Re: LED question for Neon John or ???
- From: "Calif Bill" <bmckeespam@xxxxxxxxxxxxx>
- Date: Mon, 23 Feb 2009 13:34:46 -0800
"Ralph" <n7bsn@xxxxxxxxxxxx> wrote in message
news:4e19f475-ced4-461c-af3e-39c2fededf00@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Feb 23, 10:28 am, "R.J.(Bob) Evans" <bob at rjevans dot org> wrote:
I have built some LED lighting modules using multiple banks of 4 x 3.3
nominal volt white LEDs in series. I'm getting roundly critisized for
bad design on a bus BBS and I'm perfectly willing to accept that it is
a bad design but so far nobody has been able to adequately explain the
theory behind why it is a bad design. All I've had so far is a bunch
of pablum about putting resistors in series with the LEDs in an
attempt to limit the current through the LEDs but so far nobody has
explained why that bodge is better than the bodge I currently have.
I understand that ideally I should have a current limiting circuit but
come on, these are cheap RV lights I'm building, not rocket ships. So
what's the theory behind burning up power through a resistor in an LED
lighting circuit?
--
R.J.(Bob) Evans
(return address needs alteration to
work)http://travellingwithgeorge.blogspot.com/
You don't need a resistor. Why you typically put a resistor in series
is because it's a 3.3V LED and you are driving it with 5V.
I've been using LED "night lights" in the RV like that for years, in
fact the "main" one is still in continous (24/7/365) and is on it's
2nd RV and has been in use for something like 6 or 7 years.
BTW 4x3.3 is not enough, if you are using a "bulk" charger, as they
put out more like 15 to 17 Volts. Can we say "burn out". It's why I
used 5 in series. It's the same reason that the commercial LED "tail"
light bulbs burn on in RV us. They die when the rig is plugged into
the "mains" and the charger applys too moch voltage and the LED burns
out
They are current devices, not voltage devices unless there is an internal
resister and they state it is designed for 3.3 volts. LED's if you supply
less current than they need, will be dark, and as you raise the current
flow, they will get brighter until they start dimming as the design goes
beyond the light emitting stage. They will be dark until they give a short
amount of light out and sometimes smoke. Just put a cheap resister in line
with the diode. R = E/I Look at the required Current (I) and divide that
into the Voltage (E) and you will get the resistance required. For big
arrays of 3.3V, get one resister and a Zener diode. Put the resister and
3.3V Zener in series and tap off above the zener for the 3.3V's to all the
LEDs in parallel. Calculate the required resister same way R = E/I for how
much current the zener can handle. And the E is the supply voltage - the
zener voltage.
.
- References:
- LED question for Neon John or ???
- From: R.J.(Bob) Evans
- Re: LED question for Neon John or ???
- From: Ralph
- LED question for Neon John or ???
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