M6 + MN21 + 3 batteries = 250 lumens (yes or no?)

[matt_j]

I had an "argument" with somebody (knife forum) about taking M6 and reducing the amount of batteries in there to half (3 batteries instead of 6) so you can get half as powerful output on the lamp (250 lumens instead of 500 lumens on MN21 lamp). I say it's not true and demonstraded it by recording video. Guy still insists it's true and says it works on his light. I posted similar thread on different forum and everyone calls it bs too. I got no answer from SF technical staff so I can repost it.

Any even remote chance it is possible?

 

[LED61]

No, it is not possible. The MN21 lamp draws close to 5 amps current from two stacks of 3 in series batteries, meaning 2.4 amps per stack. If you only used one stack, it would attempt to pull all that current from the single stack, thereby exceeding limits on the batteries. As far as the bulb dimming to half the output, well that's just not the way things work.

 

[CM]

No, it is not possible. The MN21 lamp draws close to 5 amps current from two stacks of 3 in series batteries, meaning 2.4 amps per stack. If you only used one stack, it would attempt to pull all that current from the single stack, thereby exceeding limits on the batteries. As far as the bulb dimming to half the output, well that's just not the way things work.

Yep, LED61 has it right. The results will be very disappointing. The setup will probably yield 100 lumens of icky yellow light.

 

[Flash_Gordon]

LED61 has summed it up perfectly. Also, underdriving this type of lamp assembly will damage it as well as damaging the batteries in this scenario.

If it would work as your friend stated, wouldn't Surefire give me a nice two stage tailcap so I could have a 250 lumen or 500 lumen M6. Of course they would.

Mark

 

[mdocod]

to the uneducated M6 owner you are talking about there, it would certainly APPEAR to him to be working as he is percieving and understanding it. But what he doesn't realize, is that the reason it is about half as bright is because he's putting SO much strain on the cells, that they can not maintain voltage, the result is that he is going to trip a lot of cells PTC protectection, making them useless, best case senario, he'll get 5-7 minutes runtime at half brightness.

The really sad thing, is that he is confused to believe that using 3 cells is somehow an advantage driving the MN21, when infact, using more cells with a low duty lamp (like the MN15) would be 10x better for low output. over 2 hours instead of 5 minutes.

The other major problem, that he will likely run into if he continues using that setup, is cells overheating and exploding before the PTC has a chance to save the day. Ruining a perfectly good Surefire M6.

 

[matt_j]

I think that what I'm arguing with him is that in my light it didn't work at all. No dim output for few minutes, no generated heat, nothing. He says it works. SOme of you guys say it works but it's useless.

I'm just trying to find out...

 

[Owen]

I just put a KT2 on one of my Z3s, with a MN21 and tried it with two different sets of 3x123. Current draw right at 4A. I'd say it might put out as much light as a MN15, but with a much larger and dimmer hotspot. Hard to really say, though, because I can't do a side by side, and the beam characteristics are very different.
Regardless, we're talking minimal(and quickly dimming), output with a huge strain on the batteries.

btw, the MN21 will light up off even 1 123, so if you aren't getting any light at all when you try it's a contact issue. I use the MN21 with 2 unprotected 18650s, and am not familiar with the M6 or its battery carrier, so can't offer any reason for it.

I agree with the consensus that it works, but is useless.

 

[LED61]

I just put a KT2 on one of my Z3s, with a MN21 and tried it with two different sets of 3x123. Current draw right at 4A. I'd say it might put out as much light as a MN15, but with a much larger and dimmer hotspot. Hard to really say, though, because I can't do a side by side, and the beam characteristics are very different.
Regardless, we're talking minimal(and quickly dimming), output with a huge strain on the batteries.

btw, the MN21 will light up off even 1 123, so if you aren't getting any light at all when you try it's a contact issue. I use the MN21 with 2 unprotected 18650s, and am not familiar with the M6 or its battery carrier, so can't offer any reason for it.

I agree with the consensus that it works, but is useless.

Owen, for how long did you run the MN21 on 3 123's ? because if you went through a 4 amp draw even for 2 minutes the battery must have gotten way too hot above safety levels. One Duracell engineer once told me that their 123's could tolerate a 5 amp draw as pulse only.

As far as the 9 volt bulb lighting up on a single 123, well, that's only about 2 volts max considering the sag on the load are you sure about that ?

 

[mdocod]

Z3s, with a MN21 and tried it with two different sets of 3x123. Current draw right at 4A

glad you took some readings... from that information.. we can actually get a pretty good idea how much the voltage of the cells sagged.

in order for the current to drop from the "design" of [email protected] to 4A, the voltage would have to drop to about 4.5V.

So we know the cells were sagging to 1.5V each. that's some narly sag.

 

[Owen]

Yeah, I wouldn't expect it to run for more than a few minutes.

Here's what a MN21 looks like off a used SF123 that measured 2.9V(no load, obviously!):

I don't know why I enjoy doing this stuff...:shrug: