Page 3 of 3 FirstFirst 1 2 3
Results 51 to 65 of 65
  1. #51
    mtbr member
    Reputation:
    Join Date
    Mar 2006
    Posts
    461
    I like this video of cooling down the BT20 and water testing!


  2. #52
    just a Newbie
    Reputation: colleen c's Avatar
    Join Date
    May 2011
    Posts
    252
    Quote Originally Posted by Vancbiker View Post
    I have a hard time understanding how the battery voltage sensing would work right at all if you raise the input voltage to 12.6 using a 3S battery. The end of useful charge in that battery will be ~9V. That's higher than the starting voltage 8.4V of the original pack. I'm guessing the driver is programmed to change the indicator color or light output at set values. Maybe it senses the voltage when first turned on and that selects values based on the starting voltage. Anyone help me get this?
    Keep in thoughts that there are buck driver that can be used in a wide range of input voltage from the battery. They basically buck the voltage down from a higher voltage and provide whatever current such as constant current or PWM to the LED. The XML led needs an average of 3.2v to be driven properly. So the driver will buck the voltage down to the proper volt at the LED. I'm not really sure where exactly does these driver sense the change. For all I know, they might be sensing the voltage after the regulation and not right at the battery input source. So you can have 3s power sorce or a 2s power source and it should not affect the driver sensor for the low voltage cutoff or indicator although one would be a nominal 7.4v and the 3s is 11.1v.

    There might be an exception in this case for the Fenix light. The picture posted from pucked up show some circuitry in the battery pack holder. Not sure what it is. Low cutoff? Voltage regulator? Who knows.

    Picture posted from member pucked up:

  3. #53
    mtbr member
    Reputation: mattthemuppet's Avatar
    Join Date
    Jul 2004
    Posts
    2,294
    that's not really how it works Colleen. Battery voltage is sensed as the difference between B+ and ground as LED voltage is determined by the current it's running at, which should stay constant as long as the battery voltage is above LED voltage + driver overhead.

    So if you program a low voltage warning for a 2S pack (6.4V or thereabouts), that will be way past the point where a 3S pack is overdischarged (8.25V absolute minimum). The easier explanation is just that there's something funky going on with the driver, which is borne out by Fenix's temporary removal of the light from the market. I would have thought they would pick up basic stuff like this before releasing a product though, it's not like they're amateurs.

    As for the board in the battery pack, it's not a PCB. For a start, there aren't enough parts and, second, 2S PCBs need a wire to go to the junction between the 2 cells (-ve pole of 1st cell and +ve pole of 2nd) to accurately sense the voltage of each cell. No idea what those 2 things do, but they don't have anything to do with preventing overdischarge that I can see.

  4. #54
    just a Newbie
    Reputation: colleen c's Avatar
    Join Date
    May 2011
    Posts
    252
    Quote Originally Posted by mattthemuppet View Post
    that's not really how it works Colleen. Battery voltage is sensed as the difference between B+ and ground as LED voltage is determined by the current it's running at, which should stay constant as long as the battery voltage is above LED voltage + driver overhead.

    So if you program a low voltage warning for a 2S pack (6.4V or thereabouts), that will be way past the point where a 3S pack is overdischarged (8.25V absolute minimum). The easier explanation is just that there's something funky going on with the driver, which is borne out by Fenix's temporary removal of the light from the market. I would have thought they would pick up basic stuff like this before releasing a product though, it's not like they're amateurs.

    As for the board in the battery pack, it's not a PCB. For a start, there aren't enough parts and, second, 2S PCBs need a wire to go to the junction between the 2 cells (-ve pole of 1st cell and +ve pole of 2nd) to accurately sense the voltage of each cell. No idea what those 2 things do, but they don't have anything to do with preventing overdischarge that I can see.
    Thanks for clarifying. I'm still in that learning curve So I guess that the Fenix driver must be programed to sense and know what the power source whither that 2s or 3s before knowing how to sense low voltage for the cutoff or mode change from Turbo to High. I do hope they get this problem fixed. I like the concept of multiple beam and hopefully others will persue the same course.

  5. #55
    mtbr member
    Reputation: spankone's Avatar
    Join Date
    Aug 2011
    Posts
    255
    They should have just kept it simple and made this a 2x18650 light. Seems pointless making it except 4x cr123s as well.


