****** NexGen Advisory!! ********

[McGizmo]

Hi guys,
I wish I had more time and information to put into this post but I don't at the moment. None the less, it has recently come to my attention that one of the NexGen's that I sold has shown itself to be unstable in low mode after the light has heated up. The unstability is manifest in a bothersome flickering on low. I have been unable to replicate this with the 4 NexGen LE's I have built that I can test other than in the case of putting a 22 ohm resistored switch on one of these after it has reached what I would consider thermal steady state. This particular LE is fine to my eyes with a 15 ohm resistor but noticibly flickers with 22 ohms.

From my limited experience and test results, I might assume that there is a threshold for these NexGens where at a certain level of resistance, they will exhibit flickering; especially after the lights have been used in high and warmed up.

I have been using three lights for quite some time now and never noticed this behavior but my three samples don't seem to be at the threshold and/or I am not sensitive enough to the frequency that they *might* be flickering at. /ubbthreads/images/graemlins/icon3.gif

Frankly, I am late in leaving for a CPF meet that I have commited myself to attend, I am behind on work promissed and I have a wife returning tomorrow from a 2 week vacation out of the country. I have not done a thing in terms of making our home presentable to her! Basically, I am screwed! The other builders of the Alephs are doing what testing they can and Wayne needs to take a look at this as soon as he can. (He has naothing but spare time on his hands these days! NOT)


So, is this a big issue to the point that we need to look at using BadBoys instead of NexGen's if a two stage switching is desired? I don't know! I do know that I am very happy with my samples of NexGens on two stage platforms.

I also know that I don't want to ship another Nexgen build to a customer until I have a better idea of what this is about.

I guess I'll leave this at your input as well as a stay tuned for what information I can come up with. I am anxious to get the "red flag" unit back so I can see for myself what a misbehaving unit looks like as well as see if it can be tamed with a lower resistor value; albeit a resulting higher low level will result.

These boost converters are not the ideal candidates for resistive two stage switching but there is enough well behaved and properly functioning samples out there to give cause for using these switches on boost circuits. Certainly they can't compete with the elegance of use on the buck circuits where the converter just shuts down and lets the LED be under driven.

If this were a mechanical problem, I would be comfortable attacking it but since it is in the realm of black box magic, I defer to the experts as well as what trial and error I can learn from with personal experimentation.

Please be advised that there may be some sharp edges to the NexGen and some blood may be lost. I feel I am loosing some right now! /ubbthreads/images/graemlins/blush.gif


*** flickering report thread was here.

 

[sithjedi333]

Another user recently reported a similar problem when using a Nextgen in his Fire~Fly II.

HERE

 

[kaseri]

Don,

I just tested my Aleph2 NexGen BB500 using two different McE2s tailcaps with different resistor values & I noticed the flickering with both tailcaps. One of the McE2s tailcaps has a 15ohm resistor and the other has a 7.5ohm resistor.

I turned on the Aleph2 BB500 NextGen light on high until it was at a reasonable operating temprature and the tested both tailcaps. Both McE2s tailcaps were "flickering"

I actually noticed the flickering during the initial test of my NextGen LE but I dismissed the flickering because I thought it was happening due to the cell not being fresh.

/ubbthreads/images/graemlins/frown.gif /ubbthreads/images/graemlins/frown.gif

I ran the above test once again while using a fresh 123 cell and the results were exactly the same. Flickering on low beam was observed when using two different McE2s tailcaps. One which has a 15ohm resistor & one which has a 7.5ohm resistor.

 

[Kiessling]

Checked my 2 NG units (one 1000mA and one 750mA on 1x123) after a warm-up time of a few minutes on 15 and 22 ohms ... no flicker.

But I am experiencing some flicker in low-modes here and there ... mostly it disappears after using another tailcap / resistor. Could it depend on the specific combo of LED-bin and driver unit?
Seldom it might also be caused by bad / dirty contacts.

