On 11/29/2014 10:12 AM, Rob wrote:
Jerry Stuckle wrote:
On 11/29/2014 4:30 AM, Rob wrote:
Jerry Stuckle wrote:
For incandescent, yes. But not for LED bulbs. If that were the case,
why would some LED bulbs be dimmable and others not?

"is it dimmable" refers to the use of a phase-cut TRIAC dimmer in combination
with a retrofit LED bulb designed to run on mains power.


No, some bulbs are not dimmable, period. Some are. None work reliably
with triac dimmer controls.

Maybe not in your world, but here we can buy TRIAC dimmers and LED bulbs
that work together.


Maybe you THINK they work. But there are a number of problems (some of
which I have identified in this thread) which show they don't work well
together.

You probably have a 13.8V stabilized DC supply in your shack.
Can you use it as a variable-voltage supply by putting a dimmer in
front of it?


Completely unrelated. The LED electronics and the power supply work
completely differently.

Maybe your power supply, but mine is a switchmode supply and it works
completely the same as any other. It is regulated for voltage, not for
current, but that is another matter.


Completely unrelated. The LED electronics and the power supply work
completely differently.

The first difference you are ignoring is your power supply is constant
voltage. A LED power supply is constant current. They work on entirely
different principles.


There are already dimmers made for LEDs which work well. And there are
commercial systems which use low voltage to drive the LEDs. But these
are all proprietary; there are no standards for LED lighting yet.
Eventually, maybe standards will be developed for the commercial market,
but right now there is zero push for such standards.

It's going to be years (if ever) before such standards are created for
the residential market. There are too many reasons to stick with 117V
wiring.

LED is about current, not about voltage. A lighting system can put many
LEDs in series and use a higher voltage. What is important is that the
supply circuit gets separated from the bulb, so that it can be made dimmable,
externally controlled, etc and the LED gets DC current supply.


Sure they can be connected in series. But that has it's own problems;
you can only go so far. And yes, the LED gets a DC supply - but it's
the generation of the constant current source which causes the problems.

Don't believe me, though. Look at some of the references I have posted
- all written by EEs intimately familiar with the technology.

The mains here is 230V AC. There even are proposals to change that
into 325V DC or even 500V DC. Not accepted proposals with a set date,
but still. DC supply is more efficient for the home these days, now
everthing uses switchmode supplies, it can transport more power
with the same amount of copper and the same class of insulation.


That's fine for you. Personally, I don't expect it to get very far.
But it's not going to happen here.

Back in the 1800's, there was a current war. Nikola Tesla (supported by
George Westinghouse) proposed using AC. Thomas Edison proposed using
DC. Both had their advantages and disadvantages. AC won, obviously.
And now, it is so ingrained into our economy there is no chance of changing.

Although the utilities are building some long distance DC transmission
lines.

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