LED Dimming (OT)

[TimB]

Hi all

As I'm taking a short break and doing some DIY. I purchased a LED light, It uses a LED driver and is not dimmable. Well not using a mains dimmer. The issue is that its a big LED strip and is very bright 

I can see no reason why I cannot PWM the low(ish) voltage once its been through the AD-DC led driver apart from the driver says it is...

180v - 265v AC to 132 - 201 DC It also has 3 wire output labeled N-, +, B-

I can find nothing online about that wiring online and even resorted to Chat gpt via Bing. It just made sh!t up about the B- being the dimming current supply. Following the source link to RS comps the page had ZERO references to B- or Dimmable anything

So I'm looking for enlightenment I want to build a PWM controller to the DC side that will be a small pot controlled mounted in the lighting driver housing.

What is B- and can I PWM it with say a Mfet?

[rick.curl]

Hi Tim-
I think you may end up fighting an uphill battle by trying to add PWM to that driver. That is a constant-current driver, so it will be trying to maintain a current of 230mA.  I suspect that if you add PWM it could cause the constant current circuit to become unstable. Also, you will have to be PWM'ing 200 volts so you'll probably need an isolated driver.
I'm thinking you will be better off to replace the driver with either a dimmable one or a lower wattage one that will supply 200 volts.

Sorry to rain on your parade.

-Rick

[TimB]

Thanks Rick

Any idea what B- is?

Tim

[RGV250]

Just a thought and I am probably wrong but could it be 2 seperate negatine outputs with one common positive. Does it look like the LED has 2 segments?

Bob

[TimB]

HI Bob

Yes your spot on. I'm thinking now that if I get a meaty power resistor I can short some of the current through it to reduce the current/voltage going to the leds.

The issue I have is they are way to bright. I need to reduce the lumens

[rick.curl]

Thanks Rick

Any idea what B- is?

Tim

Not a clue- but there's a phone number on the driver.  Might be worth a shot.

[top204]

Why not just get a strip of WS2812B RGB LEDs or APA102 RGB LEDs?

They are very inexpensive and can be driven from 4 to 5 volts directly from a microcontroller, and you can make them any colour and any brightness (individually or sections if requied), and they come in very long strips of them that only require a single (WS2812B) or double(APA102) line to them. When fully on, they do draw quite a bit of current when there are a lot of them, but they are very bright. And they are a lot safer than a series of LEDs carrying a high voltage.

[TimB]

Thanks Les

I think swapping out the leds for a COB style would be a good option

Tim

[charliecoutas]

Is it anything like this one Tim? I bought it some years ago at Costco. It's so bloody bright it has given me a tan. I'd love to dim it but haven't had the time or know-how.

Charlie

[rick.curl]

I think swapping out the leds for a COB style would be a good optionTim

Beware of the cheap Chinese COB LEDs. Those COB assemblies do not have any current limiting on each series string. The ones from reputable manufacturers have closely matched chips that share nicely, but the cheap ones tend to be very uneven and will often fail prematurely (voice of experience speaking....).

[See_Mos]

Hi Tim,

As LED's are current controlled my first thoughts were to search for 'variable current sink' to put control in the low side, but if the original controller is trying to maintain a high constant current then it may not work.

I have used CC IC's to control the high side of back lights but they were only 24 volt circuits.

[TimB]

Hi See_Mos

Hmm yes I think a variable current sink would be a good solution if it can handle say 100ma at 200v. I have a 25 watt 2k2 resistor coming today and will see what happens when I short + to one of the negs. If that works then I will see what can be done with say a 25w pot

[ken_k]

Hi See_Mos

Hmm yes I think a variable current sink would be a good solution if it can handle say 100ma at 200v. I have a 25 watt 2k2 resistor coming today and will see what happens when I short + to one of the negs. If that works then I will see what can be done with say a 25w pot. 

Hi Tim
I had a look on line and found 25W opts are available at a reasonable price.
https://www.aliexpress.com/item/32670027322.html?src=google&src=google&albch=shopping&acnt=708-803-3821&slnk=&plac=&mtctp=&albbt=Google_7_shopping&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&albcp=19373925530&albag=&trgt=&crea=en32670027322&netw=x&device=c&albpg=&albpd=en32670027322&gad_source=1&gclid=CjwKCAiAvJarBhA1EiwAGgZl0JsnL2vrwFMNEswmM5DsVHORHtvvU14YietmPdFfnDCTLfVhC41MyxoCJbsQAvD_BwE&gclsrc=aw.ds&aff_fcid=7f29628d18594caf85f6bbda72901096-1701218688165-09936-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=7f29628d18594caf85f6bbda72901096-1701218688165-09936-UneMJZVf&terminal_id=3c29050e5e2c407eb9f2f9eb4ac93f40&afSmartRedirect=y
I must admit this was a surprise to me, even 50W pots are quite cheap.

If the current shunt method works other options could be.
1/  A FET on a heatsink, a small pot and a few components to make a current sink circuit.
2/ A few power resistors maybe heatsink mounted for preset brightness levels switched with FET's, relays or toggle switches.
Have you scoped the fet drive?
Is there galvanic isolation from the mains?
kk

[flosigud]

Why not use something that is dimmable by usual means?

[charliecoutas]

In my case because I have bought the thing, struggled on a stepladder to fix it to the ceiling, only then discovering that it's far too bright. If I ever get any time, and trust myself on a stepladder, I'll take it down and poke around inside the control box thingy. It's a beautifully artistic thing.

Charlie

[TimB]

I tried the 25w resistor but it made no difference

I found the LED strip has 3 connections like the rest of the wiring. The LED strip seems to have 2 circuits and the leds are numbered B N B N...

My opinion now is if we keep it (wify is not keen on it) then I will rewire with a standard led strip and mains dimmable controller

[rick.curl]

I tried the 25w resistor but it made no difference

Remember that the resistor will have to go in parallel, not series. If it's in series, the driver will just crank up the voltage to maintain the same current.

[TimB]

I retried the resistor as I realised that one of the channels of leds (they alternate on the same strip) dimmed. So I fitted the other but all it did was dim one channel completely

Searching Aliexpress I found a number of replacement controllers that will match the specs needed. They are not Triac dimmable but they all seem have a remote.

https://www.aliexpress.com/item/1005005066525126.html

I went for that one because the size will fit in the space.

[TimB]

Not got my new driver yet but made a discovery that eluded me before


The light as it turns out has 3 modes. Each Led bank (alternate leds on the strips) is a different colour. Cool white and warm white

If I turn on the light both come on. Off then on again and just the White leds come on. Off and back on and the Warm white leds come on.

If the dimmer does not work then I at least can just chop the drive to the cool white leds and then using a few diodes make sure the warm white is the only one that comes on and use a bigger wattage R to sink some extra m amps to dim the one strip. (The 25watt got a bit to hot for my liking)

[TimB]

The new driver/dimmer arrived from China (wow quick delivery) and after wiring in now works a treat. I have to use the remote control as it does not remember the last setting on switch power down and the remote on/off does not seem to actually turn the Leds 100% off

Overall now its solved

Cheers for the help given

Tim