rear lights.... why not use lots of led's in series ?

I need some decent rear lights for my bike... but can't find any...

thinking I might get 20x3.6v flashing red LED's and wire them in series (for my 72v battery)

slide them into some clear hear shrink, and then cable tie them to the back of my bike to make me nice and visible...


could even make the heat shrink into an upside down U shape so it goes up one side of the wheel, over the top and down the other side
(won't exactly be like that, but it would look like that from behind)

then I could spread 20xflashing over it's length

and put 40xultrabrights in there too, and wire them up as a brake light ?

By the time you do all that, it's probably cheaper to buy strip lights like Auraslip and others have done, and run them off a small DC-DC converter, or even just a small current regulator (which you will still need with your idea--if you don't use something to regulate current, then the LEDs could be damaged if current ever spiked above their limit for any reason--say, a short in the wiring that shorts around one or more LEDs, etc.).

But it is certainly possible. If you dig around on my old http://electricle.blogspot.com for DayGlo Avenger's old lighting system when I was using friction drive on it, and before, there should be some schematics on how I did it resistively on a 12V SLA, with 4 LED stacks, IIRC, maybe 5, and a small transistor (like 2n2222) to switch more current into the front markers for turn signals, and toggle on/off rear signals/markers and brighten the taillight for braking.


If you don't mind the size and have a rack or seat to mount it to, you can also use DOT-approved waterproof LED tail/brake light setups off motorcycles and scooters, on a small 12V DC-DC or it's own battery. For a while now, I've used one on DayGlo Avenger on a small DC-DC that runs all the lighting on it.

running 72V through thin wires to your lighting array....*brrr*

I'll put my money on a decent dc dc converter.
Or on a 18650 battery. Charge it ones half a year with your RC charger and you're good to go...

it doesnt have to be all rocket science

Monstarr said:

running 72V through thin wires to your lighting array....*brrr*
I'll put my money on a decent dc dc converter.
Or on a 18650 battery. Charge it ones half a year with your RC charger and you're good to go...
it doesnt have to be all rocket science

Click to expand...

I'll stick a fuse on the line to it

going to have more now, flashing red for all the time, bright red for break lights, and yellow each side for indicators

knighty said:

thinking I might get 20x3.6v flashing red LED's and wire them in series (for my 72v battery)

Click to expand...

Not likely to work if all the LEDS are flashing type and kind of a waste.
I imagine one flashing one in a string of normal LEDs would make them all flash. been a while since i played with flashing LEDs though.

I'm a big fan of Maxxon lights. The batteries last forever and the lights are bright. The brake lights turn on when it senses a gyroscopic shift (or something like that.)

Link: http://www.amazon.com/gp/aw/d/B004D2KBFA/ref=mp_s_a_1?qid=1363421841&sr=8-1&pi=SL75

the problem is finding a rear light bight enough so I stand out in the dark, doing 30 to 40mph on a road with cars doing 70mph
(fastest road I go on is supposed to be 50mph, but in England speeding is normal)

and then again, I want to stand out in the day when it's bright and sunny

up one side of the wheel, over the top and down the other should give plenty of area/light for everyone to see it - including from the sides

I tested 3 x flashing LEDs in series on a 6v battery just to see what they're like - it's the first time I've ever used a flashing led... they all seamed to flash independently of each other, but I'll test again by putting extra LEDs in parallel with a one which is already flashing and see what happens

oddly enough, the LEDs I bought are 3.2v, but when I tried 2 in series on a little 6v battery they poped/blew almost instantly... no idea of the charge in the 6v battery, but it's a sla which has been sitting for months and I've used a few times... never been charged

I'll have to be careful with the 72v strong not to pop them all, I was going to build it for over 90v anyway because I'm 89v hot off the charger, not really my area but I guess I can test the resistance of the string in series and work out if I've got enough or not before I connect them up



I've got an 18watt led headlight on the front running straight from the battery too, and it's awesome, so bright I have to point it down at the floor so the focal point is about 3 feet in front of the bike... the area effect is mroe than enough to light up the road/surroundings for me, and it means I'm easy to spot from a good distance away

I'm thinking of adding another pointing straight ahead for my new bike for when I'm off road

knighty said:

they all seamed to flash independently of each other, but I'll test again by putting extra LEDs in parallel with a one which is already flashing and see what happens

Click to expand...

