OT: LED lighting configuration...

[Paul Koning]

> On Apr 29, 2016, at 4:10 PM, Bill Sudbrink <wh.sudbrink at verizon.net> wrote:
> 
> Paul Koning wrote:
>>> On Apr 29, 2016, at 3:32 PM, Bill Sudbrink <wh.sudbrink at verizon.net>
>> wrote:
>>> 
>>> ... The "bulbs" are labeled:
>>> 
>>> 15F18120-45 15 watt 36vdc constant current
>>> 
>>> I'd like to put four in a fixture and I'm trying to
>>> understand what kind of driver I need and how to wire
>>> it.  I was thinking of using a Mean Well LPF-60D-36
>>> like this:
>>> 
>>> http://www.ebay.com/itm/Mean-Well-LPF-60D-36-AC-DC-POWER-SUPPLY-
>> Dimmable-LED
>>> -DRIVER-36V-60W-CLASS2-
>> /161857068172?hash=item25af6edc8c:g:9hQAAOSwA4dWHVn5
>>> 
>>> and wiring the "bulbs" in parallel to it.  But after
>>> realizing that I'm not completely sure what a "constant
>>> current" power supply does and doing a little "googling"
>>> I don't know if that's the right approach.
>> 
>> A constant current supply is one that delivers a constant
>> current to a varying load (within limits) just as a constant
>> voltage supply delivers a constant voltage to a varying load.
> 
> Ok, I figured that much.  The problem/question is why there
> are no Amp ratings on anything?  Assuming the DC equation:
> 
> Watts = Amps X Volts
> 
> I want a constant current supply that "pushes" 0.41 Amps.
> A little more googling reveals that the above supply is
> rated "1.67A output".  This seems to support the W=AV
> theory.  So, do I want a PS labeled "15 watt 36vdc",
> regardless of how many bulbs I want to drive?  You say
> "within limits".  What specification do I look for to
> understand the limits?

15 watt 36 V is an odd spec for a device that needs constant current.  What it seems to translate to is 400 mA device current, 36 volt nominal operating voltage.  That's perhaps 10-12 LEDs in series, since each has a forward voltage around 3 volts, perhaps a bit more.

If you have a supply rated for constant current operation, 36 volt or so, settable current, you could use that, crank the current setting down to 400 mA.  If it's a fixed supply (36 volts 60 watts, i.e., 1.66 A) then that would not work.

	paul