resistors

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tommyrob123
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resistors

#1

Post by tommyrob123 »

hi, i know i ask a lot of questions but google gives so many confusing answers. i have just installed about 20 led's lamps and want to run them to one power unit using only one resistor ad i cannot solder to save my life. thanks for any advice
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Rog (RJ)
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Re: resistors

#2

Post by Rog (RJ) »

You really need to fit a resistor to each individual Led to avoid problems if you are wiring them in parallel. You can end up with one or 2 Leds robbing all the power from the the other Leds if you don't fit individual resistors. A single resistor feeding all of the Leds can get hot too, needing a higher wattage one.

If you wire 2 or 3 Leds in series then you can use 1 resistor for each group of 2 or 3 to reduce the number of resistors you use and also reduce the total power consumed and smaller value (lower ohms value) of resistor would be needed.
Tricky Dicky
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Re: resistors

#3

Post by Tricky Dicky »

Rog (RJ) wrote: Sun Jun 20, 2021 3:27 pm You really need to fit a resistor to each individual Led to avoid problems if you are wiring them in parallel. You can end up with one or 2 Leds robbing all the power from the the other Leds if you don't fit individual resistors. A single resistor feeding all of the Leds can get hot too, needing a higher wattage one.

If you wire 2 or 3 Leds in series then you can use 1 resistor for each group of 2 or 3 to reduce the number of resistors you use and also reduce the total power consumed and smaller value (lower ohms value) of resistor would be needed.
Agree completely. If you wanted to put them all in series it would require a power supply in excess of 60v. For a smaller power supply you might be able to group in several strings of series LEDs but it does not get you away from having to use a high wattage resistor to cope with the heat. If you look at commercial LED tapes there is a reason why they only group LEDs in three’s. If you are not using a constant current supply instead using resistors for current control then you need an overhead in the voltage supply so for instance if using a 12v supply that means you can have a maximum of 5 standard LEDs in series, for white LEDs you are looking at 3/4. Without an overhead in the voltage it becomes difficult to calculate the resistor value.

As Roger said the ideal is a resistor for each LED and let’s face it resistors are not the most expensive components which can be obtained for less than a penny each.

Richard
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Brian
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Re: resistors

#4

Post by Brian »

tommyrob123 wrote: Sun Jun 20, 2021 2:15 pm <SNIP> i have just installed about 20 led's lamps and want to run them to one power unit using only one resistor ad i cannot solder to save my life. thanks for any advice
Not an ideal choice IMO! One lit LED = one series resistor. Example Purchased in bulk a pack of 50, 1K resistors are just under 3p each https://www.ebay.co.uk/itm/324553216909 ... Sw0TBgaHW1 Cheaper still from China!
I've quoted 1000 Ohm (1K) resistors, which are ideal for use on a 12 volt DC regulated power source. Lower Ohm values for lower supply voltages.

You of course don't have to solder. Simply use a three way strip of terminal block (cut from a 12 way length) example 3Amp 12 way (makes four LED connections) £0.39/strip https://www.toolstation.com/connector-strip/p79740
Bring positive supply in and out to next lamps terminal block on terminal 1. Fit resistor in other side of T1 and the other end of the resistor into top of T2. Bring supply Negative into T3 and out to next lamps terminal block on T3. Connect Anode (positive) of LED into T2 with the resistors end and LED Cathode (Negative) into T3. :D

Typical non soldered LED and resistor connection...

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Tricky Dicky
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Re: resistors

#5

Post by Tricky Dicky »

If you find soldering to LEDs difficult, then these solderless LED holders are very good, a bit expensive but a search on ebay or some Chinese sites should find something similar but cheaper. You do have to trim the legs down but if you want to panel mount them the holders do fit inside the bezels just above.

https://www.rapidonline.com/mounts-holders

Richard
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