Bottomfeeder

Calling all geeks! I've been bit by the bug and I'm gonna build my own 20W 12V Halogen rechargeable. As you can imagine... I've got a few questions. This time it's about battery options. I was down at Fry's on my lunch break looking at batteries and I'm wondering if anyone here can tell me how long the following units might power a hardware store variety 20W 12V halogen given a reasonably efficient wiring harness.

1: 12V, 4 Amp Hour, lead acid battery - pretty freakin' heavy.

2: 12V, 1.2 Amp Hour, lead acid battery - about a .3 the weight of the above, and very manageable.

3: 10 AA NimH rechargeables

Thanks for any help in advance. DanO

paulrad9

Your light is 20 watts, so take the watt capacity of the battery and divide by power of the light

12v X 4ah = 48watt/hours
48 / 20 = 2.4 hours.

Note, with lead acids you should not go below 80% of capacity, so
48*.8 = 38.4
38.4/20 = 1.92 hours

StephenH

Probably try to have double the capacity you need, not just 80% of it.

In looking around, I found it's easy to find good cheap 6 volt batteries and chargers, and easy to find good 12 volt bulbs.

In addition to the normal places, consider batteries and chargers used for powering game feeders (at Bass Pro Shops, Walmart, and the like), rechargeable kiddy cars (Walmart), and emergency lights or alarms (Lowe's).

diff_lock2

Halogens are pretty useless unless you over volt them. I would recommend an OSRAM IRC 10deg spot mr16 light. Run it at 14.4v or more. (12 NiMH cells or more).

brendanmc7

Check out this link for already set up battery packs and chargers. I looked all over and they really make it easy for DIY bike light building. https://www.batteryspace.com/index.a...S&Category=499 Great prices too!!!

kk4df

+1. I run mine with a 14.8 volt lithium pack. The lithium cuts down the weight from NiCad or NiMH or SLA. I run mine into a 20W halogen, and it throws a nice, bright beam.

cyccommute 

Not useless but they do better when overvolted...by a lot. Batteryspace has lots of 4.0 Ah battery packs in NiMH in everything from 4.8 V to 24V. Some of their premade 14.4V packs seem a little bulky but they do have a very nice 5.0 Ah waterbottle battery for $60. Much more convenient size and weight than an SLA.

Bottomfeeder

Thanks for all the tips guys. It seems that the battery and charger will be the major cost on this project.

One thing that will be important is a unit I can charge in 8 hrs or less. I had a Cygolite a few years back and stopped using it because the 14 hr charge time made it nearly impossible to use on consecutive nights.

Checked out Batteryspace's purpouse built bike battery - $85 with fast smart charger and connectors. At first I thought I'd like to do better. But when you consider that it will cost me maybe $20 total to make my own light... Well, having a 20W halogen system with a burn time of between 3 and 4 hrs for a little over a C-note is pretty sweet - especially when you consider what the Cygolite or Nite Rider would be charging (pun intended) for that kind of performance.

Thanks again. DanO

diff_lock2

I got a RC grade charger, it really gives you a lot of control. I can charge 10cells at 5A, i think. I charge my 2300mAh pack at like 1.4A so few hours and its fine. I never tried more than 1.6A.

gerv 

Last year, I built a light from the following
- a $10 fixture at Harbor Light with a 20 watt halogen
- an $8.95 1.8 watt xenon strobe amber taillight. https://www.allelectronics.com/cgi-bi..._FLASHER_.html
- a 12 VOLT 5 AH GEL CEL BATTERY https://www.allelectronics.com/cgi-bi..._BATTERY_.html
- a 2 stage battery charger $12.75 https://www.allelectronics.com/cgi-bi...ATTERIES_.html
- various wires and a $3 switch.

I am still using it for early morning commutes this year.

The downside is that the battery weighs 3 pounds and is bulky, so I carry it in my rack trunk bag.
However, a lot less $$ than I see quoted above.

cyccommute 

The bulky part...and the 3 pounds...and the fact that it's an SLA...are the deal killer for me. I'd rather not take up my luggage space with a brick. I don't carry panniers except on very rare occasions - and some of my bikes can't even take them - so I use a trunk bag almost exclusively. Putting a brick in it would mean that I have to take something out.

Bottomfeeder

I'd like to see a few pic's of your set-up gerv. And what kind of performance do you get - ie, how long does it run your 20W halogen, and how fast can you comfortably ride in total darkness?

An ample battery and charger for $30 is an intriguing proposition. I am, after all, the bottomfeeder. As far as weight is concerned; I've considered adding one of those 6 pack size, mini front racks to my commuter on which to mount the beast. It would free up my water bottle holders and help balance the load I carry in the rear.

DanO

gerv 

I won't disagree with cyccommute's view that the battery is like carrying a brick. It is the one downside to the setup. It's like carrying an extra two water bottles..

I think this setup is rated for about 2-3 hours, but I've never gone that long. My commute is just over one hour, round-trip, and I immediately turn the charger on.

Riding in total darkness? The reason I built this light is that my commute is mainly on an unlit MUP. The 20 watt halogen lamp is very good. Much, much better than my 1 watt LED Cateye EL500 (although I always carry it as a backup... better than nothing!)

But anyway, pics:

the headlight from Harbor Light

headlight.JPG

the xenon strobe and the battery (sitting just behind the seatpost)
taillight.jpg

lectraplayer

For your battery, I would suggest you use LiPO's. You have to give them some special care, but they are light as all get-out, and will give you plenty of amp-hours. You can parallel them too, giving you more amp-hours for the same size and less weight of a lead-acid. Go www.towerhobbies.com and stock up on batteries, and a charger. When you do, be sure to get a balancer as well. (this is part of the special care I mentioned, and is very important to prevent a fire). You'll be able to run several of your lights with amps to spare a small model-airplane can easily want 30A from a 2AH pack.

Mobiker50

I'm intrigued by your setup (and it's low cost, 'cause if anything, I'm cheap). Weight of the battery wouldn't be a concern to me either, as I'm MTB mounted and pack enough weight of my own

I looked at the pictures of your setup and the links above, but the one area that I came up short on was the reference to a fixture from Harbor Light. On-line resource or catalog? And can you pin down the fixture you used?

Thanks.

GCRyder

I'm pretty sure he meant Harbor Freight. Several here have used that submersible 20W pond light.

balto charlie

I run similar systems, DIY 2-20 W halogens on a 7AH SLA battery. It's a brick for sure BUT I get free SLAs(used for 1 year in electron microscopes then replaced). So my entire system cost 20 bucks. I also wanted to recycle the batteries and the best way to recycle is to use them up. Also I leave 'em on the bike when I lock it up outside w/out worry.
If I didn't get free batteries I would use NiMH rechargeable. Best bang for the price and weight, but I would take off the bike when locked outside. Charlie