They'd have to be in series to flash with that one.
In parallel the only way their brightness will change is if all of the paralleled LEDs including the flashing one share a current-limiting resistor, and the current is just sufficient thru it to properly light all LEDs at the same time. When the one flashing one turns off, the others might get a bit brighter.

oddly enough, the LEDs I bought are 3.2v, but when I tried 2 in series on a little 6v battery they poped/blew almost instantly...

Click to expand...

LEDs must be current-limited, they don't operate solely by voltage. They're not quite like other diodes. (I made reference to this previously in this thread)

knighty said:

the problem is finding a rear light bight enough so I stand out in the dark, doing 30 to 40mph on a road with cars doing 70mph
(fastest road I go on is supposed to be 50mph, but in England speeding is normal)

Click to expand...

Try my creation:

[youtube]dXSZkQNI9Ok[/youtube]

Details here: http://tinyurl.com/crazybright

that looks pretty good, I thought about a red lens for a white light but wasn't sure how good it would be

I've got all the LEDs now so might as well give them a try

so what's the best way to current limit these LED's when I put them in series ? stick a red 12v bulb in series with them ?
(maybe run 12v bulb at 6v for better reliability?)

most people use a resistor to current limit an led. do you have any idea of what the forward bias is for the leds and how many you plan to use. will they all remain on at the same time or will you use something to interrupt the current to make them flash?

knighty said:

that looks pretty good, I thought about a red lens for a white light but wasn't sure how good it would be

Click to expand...

works fine but it wastes most of the light--red is only about 30% of white light.


The Fusin tailights I have on Delta Tripper here:

just under the bottom corners of the SMV sign are white LEDs with a red cover; they look pinkish-red compared to the white incandescent in the red-covered motorcycle taillight at the top of the sign. (which isn't on in the pic--the LEDs are on but the camera flash makes them less visible than the yellow (pedal type) reflector that's inside the red housing with them).

They work ok, but are much brighter without the cover on...but can't be used as taillights that way, of course.

This is what they look like close-up wth the cover on


and without it


This is what they look like with the red lens on


vs what they look like with it off:

flashing in series? bad news.
Solid in series? that can work.

If you've ever seen a string of LED lights designed to hook up to a 120v outlet, you may see them all rigged up in series. Maybe they have a resistor to limit current too but i'm not sure.

I noticed this DC-DC convertor on ebay. Just £5 for a 5 amp matchbox sized variable voltage supply http://www.ebay.co.uk/itm/251244750741?ru=http%3A%2F%2Fwww.ebay.co.uk%2Fsch%2Fi.html%3F_fspt%3D1%26LH_CAds%3D%26_udlo%3D%26_sadis%3D%26_sop%3D12%26clk_rvr_id%3D465463381448%26_sacat%3D%26_fpos%3D%26_mPrRngCbx%3D1%26_udhi%3D%26_nkw%3D251244750741%26_rdc%3D1
Perhaps you could find cheaper, but the cost is certainly manageable. Set it for 12v and you have 60w to play with. Then resistor up each led for use at 12v. A 3.2v 20mA led will want a 470 ohm resistor if used on 12vdc.
Much usefulness http://ledcalculator.net/
You will be able to turn it up and down :|

Edit: Having 12vdc on hand will make adding a further led possible, without having to use up 72v again. That can be done with a single resistor of course, but the power lost in it will be enough to run 19 more. With that in mind, you shouldn't really do the 470 ohm resistor with a single led. Instead, run 3 leds is series then a single resistor of 120 ohm. Each string of 3 along with the resistor can run off the 12v. Reducing power consumption by a whopping 66%

The 3 (or 4?) LED series for one resistor approach is what I used when I built DayGlo Avenger's original marker lights and turn signals. That's not on ES, but there is an instructable that covers some of it,
http://www.instructables.com/id/Bicycle-Safety-Lighting-and-Turn-Signals-From-Mos/#step1
(and another for the CFL lighting I used on CrazyBike2--taillight is stil in use now, years later)
http://www.instructables.com/id/CFL-Headlight-and-Taillight-for-Electric-Bicycle/step1/What-youll-need/
http://electricle.blogspot.com/2009/11/diy-cfl-hl-wdc-dc-inverter.html


and more details on my old http://electricle.com project blog, icnluding types and resistors and currents and stuff.
http://electricle.blogspot.com/2008/05/let-there-be-light.html
http://electricle.blogspot.com/2008/05/red-light-district.html
http://electricle.blogspot.com/2008/06/lights-camera-action.html

it should be simple to find the forward bias of the led so that you know what the total voltage drop across all the leds is for specific current. and the current would be determined by the resistor used so that the battery voltage is consumed byt the total led voltage drop and the voltage drop across the resistor. V=IR.

making them flash changes things though. then you are stuck using the DC converter to handle the huge current surges.

