SL-4AA pro-polymer and the NiMH conversion

[kb0rrg]

I decided that I couldn't buy the SureFire C3, because my truck needs new tires. But I did want to get a new light. The NiMH conversion of the SL 4AA pro-polymer was very intriguing to me. So I bought a 4AA and the 3C bulb. I already had 4 NiMH batteries.

Before doing the conversion, I played with the 4AA in its stock format. I would say that the brightness is the same as my 3D with a Carley bulb. The beam is a bit better. I also have the SL-2AA. The 4AA is a MUCH better light IMO. Although it is a bit bigger, it more than twice as bright and I like the performance of the switch mechanism better. It seems to make better contact; less flickering with less pressure. I measured the amperage of this configuration to be .46A. Four alkaline batteries make 6 volts. Thus the wattage is 2.76 watts. This is consistent with Brock's data of 2.5 watts. I also agree with Brock that wattage is a very good (and easy to measure) indicator of relative brightness.

I must give credit to Alan who "invented" this conversion. The original post is at: http://www.candlepowerforums.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=1&t=000366

Before switching the bulbs, I made sure that the batteries were slightly discharged to ensure that they were not in the 1.45 volt range like a very fresh NiMH can be. I discharged them to 1.3 volts, the beginning of the flat segment of the discharge curve. Overall, I belive this only consumes a few percent of the batteries energy. I am very impressed with the brightness of the light with the 3D bulb. It embarrasses my 3D mag with the Carley bulb. Plus, its about 80% lighter and has a tail switch. The 3C beam is a bit wider than the 4AA beam. The 3C bulb has a hot spot that gives it more reach than a focused ML. I measured this configuration too. .875A and 5 volts = 4.375watts. According to Brock's chart, that puts it between a 5D mag and an E2. I have found that 1watt = 15 lumens for most of the Surefire lights (again, by analyzing Brock's data) thus I estimated the modified SL-4AA to be about 60 lum. I don't have an E-2 or 6P so I can't directly compare. Alan claims it is brighter than an E-2 or Scorpion.

The problem is that the bulb only lasted a few minutes. This was a great disappointment to me, because I was so impressed by it. I am aware that this over drives the bulb by a half volt. I decided to try it again and bought another $6 bulb. I did not change the batteries as they were now in the 1.25 volt range. This bulb lasted much longer. In fact I accidentally left it on face down for what I guess was an hour, with no failures. This gave me hope that I really could make this work. But again, the bulb died after a battery change. My conclusion at this time is that the bulb is stable at 5 volts (4*1.25) but not at 5.2 volts (4*1.3). This seems like a small difference, but the bulb seems to notice. I have not given up yet on this yet and would like to try it again when I get another bulb and I will really be careful of my voltage. In both cases the bulb failed after it had been unused for about a day. I am guessing that the initial surge of current from the well-rested batteries is what is killing the bulb.

Alan, do you have any more tips for me???

I still want a C3...

 

[Alan]

I did have one bulb blown with a set of freshly charged batteries. After that, I didn't have any blew bulb again as long as the batteries set is not freshly charged. I normally put them aside for 2 weeks or 3 before using it.

If you want bright 4AA light but doesn't need tail switch, you might want to try Tec 40 with upgrade lamp. Since Tec 40 uses PR bulb, you could get high output PR lamp easily without any fear of blowing bulbs.

I have 2 of Tec 40 (Princeton) with Philips HPX40 Xenon bulb which is 4.8v 0.79A. HPX40 is rated 66.5 lumens. It's bright and smooth due to its textured reflector. I use rechargeables on these lights and becomes my favorites. Since then, I didn't touch my SL4AA anymore. The original bulb in Tec 40 is 4.8v 0.5A and rated 37 lumens.

If you want to get even brighter, try the following bulbs:

HPX41 4.8v 0.9A 78 lumens (xenon)
HPR50 5.2v 0.85A 85 lumens (halogen)

Due to high current of these bulbs, you might want to use rechargeables instead of alkaline AA. Any higher current bulb than these might melt the reflecter.

I hope this help.

Alan

 

[AluminumOvercast]

Did the watch look like this?
http://albums.photopoint.com/j/View?u=1560423&a=12216187&p=44440890&Sequence=0&res=high

Shelby

 

[PeLu]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by kb0rrg:
I have found that 1watt = 15 lumens for most of the Surefire lights (again, by analyzing Brock's data) thus I estimated the modified SL-4AA to be about 60 lum.
<HR></BLOCKQUOTE>

The lm/W rating is a lot affected by the filament's temperature. If you are overdriving the bulb so much like you are doing it, you may easily get 20-25lm/W (but on a very low lifetime).
Your NiMH cells also have the drawback of a very low internal resistance, giving a very high rush in current when switching on. This is very hard on the filament and the switch.
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
My conclusion at this time is that the bulb is stable at 5 volts (4*1.25) but not at 5.2 volts (4*1.3).
<HR></BLOCKQUOTE>
The bulb is not 'stable', neither at 5 nor at 5.2V.
As long as you drive it below the filament's melting point, you can easily estimate the lifetime. A bulb for 3 cell lamp is usually rated at 4V / 25 hours. At 4.5V it will last 2.5 hours, at 5V maybe 20 minutes.
Have you checked the voltage at the bulb under load all time? probably not. So it is hard to say anything repeatable.
If you want to drive a bulb that close, it's better to use a Willie Hunt LVR.

 

[JoeyL]

PeLu, Thanks for that explanation.

I had a similar experience but with the p61 high output bulb in the 6R with a 4.8 v nicad pack. I had two separate assemblies blow out, one in the first few seconds of use. Worse, it was brand new.

Would anyone know if the P60 standard lamp is OK to use in the 6R, (as opposed to the usual R60 lamp)

Thanks

 

[Gandalf]

I'd contact SureFire on this. I remember reading somewhere (on a webpage for a SureFure re-seller) that one of the lamps, either the P60, or R60, could be used with both rechargeables and the Nicad pack, and the other lamp couldn't. But, sorry to say

I can't remember which lamp was which. Possibly, SureFire may say to use 6P with lithium batts. , and the R60 with the NiCads, but I distinctly remember reading this.... I just can't remember, distinctly, which was which way....

Not much help, except to say one lamp will work with both batteries....

 

[JoeyL]

Actually, I did just call SureFire Customer service. They think the lamps were overpressurized. He said if they fail at too high a current, they should just burn out, not explode (as mine did, quite vividly).

He indicated that they tested quite a few P61 and P60's with the NiCad pack and they worked fine.

 

[kb0rrg]

I am happy to report that my SL-4aa has been used on many times now with no bulb failures. I guess it is absoulutly esential that the voltage be under 5.0 vdc (unloaded). A regulator may be the way to go...but how to squeeze it in

 

[PeLu]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by mrchri5:
i never knew that about nimh cells. wouldn't that make them potentially damaging to any equipment you use them in? <HR></BLOCKQUOTE>

NiMH and even more NiCd cells have a much lower internal resistance than compareable Li or alkaline cells.

If you connect you incandescent bulb to a 'strong' power source (= very low internal resistance) initial current may be 10-14 as high as the nominal current. This may even mechanically damage your filament, if there are no other limiting factors (resistance of the switch, contacts and mostly the cells' internal).
If you drive an incandescent bulb to it's limit, there is no other way than to 'soft start' it (and keep the bulb exactly at it's working point).
It's easy to check it: If you know your bulbs data, just calculate the 'on' resistance (some 4.6V 1.2 A for a P60, giving some 4 Ohm, cold resistance is about 0.5 Ohm including the spring terminals). The take a good Ohmmeter with a low range and measure the cold ('off') resistance.


And there is another difference in between let's say a SureFire 6P and its rechargeable counterpart:
If your 6P's bulb lasts 12-15 hours, you spent already a lot of money for the 24-30 123 cells. A spare bulb will not affect your overall cost very much.
A rechargeable light is usually used much more and it is easy to get it used for 10 hours or so a month. People would be annoyed by buying the monthly spare. So a little bit of efficiency is sacrified and the bulb lasts much longer.