I am replacing the SLA battery on my homemade bike setup. I have 2x20W halogen lights in my system, and am looking to replace the current battery with a smaller battery. Right now I have a 12V 7.0ah battery ( brick!). I am wondering if someone can confirm the formula I am using for calculating battery need is correct:

i.e

20W x 2 bulbs = 40 W x hours required ( 2) = 80 Watt hours

80 watt hours / 12 V = 6 amp hours.

Am I using the correct formula? If so, I should be able to get away with a 4.5 amp hour battery, considering that I run only one light for the majority of the time.

But what effect does temperature have on the number of watt hours a battery yields? I remember reading something about a percentage drain for every degree below zero, but can't remember what it was. ( I am planning on biking in winter, so this is important)

Thanks much!

my 1w red led tail light. Need to water proof it and mount it.
2.4v direct drive. Plenty bright.

Ordered 4 Cree Q5 on stars, Lidel lenses, and bFlex from Cutter last night. I hope it doesn't take too long to ship, 'cause it's getting dark in the morning. I'll go get my aluminum square tubing this weekend and start fabbing the holder. Woot!

I have a couple geeky questions:

If I have a 72V battery pack on my bike and want to step down the voltage for some lights, what bit of hardware do I need to slip in?

And if I step down the voltage to 24V, would that allow me to power 2 12V systems (front and rear lights) in the same circuit? Or do I need to use 2 separate transformers or whatever to get down to 12V for each system?

Thanks!

Here's my DIY bike light. It's based on this, with a few modification.

~700 Lumens of awesomeness with Seoul P4 U-bin LEDs. The lens configuration is L2 5°, 15°, 5°. I only ride on road, so no need for excessive flood.
It can be changed for all 15° or all 5° if need as I'm not using any glass to cover the front. Not worried about getting it wet as the led, lens holder, and wires are all sealed with silicone sealant.

The regulator is Fatman from taskled.com with 50k Log pot for a wide range of adjustable light.

With handlebar mount.

It's a bit dirty as I rode in the rain last night. I didn't get around cleaning it up.

The mounting plate is cut from Planet Bike Beamer 3, with uses the Planet Bike Quick-Cam adjustable bracket (which is quite ubiquitous in Vancouver, and works with Planet Bike Blaze, Beamers, 1200, 5000x, and Super Spot).

I choose this mounting system because I have 2 Planet Bike Beamer 5, and a 5000x (which I will convert to 2 Seoul P4 later on). The interchangeability of the system allows a lot of flexibility of lighting (to see and to be seen).

Helmet mounted.


The helmet mount is from the BLT Ultra Doppler and it allows wide range of angle for the light to point at, with the mounting bracket replaced from a Planet Bike Quick-Cam adjustable.

The battery is connected by a 9v snap connector, with allows me to carry an extra battery pack if I decide to go all night long, or as a backup.

The masking tape will be replaced with electrical tape soon.

Just the mounting plate.

I would suggest beefing up the thiner wires, like from that 9v thing. I used wires that small for my 20w halogen and they caused ridicules voltage drops (resistance). And its basically a free mod and better batt life.

So the fatman can handle up to 1A, and 3 seouls is like 10v (series), and you are feeding the fat man 7.2v (right?). So are you sure the leds are getting 1A? I am sure its really bright either way since its 100lm at 350mAh (per led).

Here is my mr16 body (any mr16 light will fit)... i ordered 16 3400mAh AAs (Ni-MH)... still waiting for them.

Why 16 AAs? I'm not seeing the power configuration. 6V packs are 5 NiMH batteries, 7.2V are 6. I'm confused. Also why individual batteries? Battery Space sells lots of packs including a couple of 4.5 Ah RC packs for fairly cheap.

Just wondering.

I've got at least three of these kicking around. I'll be building something similar, but with a 2x2 array and bflex driver. Woot!


I just finished the basic design of the light housing:


Lots of cutting, lots of JB Weld.

Well i use AAs all the time at home. And i will need 12 of them to make a 14.4v pack. 14.4v 3.4Ah for 27eu.

If i can find a better mr16 bulb i will make a pack to suit that.

Oh and they come in packs of 4.

I think that i should trim the bezel on my light cause it might restrict the flood of the light.

You might want to consider a 2"x2" heatsink for that design.


Or not.

Or yeah. I think mounting the leds on heatsink would be better. More cooling and less work (to build the light).

And can you post an X-ray styled view of the 2x2 led housing, i think im missing something.