I got these for always on
http://www.ebay.co.uk/itm/290771894024?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

and these for flashing
http://www.ebay.co.uk/itm/390124003329?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649


problem is dc-dc converter is not many are happy with my 90v hot of the charger


can I just stick a few extra in series to limit the current ?

do you understand what the forward bias of the diode is? do you have some idea of how the circuit works? you need to find out how much current you are gonna push through the diodes. find the forward bias for all of the diodes at that current. the difference between the total forward bias of all the leds and the pack voltage is the voltage you have to drop across the resistor and if you know the current you are pushing through the diodes then solve for the resistor value. and then figure out what power you need to dissipate. buy a resistor at least twice as large as the power you need to handle in the resistor. or resistors if you add them in parallel.

20mA normal, 30mA max

I think you've missed something, I'm not using a set number of LEDs, I'm going to make the string log enough to run straight from the battery

I'm just not 100% on how long it should be, was hoping one of you guys could tell me

What's the forward voltage of the LEDs at the current you want them to run at, to get the brightness you want out of them? Gotta know taht to figure out how many, and to find teh resistor size (wattage and ohms) you'll need to limit the current.

Keep in mind also that the flashing ones may only work within a very narrow voltage range--they are probably self-limiting on the current because they have internal electronics, but because of that they may work only at the voltage they say they work at, and not above or below it more than a very tiny amount. They will probably not work in series, or at least not as you expect. If the electronics inside does not interrupt current thru them entirely, but simply thru the LED portion inside, then they may be able to work in series, but it is likely that either they interrupt current almost completley or (less likely) that unless the LED is on, they can't handle the current passing thru them. You'll have to test the idea.



Also, you need to calculate number of LEDs and dropping resistor for the hot-off-the-charger absolute max voltage of the battery. And remember that the LEDs will simply get dimmer as voltage goes down. (how much dimmer depends on how much difference there is between the full charge and the LVC of your pack--high enough number of series cells and it could happen that the LEDs will be so dim as to be invisible by the time the pack runs out, depending on chemistry and voltage curve).

http://led.linear1.org/led.wiz
This ^^ says this:

Uploaded with ImageShack.us
That link also says you could have up to 28 leds in a chain using 90v, and the resistor would need only be 18 ohms. It won't run red hot either.
I set a 25ma current thinking battery voltage can only come down.

Sorry my own regulator choice won't reach past 60v supply. I was not thinking.

You are indeed at an awkward voltage. I do have some thoughts though. A usdm wall adapter of the switchmode variety may recieve 120vac but iirc it turns to it dc before it does anything. I often see a world standard specification on chargers of 85-285vac. Well 85-Something anyway. I suspect with 120vdc you could just plug them straight in. It is certainly something I would look at had I not settled under 60v

wow, great link ! thanks for that, don;t know why I didn't think to google for an led calculator !

to be exact I'm 89v hot off the charger right now

with that and a string of 27 LEDs I'll need a "120 ohm resistor dissipates 75 mW"

72v through the string will drop it down to about 80% which should be enough for me


to test the blinking LEDs, I ran 3 in series on a 6v battery and they were all fine, and flashed independently of each other


thanks guys

I'll post photos when I'm done

you should use an ammeter in series with the leds to see how much current they use and measure the voltage across the led with a voltmeter while it is on to find the forward voltage at that current.

dnmun said:

you should use an ammeter in series with the leds to see how much current they use and measure the voltage across the led with a voltmeter while it is on to find the forward voltage at that current.

Click to expand...

I've got the manufacturers specs (posted links above)

was just going to check the resistance of the string to make sure everything is right before I connect it to the battery

you cannot measure resistance. it is an led.