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Modifying led light pcb

Hkd

New Member
Hi
I have 24v led light fittings with a switch, I wish to bypass this so they can be switched remotely by powering the circuit on. Currently when powered on you need to press each switch to turn the light on so I believe this pulse input must switch a solid state latching relay? Also the same to turn off. I have tested the switch and concluded that this is how it functions.
Probably very simple for someone with more circuit board knosledge than I as I am a domestic electrician.
Thank you for your time.
 

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audioguru

Well-Known Member
Most Helpful Member
We need a schematic that shows all the part numbers and which connects to what, not a simple photo. We also need detailed spec's for the LEDs.
You need LED lights without the parts that make it "push the button for on then push again for off".
 

narkeleptk

New Member
I cant tell if the latching of the button is contrlled by transistors q1 and q2 or if its controlled by what ever ic U1 is and I am a out of my league on this but what would happen if when the button is latched on, you find and jumper the input to the output of where ever it is that's switching. Wouldnt the switching be bypassed and always on?
 
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audioguru

Well-Known Member
Most Helpful Member
Something in the circuit needs to limit the current to the LEDs. To prevent the current limiting part from getting too hot then part of the circuit switches the LEDs on and off at a high speed, with current-limiting done by the widths of the on-pulses. Does the circuit do this and which parts?

If you jumper the input to the output of the latch parts then you will have a spectacular overload if the current-limiting does not work.
 

sagor1

Active Member
I would suspect the 7 LEDs are in series, close to 24V total voltage drop (approx 7 x 3V). I also suspect U1 is checking the button press, to do the toggling on/off, and uses Q1 and /or Q2 to switch the current on or off.
But, as others say, one needs a schematic or at least visible traces to make a guess as to how that device is run...
 

Hkd

New Member
Thanks for your replies guys, I will see if I can get a schematic, not much hope from.an online retailer....
I did mange to get voltage across leds at approx 3v. An alternative would be to get default to be on at power up if possible ?
As you can see small red led next to button are on all the time, voltage stepped down to 2v on these but tricky to measure.
Choice of 24v fittings is very limited, we wanted s something warm white that looks ok for 24v off grid system.
The lights are ceiling mounted so stretching up for the button press is awkward.
 

Mickster

Well-Known Member
Maybe I'm missing something?
You have run the wires for the 24V supply to each lamp, from a common supply point. Why not remove the switch from each PCB, then run wires to each PCB from a common switch?
 

audioguru

Well-Known Member
Most Helpful Member
Mickster, there is no switch, it is a momentary button that triggers a latch circuit.
Which parts are the on-off switch latch circuit and which parts limit the current?
Hkd, what is the rated current or power of the lamp?
 

Mickster

Well-Known Member
I'll rephrase the question then.
Why not remove the momentary button that triggers a latch circuit from each PCB, then run wires to each PCB from a common momentary button that triggers a latch circuit, mounted at a convenient location, which triggers the latch circuit on all of the lamps?
 

Hkd

New Member
Each lamp was drawing about 0.7A at 24v well actually 28v with solar running.
Mickster I did consider that but I'm dealing with an existing installation in a shepherds hut so I'd have to take ceiling down to put in another cable as the existing wiring couldn't work like that. he wasn't keen to take t and g ceiling apart!
 

Hkd

New Member
Thats what im not sure of, identifying which is which circuit, looks to me like left and right areas probably have different functions...
 

Mickster

Well-Known Member
Do you have any more pics of the PCB, which show the markings on U1, so we can try to figure out what it is?
 

ChrisP58

Well-Known Member
You might try putting a capacitor across the switch. The idea is that this would make the switch appear closed for a short time after the power comes up.

But choosing what value to try without knowing what the circuit looks like is just guessing.

Off the top of my head I'd try 10uF. If you use a polarized capacitor like an electrolytic, you'll need to check the polarity and voltage across the switch first.

When you get the part number for U1, see if you can measure some voltages on it's pins as well. Pin one is in the top left in your picture, then numbered counter clockwise. Put the black probe of your meter on GND (power supply negative.) I'd actually like to see two sets of measurements, on with the switch not pressed, and on with it pressed.
 

audioguru

Well-Known Member
Most Helpful Member
Hold down the pushbutton then turn on the 24VDC power supply. Do the LEDs turn on and stay turned on?
Then solder a jumper wire across the pushbutton or mechanically hold it down. Then turn the LEDs on and off by turning the power supply on and off.
We do not know if a dimmer can be used.
 

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