Overvolting LED

[t_tberg]

So I added a tail light and turn signals to my 48v ebike. I'm using a DC to DC converting to power the lights, I read online somewhere that typical automotive electronics run on a higher voltage than the rated 12v, something more like 13v-14v. I have my DC to DC converter set to about 14V, the tails lights and turn signals work great. Now I would like to ditch the battery that came with the headlight* that I'm using (8.4v/4.4 Ah) and run it off of the DC to DC power supply. Will the higher volts destroy the light? I already purchased a 12v-85v LED for my 20s lipo bike. Should a just order another one of these variable voltage lights to avoid any incompatibility issues? I'd like to use the light I already have, if I'd have to end up getting another DC to DC converter I'd probably just get the variable voltage headlight. I'd like to see if I can save the $15 for the variable voltage light and just use the battery powered light I already have at a higher than rated voltage? Anyone have any experience with this?


*SecurityIng Waterproof 1200 Lumens XM-L U2 LED Bicycle Light 4 Modes - from amazon. I strongly recommend against this light, the battery was shorting out at two poorly soldered connections on what appears to be some kind of BMS or overcharge protection board. Also the light is only has 3 modes and it certainly doesn't appear to produce 1200 Lumens.

 

[wesnewell]

I wouldn't run a circuit designed for 8.4V on anything higher. It best it will drastically reduce the life of it. At worst it will blow the circuit immediately. As for a 12v device, it should be designed to work fine on voltages up 14.5V.

 

[t_tberg]

Thanks Wes, I'll probably just get another variable voltage headlight and tinker with the other one.

 

[Routybouty]

I have one similar to this and run it on 12V. It has a circuit inside that does a constant current to the LED. If you have a power supply, you can raise the voltage and see the current go down. This is the constant current effect (looks like constant power). The only issue I would see is if they used 10V instead of 16V caps. I've seen versions with NiMh batteries at 8.4V, but that's nominal and once charged up that's about 10.5V. I'd hope with 10.5V fully charged, they'd use 16V caps. I also modded it so it turns on full power when connected to power rather than having to press the power button every time. The one thing I did notice was the series resistance resistors with the indicator LEDs on the back were getting a bit toasty, so I disabled them. For my application (fairly narrow scope) I didn't need them and it works great.

So in short, it's been working fine for me for awhile. But, with it only costing $12 or so, I didn't care too much if it went out.

 

[Syonyk]

Now I would like to ditch the battery that came with the headlight* that I'm using (8.4v/4.4 Ah) and run it off of the DC to DC power supply. Will the higher volts destroy the light?

Probably.

I tested a similar "2000 lumen" Chinese light that's designed to run on an 8.4v pack.

http://syonyk.blogspot.com/2015/05/cree-2000-lumen-bike-light-disassembly.html

It started smoking around 12v or so.

I used a DC-DC converter to drop my pack voltage down to what the light runs on (set to around 8v) and it's been fine for quite a while.

http://syonyk.blogspot.com/2015/11/building-dc-dc-converter-to-run-cheap.html

 

[YonderGod]

Now I would like to ditch the battery that came with the headlight* that I'm using (8.4v/4.4 Ah) and run it off of the DC to DC power supply. Will the higher volts destroy the light?

Probably.

I tested a similar "2000 lumen" Chinese light that's designed to run on an 8.4v pack.

http://syonyk.blogspot.com/2015/05/cree-2000-lumen-bike-light-disassembly.html

It started smoking around 12v or so.

I used a DC-DC converter to drop my pack voltage down to what the light runs on (set to around 8v) and it's been fine for quite a while.

http://syonyk.blogspot.com/2015/11/building-dc-dc-converter-to-run-cheap.html

Nice blog. I have a light that looks exactly like yours, but the battery "pack" is the size of a single 18650 cell. Should I therefore assume that I need to use 4v instead of 8v if I do something similar to you? Also can you show how you connected it to your battery?
Thanks

 

[Syonyk]

Nice blog. I have a light that looks exactly like yours, but the battery "pack" is the size of a single 18650 cell. Should I therefore assume that I need to use 4v instead of 8v if I do something similar to you? Also can you show how you connected it to your battery?
Thanks

I would match what the light is taking. It could be using two smaller cells to get 8.4v, but stick a voltmeter on your battery pack & check.

And, connect it to your battery in whatever manner makes sense. I already had pack voltage running to the front of my bike for my Lumenator, so I split off that.

 

[YonderGod]

Nice blog. I have a light that looks exactly like yours, but the battery "pack" is the size of a single 18650 cell. Should I therefore assume that I need to use 4v instead of 8v if I do something similar to you? Also can you show how you connected it to your battery?
Thanks

I would match what the light is taking. It could be using two smaller cells to get 8.4v, but stick a voltmeter on your battery pack & check.

And, connect it to your battery in whatever manner makes sense. I already had pack voltage running to the front of my bike for my Lumenator, so I split off that.

I've never seen more than 1 device connected to a batter, do you just connect it like... parallel with the controller?

 

[Syonyk]

I've never seen more than 1 device connected to a batter, do you just connect it like... parallel with the controller?

... yes? I'm not 100% sure what you're asking. You just tap voltage off the lines.

I've got a set of Anderson connectors coming off the battery, and they connect to the bike side harness, which is mostly a pair of 10 gauge wires going to the controller. However, I tap off those wires (so see raw pack voltage) for my lighting. I've got a set of conductors going to my rear light, and another set going to my front light setup, where I've got a "Y" cable that splits this into a feed into my Lumenator, and another feed into the pair of DC-DC converters that feed my other two lights.

At some point, it might be worth adding a bus bar, but I just don't care that much right now, and the "horror show of wires" look is a decent bit of theft deterrent.