MR11 6v 6w Cygolite Rover Metro Bike Light LED Bulb Replacement?

[P.A.K.]

Hi, I have an older Cygolite Metro/Rover that uses dual 6v 6w MR11 halogen bulbs. I'd love to replace the bulbs with LED units in order to get extended battery life with the light. https://imgur.com/a/27XSqF0 I just bought a new 6v sealed lead acid battery so I'd like to be able to use it rather than replace it with a 12v. I've searched the web for a 6v 6w MR11 LED replacement but can't find any. Does anyone know if they even exist? I'm guessing that any LED bulb with different voltage or wattage won't work with the 6v battery. I'm technical, but not super handy, so I'm not entirely confident I could build one myself unless there were idiot-proof instructions. If anyone could offer me a solution or replacement idea I'd be most appreciative. Thanks, PAK

 

[gilesa]

For longer battery life, you will need a lower wattage, with the better efficiency of LEDs compensating.
You may find that one of the common 12V ones will work. The one I tested produces useful light
(but not full output) from 2 1.5V alkalines and about 50% (metered) from 5V DC. It was not happy
at 5V, warmer than at 12V and started blinking off. But behaviour will likely vary with make,
and mine was a cheap own-brand version

 

[Dave_H]

I am not sure this will work for you but this is what I discovered.

I have a novelty lamp which used a 12v 5W MR11 halogen running at lower voltage approx. 6v (ac from
a wallplug adapter) which produces adequate brightness. This funny lamp resembles a small flying
saucer, lamp shining through internal colour wheel which lights up a fibre-optic fountain on top. Fun
to watch but gets a bit warm over time so decided to do a retrofit.

Halogen bulb was`replaced with a 12v 3W 3-LED MR11 running at 6-8vac (the transformer adapter is
not regulated and more lightly loaded so a bit higher). I checked the LED at lower voltage and light
was good enough, better in fact as it was too bright at 12v.

I regret I don't recall my measurements at the time and usually keep packaging for LED bulbs but
trying to locate this one. Point is, some 12v LED lamps can run down to 6v with reduced brightness.
You might have to obtain one or more bulbs and try it out, as the tint, beamwidth, pattern etc.
may or may not all be suitable.

I am also curious about the drive circuit in this bulb, having three LEDs which I assumed would
run in series with some simple current limiting; but apparently not as it works below 9vdc. Taking bulb
apart would be tricky, probably damage it, skipped that.

Tests were also done on 12v 5W MR16 LED spots and similarly found I could run two in series at 12vdc with
reduced brightness and lower power drain; and could be pointed independently.


Dave

 

[Dave_H]

On retesting the LED MR16s they were found to cut out fairly sharply around 6v, some
flickering at the threshold. Probably not a good solution for 6vdc system. Some LED MR11s
might work better but this low-voltage behaviour is neither spec'ed nor assured by the
manufacturers.

BTW reducing input voltage on the MR16s below 12v, current increased down to about 9v, then
decreased which indicates a switching down-converting regulator trying to maintain constant
power but eventually operating in dropout mode with decreasing current and brightness. Regulator
chips typically used in automotive 12v LED lamps have low cutoff around 5-6v. Looks like three
LEDs are in series.

Fully charged 6v SLA should be around 6.8-6.9v, dropping to 6v would have about 50% capacity
which would be unavailable to anything not able to operate below that (but not that much below).


Dave

 

[Dave_H]

I got another 3W MR11 bulb, it is Luminus PLYC1953. Four LEDs, 200 lumens,
3000K and 20k hour life stated.

https://www.rona.ca/en/3w-non-dimmable-led-mr11-light-bulb-bright-white-74615063

https://www.amazon.ca/dp/B00U3QRVZS/

Prices for this item seem excessively high, I payed under $4 although on clearance.

Test showed it could operate at nearly full/constant brightness down to 6.7v,
and went off at around 6.0v; but from off it would not start from below 6.7v,
obvious on/off hysteresis.

Bike lamp might have a diode in series with SLA, which could make the situation
less good.

I speculate the LEDs are connected internally as 2-series/2-parallel which in
theory could operate down to two LED forward drops (about 3v each), which it does.

Looks like this one is not good for 6v SLA supply but was worth looking at.


Dave