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Wiring 40 or 50 LED's to 12V motorcycle battery? Answered

I would like to wire 40 or 50 LED's to run off of a 12V motorcycle battery.  Here's what I have:

Red LEDs- 2.2V typ 2.8v max @ 20mA

Motorcycle battery- 12 Volt, 10 Ah, 180 CCA

The plan was to run 8-10 series of 5 LED's in parallel. From what I understand each series would need a resistor but I am not sure if the motorcycle battery puts out enough mA to support the total number of LED's. I am a beginner so I may have this all totally wrong, hopefully someone can point me in the right direction. Thanks for the help!


I do not recommend using a motorcycle battery to run your lights. Not that it won't work, but motorcycle batteries are starting batteries. They're designed for quick burst of power in a short period of time.

In contrast, a deep cycle battery is designed to supply steady power for a long duration. A deep cycle 10 AH battery run your lights much better (and last longer) than a 10 AH motorcycle battery. It has to do with the thickness and count of the plates in the cells.

That being said, this is the kind of battery I recommend you use: 12v 10 AH Sealed Lead Acid Battery

If you use standard LED's, they have about 0.7 volts across each LED for full brightness at about 10 Milliamperes. It is more likely you will use the high brightness leds they are more common to use but they have about 3 volts across each led for full brightness at about 20 milliamperes. What all this means is you are limited to how many you can connect in series. With the 3volt led's, you can have about 4 of them in a row MAXIMUM.. and there must be a resistor also connected in series ( in a row one after another). That is because 4 led's times 3volts per LED is about 12 volts. Vehicle batteries actual voltage may be as high as about 13.5 volts in the real world though. So do your calculations to limit current to about 20 milliamperes at 13.5 or 14 volts estimated maximum. In order to get 40 or 50 LED's connected you just simply make SEVERAL strands of 4 led's in a row. Connect each STRAND of 4 to the battery individually. EACH STRAND of 4 led's must have the current limiting resistor for its own strand. I estimate about 100 ohms would probably work but it depends on what kind of LED's you buy. If your resistor is too low of ohms, the LED's will burn out soon. If the resistor is too high of ohms, the LED will be less bright. If you connect 6 or 7 led's in a row, they may not light up at all.... because 7 led's must have 7x3 = 21 volts and your battery only puts out 13 or 14 volts. so 4led's X 3Volts equals about 12volts... yes it will work.

You have it exactly right - battery EASILY puts out enough current to drive tens/hundreds of parallel strands. (designed to drive a motorcycle starter motor = huge current capability). Use the longest possible series strand length to optimize the voltage efficiency.

To figure out the right resistor, use a calculator like http://led.linear1.org/led.wiz

Tell it your optimal battery voltage, led voltage (use typical values, not max values) - and current (20mA generally okay).