VICMAX A8 8X CREE XM-L2 LED Max input voltage?

Fabian
Fabian Registered Users Posts: 134 ✭✭
in Construction #1
I have a VICMAX A8 Led bike light. It comes with a 8.4V 1A Li-ion smart charger to charge the battery pack.

Here is a web link for the light:
https://www.aliexpress.com/item/VICMAX-A8-13000-lumen-8x-CREE-XM-L2-LED-Front-Head-Bike-Bicycle-Cycling-Lamp-light/32543657145.html

I abandon the battery pack and bought a dc-dc 24v-7.5v dc buck converter which I connect to my ebike 24v battery to power the Led light.

What I want to know is if its safe to power the light from 9V? as I was planning to buy a 24v-9v dc buck converter to use which would make the light much brighter.

Seeing that 9v is not far from the 8.4v output of the charger as when the battery pack is fully charge it reads 8.4v would the 9v cause any issues with the circuit or the led bulbs causing them to degrade faster or burn them out immediately or any other issues?

if not would it be safe to run it on the 9v constantly like with the 7.5v?
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Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    LED's are a current device, not a voltage device.   Most "lights" have a internal driver to control the current.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #3
    My understanding may be flawed (if so, constructive critics welcomed). At a higher voltage, the risk would be insulation within the light being insufficient to prevent an arc/short. 8.4v to 9v seems to me to be likely within a reasonably safe range though.

    That said, some DC-DC converters are fixed output, and others proportional. If proportional, and the bike battery charges at say 29v, the light may see more like 11v.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
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  • Fabian
    Fabian Registered Users Posts: 134 ✭✭
    #4
    i test the 7.5v converter. It always read 7.5v
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,626 admin
    #5
    With LEDs, the actual explanation is more complex...

    LEDs (Light Emitting Diodes) are forward biased diodes. And they have highly variable "resistance". Depending on current and temperature, the "resistance" can either drop the light output by a bunch, or let so much current through (hot LEDs, the lower the threshold voltage), the LEDs overheat and fail.

    Typically, for LEDs, you have a voltage source and some sort of "ballast" to control the current flow (1.0 amp, or whatever). That can be a simple resistor (wasted energy "heating" the resistor to limit current flow). Or, instead of a "voltage regulator", you use a "current regulator" instead (turns out that voltage and current switching power supply regulators are almost the same--Just a change to the feedback circuit).

    So, when you have an 8.4 volt Li Iion battery bank (18650 cells, probably 4.2 volts maximum), you can either have a "simple" resistor circuit to limit current (and as the battery bank discharges/drops voltage, the resistor lets less current through)... Or you can use any number of different solutions (switching, buck switching regulator, etc.).

    And, depending on the regulator type, that will set the acceptable input voltage.

    If you want to hack your light... Here is a very good forum to browse through (lots of LED information and driver electronics):

    https://www.candlepowerforums.com/vb/forum.php

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • kc8adu
    kc8adu Solar Expert Posts: 50 ✭✭✭
    #6
    your xm-l2 led has a vf of around 3.2v.
    so a 2s(8.4v) setup must use a buck driver.
    i am guessing you have a light based on a common flashlight driver and many of those run up to 4s without issue.
    a pic of the driver will help a lot.
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