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rewiring an emergency light with tubes for LED strips

Discussion in 'Electronic Repair' started by [email protected], Mar 29, 2013.

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  1. Guest

    Hi there,

    Maybe can someone could voice some ideas on the best path for this:

    I have not one or two but 8 emergency lights, each having an internal lead-gel 6v battery, and two fluorescent tubes. The fixture plugs into 220v AC and when power goes out, the batt kicks in and lights the tubes, simple huh?;-)

    My main goal would be keeping the case, the battery, and as much of the circuitry as possible, but instead of feeding fluorescent tubes, replace thosewith LED strips.

    I have disassembled the unit and found that the circuit board is just one, that integrates all functions, battery charger, switching from AC to battery, and doing the tubes startup.

    I've also measured the voltage of the wires leading to the batteries, and while the battery is 6V, I get 10 volts of charging voltage when the unit isplugged into AC -I guess this is normal-.

    The tubes are a pair of 30-cm (11.8 inches) wide, labeled F8T5/D

    Now, I know nothing about tubes, except that normal tubes come with a ballast and 'starter'. On this circuit board I see no 'starter' but there's indeed a small transformer, although I'm not sure if this is related to the conversion from battery DC to AC or as a step down to turn the 220vAC into the10V used for charging.

    What would be the best route to do this conversion?.

    I thought that ideally, I'd keep the circuit board unmodified, and just addany additional components needed to turn whatever voltage the unit feeds to the tubes, into the 12V DC expected by LED strips...

    Now, anyone has more information on what voltage gets into these "F8T5/D" tubes?
    and would the 'starter' effect used by fluorescent tubes fry any circuitry I add at the end of the wires before the tubes, to turn it into 12VDC ?

    here, it only says

    "This F8T5 linear fluorescent lamp operates at 8 watts. It has a color temperature of 6500K, a CRI of 75, and an average life of 7,500 hours. "

    ....but no words about voltage

    yet over here

    it reads: Lamps_Directional_MR_GU10

    Open Circuit Voltage (rapid start) (MAX)
    190.0 V
    Open Circuit Voltage (after preheating) Max @ Temperature
    210.0 @ 10.0 V
    Open Circuit Voltage (rapid start) Min @ Temperature

    So basically I'd need an IC that can turn anything from 210v to 57v into 12VDC ?

    Let me know if my reasoning so far is OK or flawed, because I've never worked with fluorescent lights before and there's too many unknowns in my drawing board. :)

    Thanks in advance for reading and any leads...
  2. mike

    mike Guest

    As always, what you do is critically dependent on your final objective.

    If these are used as REAL emergency lights, there are a bunch of regulations
    you need to comply with.
    You can't just modify them. Inspectors don't care about the specs.
    All they care about is that they have the right stickers on 'em.

    If you just want a portable light, the LED's aren't significantly more
    efficient than fluorescent lamps.

    And if they're emergency lights, they won't be ON enough to make
    efficiency an issue.

    This has the possibility of being one of those projects you spend a lot
    of time and money on just to stick them in the closet.

    Might be better to define your objective and start from scratch.

    replace the 6V with 12V batteries and build a charger.
  3. On Friday, March 29, 2013 5:12:55 PM UTC-4, mike wrote:

    First, thanks for reading me and replying Mike!
    These are inside my home. Down here at least there's no rules or regulations (or inspections for that matter) about what one installs in your own home..
    Yes I can. ;)
    There are no inspectors. :)
    I want to get a light that can withstand a 2-hours long power cut like happens often in mid summer amid a heat wave, instead of the paltry 15-20 minutes I get from flourescent tubes. Given that leds can use 3-4 watts vs 2 tubes x 8 watts each = 16W, I' d say that the increase in time will be significant with regards to how long the lights will last in case of outage.

    What's even better, I already have the 12V LED strips and the old fluorescent fixtures and batteries, so in my view what's left is some clever design (voltage regulator?) and some soldering vs buying completely new LED based fixtures.

    I hate throwing away perfectly working kit.
    Well it depends. there seems to be a market for this type of conversion... here for instance I found someone selling replacement 'tubes' that use ledsinside but which are direct replacements for F8T5 tubes... but in the linked videos they bypass the ballast, which is a separate board... in the board I have everything is in a single board (charger etc).

    So maybe I thought if there's some clever multi-purpose voltage regulator Icould use to turn whatever the unit feeds to the tubes (including voltage spike for tubes warm up) into 12VDC ... I was thinking that maybe some ready-made module used for charging batteries, RC toys or something?

    Just thinking aloud... but thanks for your reply and ideas. Comments are welcome. :)

  4. mike

    mike Guest

    Ok, if you're intent on using what you have, what do you have?
    Are the led strips just leds or do they have any regulation capability?
    What is the minimum/maximum voltage for the nominally 12V led strips.
    Current vs voltage?

    I'd disconnect all the fluorescent stuff and build a current-mode boost
    that runs off the 6V and supplies 12V to the leds. Exactly how depends
    on exactly what's in the led strips. Leave the charger alone.

    IF you can cut the strips in half and parallel them as 6V, you may be
    able to add a resistor to limit the current at the maximum battery voltage
    and be good enough.

    Or you might be able to rewind the transformer and use the existing
    high voltage supply to get 12V.

    There are solar powered outdoor lights. Local dollar store has them for
    a buck.
    They turn on when the sun goes away, so just replace the solar cell with
    charge current.
    They don't put out a lot of light, but will keep you from stumbling over
    stuff. Use a lantern at point of use. Or just turn on the fluorescent
    components when needed.
    The chip is QX5252. problem is that it's designed for one or 2 1.2V
    rechargeable cells and 1-2 leds. Depending on who made the light,
    the chips are removable or bonded directly to the board and covered
    with a blob of epoxy.

    Are we having fun yet?
  5. Guest

    For starters, something is wrong with your voltmeter. There are no 6V
    lead-gel batteries that tolerate more than 8.0V while charging unless
    the battery is defective.
  6. gregz

    gregz Guest

    I was thinking the battery is defective.

    Where is the OP ?

    You have to define your lighting needs. What you have or had, is that
    perfect ?
    There are strips that run 12 volts. You can add strips to get more light.
    The old circuitry is useless. You probably need batteries, so it would be
    better to start from scratch.

  7. Maybe I will have to re-do the readings. I used an ancient analog tester.
    In the unit I have currently disassembled, yes. The rest of the fixtures, no, the batts were working perfectly when the units where removed.
    Here, here. I'm just not glued to the puter 24/7. :) and I read this whole thread. Thanks to everyone.
    I know, thanks.
    Hmmm it seems to me that there is more people interested in proving that my idea is silly than people thinking about a creative solution to turn the variable AC output leading to the fluorescent tubes into 12VDC. ;-)

    But thanks anyway for the "constructive discouragement". JOKE JOKE

  8. With a buck-up converter, yes.
    Fluorescent drivers, now we're talking. Keep in mind I never worked with fluorescent tubes before, so I didn't know there was a thing called 'fluorescent driver' to begin with :)

    Now looking at the board, I see one Fairchild semi KA7808 1A voltage regulator, and two HS882 3-pin ICs next to test pins labeled 'output 1' and 'output 2' which surely means for tube#1 and tube#2.

    Looking at the HS882 it's a 'switching power amplifier'... hmmm...

    food for thought... but no more ICs...
    after your comment wrt 'fluo driver' I was expecting it to have something like this

    but it doesn't.

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