• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Get free circuit help 24/7

  • 1000+ Circuits
  • Privacy Policy
  • About Us
  • Contact
  • Disclaimer
  • Videos – Circuit Test Results
You are here: Home / DIY LED Projects / How to Connect 5mm LEDs to a 3.7V Li-Ion Cell

How to Connect 5mm LEDs to a 3.7V Li-Ion Cell

Last Updated on May 22, 2019 by Swagatam 23 Comments

The article explains regarding how to connect and illuminate a few 5mm LEDs using a 3.7V Li-Ion cell, normally used in cell phones.

I keep receiving requests from the readers who seem confused with the connection details of 5mm LEds with a 3.7V Li-ion cell. The requests inspired me to write this post, hopefully it would answer the many related queries.

Using a Cellphone Li-ion Cell

Since standard 3.7V Li-Ion cells which are normally used in cell phones are rated at around 800 to 1100mAh, are quite capable of supporting a few 5mm LEDs, and would be able to keep them illuminated for quite sometime.

A normal 5mm white LED requires about 20mA current at 3.3V for getting illuminated optimally.

The circuit involved for illuminating 5mm LEds through a 3.7V Li-Ion cell is actually too simple, primarily because the parameters are closely matched with each other.

Here, connecting the 5mm LEDs in series wouldn't be feasible because the maximum volts from the cell is just 3.7V while even two LEDS in series would call for above 6V.

Therefore the only option left is putting them in parallel.

Ideally when parallel connections are involved, a series limiting resistor becomes imperative with each LED in the array. This helps ensure uniform light distribution or emission from the LEDs.

However it's not an absolute requirement, especially when the driving voltage is close to the forward voltage of the LEDs.

Also taking the simplicity factor into account, a single limiting resistor may be used in such cases and therefore here too we have eliminated individual resistors.

How to Connect the LEDs

The circuit diagram below shows a simple configuration comprising of a 3.7V Li-ion cell, 5nos 5mm LEDs and a limiting resistor R1. The procedure shows how simply a Li-ion cell may be used for illuminating 5mm LEDs for a reasonably long period of time.

Each LED is supposed to consume 20mA current, therefore 5nos would together consume around 100mA, therefore R1 may be calculated as follows:

The Formula

R = (Supply voltage - LEd forward voltage)/LED current
= (3.7 - 3.3)/100 = 0.4/0.1 = 4 ohms.
The required wattage would be 0.4 x 0.1 = 0.04W, so a 1/4 watt resistor would be more than enough.

Assuming the cell to be rated at 800mAH, with 5 LEDs, the approximate back up time available from the cell could be calculated using the following cross-multiplication.

800/100 = x/1100x = 800x = 800/100 = 8 hours ideally.

However practically you would find the above calculated back up time to be considerably less due to many inherent inefficiencies associated with the system or the circuit.

More LEDs can be added, if you are ready to compromise the backup time proportionately.

connect 20mA LEDs with 3.7V Li-Ion cell



Previous: 55V 110A N-Channel Mosfet IRF3205 Datasheet
Next: Make this Car Air Ionizer Circuit

About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

You'll also like:

  • 1.  Greatest Myths about LED Lighting
  • 2.  How to Make a LED Flashlight Circuit
  • 3.  Make this Foot Activated Staircase Light Circuit
  • 4.  3 Watt, 5 Watt LED DC to DC Constant Current Driver Circuit
  • 5.  How to Make a Simple 12 Volt LED Lantern Circuit
  • 6.  How to Drive High Watt LEDs with Arduino

Please Subscribe (Only if you are Genuinely Interested in our Newsletters)


 

Reader Interactions

Comments

    Your Comments are too Valuable! But please see that they are related to the above article, and are not off-topic! Cancel reply

    Your email address will not be published. Required fields are marked *

  1. Search Related Posts for Commenting

  2. Joe says

    Hello, I am try to find a way to avoid expensive Owl predator flashing lights–My knowledge of electrical mini devices is limited to + and –
    I bought some red flashing led diodes, I would like to wire in a photocell and use a solar charging system with a rechargeable 3.7 battery as power-
    I do not understand the electronic schematics and their icons. think You all might show me in a + and neg.- graphic (pencil drawing) the circuit I could solder my pieces into place.You may not have time .to decipher this writing.

