halogen light battery question

[scubachris82]

Hi,

After seeing all the great work everyone has done building lights, I'm interested in building my own. I have a question regarding batteries, and I was wondering if anyone here with more experience could help me out.

I am planning to use a 30 watt, spotlight, mr16 bulb for my light (12 volt). In order to power that, I was hoping, I could get away from the starndard block shaped 12 volt batteries and use a Nimh battery pack set up in series. I was looking at the batteries shown at this site:

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=711

I was wondering if it would be feasible to hook up 10 of those in series in order to power the bulb, and if so, would I get a decent burn time (compared to the block batteries)

If anyone could help me out that would be greatly appreciated.

Thanks for your time,
Chris

 

[jonnythan]

What you describe is exactly the setup most can light manufacturers use when creating a 12v NiMH pack. They simply solder a 10 cells in series to get 12 volts, then put those batteries of 10 cells in parallel with another battery of 10 cells to get higher amp hours.

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=988 <--- this is, IMO, the quickest and easiest way to get a lot of burn time. It's a battery of 10 D-size cells and you'll get 3-4 hours on a 30 watt halogen bulb.

 

[scubachris82]

Thanks for the reply jonnythan,

I know I'm on the right track, then. I will probably make it myself, because it is still a little bit cheaper, and if I get those batteries, that I put the link to, they have a 10,000 mah hour rating.

I have another question now (it's just a quick one). I read that you can add a voltage increase of 10% (1 extra cell in series) to an mr16 light, and you will get about a 30% increase in light (lumen rating).

http://www.gelighting.com/eu/downloads/prod_data/hal/mr16_start_datasheet_en.pdf

This does make the bulb only last 30% of the time, but at $5.00 a bulb, the benefits exceed the costs.

Any thoughts on this, has anyone done it, does it make a significant difference.
Thanks,
Chris

 

[jonnythan]

If you're soldering batteries, be sure you get the ones with tabs made specifically for it. You don't want to heat up NiMH cells directly.

Adding a cell will make the bulb a bit brighter, sure. $5/bulb isn't as much of a concern as the greatly inreased risk of blowing it out during a dive. I'd much rather run the bulb at the rated voltage than press my luck diving with the thing at night.. and underwater I want to be worried about the fewest pieces of gear as possible.

 

[Charlie99]

Adding a cell will make the bulb a bit brighter, sure. $5/bulb isn't as much of a concern as the greatly inreased risk of blowing it out during a dive. I'd much rather run the bulb at the rated voltage than press my luck diving with the thing at night.. and underwater I want to be worried about the fewest pieces of gear as possible.

You might take another look at the expected lifetime of whatever bulb your divelight has.

The MR16 series has a nominal life of 2,000 hours. Even at 10% overvoltage the expected life is still 600+ hours ----- way beyond the expected life of most commercial divelight bulbs, since they are overdriven much harder.

Even taking into account that a 11 cell NiMH battery will run up to almost 15V at the beginning of discharge, the expected life of an MR16 bulb would still be >200hours.

 

[scubachris82]

Thanks for the reply,

I'm not worried about the costs of the lights. I'm more concerned with them spontaneously "blowing it out". If this is a real issue with a 10% overvoltage, I'm not all that interested, but if it's not really a worry I would still probably go this route. Coes anyone have any experience with this.

Chris

 

[TomP]

Rather than overdrive a 30 watt why not go for a 50 watt mr16?

 

[Charlie99]

Rather than overdrive a 30 watt why not go for a 50 watt mr16?

It's brightness vs. size of battery pack. MR16 bulbs are designed for home use with a nominal 2000 hour life.

If you look up the info on whatever halogen dive lights you have, you will probably find that the expected bulb life is in the range of 10-50 hours (other than the Halcyon Scout and equivalents, which have much longer life since they use just 3 cells to drive the same bulb used with 4 cells in UK divelights).

Overdriving an MR16 by 10% will still leave the bulb with around 500hour expected life. Overdriving by 20% would still leave bulb life of around 200 hours -- longer than most other dive lights. Unfortunately a 12 cell pack is a lot more than 20% overvoltage right at the beginning of life, so I'd stick with 11 cells in series.

Some commercial companies, such as Nocturnal Lights drive their MR16 lamped dive lights with a 14.4V NiMH battery pack.

 

[TomP]

It's brightness vs. size of battery pack. MR16 bulbs are designed for home use with a nominal 2000 hour life....

I agree. My point was that given the same battery pack, overdrive or not, a 50 watt mr16 will be brighter than a 30 watt mr16. Burn time per charge will be shorter but it should be more than enough for most profiles.