bloodhound

Nothing new to most of you, but I may have a new idea or a new source.

6V, 10W, Halogen, 2100mAh, rechargable bicycle light setup. For less than $50 (including charger).

https://back2dabike.wordpress.com/200...-a-bike-light/

Now all I have to do is build it...

Cyclaholic

You'll be pulling about 1.6 amps from the battery, you'll get a bit less than 1 1/2 hours runtime (probably less than 1 1/4 hours before it starts dimming noticeably) is that enough runtime for you?

If you spend just a little more you can replace that halogen bulb with one or two LEDs and get up to triple the runtime for the same ammount of light. Although there's a bit more work in building it.

If you're keen on going halogen you'll get a little more efficincy with a 12v 10w setup.

bloodhound

Well, my commute is about 20 minutes each way, and only one way is in the dark. So, this setup will actually last me all week. Then I recharge it on weekends.

Thanks for the input, though. I'm a little rough in battery theory, and had figured over 2 hours of run time since I was running a 12V bulb at 6V. But, since I have such a short distance to go, there is no point in carrying around the extra battery weight.

These are only my plans for now, I haven't bought the parts yet, so I may still go 12V. I'll update when I decide.

Thanks again!

znomit

A few points.
A 12V halogen will run very dim off 6V.
35 degrees is a big spread too. You want most of the light pointing out the front.

Last winters setup for me was a 12W halogen MR11 7degree. See here :
https://www.bikeforums.net/commuting/278532-diy-bike-light-problem-casing-too-hot.html
Was pretty good. Get about two hours usable light out of a 2.4AH SLA battery(as the voltage drops the bulb dims). I used silicone sealant to glue it into a tennis ball. Cable tied a tennis ball holder to my stem. All up took about an hour. Bulb must have a glass front(some are open). Wouldn't run much more than 20W as things get warm.
Need:
Bulb
bulb socket
Tennis ball & holder
switch
silicone glue
12V SLA battery
An hour or two of spare time.

I was very happy with the output but the SLA battery is a pain, carrying it in my camelpack. Have just put together a LED system (using 2 XR-E kits from cutter.com.au )whch has similar light but runs off 6AA rechargeables for 3-4 hrs.

Cyclaholic

Runtime won't be an issue then, but recharge the battery before it gets run right down and it will last much longer. It's called depth of discharge the less you discharge it between charges the longer and healthier it will stay. At $50 for the whole setup I suppose a bit shorter battery life probably isn't that much of a concern, which is why I run a $20 battery

Don't run a 12v halogen at 6v, you'll be shooting yourself in the foot. Get a 6v lamp or run a 12v battery. Halogen lamps become incredibly inneficient when run at less than their rated voltage. A 12v halogen lamp at 6v will convert something like 90% of your battery's energy to heat and throw a very dim light.

If you want good bang for the buck, and stay at around $50 for your whole setup, you're better off with a 12v SLA battery and a 12v 10w MR16 halogen lamp. The SLA battery is very cheap, readily available anywhere, and quite tough. It will put out about 13.2v when fully charged so your halogen will be slightly overvolted making it noticeably brighter and actually more efficient in lumens/watt. You need 100 minutes of runtime, lets say 120 for a safety margin. The lamp will pull about 840mA from the battery for a total of 1.7Ah, multiply that by 1.3 to allow for the discharge derating curve = you need a 2.2Ah SLA battery and you will run all week on one charge without risk of damage to the battery.

I just looked at batteryspace and they have this 12v 2.3Ah SLA for $15.99 which would be a good option for you, it weighs about 2lb...



If you want to save a little weight they have a 1.2 Ah SLA that weighs 1.3lb and is a few dollars cheaper, but you'll have to recharge midweek.

One other thing, try to stay under 30 degree beam on your lamp, preferably under 20 degrees, they spill plenty of light to the sides so you won't have a problem.

bloodhound

Hmmmm... Excellent notes znomit and Cyclaholic.

I see that I may have not planned the best setup. I had read that undervolting wouldn't be a problem (though it would be obviously dimmer), but did a few more "googles" after reading your posts, and agree that it is best to go with 12V for a 12V. Of course if I go with the NiMH's, then this will be an expensive option. The SLA's are definitely the cheaper way to go, but a 12V SLA/AGM will be heavier than the NiMH setup. So, weight savings or cost savings...

