LEDs - are COB or SMBs offering the widest operational range in voltage and current?

It's time to put some lights onto my first e-bike project! My battery is 52V and it delivers in the range of 42-58V (roughly), and i'd like to be able to use four 12V LED in series without a DC/DC converter.

However when the battery is full, the LED should still glow with only 42/4=10.5V and when it's full at 14.5V it should not blow up.

I am wondering which (if any) of the following two LED modules is more likely to fit my requirements, the mono COB chip or 5730 triplet (which seem to have 151ohms resistor in between each LED according to one of the pictures from the link below):




Here are the links to the relevant products (chinese website), however, no clear information on forward voltage or max current is provided there...


COB module on Tmall
5730 triplet module on Tmall

I would be tempted to run a converter so light output is constant across the discharge cycle.

lionman said:

I would be tempted to run a converter so light output is constant across the discharge cycle.

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I get you, however that'd be yet one more electronic component to protect from water, hide and pay for. If someone would demonstrates that these type of light won't light up at 10.5V or will blow after 10 hours of use at 14.5V, then I'd consider the converter, for sure

It will hardly break the bank.

Waterproof ones can be had pretty cheap.

https://www.ebay.com.au/itm/Waterproof-DC-DC-20V-60V-Step-Down-to-12V-10A-120W-Voltage-Buck-Converter/182779988487?hash=item2a8e894a07:g:W9cAAOSwR2RaNmzC

You will also have more flexibility in the number of LEDs you can install.

There are plenty of cheap and effective lights that feature internal regulation. Search eBay for "12-80v led" or "12-100v led". The ones I've tried have the same or at least very similar brightness whether they're powered with 12V, 24V, or 48V. They all cost less than $5 including shipping. At that price, the couple of defective ones I have received are no big deal.

My e-bike has two of these at the moment:

It's is the brightest of four different kinds of lights I tried out. This kind consumed about 3.5W when I tested it on 12V. After popping the wire lead like a fuse on the first one I installed, I found that the wire passes internally through a very sharp-edged hole in the structural bracket/heat sink. I sleeved the problem area with some heat shrink tubing before installing the other two I had.

All the other three styles of voltage-versatile lights I tried had tilting mounts that seemed pretty flimsy compared to this one. The one I'm using has a formed piece of sheet steel serving as both heat sink and mounting bracket. It must be bent to tilt the light, but it appears to be stronger and less failure prone than the others.

I use this light as a taillight. It's the only red one I found that would run on a similarly wide range of voltage:

It is extremely bright, flashes at a higher rate than most blinky bike lights, and casts a needlessly concentrated spot of light. I scuffed the plastic lens with a Scotchbrite pad to diffuse the beam.

respire said:

COB module on Tmall
5730 triplet module on Tmall

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5730 version has written "digital constant current chip" but clearly shows two 150ohm resistors (in parallel? that's 75ohm). If those resistors are in parallel, then there's about 30mA draw @ 12VDC. 14,5V will roughly double the current. 10,5V from my experience means about 15-20% from full 12V.

Neither of the lights have any optics to them, so that alone makes them useless as headlights. COB LED's are especially bad in that there's virtually no optics available due to their form. COB's are meant for wide area lighting.

From pictures it looks like both have plastic housing, which in effect will limit their power to ~0,5W or less - again useless for a headlight.

There are many decent lights that have high voltage driver built in. Try to get with decent LED (from Cree, Philips Lumileds, Osram etc) and optics.

Appreciating everyone's input, thanks. Still, I would love to know if people have information about the question I put as a topic title. Is it fair to guess that based on their architecture (no PCB, built on a sheet of aluminium), the COB will dissipate heat more efficiently, and then dissipate the Watts of overcurrent better provided there is something to act somewhat as a heatsink ?

To be more specific on my needs:
- We're talking about « be-seen » lights here rather than « seeing ». I am planning with a 12-80V headlight with integrated driver as a complement.
- On my setup, these day running lights need to be encapsulated in a 26mm diameter aluminium tubing. I haven't found a light with integrated driver that meets this criteria. For the curious the bike is an Omnium cargo, and the lights will be encapsulated in the tubing of the rack.

@Minimum, I appreciate the quantified estimates . However the housing of these LED module is aluminium, not plastic, which could perhaps help draw some heat away from the LED (in particular in the case of the COB?). I was actually planning to wrap the threaded area with aluminium foil up to the point they are a snug fit in my 26mm tubing. That could allow more heat dissipation but it all depends on how good is the contact between the COB and the alu housing...

Does dissipating the extra Watts due to overcurrent (@14.5V) seem a feasible option to preserve the light longevity?

respire said:

Does dissipating the extra Watts due to overcurrent (@14.5V) seem a feasible option to preserve the light longevity?

