LED Light Question

[eflyguy]

Lowering the frequency doesn't cause them to dim, lowering the duty cycle - the amount of on vs. off time - does. I explained it back in post 7.
..a

[JohnnieB]

Originally Posted by eflyguy

Lowering the frequency doesn't cause them to dim, lowering the duty cycle - the amount of on vs. off time - does. I explained it back in post 7.
..a

There are three primary types of of Pulse Modulation, PWM, PFM and PAM
Pulse Width Modulation = Constant Amplitude, Constant Frequency and Variable Width (Duty Cycle)
Pulse Frequency Modulation = Constant Amplitude, Constant Width and Variable Frequency
Pulse Amplitude Modulation = Constant Width, Constant Frequency and Variable Amplitude

In some applications, two or more are used simultaneously, but probably not for controlling the light output of LEDs used for task illumination and other applications where color shifts are tolerable.

Analog LED dimmers vary the current flow thru the LED, which both changes the light output and changes the color (slightly), but LEDs will only produce light over a fairly narrow range of current. (About the same way as Zener and Avalanche diodes only maintain a regulated voltage over a narrow range of current.)

On the other hand, when pulsed on/off rapidly using PWM or PFM, they have the same light output and color when on, but average light output varies, so they appear to get brighter/dimmer.

[yurtle]

I assume the same thing can be incorporated to limit inrush on halogen bulbs as well? Give it a second or two to heat up, then go "across the line".

I'm obviously overthinking this. I liked my 55 watters, as a very simply solution to bright and dim was simply a DPDT (middle off) toggle between series and parallel. Since they've bought the dust, and I'm uncomfortable with the inrush on my poor reducer, I'll have to figure out whether to try the LEDs, which cost three times the cheap halogens.

Obviously, the reducers can take the momentary inrush, but I wonder if they have internal limiting, or are slowly getting over-taxed. Obviously not a problem with an aux battery.

[JohnnieB]

@ Yurtle: Some food for thought.

Running the bulbs is series for "Dim" will work, but probably not satisfactorily so, since reducing voltage by 50% reduces light output by over 90%.
(See attached nomograph of Voltage vs Current vs Candlepower vs Life Expectancy for incandescent bulbs)

Might work if an appropriate sized resistor was added in series for Dim. However, low voltage will cause halogen bulbs to blacken.

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The voltage reducers must have some form of current limiting or they would blow when the headlights were turned on.
It depends on the design, of course, but I suspect putting them into current limit isn't good for them.

Perhaps something akin to a start relay on a capacitive start motor would work. It would probably have to be a solid state device, since a mechanical one might be too slow and finding one with the right drop-out current might be difficult.

Maybe an arrangement that defaulted to "Dim" with power off and a momentary button that closed a self-holding relay for "Bright".

[yurtle]

Worked just fine since I wired them that way, 'til they were murdered. FWIW, they were always on high, until I was landing near other parked buggiers, and didn't want to blind them 'til I landed, so maybe they ran that way a few minutes a week, after (and before) hours of running on high.

Just talking about the halogens, not the reducer. As I mentioned, shouldn't be a problem on aux battery, but I don't wanna tax my reducer.

I still haven't come up with a way to keep my radio memory wire happy, while on a reducer, so I may revert to an aux battery.

[yurtle]

Originally Posted by yurtle

I'm obviously overthinking this.

Originally Posted by JohnnieB

@ Yurtle:Some food for thought.

Great, let's fan the flames.

[JohnnieB]

Originally Posted by yurtle

I still haven't come up with a way to keep my radio memory wire happy, while on a reducer, so I may revert to an aux battery.

A 2 Farad capacitor and a couple steering diodes.

Amazon.com: Soundquest SQCAP2M 2 Farad Power Capacitor with Digital Display: Car Electronics

Amazon.com: Soundquest SQCAP2M 2 Farad Power Capacitor with Digital Display: Car Electronics

Fan - Fan - Fan

[yurtle]

That's not the only problem. I have a 50 mph hwy that I routinely cross, so I have my 4855 set prolly WAY too aggressive, but I also drive way too aggressively so...

We've discussed this before, and my stereo cuts out for what seems like a lifetime (prolly less than two seconds), which is "easily" fixed by a cap and diodes. However, I was concerned with inrush on my caps at 12 volts, and it started getting into limiting inductors, so I would probably be better served with caps/diodes on the 48 volt side of my reducer. After a while, it sounds like an aux battery might be easier for my particular needs.

[yurtle]

Gotta get Mr. Sparky ready for Halloween, before the storms hit us, so my mind is elsewhere today.

Weather hasn't been kind the past two years, so I'm doing a full recommissioning, since 16.8 kV to 900 or so kV at 25 kVA needs more attention than I've given it the past coupla years.

'Specially around kids.

[yurtle]

Earlier this week, I ran into two pretty big home project unforseen conditions, not to mention weather threats (900 kV and rain are a little more than I'm willing to risk) so last night was kinda iffy.

I limited my input to 280 volts and between 80 and 90 amps.

Big Tesla was running, in all it's glory, and was working fine given its designed duty cycle. I had a BIG flock of folks show up late, so I exceeded the duty cycle of my one ohm 25 kVA resistor's heat sink, which literally resulted in big flames in my garage. Not wanting to disappoint, (and ignoring concerns by wifey) I ran through the flames for nearly a minute, and solved the problem with Bud Light, rather than a fire extinguisher, which put me back online in less than one minute. It still stinks, but allowed me to keep running 'til the last trick-or-treater was done.

We microwaved nearly everything the manual says not to put in a microwave, including HUGE sodium vapor light bulbs.

Lotsa fun.

After the "fun" I went buggying around and visited a neighbor who had been following orders and had a buncha dead incandescent light bulbs in a bag for me. I went home and grabbed my microwave and extension cord and took my show to his house. They couldn't believe it. I used up a bag of his steel wool, microwaving it, after "lighting up" all his bulbs.