Electronics, Lighting, & Gadgets - Best way to power 12V system with 9V battery holder?

I bought a battery holder that has a 9V (PP3) clip (like this (http://www.bitsbox.co.uk/images/batts/4xAAholder.jpg) but holds 10 AAs, not 4), and I'd like to power two 12V halogens and a rear strobe (similar to Steven Scharf's setup (http://bicyclelighting.com)) which I've already bought. I bought a 9V clip (like this (http://shop.rabtron.co.za/catalog/images/pp3clip.jpg)) and hooked everything up, and found out that doesn't work. What do I need to do? Skip the 9V clip and solder my wires directly to the battery holder?

Have you checked how much voltage you're getting out of your loaded battery holder? Are the 10 cells all hooked up in series (to give about 12.5V for NiMH or 15V for alkaline) or in parallel (to give 1.25V - 1.5V), or some combination of series and parallel? Also verify that you have the right polarity, i.e. +12V instead of -12V - shouldn't matter for the halogens, but probably does for the strobe. Finally, what total wattage are your lights and are the cells you're using up to providing that much power?

You're probably about to smoke the wires on the 12v clip. To run two halogens and a strobe, you probably need at least 3 amps, maybe more. NO WAY can the wires out of a typical 9v clip (what, maybe 20 gauge?) handle that kind of current.

Also rechargable AAs probably shouldn't be called upon to deliver more than maybe 2 amps continuous. They can spike up higher than that but if you draw 3 amps from them continuous they'll get plenty hot, the runtime and lifetime will be reduced. I'd use rechargable C cells for that kind of draw, personally.

Also rechargable AAs probably shouldn't be called upon to deliver more than maybe 2 amps continuous. They can spike up higher than that but if you draw 3 amps from them continuous they'll get plenty hot, the runtime and lifetime will be reduced.Amen to that. I found this out in one DIY light project. (I'm sure the info was out there, but I just had to try it myself :))

--J

I don't fully understand electronics, nor thus what I'm doing, but I'll do my best. My batteries are 1.2V 2500mAh NiMHs. I charged them last night so I can answer prathman. I set my multimeter to 20 in the DCV section (http://www.promzone.ru/img/catalog/5612.jpg) and test some batteries: 223-228. I set it to 200 and test the whole battery pack: 228. What does this mean? that the batteries are 2.2 volts?

I hook the pack to the strobe (not using the 9V clip with the 20-gauge wires). It works. I hook the pack to a halogen. It doesn't work. Why not?

I would probably use only 1 halogen and the strobe most of the time, not both halogens and the strobe. Does that make AAs OK? They were free, and I imagine C cells + a charger will add a lot of money to this system. I don't use batteries for anything else, so even if they burn out early, I'd use them as long as it's not dangerous.

How many watts is your headlight? I looked at Scharf's web site, but there's too much info there to find that detail quickly.

--J

14w

So, taking nominal ratings, you have a 14w lamp running off a 12V battery, drawing roughly 1,2A. Your battery capacity is 2,5Ah, so you're looking at getting 2 hours of burn time. In real life things will be worse of course, especially if you connect more lights besides just one 14w halogen, but those are the theoretical numbers.

In my project, trying to run 10w-15w halogens at roughly similar specs (6V system, but resulting in 1,5-2A current draw) off a AA based battery pack did not turn out too well. The burn time was less than expected, the voltage dropped from nominal value quite fast when in use and the batteries did not last many recharge cycles. I think the steady load was too much for the oldish NiMHs I had. It can also be difficult to find AAs that are roughly equally good. One weaker AA in the pack is enough to bring performance down drastically. In your case (10 used batteries) this is even more of an issue.

I'm no professional, and not sure if all this is enough to cause your lamp to not function at all. It seems likely you have some other problem there. But even if you fix it, you'll face these problems. I'd probably look into other battery packs, more suited for this kind of use. I'd also consider overvolting the light by 20%, running it off a 14,4V battery. It gives a lot more light, at the cost of slightly reduced bulb life.

--J

10 unused batteries, actually. They're all the same kind, too. They are a few years old, though. I bought them because I got some free college bookstore credit. If I go with a better battery, what's the cheapest solution?

Your options are to build a pack as you're doing now, but use C shells for example. Or get two 6V batteries, or even a single 12V battery. Some people have used 14,4V drill batteries for their lights. There is this (http://www.bikeforums.net/showthread.php?t=42629) beast of a thread on DIY lights. It has a ton of posts, but lots of good info too.

I really don't know what's best available for you and at what price. I do know that some of the US prices I've seen quoted on the Forums for electrical parts seem unbelieveably low compared to our local prices. It's probably best someone more local chimes in on that subject.

BTW, my batteries were all the same brand and model too, but still there were significant differences between individual shells in terms of capacity and voltage off the charger. They were old and used though.

--J