Malkoff M91

Kestrel

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Still an M91 fan after all these years. I'm a late-adopter, so only just had the opportunity to put a modern M61 (SST-20) against my nearly-obsolete first-gen M91N. Difficult to compare because the beams are so different, but even pushing 15 years old, the M91 is still a performer - and what I'd reach for.

Am fortunate to have an updated M91BN as well as my old M91N; between the two I'm still set. I just can't use them in my Nitrolon SF hosts, is all. :-/
 
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tech25

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I have been impressed with the 91B the last few weeks. The wide voltage range is amazing. An interesting phenomenon doing chores last evening. After about 30 min or so it started strobing. It was in an MD2 with an extension and two Keeppower 18500's. Very curious.
I ran the unit in a different body on one cell for over an hour with no problems. so not an issue with the 91B itself.
Put it back into the original body and the same batteries with the same thing, strobing. Must be the protected cells doing something funny. I have it running in the original configuration with fresh cells and no issues after 45 min so far.
The same thing happened to me. Same setup and same batteries, just one of the sets did this the other set and a few different 18650s had no issue.

I'm trying to get a few pairs of Vapecell N20 button top 18500s. With a 10A rating I'm thinking it will help them have a longer life.
 

Alaskantinbender

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The same thing happened to me. Same setup and same batteries, just one of the sets did this the other set and a few different 18650s had no issue.

I'm trying to get a few pairs of Vapecell N20 button top 18500s. With a 10A rating I'm thinking it will help them have a longer life.
I just did a short run test on my 2 M91B,s with the same setup on 2 18500 batteries. Both of them got to 134 F in 15 min. I wonder how hot is two hot? Running on a single 18650 gave me long run times but I didn't notice them getting near this hot.
 

thermal guy

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I just did a short run test on my 2 M91B,s with the same setup on 2 18500 batteries. Both of them got to 134 F in 15 min. I wonder how hot is two hot? Running on a single 18650 gave me long run times but I didn't notice them getting near this hot.
Ya on a single 18650 they won't get hot at all. You're not getting anything near full output. Maybe 500-600 Lumens so it should run cool.
 

md17

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No, they are the 2300 mah. On the current test the light went out at 1 hr and 10 min. I was very surprised at the temperature. I have run it before and recorded about 116 deg F but this time it was 169 deg F. WOW. All cooled off now. 1 batt at 2.8V and the other at 3.1V.
I went through this a few months ago with the 2300 mah 18500 with a Hound dog and m61hotv2.

Gene's response to The flickering issue:

That is normal. Generally, if the cells are reading somewhere below 3.2v they are for all practical purposes dead. If you put any reasonable load on them the voltage will drop quickly and cause a flickering/flashing behavior. I usually don't let my cells get below 3.4 – 3.6 volts (as read by the charger). Resting voltage is a notoriously inaccurate way to read remaining capacity of a battery. You may find that most of the other batteries you have are OK once you charge them.

The only reasonable explanation is that when under load, the voltage drops way below what we can read with the cells out of the light, not under load, causing insufficient power.

I charge around 3.6v and haven't had an issue since.
 

Alaskantinbender

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I went through this a few months ago with the 2300 mah 18500 with a Hound dog and m61hotv2.

Gene's response to The flickering issue:

That is normal. Generally, if the cells are reading somewhere below 3.2v they are for all practical purposes dead. If you put any reasonable load on them the voltage will drop quickly and cause a flickering/flashing behavior. I usually don't let my cells get below 3.4 – 3.6 volts (as read by the charger). Resting voltage is a notoriously inaccurate way to read remaining capacity of a battery. You may find that most of the other batteries you have are OK once you charge them.

The only reasonable explanation is that when under load, the voltage drops way below what we can read with the cells out of the light, not under load, causing insufficient power.

I charge around 3.6v and haven't had an issue since.
Great info, Thank you.
 

tech25

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I'm not sure. I believe mine were still within an acceptable Voltage. I even tried them after recharging and resting. I will try it again and report back.
 

md17

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Are there any other md2 configurations with an 18650 that would be a higher output than an m91b. I have been using this for 2 months now, and it's perfect, but maybe I am missing something.
 

tech25

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Maybe the 18650 hound dog or wildcat?

Also tested my M91BN and it's that specific set of batteries.

Now I'm trying to find a trustworthy site that has the Vapecell N20 18500 button top in stock.
 

md17

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Maybe the 18650 hound dog or wildcat?

Also tested my M91BN and it's that specific set of batteries.

Now I'm trying to find a trustworthy site that has the Vapecell N20 18500 button top in stock.
I think the wildcat is next, but the size of md2 is ideal.

I had a what I believed to be 4 bad keeppower 18500 batteries. I posted a thread in the flashlight electronics section in October titled "Keeppower Protection Circuit Issue". I thought it was a fluke, but I truly think there was a defective Batch of the 2300 mah batteries released.

I have had no issues with 2 new sets of 2300mah keeppower and the 2000mah ones work well also. Not sure if the Vapcell you are looking for are unprotected, but unless your checking the voltage often, it would be easy to overdischarge with the m91b, in my opinion.
 

thermal guy

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The V6 is a great light. Gets real hot though. My favorite is the V4.Very broad beam with plenty of throw
 
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