Ebike lighting and power -- a discussion

[amberwolf]

Note: The previous posts were split off from a discussion started over here:
viewtopic.php?p=496040#p496040
at the request of multiple members.

 

[d8veh]

I've ordered one of these and I'm waiting for it to arrive. My present light is a single Cree T6 LED and it's as bright as any halogen spotlight at 1800 lumens, but the beam is not very wide. Hopefully the new one with three T6s and 4000 lumens should give the brightness and spread of a halogen spotlight, but with only 6watts of consumption. That saves a lot of weight.
http://www.ebay.co.uk/itm/160682688338?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

 

[Alan B]

I've ordered one of these and I'm waiting for it to arrive. My present light is a single Cree T6 LED and it's as bright as any halogen spotlight at 1800 lumens, but the beam is not very wide. Hopefully the new one with three T6s and 4000 lumens should give the brightness and spread of a halogen spotlight, but with only 6watts of consumption. That saves a lot of weight.
http://www.ebay.co.uk/itm/160682688338?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

The small reflectors and multiple LEDs should give a wider beam and less "throw" which is what you want for the bicycle.

A Cree XM-L at full power requires 10 watts. They are probably not running them at full power but they don't seem to indicate what power they are using. If they used the full 30 watts in that head:

1) it would overheat quickly, there is not enough heatsink there (though on a bike it would not be as problematic).
2) it would require too much current from the 18650's and likely trip their protection circuitry (more than 4 amps).
3) it would exhaust the battery very quickly, in like about 30 minutes.

While it won't likely be 4000 lumens, I'm sure it will be bright and when you know how much current it draws we can calculate the approximate brightness.

 

[hillzofvalp]

I have an ancient 10W TRek branded light that my bike shop just gave me with a new bulb.... It works fine at 30mph. Not sure if I'm overdriving it or not... but I'm going to use it for now.

 

[Alan B]

A lot depends on your road conditions and stray light, and how well you see in the dark. If it is really dark and road conditions are good then less light is needed. When there is a lot of stray light in your eyes and when road conditions are poor so you need to see the surface then more may be needed.

People tend to overdrive their ability to see in cars, why should ebikes be any different.

 

[d8veh]

I've just done some calculations on my single Cree XM-L T6. It runs for about two and a half hours on full power and the battery pack is 4 18650 cells, so I'd guess at 5aH regardless of suppliers claims. So, that makes two amps at about 8v so 16watts of LED.
http://www.ebay.co.uk/itm/250914024911?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
I'm still waiting for the 3 LEDs Cree XM-L T6 one.......
http://www.ebay.co.uk/itm/160682688338?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
but in the meantime I got this one with 3 Cree R5s. It runs off 2 18650 cells. The light it gives out has quite a wide spread and I'd say that it's comparable with a halogen spot-lamp. I haven't yet tested to see how long the batteries last, but I guess 20-30 minutes.
http://www.ebay.co.uk/itm/150642124764?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

 

[hillzofvalp]

I'm liking my incandescent 10W bike light very much. Especially since it was free. I'd like to get a nice LED light second hand... or maybe find a single halogen at a mechanic

 

[StudEbiker]

I picked up a Dura Micro AC Adapter DM5127 at the local Goodwill this week for a couple of bucks. It has a dual output of 5v and 12v. Could be useful for someone. Here they are on Ebay.

http://www.ebay.com/itm/Dura-Micro-AC-Adapter-DM5127A-5V-2A-12V-1-2A-4-PIN-Cord-/400260005104?pt=Laptop_Adapters_Chargers&hash=item5d315afcf0

 

[Joseph C.]

I bought the Magic Shine 1400 lumen 'Mickey Mouse Ear' light. The handle bar mounted light switch is very handy.

I don't suppose anyone could tell me what lumens the light is really outputting? The battery is 4.4amp hours and is said to last 2 and a half hours. If I had to guess I would say about 900 lumens.

 

[Alan B]

Figure out the watts (volts times amps) and multiply by 90% converter efficiency and then by 70 lumens per watt. That's led lumens, about 70% will make it out the front. So volts times amps times 0.9 times 70 times 0.7 should give a good estimate.

 

[Joseph C.]

Figure out the watts (volts times amps) and multiply by 90% converter efficiency and then by 70 lumens per watt. That's led lumens, about 70% will make it out the front. So volts times amps times 0.9 times 70 times 0.7 should give a good estimate.

Thanks Alan. As the battery is 8.4 volt 4.4 amp hour and it has a run-time of two hours that should be a draw of 2.25 amps.

Therefore, only 833 lumens out of 1400. Not too bad.

Edit: That also means that the 1600 lumen Magicshine only outputs 870 lumens - assuming the batteries sold with it are 9 amp hours and it lasts four hours on full. Hmmm...

 

[Alan B]

The loaded battery voltage might be a bit lower, probably 7.2-7.4V.

 

[Joseph C.]

The loaded battery voltage might be a bit lower, probably 7.2-7.4V.

Don't depress me.

 

[Alan B]

I bet they're still bright!

I have an SST-90 LED here, unmounted. 4 volts at NINE amps. A 36 watt LED. This one is a couple years old, I'm sure there are bigger ones now. Even this one is pretty hard to keep cool. 2500 LED lumens. Need a temperature sensor on it, only run full brightness when moving fast. Or fan cool it. Or make your handlebar of aluminum and use it for a heatsink.