Modifying a 50W Halogen spot light

[jasonck08]

So I've got this nice looking 50W 6v halogen spot light with some sort of a 6V battery inside. I opened it up once to replace the bulb. I think the battery is dead and was thinking about throwing 12xAA's in there and slightly over driving a 12V 100W bulb.

I have a few questions... The batteries I have are all Ni-Mh's ranging from 2100 mAh to 2500 mAh. I have 4x Sanyo HR-3U 2500mAh, 4x HR-3U Sanyo 2100 mAh and 4x Panasonic HHR-3EPA 2100mAh cells. Is there a problem to mix different types of cells? Obviously the lower mAh cells will wear down faster.

Do I direct drive the 100W bulb from the 12AA's? Is that bad for them? Will they provide enough current? If I'm not mistaken would the current draw be about 8000ish mAh from each cell? If so then I believe that is too much. Is it true that most AA's can only take about 5000mah? If that is the case, then maybe I'd be better off overdriving a 50W 12V bulb...

Thoughts please!!!

 

[FILIPPO]

-I think that mixing batteries isn't a good idea...
-you need some high current batteries like ELITES 1700, CBP 1650, TITANIUM 1800, IB2100...
-with this type of batts you can overdrive 12V 100W batteries with no problems...(if you have a good "stock"...you need to make sure your spot light won't melt with double of power!)

 

[jasonck08]

Well I think I'll stick with overdriving a 55W 12v bulb to around 66W's @ 14.4v. That way I would only be pushing each battery to ~3.8amps, I know my Sanyo batteries can handle 5amps and assume the panasonics should hold up to 4-5amps as well... Most of the bulbs I have been looking at are around 1500 lumen's. So overdriving it should be around 2000 lumen's. The reflector I'm using is aluminum, and so is the flashlight body.

 

[jasonck08]

77 views... 1 response? Could someone give me some feedback? Is direct driving the bulb ok?

 

[FILIPPO]

Well I think I'll stick with overdriving a 55W 12v bulb to around 66W's @ 14.4v. That way I would only be pushing each battery to ~3.8amps, I know my Sanyo batteries can handle 5amps and assume the panasonics should hold up to 4-5amps as well... Most of the bulbs I have been looking at are around 1500 lumen's. So overdriving it should be around 2000 lumen's. The reflector I'm using is aluminum, and so is the flashlight body.

-if everithing is in metal you'll have no problem...
-have you thought about how you'll connect batteries in series?:thinking:

 

[mdocod]

you MUST use 12 cells that are closely matched in internal resistance and capacity for that to work. Mixing various brands and capacities will lead to over-discharged and overcharged cells every time. It's not worth trying.

Another issue that needs to be taken into consideration, is what bulb you decide to drive... If you just grab an automotive 12V bulb, keep in mind that they are actually ~13.X V bulbs already, so 12 AA cells really won't overdrive it *too* much, It'll probably work pretty well provided you have good quality low resistance cells and put together a low resistance pack. For simplicity prepossess you might look into just buying a pair of 6 cell RC NIMH packs. Just install a pair of plugs in the light to plug em into, (wired series), then you could just use a simple, cheap pack charger to top em up.

 

[jasonck08]

I ended up picking up a Philips HR 12v 55W 12336 Premium Halogen Headlamp for less than $4. Says on the box + 30% light over standard halogens.

I have a 8AA battery pack and a 4AA pack. I'm just going to do a few short tests, then perhaps later on I'll purchase some more 2500 Sanyo's or might splurge and grab some eneloops. I'm going to give the bulb a test run right now...

 

[jasonck08]

Ok, so I connected the 12 AA's to the halogen bulb in an aluminum reflector... I tested the battery packs and the reading was 15.8v from the 12AA's. As soon as I connected the batteries to the bulb and measured the voltage it was about 9.2v's. But it should be ~15v. So does that mean that the batteries are not able to supply sufficient current? At 9V's the bulb was still quite bright, but not near as bright as it should be.

Also, I'm in Taiwan, and do not want to pay for batteries to be shipped, so would enloops be my best bet as the are capable of handling high current...

Please advise. Thanks!

 

[FILIPPO]

maybe eneloops will work better...
you may have too much resistance in your spotlight....and this makes your light run dim because not enogh voltage id deliverd to the bulb...

 

[jasonck08]

The bulb is connected directly to the two battery packs... I have a digital multimeter but the only thing I know how to do with it is check voltage. How the heck do you check resistance on the silly thing?

 

[jasonck08]

Anyone know???

 

[jasonck08]

Anyone...????

 

[electromage]

The resistance you need to worry about is in the cells themselves, between the cells, and the wires between the batteries and the bulb. How did you connect the cells together? What size wire are you using between the pack and the bulb?

 

[mdocod]

some multi maters will not check the resistance between 2 points if those 2 point have a potential between them.

 

[Mr Happy]

OK, let's look at this.

You have 15.8 V open circuit from 12 AA's. That's 1.32 V per cell, which is about right for many cells, depending on the state of charge.

Now we have a 12 V, 55 W bulb, so at design it will draw 4.6 A.

Consider now the cells. Average cells may have an internal resistance of 0.1 ohms per cell, or more. If we assume 0.1 ohms and 12 cells in series, that is 1.2 ohms total internal resistance.

Let's put 4.6 A through 1.2 ohms. That will give a voltage drop of 4.6 x 1.2 = 5.5 V.

We subtract the voltage drop and find 15.8 V - 5.5 V = 10.3 V. You measured 9 V. This is quite within expectation since the internal resistance of the cells might be more than 0.1 ohms, and we have made lots of assumptions along the way.

In summary, nothing is strange about this at all. You need to come up with a better match between your bulb and your battery pack by changing one or the other or both of them.

 

[electromage]

some multi maters will not check the resistance between 2 points if those 2 point have a potential between them.

I don't know of any multimeter that will do that, if there is potential between them, you would need to do a voltage drop test with a known load applied to figure out the resistance.

 

[electromage]

I agree with Mr Happy, and he didn't even calculate loss in your cell interconnects, or between the pack and the bulb. Your cells are probably the weakest point, I would suggest trying some SubC cells, maybe in a pre-built pack. You should be using at least 14AWG wire to connect the bulb, and I think you'll notice much less drop in the circuit.

 

[jasonck08]

So many mag mods use AA's, yet no one ever talks about the extreme drop in voltage due to internal resistance. Do eneloops have a very low internal resistance? There has got to be some way to make this work. I don't want to go out and buy a whole bunch of batteries and bulbs. But do you think that perhaps a 6V 55W bulb with 12AA's wired in parallel would be any better?? Suggestions?

 

[Mr Happy]

For any given wattage, you will always be better off with a higher voltage bulb than a lower voltage bulb. Circuit power losses are proportional to the square of the current, so when comparing a 6 V 55 W bulb to a 12 V 55 W bulb the current ratio is 2:1, but the power losses are 4:1. The 12 V bulb is better.

Eneloops do have a lower internal resistance than many regular cells. I believe Eneloops should be able to maintain 1.0 - 1.1 V per cell when delivering 5 A. However, the best cells for high current are the ones designed for RC applications. There are some 'Elite' brand AA cells like the 1700 that will deliver over 10 amps without voltage sag, but the very best performance is found in sub-C size cells.

The unfortunate truth is that hotwiring lights in a serious way does mean buying a whole bunch of batteries and bulbs (and all sorts of other things). If you are on a budget, you might try milder bulbs that don't draw more than 1-2 amps. Try a 12 V 20 W rather than 12 V 55 W.

To overcome the voltage drop with standard cells, you can stack up more cells. Try 16 in series rather than 12. Also make every resistance mod you can to the light to reduce voltage drop in the battery holders, the springs and the switch.

 

[electromage]

You could also try these AAs http://batteryjunction.com/taapowermax-1800.html They have a very low internal resistance and might work perfectly for your project.