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Re: Strip LEDs
Posted: Wed Jan 23, 2019 5:42 pm
by Tricky Dicky
ajcooper4 wrote: ↑Wed Jan 23, 2019 3:31 pm
Having done some beginner's research briefly I am thinking maybe the number of LEDs I use in each building is going to be a factor.
Maybe there's a basic calculation I can use? I am familar with Ohm's law but not sure of my for this set up.
No need for any calculation the Resistor with each 3 LED strip has already been calculated, however it will have been calculated to give a bright light from the LEDs which may be too bright for your purposes. I am afraid dimming the LED strips is a matter of trial and error, LEDs do not dim linearly so adding a certain resistance does not say dim the LEDs by half. If you can lay your hands on a 5K or 10K linear potentiometer put that in the positive lead as Brian has indicated and twiddle with it until you get the brightness you need. Take it out of circuit and measure the resistance between the two terminals you had connected (which should be the centre terminal - wiper and one either side) Then obtain fixed value resistors of the same value as the reading. Do not worry about blowing the LEDs as the onboard resistor limits the current to prevent that. As Brian has already indicated treat each 3 LED strip as an individual light source even if you intend to put more than one strip in a building, if you start using them in 6, 9 &12 or more than the additional resistor value will change each time. Finally if you have a multimeter measure the current drawn by an individual strip with your added resistor, by adding up the total currents drawn by all you lighting you can ensure your PSU can deliver sufficient current. It is good practice not to run PSUs constantly at their maximum output and I would advise you to leave an overhead in the region of 10-20% spare.
Richard
Re: Strip LEDs
Posted: Thu Jan 31, 2019 12:52 pm
by ajcooper4
Tricky Dicky has given a detailed explanation about how I might assess the level of resistance required - and having got the strip LEDs working they are too bright, three in one strip per room is definitely too bright.
Notwithstanding Dicky's helpful and detailed analysis can anyone offer a few ideas in simpler form, please, about ow much resistance might be appropriate to reduce the brightness, by say 30/40%?
Many thanks.
Re: Strip LEDs
Posted: Thu Jan 31, 2019 1:14 pm
by Brian
Its almost impossible to give a detail value of resistance for a certain percentage reduction. Trail and error is really the only way...
Try initially a 5K (5,000 Ohm) resistor in series with the positive lead. If still too bright try a 10K (10,000 Ohm) resistor in series. If still too bright add the 5K to the 10K together in series with each other - making 15K (15,000 Ohm) and retest.
If you obtain three 5K resistors then start off with one and if need be add additional ones to the first in series (daisy chain them) then you will increase resistance by 5,000 Ohms with each resistor!
Also what voltage are you feeding to the LED strip(s)?
Re: Strip LEDs
Posted: Thu Jan 31, 2019 1:15 pm
by Steve M
I am certainly not an expert (I don’t hear anyone disagreeing
) but in the absence of a specific answer surely a bit of trial and error is called for.
Try putting an extra resistor in one of the feed wires and see if it gives the result needed. Doesn’t matter what value you have as you can add more resistors to vary the result if necessary. I think they should be added in series for the best result (but I’m not absolutely sure). If adding them in series then once you have the right result add up the individual values to give an overall resistance - that should give you a guide for buying an individual resistor.
Alternatively do what I do and add a drop of paint, yellow or white, to the led - that dims it quite nicely. Sometimes keeping it simple is all that is needed.
Re: Strip LEDs
Posted: Thu Jan 31, 2019 1:16 pm
by Steve M
And as usual Brian types faster than me.
Re: Strip LEDs
Posted: Thu Jan 31, 2019 2:37 pm
by ajcooper4
Thank you, all sound advice as always.
Re: Strip LEDs
Posted: Thu Jan 31, 2019 4:32 pm
by Rog (RJ)
Alternatively, put some paint on the LEDs but again, you need to experiment to find how much paint is needed.
Re: Strip LEDs
Posted: Thu Jan 31, 2019 5:08 pm
by shroomy
Get yourself a breadboard and wires of eBay saves any soldering
https://rover.ebay.com/rover/0/0/0?mpre ... 1353347660
Re: Strip LEDs
Posted: Thu Jan 31, 2019 5:26 pm
by dynax
+1 for breadboard, got mine from same place as shroomy's link, worth getting a couple, cheap enough, if doing multiple projects,
Re: Strip LEDs
Posted: Thu Jan 31, 2019 6:45 pm
by ajcooper4
Thanks everyone. A little bit of experimentation has shown me a resistance of 5.6k ohms +/- 5% is ideal. I will look at the other stuff also.
Again, many thanks.