    Sent from my iPhone using Tapatalk

  6. #56
    mtbr member
    Reputation:
    Join Date
    Mar 2006
    Posts
    461
    Quote Originally Posted by colleen c View Post
    Thanks for clarifying. I'm still in that learning curve So I guess that the Fenix driver must be programed to sense and know what the power source whither that 2s or 3s before knowing how to sense low voltage for the cutoff or mode change from Turbo to High. I do hope they get this problem fixed. I like the concept of multiple beam and hopefully others will persue the same course.
    The guys at Fenix have told me that the low voltage is set at 5.6v. The BT20 will step down when the batteries reach this point.

    Too bad I can't measure what mah my batteries are at when charged/dis-charged. I would like to see if they're anywhere near the 2500mah it claims.

  7. #57
    mtbr member
    Reputation:
    Join Date
    May 2005
    Posts
    2,247
    Quote Originally Posted by pucked up View Post
    The guys at Fenix have told me that the low voltage is set at 5.6v. The BT20 will step down when the batteries reach this point.
    This more like what I expected. So if one was to run this light on a 3S battery the voltage sensing would not work to protect the battery nor warn the user of impending shutdown.

    If the battery had its own protection board then it would kick off the light. If the battery was unprotected the it would run down until the battery was damaged due to overdischarge.

    For use with 2S 18650s, IMO the 5.6V should be where the light shuts itself off at. 6.2v for a low power step-down would be much kinder to the battery.

  8. #58
    mtbr member
    Reputation: spankone's Avatar
    Join Date
    Aug 2011
    Posts
    255
    My cells on Tuesday where at 4.19v before I set out and after my ride both cells measured 3.66v. I don't think I would like to run them any lower than that.

    Can some one remind me of the lowest voltage a cell can drop to before its damaged?


    Sent from my iPhone using Tapatalk

  9. #59
    mtbr member
    Reputation: spankone's Avatar
    Join Date
    Aug 2011
    Posts
    255
    Part 2

    http://youtu.be/84Pv_cztqsM

    It's a solid light but not quite there yet.


    Sent from my iPhone using Tapatalk

  10. #60
    mtbr member
    Reputation: mattthemuppet's Avatar
    Join Date
    Jul 2004
    Posts
    2,294
    Quote Originally Posted by spankone View Post
    Can some one remind me of the lowest voltage a cell can drop to before its damaged?
    most manus state 2.75V, although there's barely any capacity left after 3V

  11. #61
    mtbr member
    Reputation:
    Join Date
    Mar 2006
    Posts
    461
    So I got some Panasonis 3100mah protected batteries from DX and tried a turbo run test. With my Trustfire batteries it would only last 5mins on turbo mode before drpping to high. The panasonic beat the 5 min mark, but then dropped to high at the 12 min mark. I was using the 2pk battery case that came with the BT20.

    I would assume that there is an issue with the light or the unit as a whole doesn't like it when protected cells are being used. I stop the test after the 12 mins.
    "By Your Command"

  12. #62
    mtbr member
    Reputation:
    Join Date
    Oct 2011
    Posts
    2
    Officially there is a problem with driver. Manufacturer is actually solving this problem and then you can change your light. It can be resolved till the end of year.
    Last edited by MirosPikos; 12-10-2012 at 09:26 PM.

  13. #63
    mtbr member
    Reputation: spankone's Avatar
    Join Date
    Aug 2011
    Posts
    255
    My bracket unscrewed its self from the light head the other day. Slightly annoying.


    Sent from my iPhone using Tapatalk

  14. #64
    mtbr member
    Reputation: spankone's Avatar
    Join Date
    Aug 2011
    Posts
    255

    User review Fenix BT20

    Well I've been playing with my light today. And using some camera to gopro converters I've been able to mount the light lower on the helmet. As well as gain the ability to quickly unclip the light to switch helmets.










    I recon I could also make a gopro bottle carrier mount. So I could clip the battery there. And use my kedge gopro bar mount to hold the light head. I should then be able to switch the light between bikes or helmets with in seconds.



    Also fitted a clear lens to test it out.


    Sent from my iPhone using Tapatalk


    Sent from my iPhone using Tapatalk

  15. #65
    mtbr member
    Reputation:
    Join Date
    Mar 2006
    Posts
    461
    Updated with video.

    "By Your Command"

Page 3 of 3 FirstFirst 1 2 3

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •