Wiring single LEDs

[builderbob]

I'm working on a cool little project for the FJ that involves wiring up some single LEDs.  I want to combine 3 LEDs in one fixture.  As far as I have been able to tell, you have to combine as many LEDs in series as it takes to equal the voltage of the power source, or put a resistor in the series to drop the voltage down to equal the voltage demand of the LEDs.
 
My project uses 3 LEDs at 2.2 V and 20mA each.  Combined in series, they will require 6.6 volts.  Any more than that from the power supply (12 V) will fry them.  Question is, what resistor should I use to create the 5.4 V drop that I will need?  Also, will the resistor be installed in series with the LEDs or another way?
 
Thanks in advance!
 
 

[angrygirafe]

I might suggest doing this differently, but LEDs are cheap, so feel free to experiment. The three LEDs don't require 6.6 volts; each one requires 2-2.2V. In series, if you want the last LED to get 2.2V, the first one would have to get 6.6V. Voltage drops in series, so if you wire them in series with a resistor, the first LED will get 6.6V, the second LED with get 4.4V, and the third LED will get 2.2V. Depending on how sensitive they are, that might just blow the first two LEDs. Personally, I'd wire them in in parallel with each other, and in series after a resistor, that way each one is getting the 2-2.2V. V=IR, you want a 9.8-10V drop, current adds in parallel, so you have a draw of 60 mA. So R = (9.8 to 10V)/(60x10^-3A) = 163.3 to 166.6 Ohms. So you'd have you power source, then resistor, then each LED connected to the end of that resistor, and each LED then going to ground.
 
If you want to try it your original way, with a 5.4V drop, current is constant in series, so R = 5.4/(20x10^-3) = 270 Ohm. Again though, it means that first LED is getting hit with 6.6V, and might just pop.
 
Hope that makes sense.

[builderbob]

Appreciate the tip. Electronics of this nature are not my forte.
 
I ordered a breadboard with some jumpers and a variety of resistors. I'll do some experimenting.

[estell]

what resistor should I use to create the 5.4 V drop that I will need?  Also, will the resistor be installed in series with the LEDs or another way?

 
You can use either of the following circuits.
 

 
I recommend to connect the diodes in series. You'll get 2.2 Volts ACROSS each diode, you'll draw less current from the battery (20 mA vs 60 mA), and you dissipate less power in the resistor (108 mW vs 600 mW).
 
 
 
 

[BBB]

Voltage is shared in series according to resistance so Estell’s top diagram looks good to me and the maths looks good.

[builderbob]

Ok, I'm back. I've got my breadboard and resisters. I wired up 3 of the LEDs in parallel to each other downstream from the resistor. I tried several different resistors and they didn't seem to make any difference. The LEDs all lighted and I didn't blow any.
 
That said, I think I want to go with brighter LEDs, which take 20mA and 3.2 V each. I also want to use 4 instead of 3. What resistor should I use with this setup?
 
Thanks for your help!

[builderbob]

I found an easy to use dropping resistance calculator online.  According to this, I need a 150 ohm resistor for this circuit.
 
I'll post up some pics of what I'm doing a little later.

[boybot]

Don't forget your FJ is putting out closer to 14V when running and 12V when off. Are you using a reflector because these LEDs have a tendency to be washed-out in daylight.
 
I'm in the process of doing a custom lighting job on my Givi V47 with running, brake and turn signals. I opted for Chip On Board (COB) LEDs. Easy to wire as they can be found in a variety of low voltage (3-40V), low profile. They are extremely bright and visible in the day light. You can also get dual-color (white-amber & red-amber) options now. The only major downsides that I've found thus far is the available sizes, rigid (I bent a curve in mine but it's a careful process a.k.a. buy spares) and excessive heat if run at full power for a time. - I'm using a 3W 12V rated COB, operating at about 1W for my running light and kicking it up to 2W for the brake. No noticeable heat build-up issues in preliminary tests.
 
I'm using the 12010 (12-14V, 3-10W) here - https://www.aliexpress.com/item/10pcs-50-7mm-3W-5W-COB-bar-wall-desk-lamp-lighting-source-LED-chip-on-board/32722604378.html?spm=a2g0s.9042311.0.0.75e84c4dFPqIkn
Link to the dual color COBs. https://www.aliexpress.com/item/12V-COB-LED-Lamp-Light-Bulb-5W-DIY-High-Power-Lights-Strips-Lamps-Source-400ma-Red/32853719037.html?spm=a2g0s.13010208.99999999.291.5b213c00iUNyWa

[builderbob]

Don't forget your FJ is putting out closer to 14V when running and 12V when off. Are you using a reflector because these LEDs have a tendency to be washed-out in daylight.

Thanks for the info.  I'm doing sort of an accent piece that doesn't necessarily need to be seen in the daylight, so the LEDs that I have will work fine.  Looks like my installation will need a circuit board though, so I'm on hold again until it arrives. 
What's your project?

[boybot]

If your building a super simple circuit, say an in-line resistor plus LEDs that are mounted in something, you can skip the circuit board just use a piece of heat shrink tube or liquid electrical tape to protect/insulate the circuit components. This is my plan since my circuits are resistors and a diode, although I still need to house my homemade (repurposed relay connector) fuse block. Circuit boards are great for organizing and building complex circuits but add bulk that you have to figure out how to hide, house, protect.
 
I'm in the process of putting turn signals, running and brake lights on my Givi top case. Givi sells the brake light kit for $65 but I wanted all the lights tail lights...and a project. I think I should have it fully wired/operational within the week.
 
 

[builderbob]

If your building a super simple circuit, say an in-line resistor plus LEDs that are mounted in something, you can skip the circuit board just use a piece of heat shrink tube or liquid electrical tape to protect/insulate the circuit components. This is my plan since my circuits are resistors and a diode, although I still need to house my homemade (repurposed relay connector) fuse block. Circuit boards are great for organizing and building complex circuits but add bulk that you have to figure out how to hide, house, protect.  
I'm in the process of putting turn signals, running and brake lights on my Givi top case. Givi sells the brake light kit for $65 but I wanted all the lights tail lights...and a project. I think I should have it fully wired/operational within the week.
 
 
 

That's a good suggestion.  I'll have to do some more thinking about how I'll arrange it. 
Post up when you've completed your project.

[rain]

Here's an online calculator for LED circuits.
https://www.quickar.com/bestledcalc.php?session=
 
 
I made this for my old RT:
http://mkb.users.sonic.net/bike3.jpg
http://mkb.users.sonic.net/LED1.jpg
 
 

[builderbob]

Here's an online calculator for LED circuits. https://www.quickar.com/bestledcalc.php?session=
 
 
I made this for my old RT:
http://mkb.users.sonic.net/bike3.jpg
http://mkb.users.sonic.net/LED1.jpg
 

That calculator is perfect!  Thanks for the link. 
Your light bar is Cool!

[builderbob]

A little preview:
 

 
The emblem is just held on with some scotch tape for this pic, but will be secured with 3M trim tape for the final installation.  The whole thing will replace the emblems on the side of the fairings.  4 LEDs will stay lit while the bike is running.

[builderbob]

I redid the lexan bases for the project. Wanted them to flair out a bit from the emblem to where it attaches to the body work. I like the results, but there are a couple of things I would design differently if I attempted it again.