How I dim LEDs, and slow down fans.

[sternwake]

Gary, while this one is rated for only 2 amps, it can both boost and buck voltage easily, is enclosed, comes with a knob.  You can use it on the 10$E papst 24v fan, but once above ~28 volts, it will exceed 2 amps and perhaps release the magic smoke instantly, or not so instantly.  Hard to say.

https://www.amazon.com/dp/B071CZ5P1Z/ref=sspa_dk_detail_2?psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzUlZGVVk0WkE4NjNPJmVuY3J5cHRlZElkPUEwMjA5OTI5MUJNMFcxOEhPV0FVMSZlbmNyeXB0ZWRBZElkPUEwMDU0MjU3MzI3WDdJRFkySTJLQyZ3aWRnZXROYW1lPXNwX2RldGFpbDImYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

https://www.surpluscenter.com/Electrical...6-1553.axd

Read one review of that 7$ 2a buck/boost and it says it will not power a 1 amp motor.
So forget it.
The 24v papst fan is worth it to own though, even if only is fed 12.8v.

[Snikwahjm]

SW, I apologize. My attempt at light humor was offensive to you. Snik

[tx2sturgis]

One very handy tool to have around for experimenting with LED dimming (and many other electronic projects) is a resistance decade box.

I have an old one that is decades old...no pun intended. They dont work as well for very high power, high brightness LEDs, but for small low power LEDs, especially strings of LEDs and LED ropelights, etc......they work great...you can spin the knobs until you find the perfect amount of dimming, then note the value on the knobs.

It's easy to find an ohm value for 'low' dimming, or 'medium' dimming, and then simply choose a discrete resistor with the same (or similar) ohm rating and enough wattage rating to do the job. You can solder that resistor on a 2 position toggle switch and poof, instant HI-LO brightness selector.

The decade box I have is probably at least 50-60 years old. They tend to last longer then the original owner...I bought mine used, more than 30 years ago!


Here is a cheap kit version, not really a decade box but close enough for most projects:

https://www.amazon.com/Elenco-Resistor-Substitution-Box-RS-400/dp/B00R6SOXLG/ref=pd_sbs_469_7?_encoding=UTF8&pd_rd_i=B00R6SOXLG&pd_rd_r=77f0450f-3fd0-426a-8544-f31e26c7e8c5&pd_rd_w=mBvn8&pd_rd_wg=rHZDG&pf_rd_p=1c11b7ff-9ffb-4ba6-8036-be1b0afa79bb&pf_rd_r=T9T147P4PV3KY5PSD5CX&psc=1&refRID=T9T147P4PV3KY5PSD5CX


Here is a midpriced substitution box:

https://www.amazon.com/Elenco-Resistance-Substitution-Range-Precision/dp/B0002KX76M/ref=sr_1_3?hvadid=78134096180923&hvbmt=be&hvdev=c&hvqmt=e&keywords=resistance+decade+box&qid=1567190729&s=gateway&sr=8-3


And here we get into the pricey units...way past my interest:

https://www.amazon.com/NEWTRY-Precision-Adjustable-Resistance-111-1110MR/dp/B078KR8HZF/ref=sr_1_21_sspa?hvadid=78134096180923&hvbmt=be&hvdev=c&hvqmt=e&keywords=resistance%2Bdecade%2Bbox&qid=1567190729&s=gateway&sr=8-21-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzNTRDRVA4SVIxRllIJmVuY3J5cHRlZElkPUEwMzA4NjQ1MlVMRDZYUDdSSEkxNSZlbmNyeXB0ZWRBZElkPUEwNTkyODk1MUEySEFKSEdFTUNZRyZ3aWRnZXROYW1lPXNwX210ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU&th=1

[sternwake]

Those look like a low power DC Variac.

Pretty neat.

I personally am hooked on a dial/knob and infinite adjustment between minimum and maximum brightness/speed.

I kind of wonder how much wattage is lost as heat in the resistor, vs is lost as inefficiency and heat due to the buck boost chips in these voltage manipulation devices I am employing.

Many of my NOctua fans come with 'low speed' adapter cables, which have a resistor in them, and when I use them the, resistor itself on the cable can get nearly hot enough to burn my fingers if I were to squeeze and hold, and this is with a 0.05 amp fan.

I know with either PWM led dimmers or the voltage bucker I am using, I cannot deliver the same voltage out as I can deliver to them, the buckers shave off a bit more than the dimmer, but the 0.33v loss is hardly upsetting to either fan speed or brightness when the brightness or max speed of the fan is up in the insane range at 12.x volts anyway, and half the day I am up above 13v.

[tx2sturgis]

Yep to all of the above but these are used for testing, breadboarding, etc, where you intend to repair a circuit or install a resistor when you figure out the value needed.

Sure, you can use ohms law to arrive at a value you think might work, but seeing the actual result without having to manually mess with a box of 100 different resistors is a real time saver.

As I mentioned, you dont use these where high power levels are involved. You need to stay with low current, low power circuits, so they are fine for low power LEDs.

I give you an example of how I recently used my decade box:

I bought a string of about 100 low power LEDs that work on a little solar module with a rechargeable battery. We've all seen them. I did not need the entire string, about 50 feet long, so I cut it down (twice) to finally about 8 feet. That section works fine on the rechargeable module.

But now I have two orphan strings of LEDs with no power supply. Hmmmm.