    Reply
    • Swagatam says

      Hello, you can configure the LED solar panel with a transistor to achieve your idea, as shown below:
      LED solar panel circuit

      Reply
  3. Sison says

    sir, Greetings..
    i tried several times with this formulae but failed .i use only 5 led.The problom is when after charging the lion battery output voltage should 4.2 volt then this voltage pass through led immediately burn one or two leds.Anyway to maintain constant current irrespective of voltage?expecting your valuable reply.

    Reply
    • Swagatam says

      Sison, I have tried this in many applications and has worked without any problems, in fact all cheap emergency lamps use the same concept. If it is not working for you then better use each resistor separately for each of the LEDs. Use the same the formula for calculating the values. In the formula the current will now reduce since a single LED is being calculated.

      Reply
  4. Ash says

    A single limiting resister can be used or not, when a 5V, 1A, 10400mAh output powerbank is used as a source.

    Reply
    • Swagatam says

      Single resistor is enough if the LED specs are identical.

      Reply
      • Ash says

        Thanks

        Reply
        • Juan Carlos says

          Greetings, sir. I want to connect a flash LED like what the cell phones use to a 3.7v battery equally the one used by cell phones, which resistance recommends me to use in this case? First hand thank you very much

          Reply
          • Swagatam says

            Hi Juan, different mobiles have different ratings for the flash LED, so you will have first confirm the current rating of the LED, then I can suggest the resistor value.

            Reply
  5. Sunil says

    Hi Swagatam,

    Your blog and explaining technique is very good. I learnt a lot about powering LEDs. Thank you.

    I need some help from you about my emergency light project which powered from 18650 x 2 batteries (3.7 v + 3.7v). I would like to glow 20 led (white bright) using parallel circuit. Please help.

    Reply
    • Swag says

      Thank you Sunil, glad to know you liked my site.

      Here’s the formula and calculations:

      Assuming you want to illuminate 5mm LEDs high bright type LED with 20mA current each, 20 of them in parallel would consume 20 x 20 = 400mA or 0.4 Ampere.

      The formula for calculating the current limiting resistor is:
      R = (Supply voltage – LEd forward voltage)/LED current
      R = (3.7 – 3.3) / 0.4 = 1 Ohm
      wattage will be (3.7 – 3.3) x 0.4 = 0.16 watts or simply a 0.25 watt standard resistor could be used

      for the emergency light circuit you could tr the following concept

      https://www.homemade-circuits.com/how-to-make-efficient-led-emergency/

      Reply
  6. Jason Nguyen says

    I think one drawback when you’re connecting LED in parallel is if one burn out the rest not emitting light.

    Reply
    • Swag says

      In parallel connection even if one of the LEDs burn others will remain illuminated, however today the LED quality has improved a lot and they will not get damaged as long as the specifications are correctly maintained, regardless of whether they are connected in series or parallel.

      Reply
  7. Swagatam says

    Hi, the problem is caused due to their higher FWD voltage drop rating than the other LEDs in the group.

    You must add resistors to each and every LED through proper calculation, as per the following formula:

    R = Supply voltage – LED optimal FWD drop rating / LED's safe current rating

    for example, for blue the above formula would go in the following way

    R = 3.7 – 3.3 / 0.02 = 20 ohms

    Reply
  8. Harry Cacharrytos says

    Hello, Swagatam. I like your blog very much.
    But you are wrong, the resistor is not at 3.3V, but it is under 3.7 – 3.3 = 0.4V, and the power it manages is 0.4 x 0.1 = 0.04 W
    Then, the resistor may be 1/8 W or less.
    Regards.

    Reply
    • Swagatam says

      thank you Harry, yes that's a typographical error by me.

