Increase bike light brightness - QX9920

Flashlight Modding and DIY Parts
1

Hey there,

And I hope someone would be able to help. I have found an old thread regarding similar situation, but haven’t mange to obtain info that would help me.

I have a light from an ebike, that isn’t on a budget, but looking to make it better on a budget. :slight_smile:

It’s a Monkelink, rated at 50 LUX and 130 Lumens, however, when I compare it to the one I used previously, it ain’t enough. (500 Lumens)

What I like about this light is that fits and removes from a bike quickly via magnetic connector, and it’s getting power from the bicycle, big plus.

Ligh is also rated 6-12V and 1.6W, not sure if 1 6W is for the LED or…

It’s using QX9920 controller with a stepdown voltage regulator as far as I can see, and LED current is defined via 0.56 ohm resistor, the only one on the board.

I have no schematic, but I believe it not far away from a common one in datasheet of the QX9920.

What I am not sure, if I can only replace resistor with a less value one, or components like Coff and inductor maybe. :confused:

Also, I have no data what type of LED is inside, and how much can handle, but we’ll replace it anyway, once I figure out values. LED has a decent heatsink at the back of the board as well.

There is the same light rated at 250 lumens, I might look for those values if higher is not possible. And I have a feeling it’s just the same light, just tuned differently perhaps.

Attached are some pictures of the board, maybe someone can figure out from it what I can do.

Thanks. :slight_smile:

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2

No idea about the innards, but doubling the lemons from, say, 250 to 500, will visually only look about 30% brighter.

When I compared a 1000lm light with my new 2000lm light, my reaction was… “that’s it??”.

Anyhoo, those controllers normally use the inductor as a whole to determine the output current, and the smaller the inductance the more current is delivered, but at the expense of efficiency.

The resistor might only be a sort of ballast resistor, no idea.

Maybe check out some of The Big Clive’s videos, as a lot of things he dissects use similar control chips.

3

Might be a LED driver board of similar dimensions on AliExpress or kaidomain that will fit, might be easier than replacing components?

If you take a photo of the LED, people on here can advise about upgrades etc

4

Wellp, I goggled the datasheet just for shiite and giggles, and that resistor is most likely the current-sense resistor, set to whatever current puts ¼ V across it.

So if it’s 0.56Ω, it’d end up being roughly ½ A through the LED.

You could try parallelling a resistor on top of it, or in the “R2” spot if they’re in fact in parallel on the board, to boost the current… within reason.

Try for too much current and the inductor saturates before that, and it’ll just heat up if not burn up with no more current.

And the way those doodads are designed right on the edge, I wouldn’t try for pushing too much current through it.

And even if the LED can handle more current on paper, it’s gotta be heatsinked right, else it’ll just cook in its own juices.

So yeah, you can try it, but…

5

Was thinking getting similar sized board and LED to replace. But was thinking of trying out first. :slight_smile:

Below is picture of LED, and has a heatsink behind the board as well, that is actually whole top cover of the light made of allow, back of the LED pcb as well. So cooling should be good.

What I like about this light, next to the thing that takes power from the bike and clips in via magnets, it is design, more like a car headlight, where beam is directed, and probably I can achieve better road illuminance with less lumens. Compared to the other light I have, that scatter light all around, but still gets brigher as it’s way powerful.

If I achieve half of that other light, I’m happy, just need a bit more, then I have this rechargeable 500lm one for when I really need it off road or so.

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6

And the heatsink as well.

Also, I have found another resistor of 0.47ohm and gave it a try, current went up from 400mA to 480mA.

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7

Sorry for replying to myself… :slight_smile:

But I ordered some resistors and spare 2.5W (700mA) LED as it was only one matching dimensions of mine and available locally.

So I have replaced resistor with 0.33ohm one and current is now 700mA, left the factory LED and if it gets melted, I have a spare to replace. Not sure if I shall push it more due to the other components, looks quite bright now, I will test in the evening. But cooling really looks good here, so I might upgrade everything at some point.