/ubbthreads/images/graemlins/icon3.gif

bernhard

 

[mut]

I know that when there is too much of a resistor the light flickers on very low beam. I have tried a nexgen BB/1000 with all of the different McE2S values that I have. If the value is more than the 22 I think the board is reading it as the battery is low therefore the nexgen thinks the battery is below the 2.7 or whatever the cut off is and act appropriately.
Just a thought and observation. I could very well be wrong though.

mut

 

[Kiessling]

Happy birthday mut, and IMHO the 2.7V cut-off is with the Wiz2 and not the NG ... /ubbthreads/images/graemlins/icon3.gif

bernhard

 

[McGizmo]

Hey guys,
Thanks for posting. I now need to jam down to a CPF meet that I felt somewhat "roped" into attending by sithjeddi333 but I would rather hang here and find out what is being reported. Kaseri's statement that he is getting flickering on 7.5 ohms seems to shoot the idea of a lower resistor value solution full of holes! /ubbthreads/images/graemlins/frown.gif Dang! It may well be that the NexGen will be illadvised for the two stage program unless one is willing to accept going from a constant on run on high to low with flickering. This seems dubious to me. Personally, I only use the lights momentarily but that is an exception and not the rule. Ironically I have done run time tests on resistored low with no ill effects but I assume this is because the light never got hot on low?!? /ubbthreads/images/graemlins/icon3.gif

In light of these issues, I will be offering refunds to anyone who has a NexGen and finds that their unit does not meet with their expectations. Bear in mind that you will not get the high output like the NexGen gives should you opt for a BadBoy replacement. You will also suffer in the efficiency realm. Another alternative is to go to single stage, strictly high level output.

Well this issue needs to bloom and then be addressed.

 

[kaseri]

Don,

I ran the test again, this time being sure that all contacts were "clean" and I am seeing the same results with my NextGen LE. In addition to the 15ohm & 7.5ohm tailcaps I also tried out my 10ohm tailcap and each time the results were the same. "Flickering" on low.

 

[Chop]

Actually, the Wiz2 has a 2.5v cutoff.

Anyway, back to the point. When the NG is kicked off and it starts in regulation, it will suck a battery down to about 2v.

There have been some reports of NexGens flickering in low mode after the lights gets up to running temp. This has no affect on the operation of the light in high mode.

The thing about boost converters is that they are trying to boost, all of the time. In typical LED lights, the flickering is usually a sign that the battery needs to be changed. What is happening in a light with a two stage switch is that the converter is being fooled into thinking that the battery is low and allows a direct drive low level output. "Moon mode" if you will.

As has been described before, the way the NexGen works is that for every bias level, there is a threshold voltage that the battery must meet in order to start the converter in regulation. If this threshold voltage is not met, then the converter goes into "safe mode" which is just an internal current limiter. It limits the current drawn to about 1A.

Now I'm sure that CPF being the community that it is, will be willing to help trouble shoot this condition in low mode. I have a theory that I would like to check out and it would help if others did so as well.

Now I'm just trying to narrow things down here. It would help if we could insure that the light was in regulation, so a NexGen500 would probably be good for the following test.

First, start with a new battery and kick the light off and let it get up to operating temp, then kick it down to low mode and see if it flickers. If it does, then completely turn the light off and then turn it on to low mode, and see if it flickers.

What I'd like to find out is whether the flickering is more associated with an operating mode of the converter, ie., whether it flickers dropping down into low mode after having run in regulation or whether it flickers dropping down to low mode after having run in safe mode.

My reasoning behind this is because of the way the converter works. If you think about it, the converter, once started in regulation, will drain the battery down to 2v and quit. Maybe dropping down to low mode from a regulated state convinces the converter that the battery needs to be changed NOW. On the other hand, if the light were running in safe mode and you drop it down into low mode, the converter may see the drop as simply a continued stage of safe mode.

