On 05/12/16 02:44, Dave Liquorice wrote:
On Sun, 4 Dec 2016 20:28:01 +0000, Tim Watts wrote:

A full brightness strip showing white takes a fair bit of juice.
Each
pixel draws around 60 mA (18.5 mA/LED), 240 pixels is as near as
damn
it 15 A! Depending on the display patterns a car battery might not
last very long. And car batteries don't like being deep discharged
either.

24V makes a lot of sense with long LED strings, but I don't think anyone
has done a version of these addressable LEDs...

I don't think there are any 24 V LEDs ... Higher driving voltage LED
strings have series connected LEDs which makes controling each one
individually a bit tricky.

Hmm. I looked at the separate driver chip for the addressable, the
WS2811. It does seem to show 1 LED = 5V supply and 3 in series = 12V, so
that would explain some of the addressable tapes that have 1 pixel=3LEDs
as the addressable element (being 12V tapes).

I suppose one option would be to have a 4 wire system (24V, 5V, OV and
Data) and have a DC-DC converter module every X-LEDs to maintain the 5V
rail.

I'm thinking very long strings here...

I've investigated the "normal" set of lights we have in view of PWM
driving them from a Pi. 2 channels, 240 LEDs, 32 V drive. LEDs
arranged in 12 parallel connected blocks of 20 LEDs. Within a block
there are two 10 LED series connected chains from each channels drive
to a common rail.

The rating plate says total 8.5 W @ 32 V, so I = 8.5/32 = 265 mA =
130+ mA per string. I only have a stock of small signal transistors
but do have some L293D H bridge drivers (up to 600 mA and 36 V).
However the control box must have some suitable switching and be
microprocessor controlled so just hacking into that is probably
easier.