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The response of LEDs to small changes in voltage with large changes in current makes overvolting them a very bad idea. However, there's an easy fix. Figure out what their rated current is, and then test them to correspond that current with a specific voltage. Then add a dropping resistor in series to consume the overvoltage at that current. For example, say your COB is rated for 500mA, and it consumes that amount of current at 12.0V. If you want it to behave well at 14.5V, add a resistor that drops 2.5V at 500mA and is capable of dissipating at least 1.25W of heat. That's a 5 ohm, 5W resistor. It should cost you about two bucks.

My six watt example is probably more than you need for a be-seen light. So in your case you'll most likely be able to use a 1W resistor.

You could use a series of power diodes to drop a fixed amount of voltage, but the beauty of the resistor is that it will drop more voltage when there's more current, and less voltage when there's less current. That way your loss of light output is less pronounced as the battery voltage diminishes.

You might try looking for a regular flashlight that has the right OD and just make a driver for it. Constant current drivers that handle a wide range of input voltage are not that expensive.

The aluminum-mounted LEDs might be easier to sink the heat from...but it's better to not generate that heat in the first place.



Off the topic of which LED type is more applicable, but on the topic of be-seen lighting, from my years of street riding experience using various lighting setups:

Larger surface area lights are better than bright small area lights, given the same total illumination. It's easier to see, and can make you appear closer to the viewer than the small lights do, which tends to make them react faster to changes in your riding/direction/speed/etc.

If you can use LED strips (available in rolls of waterproof, cuttable sections, that run off 12V), mounted along the frame in traffic-facing directions, with appropriate colors for each end/side of the bike, it'll make it pretty visible day or night.

At night, you can also add white lights mounted on the bottom of frame sections all over the bike, that shine down on the road and the rest of the bike itself, so the lights themselves are not visible. This makes the area around the bike a light pool that moves with the bike, and makes it appear larger / closer to viewers, again making them react sooner to you, and pay more attention to you.


Basically the more surface area you can light up, day or night, it'll make you more visible, without any individual light having to be all that bright.



Single bright lights can also work, but they're easier to miss than a bunch of other lights (or a large area of light) all moving together.

For daylight "be seen" lights I'd seriously consider something that flashes (check local laws first - and note that motor vehicle laws may or may not apply to an e-bike.) I run a second small headlight during day riding that I can set to flash. At night I set it to amber. Flashing lights at night can, IMO, be a bit obnoxious. But during the day, they are more likely to be noticed.

My concern with your series arrangement is that if one light fails, they all fail. FWIW, I run a 12 v converter that is potted and waterproof. The extra device doesn't add enough weight or complexity to be a noticeable bother or problem. I went this way because there are so many 12 volt lighting options out there.

It is always nice when things can be kept simple, and easy. For this particular scenario, I think you are stretching it into the range of "need to replace burnt out units very often" range though.

But lets look at some data.
Here is an example of the typical characteristics of a white LED.
http://www.resistorguide.com/applications/resistor-for-led/led_i-v-characteristic/

The difference between nothing (0mA) and 20-25% too much (25mA) is only 1V

In 12V strings, with 3 LEDs in series, this typical characteristics allow for a span of 3V between 0mA and 25mA, for your 12V LED string.
You are wishing for 14.5V - 10.5V = 4V range.

It seems to me that you will need to study datasheets, and/or do some testing, in order to find a LED string (or COB) that has the 4V range that you want.

Also be aware that an overheated LED will eventually experience a thermal-run-away-condition, as the internal resistance is lowered at higher temperatures, which causes more current, which causes more heat, which causes..... and you LED died.


Another issue is, that when your battery is fully charged, you will be wasting energy on something that is not needed or wanted. You do not need that much light, nor the heat that they produce.

Is dipping a DC-DC converter in some epoxy (or getting one that has already been dipped) really such a big or difficult task, that it is worth it, to try to run things at the limits of their physical abilities?


I do however like your idea of lights to make you seen, and not only headlights to make you see the road.
So I already ordered some COBs (white and red, last week, and am currently waiting for them to arrive. And then I will be testing COB versus LED strips.
Only, I have already decide to use DC-DC converters.

You all convinced me. I'm getting a DC-DC converter.

Also I'll be getting these eagle-eye lights in white and in red with integrated turn signal. That is to say, half of the 12 4014 LEDs are powered with a different wire and shine amber. Now I'll need to wire a blinker of some kind to get the proper « turn signal » effect. Just mentioning for those who didn't know that existed.

This vendor has white+amber and red+amber (the red+amber version is quite rare)

I just use a regular car LED-compatible blinker from Checker/autozone/etc. Works fine. On my bike I used an old 1980s Honda scooter handlebar control for the switches. On my trike I'm using a plastic "ebike" version of the same thing, that actually came with a kit as a 3-speed switch (but is marked with turn signal arrows), and I use the headlight switch to control the separate downlighting.

Teklektik's Yuba cargo bike thread has detailed wiring / schematics / parts lists for his lighting/signals/etc if you're interested.