(ET) LEDs

["Robert" <euclid delhitel net>]

Charlie,
LEDs are best if current regulated not voltage regulated. What that means is 
that the control circuit should limit the current to the LED regardless what 
voltage you hook them up to. IF you lights are designed to run specifically 
on 36 V than the design should current limit the LED at that voltage to give 
you optimum light for the LED they are driving. You can check your circuit 
to see if it is functioning correctly by finding out what LED it is driving. 
Once you get the LED designation look up the data sheet on the net to find 
the maximum current it should run under. You can then isolate the LED from 
the drive circuit and test it with a variable power supply. You can also put 
an amp meter between the LED and the drive circuit to see if the current is 
up enough, sounds like your current is off to me. Here's  a general guide 
line to figure your current. A one watt LEDs runs about 350 ma. (.350 amps). 
For every watt figure about the same 350 ma. So a 5 watt LED should run 
about 5 x .350 or 1.5 to 2 amps, for example
Usually switching regulators that control LED current can run just about any 
voltage up to the switching regulator limit from their spec sheet. Once the 
voltage gets above their minimum input voltage the current should be 
constant.You can try checking to see if the current to your LED varies by 
varying the input voltage to see what you get. I'll be you're current 
limiting well below the working voltage of your LEDs.

Rob

Message: 1
Date: Mon, 18 Feb 2013 11:52:40 -0500
From: Charlie <medievalist gmail com>
To: Elec-Trak <elec-trak cosmos phy tufts edu>
Subject: (ET) Disappointing 36vdc LED headlight results
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A couple months ago I bought socket-compatible 36v LED lamps for the
headlights and dash light of the I5.  They were expensive and took a
long time to ship.

I thought I'd just be moving one wire - I forgot that the I5 has a
12vdc horn which is jumped into that circuit (Geo's site has pictures
of the AP69 horn and wiring).

But anyway I hooked them up last week.  They fit perfectly, correct
bases and polarities.  The dash light glows weakly at 12v or 18v but
works well enough for the purpose at 36VDC - I consider that one a
success.

The headlights do not come on at all at 12v or 18v, glow weakly at
24v, and behave kind of strangely at 36vdc.  When you flip the switch,
the LEDs flash very brightly, brighter than the old 12v incandescents.
But that lasts only a fraction of a second, then they settle down
into a useless, weak glow no more illuminating than a single firefly.
You can do this repeatedly and they flash/glow every time.

Very disappointing.  I am considering unsoldering the unit, to see if
it has semiconductors under the LEDS.

--Charlie