Help wiring 7,4-8,4v Cree light to 6v ebike light output

Hi,

I have a stock ebike with an Impulse Evo RS stock mounted system which works on 36V, but has two light connectors ( front and rear each outputting 6v) which seems to be enabled by default, even though the bike came brand new without lights. As I have a Chinese 3xCree headlight ~1000 lumens which has a died battery pack of 4x 18650 batteries outputting 7,2-8,4v I decided it would be easy connecting it to the 6v port and that it would just be dimmer, but It appears that there are other factors I have to consider.

1. It seems that the the headlight might have cut-off voltage controller and might not work with 6v. In such case I could try to open it and bypass it, but I don't know how safe that would be
2. It seems that the lights outputs of my bike have some limitations (I cannot find the exact values, but Bosch ones have similar and output 6v 8w for the front and 6v 0,8w for the rear light). The stock lights for my model are Supernova 160-200 lumens, but they put them only on the road versions and I have the MTB version. What would happen if I use the Chinese light which obviously has greater consumption? Would it just be dimmer, or would it not start, or would it demand higher power and eventually melt the stock wires?
3. I also have two 3v 2xAAA LED taillights. How could I safely connect them to the 6v 0.8W bike output. Just add the proper resistor (that should lower the current only, but should lower the possibility of overheating caused by the higher voltage) in series with one of them, or I should have DC-DC converter? Could I just wire both of them (as they are 3v each) in series, or LEDs don't work as normal bulbs? I know LEDs have forward Voltage and forward current but don't completely understand them and know how to measure them.

I like the idea of having stock-like lights connected to the main battery and don't have to charge/change batteries etc, but the original ones (Supernova 6v) are so expensive- the set of front and tail light costs around 200Euro. What is so special of the 6v ones that I haven't seen any Chinese ones?

If my idea is hard to accomplish I might use my Lezyne 900XL, which I use for helmet-mounting during night rides with my normal bike.

Why not just buy new lights that will work on your 36V battery pack?
http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=motorcycle+headlight&_sop=15
http://www.ebay.com/itm/2-pcs-LED-Work-Light-Motorcycle-Bike-Super-Bright-Aluminum-LED-Headlight-lamp-/132138484353
http://www.ebay.com/itm/Motorcycle-Car-Led-Fog-Tail-Lights-Rear-Anti-Collision-Safety-Warning-Lamp-New-/291737641782

@wesnewell - that is probably the easiest way, indeed, however:

A) I cannot just plug them into the system, because there are no available 36V free sockets and I don't want to void my warranty by tampering the wires. The battery charge plug does not output 36v- it is disabled by the BMS when not in use.
B) I won't be able to turn them on and off trough the system, which I want. Also the system has battery reserve for lights, which is considered in the remaining milage

My main concern would be burning out the drive circuit in the controller if the lights draw too much current. If I believe your Bosch numbers, 6V and 8 watts means the front circuit supplies 1.2A, and 6V 0.8 watts means the rear will supply .12A.

I have a 2LED "Cree" light, supplied with the usual 8.4V battery pack. It has no cutoff. My bench power supply will run it at 3, 4.5, 6, and 7.5 volts, although it's pretty dim at 3V. At 6 volts, my Cree's three brightness settings draw 0.4A, 0.8A, and 1.2A. I haven't checked it with my battery pack, because that's dead after sitting for several months. A three LED light might be expected to use 50% more current.

By the way, I once tried my Cree light on the 5V USB port from a Dolphin battery. It never powered up. Not enough current available.

If I were a customer service engineer, the above numbers are uncomfortably close to the Bosch specs, and I would follow the company line and not endorse using my light on your bike.

Thanks for the reply. That's what I am scared of - that I might burn something with the higher draw. I'll probably won't risk it and will use my all in one Lezyne light.

This is an 8.4V battery that I bought last winter on ebay. The charger stayed green, so I thought it was charged and never used it til this week. Well, it was dead. I opened it up.



What a POS. It was made with two unconnected cells. The blue ones were spot welded together. One of them is dead at .20 volts and the other is overcharged at 4.55 volts. The yellow ones have no connections at all, and read 3.5 volts. That's crazy.

There's no circuit protection either, and the cells do not have PCB circuits either. Thee things are crap.

I'm going to use a 110/220VAC power brick with a linear supply to run my light. I found a 12 volt unit that runs off 36V DC and will power my Cree.

The battery pack of my Chinese Cree light was absolutely the same knock-off - it had 2 unconnected dead cells packed there, so the Mah rating of the pack looks more plausible. Dead weight.