I don't know, I'm shooting in the dark and am in the data gathering stage.

The theory that I stated above is also kind of confirmed by Kiessling's post above. He's running a couple of really hot Nexgens. On anything less than a fresh batt, they will likely start in safe mode and he is not getting any flickering. I just don't know at this point.

I can assure you that we are all working to get to the root of the problem. I can say this though. It is likely that going to a lower resistor value may reduce or alleviate the problem. 12.5 ohms seems to work well with buck/boost circuits and may help with the Nexgen situation.

I'm sure that other builders and Don, himself, will follow up on this situation.

Keep posted on this thread for any updates.

I'm going to start another thread for those that would like to report whether they are getting the flickering, and if so, under what conditions.

 

[kaseri]

[ QUOTE ]
Chop said:
If it does, then completely turn the light off and then turn it on to low mode, and see if it flickers.

[/ QUOTE ]

Should I let the light cool down 1st or just turn it off & then back on right away?

 

[Chop]

Turn it off and then back on right away.

 

[kaseri]

testing it out right now. Give me about 5 min.

 

[kaseri]

Ok tested it per your request with a fresh cell & when going from high to low it flickered. I shut off the light & turned it back on to low beam & the light still flickered.

 

[Darell]

Tony -

I can tell you that in my sample (NG 917) with a half-dead bettery, the flickering happens if going from warm high to low... or warm and off to low. I have (only a few times) also seen the flicker when the light is cool and just going into low directly. I'm having trouble finding a consistent pattern. I need a larger sample base, but am low on circuits at the moment.

 

[McGizmo]

Hi guys,
I bailed on the CPF meet. I got too much goin on not to mention that I need to get the house in order for return of Wife! /ubbthreads/images/graemlins/icon15.gif

I spoke with Wayne on the phone and he will be getting on his bench late tonight to see what's up. The NexGen shuts off at around 1.8 V. Wayne suggested that I stick a LE on the bench supply and bring the Vin down and approach the 1.8v shut off and monitor the beam as it dims (this is essentially replicating what the resistor does).

Now on the sample I tested, I did start to notice some flicker just before shut down (1.8V) but it was at a level dimmer than what I have with the resistored switch.

What I am curious about is the degree of flickering you guys are seeing?!?! In other words, I had a CRT computer display at my last place of work that was fine for me but some people would ask me if the flickering didn't bother me; something I didn't see I guess due to different image retention times between people?!?! So Kaseri and others, the flickering you are seeing, is it blatant and obvious or somewhat subtle?

 

[kaseri]

Don,

To my eyes it's obvious. My eyesight is the one thing that is working these days!

 

[mut]

Thanks Bernhard.
My bad on the 2.7 thing.
I use the R123's from JS B's so I don't see this problem.
I did try a old 123 that only had 2.9V on it and let the head heat up to temp on high and then turned to low and I know get a flickering. I guess that using the r123 cells has caused me not to get this flickering thing.

mut

 

[kaseri]

I hate to make things worse but...

I just tested the light again. This time I had the light on high for about 20-30 seconds then I went down to low and noticed the flickering. I turned off the light & then back on & the flickering was still there.

 

[NewBie]

Curious, have you tried a Duracell Ultra 123?

 

[gtwace]

My prototype nexgen1000, TYOJ with 15 ohm McE2S, Energizer Photo lithium works fine after 10 minutes at high then switch to low and subsequent switching. However there are a few observations :

1. The light will flicker at the transition point of switching high to low - at high, turn the McE2S to low slowly, at a point (very slightly) the light will flicker before further turning makes it stable low mode. This should be cause by the McE2S, perhaps the heat caused the connectors to expand and therefore the switching isn't that smooth, further turning or slight pressure on the McE2S also caused the light to flicker.

2. There is a hissing sound coming from the light sometimes when in low mode but switching it off/high then back to low will stop it, don't know what is causing it.