Mountain Biking - building my own high-power light/battery system

ok, i have a 15w Nightrider Digital 6, but it's in storage in the US and i don't want to ask my sister to search through all the boxes...

here in Germany it's still not technically legal to buy bike lights with more than 5watts b/c of the rules for city bikes... anyway i was looking at ordering something from the US or ordering something here in Europe, but the prices are pretty high...

i found a 6volt 20 watt halogen bulb/reflector for $30 and i've built a battery back using 5 NiMH rechargeable D-cells. Wednesday night's weekly MTB ride will be the first test to see how bright and how long it lasts...

i have a charger that charges the individual cells in parallel (4 at a time) but i want to leave them in the battery pack for recharging. anyone know if there are chargers that work this way -- i.e. allow charging of multiple batteries connected in series?

i'm considering buying a 5-watt light to allow for low/high setting...

anyone have any other suggestions for batteries or lights?

Nathank,

I `ve build my own light as well (see Headlight version 1. in commute forum)

I had the same problem with the batterypack and i still can`t find a charger who can charge 10 AA cells Ni-mh the same time.
The only one i found was a multiple charger for Ni-mh 9.6 V in the Radio store, but nothing for 12 or 6 V

You can also check this
links page (http://www.mikebentley.com/bike/headlights.htm)
It provided me with some good info, show us some pics if you finish it

cheers:beer:

I haven't seen Alister around for a while but he had a play a while back - might be worth anb email.

Richard

toolfreak,

thanks for the links. i followed some links from links from your link and got some good ideas...

then i did some searching on the web and found some good info about NiMH batteries and chargers... was going to buy one online but then went to the local do-it-yourself electronics store and found a charger for $40 (online was $45 plus shipping) that looks good with processor overcharging protection technology (main danger to life of NiMHs is overcharging). unfortunately the description of the physical techniques it uses are not so good - just says "3 safety methods" which i think is delta V, delta 0 and timer (the 4th possibility is delta Temperature but it doesn't have a temperature sensor) - sorry i've been reading lots of technical specs.

anyway this one comes with various connectors - the one i used for my light is included - and then can charge 4.8-12V systems (mine is 6V) of NiMH and Cadium batteries in it says 1 to 6 hours depending on capacity. and then the processor senses that the batteries are full and shuts off quick-charge high current and then runs slow trickle-charge.

according to the formulas i've found, i am calculating a duration of 8.5 hours at 20W!! which sounds too good to be true. i tried the light out in my apartment last night and it is pretty bright, but hard to assess when not on the bike.

* capacity = #batteries x individual battery capacity(7000mAh) = 5 x 7Ah = 35Ah total
* bulb P(power) = 20W at V(voltage) = 6V
* I (current) = P(power)/V (voltag); I=20W/6V=3.3A (amps)current draw
* T (time in hours)=P/I = 35Ah/3.3A = 10.5 hours theoretical duration
- then about 10% loss due to inefficiency
- about 10% loss b/c of cold
* so 10.5 x .9 x .9 = 8.5 hours!

in the end it's still not cheap, but cheaper than the expensive systems ($30 for 20W sealed halogen bulb with switch, $40 for 5 NiMH D-size batteries, $40 smart processor charger, $5 for wires, connectors, solder, tape = $115 -- but i will also use my charger for all my other NiMH batteries like for my digital camera and i could also use the batteries for something else as i didn't solder them but created a pop-in battery holder pack, so my real "cost" is about $75). plus, most of the expensive systems like the NightRider only last for 2-3 hours. if this one really lasts almost 8 hours, then...

about the only thing missing is a good helmet mount b/c this bulb came set up for bar-mount (i had a bar-mount for my 15W Nightrider and changed to a helmet-mount and was MUCH happier). i currently have it strapped to my helmet with 2 velcro-bands... if it works well i will design something better so i can aim the beam and adjust the angle.

anyway, all sounds good - or actually too good...tonight will be the test. i'll report back how it works. if all goes well, i'll try and get some more stats like weight of the battery pack and actual light duration during actual use, etc.

Sounds good!

But i think you have to recalculate, if i`m right you have 5 D- cells, wich are serial connected.
The point with serial loops is that you can multiplie the voltage with the amount of cells, but the current stays the same.

Serial loop;
U= 1.2 V
Ut= U1 + U2 + U3 + U4 + U5
Ut= 6 V

I= 7000mAh
It= I1
It= 7000mAh

P= U*I
I= P/U
I= 20W/6V
I= 3.3A

7Ah/3.3A = 2.12 hour (in theory)

Sorry mate, but that was the main reason for me to build one with LEDs.

Both bulb types have advantages and disadvantages.
LEDs are efficient with power but not as bright as Halogen.
Halogen bulbs are far more brighter but the most energy is converted to heat.

For me, i`m not satisfied yet, i hope to make my lights more brighter.
Compared to my Petzl Tikka headlight they suck! :D

cheers :beer:

Toolfreak,

yes, you're unfortunately right. somehow i just couldn't believe that it was 8 or 10 hours when the super-expensive systems are only 2-3 hours... i incorrectly added the AmpHours when they should not be added when serially connected.

anyhow, i should still have around 2 hours (1.7 to 2.1 hours depending on temperature and efficiency loss) which is pretty close to what most of the commercial systems have.

i tested it last night although not for a full ride because everyone else cancelled on our weekly mountain bike ride...

anyway, i only rode for an hour and a half so i stilll don't know the actual duration (it was still going strong), but the lighting is great -- it's a focused spot beam that also casts enough light in maybe 160degrees or so. i didn't ride on any single trails but i think there it should be fine. on basic super-dark trails it was fine and on the streets it was good - i blinded a few car drivers as they approached from side streets and i aimed the light right in their faces.

i'm considering added a 5W or 10W bulb next to the 20W so i can switch between 2 power settings to increase the burn time so i can get around 3 hours or so...

i'm totally satisfied and it seems as bright as my Nightrider Digital 6 (which costs something like $180 or $200 i can't remember) with proabably about the same burn time (still to be exactly determined) and my battery is lighter and it of course cost less... plus my charger is a true smart charger (NightRiders just uses a timer)

again, i'll report back when i have some test values for burn time and i'll try and take a few picture of the battery pack and the lighting.

Time to resurect this thread....got any photos of your setup? I am currently building my own light system with a 20W Halogen bulb with a 10deg spread. I'm going to mount the light somehow, and the battery I pick up on Monday (Gel Cell battery, about 3.5AH) and see how it all goes. My dad is a sparky so yeah.

Brendon

P.S. I am attatching to the handlebars cause I am a roadie....i came across this thread when I did a search

Brendon