As the title says, I have two 4.5 volt LED light strips (each one originally ran off 3x1.5 AA batteries). Can I use one 9 volt AC-to-DC power supply (wall wart type) to power these?
If so, do I wire these lights in series, or parallel?
Thanks!
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Keep your 9V AC adapter. Connect your LED strips in series. Use a resistor from your adapter to the LED strips.
You do need to know what LED's you have and how many. Typical values for LEDs are:
Red LED: 2V 15mA
Green LED: 2.1V 20mA
Blue LED: 3.2V 25mA
While LED: 3.2V 25mA
To figure out the size of the resistor use R = (V1 - V2) / I
R=(9-4.5)/I
(9-4.5)/0.02
4.5/0.02=225 ohms (easiest available resistor would b a 230ohm resistor)
Or you can use this calculatorto figure out how to wire it by using resistors.
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the resistor values given are quite not right.in series connection , the current through one led passes through the rest of the leds.so the current stays constant.[inthis case 20mA.
@renre thank you and it has been corrected
Remember that a resistor will dissipate some power, perhaps as much as your LED strip [constant 20mA current x (9-4.5)V=90mW; 1/8W should be fine] so always check the power rating of a resistor before finishing your design.
It's worth trying both strips in series, (+)-[strip]-(-)(+)-[strip]-(-); if they have some internal current regulation, you may not need more at all.
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Connection will be in series
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Would you anticipate problems doing this? Would it be better to use TWO separate power supplies, 4.5 volts each?
No as long as you connect in the series no problems ..... resistance = V/Amps if you want can add a resistor , considering current 40ma for 2 led strips ....
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