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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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20th Dec 2022, 1:12 am | #1 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,051
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LED panel question
Can anybody please advise how to light up this 48 LED panel, which I have taken out of an old solar charged PIR light fixture. There was an 8.4V lithium battery inside it, but the battery was connected through the PIR unit and another board, which I think was for charging the battery. I fed it with 9V from my bench supply, with positive to V+ and negative to the ground but it did not light up. It doesn't light up with the negative supply connected to the middle pin either, as shown in the photos.The LEDs are fine, because they light up when both the PIR unit and battery charging board are connected.
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20th Dec 2022, 5:54 am | #2 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,324
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Re: LED panel question
Try feeding + and - to the two outside pins as marked and short the FB pin alternately to the + and - pin.
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20th Dec 2022, 10:44 am | #3 |
Dekatron
Join Date: Dec 2004
Location: East Yorkshire, UK.
Posts: 3,959
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Re: LED panel question
I suspect this board may have contained some sort of Boost Converter to increase the voltage while reducing the current available. Can you work out how the LEDs are connected? John.
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20th Dec 2022, 1:14 pm | #4 | |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,051
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Re: LED panel question
Quote:
Last edited by Jolly 7; 20th Dec 2022 at 1:16 pm. Reason: Additional information |
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20th Dec 2022, 1:19 pm | #5 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,051
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Re: LED panel question
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20th Dec 2022, 2:16 pm | #6 | |
Dekatron
Join Date: Dec 2004
Location: East Yorkshire, UK.
Posts: 3,959
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Re: LED panel question
Quote:
John.
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20th Dec 2022, 5:40 pm | #7 |
Heptode
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 947
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Re: LED panel question
Hi leds forward voltage of around 1.8 to 3.3 volts so with 12 in series =21.6 to 39.6 volts with a resistor in series to limit current , what voltage was the battery > Power this from a variable dc supply noting + - polarity monitor current of 10-15 MA ish x4 just noticed 8.4v batt so has a joule thief circuit to boost the b+ Mick
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20th Dec 2022, 6:40 pm | #8 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: LED panel question
The ones I came across as emergency-lights, "Sustained Luminaires" in H&S-speak, always used series-parallel networks of LEDs and a boost-converter; they generally had 'series resistors' only for sensing the current through the LEDs in order to monitor and regulate the power from the converter.
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20th Dec 2022, 7:45 pm | #9 |
Heptode
Join Date: Feb 2022
Location: Leicestershire, UK.
Posts: 690
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Re: LED panel question
Have you measured the voltage into the LED's with the PIR & Charging board connected in order to duplicate from you alternative PSU ?
Rog |
20th Dec 2022, 7:54 pm | #10 |
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
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Re: LED panel question
You can achieve the illusion of continuous illumination using LED’s with astonishingly low on times.
You could easily knock up a generator of square pulses of the right amplitude and power for the panel to be illuminated, with a handful of components. There ain’t no Joules to be thieved anywhere, but yer pulses will do the magic trick for you. But not using DC from the battery you describe and bypassing the original circuit. It was there for a reason
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Al |
20th Dec 2022, 8:01 pm | #11 | |
Heptode
Join Date: Feb 2022
Location: Leicestershire, UK.
Posts: 690
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Re: LED panel question
Quote:
Looks like I am on a learning curve here ..... do I take it that these type of fittings require a square wave supply to work instead of a DC one ? Rog |
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20th Dec 2022, 8:28 pm | #12 | |
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
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Re: LED panel question
Quote:
Others have already commented why. I've suggested a remedy, which points back to the OP's insight about the role of the original circuitry.
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Al |
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20th Dec 2022, 9:27 pm | #13 |
Nonode
Join Date: Jan 2016
Location: Stafford, Staffs. UK.
Posts: 2,529
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Re: LED panel question
Yes, I'd agree, it has to be worth checking the voltage the working circuit applies to the terminals when working off the original circuit. Especially since sometimes LEDs are actually a number of LEDs on one chip so the Vf actually has to be quite high on each module. I have one where I haven't mananged to get even one module to light even with a 20v Vf.
The previous comment about series and paralell combinations is for sure worth checking. Regarding the feedback (FB) it could be a simple temperature monitor to ensure the array doesn't overheat. I noticed a single resistor mounted on the corner of the PCB, and the PCB is often used as a heatsink for the LEDs. Could it actually be a thermistor feeding back the temperature of the PCB? |
20th Dec 2022, 11:10 pm | #14 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,051
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Re: LED panel question
I have now successfully lit up my LED panel using a joule thief circuit I built some time ago for a different LED setup. The circuit I built is based on a BD948 transistor and a toroid core.
of unknown specifications. I wound the core with a bifilar winding using some enamelled copper wire I had lying around. I had originally designed my circuit to operate from a 5V USB power source, but during my experiments today found that it works ok without any heating of the transistor or toroid at up to 9 volts. I was reluctant to go higher than that as I do not want to damage my LEDs and they are bright enough at 9 volts. I am not sure what is the actual voltage that's being output by my circuit, as my multimeter still measures 9V DC. However, this is not a problem as my LEDs are now working the way I wanted them to. |
20th Dec 2022, 11:53 pm | #15 |
Octode
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,051
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Re: LED panel question
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21st Dec 2022, 8:58 am | #16 | |
Heptode
Join Date: Feb 2022
Location: Leicestershire, UK.
Posts: 690
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Re: LED panel question
Quote:
Rog Last edited by Roger Ramjet; 21st Dec 2022 at 8:59 am. Reason: typo |
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21st Dec 2022, 11:14 am | #17 |
Dekatron
Join Date: Dec 2004
Location: East Yorkshire, UK.
Posts: 3,959
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Re: LED panel question
Hi Rog, A Jacobs ladder has a few uses other than making a pretty lighting effect, the circuit is here, the circuit repeats itself hence, "Ladder"
https://www.elprocus.com/voltage-multipliers-working/ Joules Thief, here by big Clive. skip through video to get the idea. Please watch from 4.30 for 5 minutes to get the circuit explained. https://www.youtube.com/watch?v=K53beWYdIpc
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My favourite text message "I'll be there in five minutes, if not read again" Last edited by 60 oldjohn; 21st Dec 2022 at 11:19 am. |
21st Dec 2022, 1:32 pm | #18 |
Heptode
Join Date: May 2015
Location: Bradford, West Yorkshire, UK.
Posts: 510
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Re: LED panel question
Instead of joule thieves, maybe they should be called "flyback ringers", a better description of how they work?
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worried about the electrons entering the circuit and the smoke leaving Andrew |
21st Dec 2022, 6:53 pm | #19 | |
Dekatron
Join Date: Nov 2006
Location: London, UK.
Posts: 3,496
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Re: LED panel question
Quote:
The circuit takes minutes to build from point-to-point guides on the internet and has so few components that this simplicity feeds into this magical aura. Ages ago, I was working through my understanding of oscillators, I built a blocking oscillator (another name for the same thing) using a valve design. Others will know that this was established early last century and for example had a crucial role in Radar... Here's one such design. https://www.radarpages.co.uk/theory/...ec2ch9p150.htm It would be a shame if the conclusion of this thread didn't properly illuminate (hah!) how the LED panel is being lit by high-frequency, high voltage pulses that are approximate square waves. ('High' being relative to the DC input voltage).
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Al Last edited by Al (astral highway); 21st Dec 2022 at 7:03 pm. |
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