help needed for running a bike led light as a headlight.

giannisblessed

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Mar 28, 2015
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Hello everyone!
My name is john.

I want some help with a project.
i bought this light "7500"lm 5 xm-l t6 etc etc off ebay.
http://www.ebay.com/itm/391029237067?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

I want to install it on a little moped bike.
It has a 12v, 5ah, lead acid battery.

The light has a driver that *i think* has a max input voltage of around 8.4v.
the seller told me that it wont work below 7.4v but i have tested it with a battery pack made of 4x1.2v-AA bat wired in series and -albeit "just" 4.8v- it worked.
Then i hooked it up on my trimmer charger (ac 220v to dc? 3v @ 1000mA, 3VA) and it worked again.
so i suppose it doesn't matter at all even if the voltage is down to 3v.
I didnt notice any difference in brightness when using 4,8 vs 3 volts.
Do you guys think it has any diference?
maybe from 7-8v range?
The button led was solid red when 4.8v was used and blinking red when on 3v supply.

So the real question is...:confused:
i was thinking of buying a usb charger wich converts 12v to 5v and use it as a converter.

Is it a good idea or not?
also.
why?
will it be dimmer when on 5v rather than 8.4v?
if you guys think that it will be a good idea, what mA rating should i get.
is 1000mA enough?

please help me clear this out!
thanks in advance folks! :wave:
 

giannisblessed

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Mar 28, 2015
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update:

i tried wiring an extra aa bat to the pack (now total of 5 @ 6~7) and the button light turned green.
i can clearly see the perfomance increase.
so now the main question now is what route should i follow for converting 12-14v to 7-8.
 

RetroTechie

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Oct 11, 2013
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Hengelo, NL
Welcome to CPF, John! :)

7500 lm, you'll be lucky if it can output half that. :laughing:

Ehm.. would it be possible to have a look at the electronics inside? Parts used etc in the driver circuit may tell a lot about what input voltage it can take. Perhaps it could be wired directly to a 12V lead acid battery (but unless you know more, it's not safe to assume that).
 

giannisblessed

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Mar 28, 2015
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Welcome to CPF, John! :)

7500 lm, you'll be lucky if it can output half that. :laughing:

Ehm.. would it be possible to have a look at the electronics inside? Parts used etc in the driver circuit may tell a lot about what input voltage it can take. Perhaps it could be wired directly to a 12V lead acid battery (but unless you know more, it's not safe to assume that).

Thanks for the greeting!Nice to be here!
i tried to see but the pcb is glued on the allu heatsink and i didnt want to force it.
there is another update.
i found that the best and easiest solution would be to buy a universall car dc to dc converter (12 to 1.5,3, 4.5, 6, 7.5, 9) and set it to 7.5.

but i need to know what max amperage supply it should have.
if it can supply less than the light needs what will it happen?
does anyone know how many amps those chinese 5-led lights draw?
 

giannisblessed

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Mar 28, 2015
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just fyi i got hold of a multimeter and hooked it up.
@5.8v hi power was drawing only 190mA and lower 50mA
@6.8v hi power was drawing 1.2A and low 0.3A.
@7.2 1.45A and 0.45A

the brightness difference wasn't that big.
it is very interesting because if someone wants to save power and retain a good light output, that way this might be a good tradeoff.
so fwiw i ordered a minwa mw 292 http://www.soselectronic.com/?str=371&artnum=60940&name=minwa-mw-292
it is rated @ 2Amps max so i suppose i am ok.fingers crossed!
 

RetroTechie

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Oct 11, 2013
Messages
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Location
Hengelo, NL
i tried to see but the pcb is glued on the allu heatsink and i didnt want to force it.
Could you post a photo of the pcb as it is (glued to the heatsink) ? Or see if there's any IC's with readable markings on it?

@5.8v hi power was drawing only 190mA and lower 50mA
@6.8v hi power was drawing 1.2A and low 0.3A.
@7.2 1.45A and 0.45A
Haha... 7.2V @ 1.45A is ~10.4W, per LED that's ~2.1W. Which would give output of max. ~280 lm for that output bin (T6), cool white XM-L. For the 5 LEDs total, that would be max. ~1400 lm then. That is: with LEDs as claimed, well-cooled, and neglecting conversion losses. Don't think another Volt would make the output jump 5x ! :crackup: Makes one realise how ridiculous those claims for cheap eBay kit often are...

Btw. there's some cheap DC-DC converter modules (bare pcb) around that would have saved you the cost of lighter plug, wires, plastic case & adapter plugs. Personally I'd replace the innards of that bicycle light with such a module, so that you're sure it takes at least 15V or so directly. But I suppose that's a job for more advanced electronics modders. :)

Ah well, if that DC-DC adapter does what it says on the box, that should do fine.
 

giannisblessed

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Mar 28, 2015
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i managed to open it up.
how do i upload photos from my pc?
i measure the voltage that the driver is pushing to the leds.it was 14.5v
it seems that the driver steps up from 7-8v to 13.5-14.5 and the led are wired in line...
stupid question...
can i just wire them straight on the bike?
since they operate at that voltage?
 
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