mA, but was 100% linear among the LEDs.
Every one of the LEDs started dim and ramped up linearly and identical to
each other just as one would expect in a series string.
A retest of the original set still showed the totally erratic threshold
effect of each of the LEDs flicking on and off until all were on at the same
80vdc and 60 ma. -still unexplained-
-Original Message-
From: Robert Bruninga
Sent: Friday, July 27, 2018 10:04 AM
To: Electric Vehicle Discussion List
Cc: Robert Bruninga
Subject: RE: [EVDL] Reduce EV: Charging load on the grid ... LEDs
> If you're running the LEDs on 120vac, the voltage drop needed is much
larger.
The 60W equivalent I just took apart had a full 14 LEDs in series but still
used a PWM controller.
It took 80 volts DC to get the LED's to their proper brilliance. So just a
small resistor will do.
This is just the metal disk with the 14 LEDs all in series, no other
electronics.
What was interesting was that 3 came on at around 15 volts, then more and
more came on as the voltage was raised. And they shifted back and forth at
various levels until they were all on. Since the bulb was rated at 9 Watts,
and assuming 80% PWM efficiency, then I assumed the LED's were rated at 60
mA. And that took 80 volts.
All the flashing back and forth as each began to illuminate surprised me.
It was almost as if there was a threshold effect. As a new LED decided to
illuminate, then the series string suffered due to the greater current and
so all the other LED's adjusted. Some ablve and some below threshold.
All being in series, it looks like there is a significant variability in
their characteristics. But once I hit 80 volts the current above that was
linear. But at 80 is also where it got to 60 mA and I did not go much
higher.
I was using a regulated variable DC supply with no series resistor (Supply
was current limited at 120 mA).
PS, this divides out to be about 5.7 volts per LED. Much higher than the
2.8 mentioned?
Bob
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