So...we wonder....what are the specs for these LEDs? How much current do they need? What voltage will they handle? There are no printed specs or any way to know...other than a rough guess that they need about 2 or 3 volts....maybe. But what value of resistor will provide the proper current limiting with 12v input so that they will glow brightly, but not get too hot? Care to guess? 10 ohms? 100 ohms? 1000 ohms?

Its a simple matter of hooking them up to the 12v supply in series with the decade box, set to maximum. The LEDs are OFF. But power is being supplied.

I rotate the knobs, one by one until the LEDs start to glow. After a bit of knob twisting, the final value turns out to be about 200 ohms for a nice glow from the LEDs...any less resistance and the LEDs are way too bright, and get kinda warm when pinched between my fingers....no...lets run them dimmer and cooler so they will last awhile.

I gather up two 100 ohm, 1 watt resistors, put them in series, solder them to the LED string. Power on...and what a nice glow from the string of orphan LEDs. The current measured was about 50 ma on one string of 34 LEDs....not enough to heat anything up.

Add a switch and a connector, poof....instant, and nearly free, string of 12v LEDs that can be used anywhere you want to use them.

So now I have two, actually three, sets of LED string lights for the price of one.

The decade box makes this type of thing easy.

Will it control the speed of a motor that draws 100 watts? Of course not....its not designed to do that. But for simple, low current resistor substitutions, it works great.

[sternwake]

Does sound like a good device to have, thanks for the info.

These voltage buckers I use that have the current potentiometer work to dim my t10 leds with either current or voltage potentiometer, but it seemed the current pot worked better, with a wider brightness range and no flickering, butthe buckers without the current pot cause no flickering.

I have some red rope LED lighting from 2007 or so, but the amount of light it puts out for the amperage consumed is pretty bad compared to the multicolor strip lights I just installed in a friend's vw bus.

I like the non night vision destroying red light, and it makes it easier to fall back asleep than white light does at 4am.

[B and C]

Stern, are you saying you live in the red light district? Couldn't help myself as it just popped into my head. I do leave a led strip light on very low when I camp. It is just enough to see by without waking me up much and I don't look directly at it. I might have to replace it with a red version, although if someone sees it, I don't want to send the wrong signal

[sternwake]

I can't sleep with lights on, but the red leds activated and dimmed low when I wake up an have to piss, make it easier to fall asleep again. Any light with a bunch of blue in the spectrum tells the brain its time to wake up and stay up.

Reading shit on the smartphone does not make me sleepy, but reading a book with a dimmed led, does. Dimmed warm white leds being better than cool white for this, but I am hardly the master of falling asleep at a reasonable hour anyway. Laptop and phone reading is a million times worse though.

[B and C]

All my lighting is warm white. I don't care at all for the blue high intensity light. The light I leave on is actually in the bathroom with the door closed. There is a couple inch gap at the top that light escapes from and doesn't shine on my face. Where my bed is in the back sideways, my face is in the shadow. I only turn it on when it is really dark as in barely a moon. When there is a bigger moon, the fantastic vent lets in plenty of light. I usually get up before dawn and it is nice to not have to fumble for a switch.

I guess I am one of the lucky ones that gets to sleep uninterrupted all night. I'll be 71 in october and take no prescribed medications other than a baby aspirin. I do have a cpap machine though.

[sternwake]

I tried a few different warm white leds, but something about their color rendering was not agreeing with my retina/brain interface.  It seemed to fake or artificial, or something else I can't quite pinpoint but it caused me to lean back towards cool white options

Earlier LEDs which were obviously blue tinged were similar and when I found a white no blue LED, I'd order more from the same supplier and would often find them to have different color even in the same batch, sometimes on the same dang bulb.

I've not really tried warm white since, as most I have ordered have been consistently white without obvious blue tinge to them.

I do have some discontinued overpriced then, Phillips T10 warm white LEDs several years old now, whose light color is not bad, but they are on the same circuit as my laptop dc to dc converter, and when that is powered up it causes those leds to change brightness quickly and flicker, and I quickly turn them off.

The phillips have been ultra reliable and make a lot of light for very little currrent though.  probably the most efficient LED I have lumen per watt. but I have not really applied any measuring tools to them.  and opinion can be next to worthless.

Lately I just want insanely bright bulbs  with the ability to be dimmed via pwm or voltage bucker and care much less about lumens per watt.

Seems LEDs being driven well below their maximum potential can be quite efficient, and that last 20% of their potential brightness, wattage consumed doubles for perhaps 20% more light and they can get ridiculously hot up there too.
The recent bulbs with 3030 chipsets have been extremely bright.  My previous favorite was 5730's.

I'm kind of done experimenting with LED offerings for a while though.
I recently got these, and they are by far the brightest LED t10 bulb I have used, and rarely do I need to crank them more than half their potential brightness.
Many previous bulbs when I have cranked them up and forgot to turn them down they have overheated, and usually it has been the smell to alert me to this occurrence.  These I have forgotten in daytime that i cranked them to the max searching for something, then left them up there and left,  but have yet to smell them getting too hot.

https://www.amazon.com/LncBoc-Backup-Chipsets-Extremely-Reverse/dp/B07LF853V4/ref=sr_1_2?keywords=lncboc+921&qid=1565585233&s=gateway&sr=8-2

While these say 370 lumens per bulb and 740 for the pair n the description, I am pretty sure one bulb is 740 if not more lumens above 12v.