As for the lamp, I only see them in the 35° versions. I'll have to look around more, but I didn't know that they came narrower than that. I thought 35° would have been narrow enough, but just roughed out the angle on paper and see that it is more of a flood light.

Anyway, I'll be updating the information on my blog post as soon as I figure out a new battery setup.

Thanks again!

cyccommute 

If you overvolt the lamp, you get more light at a slightly reduced lamp life (it's still pretty robust). You also get a longer battery life because you are drawing fewer amps off of the battery. Use the equation

(Volts*amphours)/wattage = hours

to figure out the run time.

The battery you want to use, an SLA, is not a great choice. Yes it is cheap but it is also less robust than NiMH and even less robust than NiCd as well as heavier than either. You can get NiCd or NiMH RC car batteries for pretty cheap in the 2.1 Ah range at All Battery at as little as $13 per battery. You can wire the batteries in series to get a 14.4V battery. Another advantage of the nickel chemistry batteries is that they work better in cold weather.

For lamps go to Battery Space. A 12 degree spot is pretty tight (10 is even better) and a 24 degree flood is almost too wide. The 35 degree flood is next to unusable.

For cabling, use heavy gauge speaker wire from Radio Shack and for connectors go to a hobby shop that carries RC cars and get Dean Ultra Connectors

Cyclaholic

What do you mean by "robust" when you say that SLA is less robust than NiMH or NiCd? in my experience with deep discharge applications I found SLA to be a more reliable chemistry, and cheapest per Ah, although it's the lowest energy density.

BTW I like how you paralleled two NiMH R/C car battery packs, I'm going to give that a try.

cyccommute 

SLA doesn't like deep discharge at all. SLA can be discharged to around 1.75 V per cell from 2V (around a 12% reduction in voltage). NiCd and NiMH can go to around 0.9V from 1.2V (a 25% reduction in voltage) without problems. Nickel chemistrys, especially NiCd, even withstand some cell reversal which happens when you get to very low cell voltages.

As for cost, look here. On a dollars per cycle basis, the NiCd beats the pants off of any other chemistry...including SLA...mostly because it can to to 1500 duty cycles which is 3 to 5 times that of the other batteries.

I've been doing the RC battery thing for years. It works very well and I'm seeing lots of 4000+mAhr batteries around now for pretty cheap.

krushnoi

Biggest reason to avoid SLAs (besides the weight) is you have to recharge them immediately after using them, (even if you only used them a few minutes) because they will sulfate quickly and you won't get many usable cycles if they are left uncharged for very long.
Nicad or Nimh or Lithium can be left uncharged without damage.

bloodhound

Well, I built and used a test light... and didn't follow my own plans.

Here's what it looks like when you use a 50W MR16 spotlight bulb and 12VDC from a car battery...

https://farm2.static.flickr.com/1371/...71df0fad3d.jpg

The PVC didn't start out all caved in like that.

More photos here: https://www.flickr.com/photos/back2dabike/.

Next time, I'll stick to the plan

hr2510

I've read that the MR16 bulbs get HOT. I was at the hdwe store and saw a MR16 track light on display and I almost cooked my finger tips when I touched it That is the main reason I decided to use a Malibu yard light with finned aluminum housing so it can dissipate the heat.

znomit

Halogens get HOT. You *might* find that out riding there is enough breeze to keep 50w cool. If you really need 50w(100mph off road downhills? You're too cool to take off your sunglasses? You get bored riding so like to make shadow puppets?) you might want to include a second 10w or 20w bulb that you can switch to for climbing or when stopped.

Frankenbiker

Yep, halogen lamps get really hot. The instructions for my old 9 volt Cygolite said not to stop for more than five minutes with the light turned on or the housing will melt. Not good. I recommend using a metal housing for homebrew MR16s. The chrome Optronics driving lights are designed to handle the heat from 55Watt MR16s. I use them myself and highly recommend the housings.

hr2510

Thanks for the tip on the Optronics lights. They are only about $1 more a piece than the two yard lights I -was- going to order. I decided to get two headlights. 1 for the single & 1 for the tandem and just swap the battery to which ever bike I want to ride. I like the smaller size and chrome is cool too.