Ask and ye shall receive:

The unit is about 2"x2"x2" at present. The 1/8" thick piece right in the middle is the backing plate for the LED/star mount, and the plate at the back is drilled for switch and power supply. A heat sink mounted on one side might be a good idea, but since the entire thing is metal, wouldn't the heat from the plate conduct out to the housing okay? If it doesn't, I can always JB on a heat sink from an old processor or something.

Edit: Oh, I apologize for my crappy drafting skills - the draft I'm most familiar with is beer...

Im running 4 crees at 500mA in an Al housing off a bflex. They do not get hot at all when riding...slightly warm to the touch but only in comparison to the bike frame. A heat sink is not needed, well maybe if you plan to ride a lot a 1mph. As long as there is a good thermal path from the LEDs to the case they will be fine.
Do you need the cross bits separating the LEDs?

"I have a couple geeky questions:
"If I have a 72V battery pack on my bike and want to step down the voltage for some lights, what bit of hardware do I need to slip in?
"And if I step down the voltage to 24V, would that allow me to power 2 12V systems (front and rear lights) in the same circuit? Or do I need to use 2 separate transformers or whatever to get down to 12V for each system?"

I would assume a 72v battery pack was made up of a bunch of smaller units generating 1.2 or 1.5 or 2 volts each. The ideal way to drop that to 24v is to rewire it so that you have three sets of units each producing 24v, or 6 sets producing 12 volts, and and then wire the sets in parallel with each other. If this is a single factory-made battery that produces 72v, I'd probably just look for a different battery, myself. If this is a rechargeable battery, you may have trouble finding a recharger. If it's a drycell type thing (seems like I used to see those in stores long long ago- big long battery about 8" long), then it'll be expensive.

Transformers work on alternating current, like house current. You can't just use them on a battery unless you have some way to convert the DC to AC, which gets awkward. I think there are transister units that can do this kind of thing with low voltages (like 12v to 5v), but I doubt you'd find much to help with 72v to 24v.

If you get down to 24v, you can power 12v front and rear units IF they have the same wattage/amps. But normally, a headlight would be much more powerful. If you connected the two in series, the headlight would burn very dim, and the taillight very bright until it burned the bulb out. Essentially, the high resistance in the taillight would limit the current through both of them, and would also cause a bigger voltage drop across that item. And if either bulb burns out, both go out.

Yah, I didn't think that the housing would get too hot. I'll be running this setup at 700 mA, and the ambient temperature will usually be between +10C and -30C [-50C with windchill]. As to the cross bits, I guess they aren't needed, since the LEDs+lenses are attached to the plate in the middle, which will be in contact with the casing. I will probably leave them in there, but if I wanted to eliminate them I'd switch to 2"x2" square tubing instead of using 1"x1".

Any other suggestions?

So what do you use to attach the various pieces of aluminum together?

JB weld.I think thats what he said. And JB weld is thermally conductive and it expands at the same rate as the metal or something like that. My fav is this stuff for Al, its like a solder. just use a butane torch and solder the AL together and its as strong as the welds apparently.

Hmmm, interesting. I think the solder you're referring to is just silver solder, but it would be good to know for sure...

JB Weld FTW! I've heard of silver solder being used for steel bike frames [it melts at a lower temperature than normal soldering rod], but not for aluminum. Most Al gets TIG-welded. Actually, it would be very cool to CNC this whole thing. Precision machined insets for the LEDs and driver to mount into, inset screws holding things together, o-rings and gaskets... I'm sure somebody is already doing this.

Lower than brazing rod, you mean? Yeah, I think you're right. It melts at a higher temperature than regular solder, though.

And yeah, someone IS doing this... Dinotte.

Check this (what im talking about).

https://durafix.com/

Touche! Yes, Dinotte makes a nice light. I was going to get my wife a 200L, but she wanted a Princeton Tec Singletrack 2. Go figure! I suppose I could have picked up a Dinotte 600L, but it's a fun project to build my own. I was describing the DIY light to my wife, and she suggested that I go into business producing them. I explained that the market for a 400+ lumen bike light was actually fairly small, and that there were plenty of other players out there already doing this. Still, it would be a nice sideline if I had a complimentary buisness going, like my own bike shop...

This is the rod, works very well with a propane torch......I've used it for about a year to fix several things...

Ok, this isn't total geekiness, and I doubt it even counts as minor geekiness, but it has geek elements in it. I was curious to see if the Energizer Energy to Go battery packs for cell chargers would work to charge a Garmin 305, so I plugged it in tried it out. Not only did it work, with some help from velcro, I was able to run the GPS off of the Energy to Go battery pack while riding. No interference, nothing. So now I can run at night, with the backlight on the entire time, and not worry about the GPS crapping out halfway into the ride.