      The wattage is always equal to potential difference across the resistor multiplied by the current flowing through it, that's simple Ohms law

      I'll correct it soon

      Reply
    • ta ajithg says

      Hai iam have 3.7v nokia battery and also have 3v bulb iam light a bulb easily but please tell what problem cause if i not vonnect a ohm resistance and also tell what type v resistor i need to light a 3 v bulb using 3.7v battery please help me thank you

      Reply
    • Swagatam says

      Hi, you won't require a resistor for a bulb, resistor is required only for LED….still for better safety you can use a 1 ohm resistor in series

      Reply
  9. grade school days says

    Resistors measured in Watts? What???

    Reply
  10. Irshad Qalandary says

    how to add auto charging and auto on/off LEDs when charger is plugged in

    Reply
  11. Swagatam says

    Hi, here are the details:

    3.0-3.4VDC Forward Voltage
    80mA Forward Current
    30 degree viewing angle
    16,000-20,000 MCD output

    connect them in series, use a single 10 ohm resistors, 1/2 watt

    Reply
  12. Ziyad Kanakkayil says

    Hi, who much voltage and current a 10 mm led require. I want to connect 4 10mm led to 12v bike battery in parallel. How much ohms resistance should I give. Whether parallel or series connection is optimum.

    Reply
    • Alex says

      Nobody can tell as there are thousands of different LEDs – you’d have to look up your particular LED and its specifications.

      Reply


  13. COMMENT BOX IS MOVED AT THE TOP


Primary Sidebar

Electronic Projects Categories

  • 3-Phase Power (15)
  • 324 IC Circuits (19)
  • 4017 IC Circuits (51)
  • 4060 IC Circuits (25)
  • 555 IC Circuits (92)
  • 741 IC Circuits (18)
  • Amplifiers (49)
  • Arduino Engineering Projects (82)
  • Audio Projects (84)
  • Battery Chargers (75)
  • Car and Motorcycle (87)
  • Datasheets (45)
  • Decorative Lighting (Diwali, Christmas) (31)
  • DIY LED Projects (81)
  • Electronic Components (97)
  • Electronic Devices and Circuit Theory (35)
  • Electronics Tutorial (99)
  • Fish Aquarium (5)
  • Free Energy (34)
  • Games (2)
  • GSM Projects (9)
  • Health Related (17)
  • Heater Controllers (23)
  • Home Electrical Circuits (98)
  • Incubator Related (6)
  • Industrial Electronics (26)
  • Infrared (IR) (39)
  • Inverter Circuits (94)
  • Laser Projects (10)
  • LM317/LM338 (21)
  • LM3915 IC (24)
  • Meters and Testers (54)
  • Mini Projects (153)
  • Motor Controller (64)
  • MPPT (7)
  • Oscillator Circuits (12)
  • PIR (Passive Infrared) (8)
  • Power Electronics (33)
  • Power Supply Circuits (66)
  • Radio Circuits (9)
  • Remote Control (46)
  • Security and Alarm (56)
  • Sensors and Detectors (115)
  • SG3525 IC (5)
  • Simple Circuits (72)
  • SMPS (30)
  • Solar Controllers (60)
  • Timer and Delay Relay (51)
  • TL494 IC (5)
  • Transformerless Power Supply (8)
  • Transmitter Circuits (38)
  • Ultrasonic Projects (12)
  • Water Level Controller (45)

Follow Homemade Circuits

Facebook
Twitter
YouTube
Instagram
My Facebook-Page
Quora

Feeds

Post RSS
Comment RSS

Circuit Calculators

  • AWG to Millimeter Converter
  • Battery Back up Time Calculator
  • Capacitance Reactance Calculator
  • IC 555 Astable Calculator
  • IC 555 Monostable Calculator
  • Inductance Calculator
  • LC Resonance Calculator
  • LM317, LM338, LM396 Calculator
  • Ohm’s Law Calculator
  • Phase Angle Phase Shift Calculator
  • Power Factor (PF) Calculator
  • Reactance Calculator
  • Small Signal Transistor(BJT) and Diode Quick Datasheet
  • Transistor Astable Calculator
  • Transistor base Resistor Calculator
  • Voltage Divider Calculator
  • Wire Current Calculator
  • Zener Diode Calculator

© 2021 · Swagatam Innovations