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Discussion in 'General Electronics Discussion' started by wat180, Nov 29, 2014.

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  1. wat180

    wat180

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    Nov 29, 2014
    Hi
    I have a 100v DC electric bike and I wish to step down the voltage to run lights at 6v 1A
    I have been told that I could use a AC to DC standard wall adapter to do this
    would like anyone's expert advise as I am not sure
    MANY THANKS
     
  2. duke37

    duke37

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    772
    Jan 9, 2011
    If the adapter contains a normal transformer, defiantly NOT.

    If the adaptor is a switched mode power supply, perhaps.
     
  3. wat180

    wat180

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    Nov 29, 2014
    Thanks Duke
    thought it was too good to be true
    any ideas on what I could use as I am finding it hard to get something small
    enough to reduce the 100vdc to 6vdc to do the job
     
  4. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    You need a buck converter, there are many around but mostly about 30V input.
    If you really want to do a lot of work, you could modify a computer power supply. These are capable of much more power than you need.
    My broadband is only slimband so searching is painful.
     
  5. Bluejets

    Bluejets

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    Oct 5, 2014
    Use an LED headlight for a pushbike with it's own internal battery.
    They run for long periods.
     
  6. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    A buck converter is probably not what you need. A flyback converter and transformer with a rectifier on the secondary would be sufficient to run a 6V lamp load at 1 A.. I have attached a Linear Technology datasheet for their LT83000 series of Flyback Converters which are rated to operate with 100 V DC input. Note that 100 V is right at their maximum input voltage specification, but I would try it anyway. They cost about three dollars. You will also need a flyback transformer and a fast Schottky rectifier diode. Read the datasheet to see if construction of this is within your capabilities.
     

    Attached Files:

  7. wat180

    wat180

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    Nov 29, 2014
    Thanks everyone for your feed back
    will let you know how I get on
    Once again thanks
     
  8. duke37

    duke37

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    Jan 9, 2011
    A CFL contains an inverter which runs off rectified mains (>300V) and this circuit could be used on 100V to supply the 5V required. The circuit is simple and very small.
    Do you wish to do some development work?
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    You said your electric bike uses DC, at 100V.

    What is the actual supply voltage range over which the headlight needs to operate properly?
    What is the actual supply voltage range that the headlight needs to withstand without damage?
     
  10. wat180

    wat180

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    Nov 29, 2014
    Hi kris
    on my ebike there are 2x LI NMC batteries 48v 5c in series @96vdc
    fully charged at 100v then with use they can go down to aprox 86v
    the front light is a halogen bulb rated @ 7v 1A rear one is a LED
    now these were working with the old ebike motor controller at 36v the unit had a separate low voltage feed for them but I have now removed this
    as I have upgraded the motor and controller to a 96v system
    I was hoping to find a simple solution to reduce the voltage so I could use the vast
    energy of the batteries
    many thanks for your interest
     
  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    That voltage is just a bit too high for standard DC-powered converters, and a bit too low for standard line-powered converters. Even universal input line-powered supplies need an absolute minimum of 70V AC which will produce about 100V DC after rectification. That's too close to comfort.

    If it was me, I think I would get a universal input power supply rated for a higher output voltage and output current, and modify it for a lower input and output voltage. This would require changes to a few components on both sides of the transformer, but no rewinding of the transformer itself. If you want to go this route, get a good quality universal off-line power supply rated for 12V at 3A or more, open it up, and upload photos of both sides of the board.
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Take a look at the NCP1014, There are some circuits in here.
     
    hevans1944 likes this.
  13. wat180

    wat180

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    Nov 29, 2014
    Hi Kris
    im confused you mention 70VAC
    the system I have is 100vDC and I was going to use A AC 110V to 6VDC wall adapter but was told I couldn't do it
     
  14. duke37

    duke37

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    Jan 9, 2011
    The peak voltage of an AC wave is 1.4 times the quoted voltage. So 110V AC has a peak of about 150V If the input is rectified this is what you get. Running the PSU at 100V means the input is underdone but it may work. Some switch mode power supplies have a wide range of permitted input voltages.

    Read what Kris says about voltage.
     
  15. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Right, you can't. As duke37 says.

    In a standard mains-powered ("off-line") power supply, the incoming mains voltage is converted from AC to DC by a bridge rectifier and smoothing capacitor. This DC voltage then powers the next section of the power supply, which is a switching converter that passes power across a transformer to the output circuitry.

    When you rectify and smooth an AC voltage, the DC voltage you get is about 1.4 times the AC voltage. So for example, a power supply that's designed to operate from 110 VAC will have a switching converter that's designed to operate from (110 × 1.4) = 154V DC.

    If you connect that circuit to a 100V DC battery, it's unlikely to work, because it's designed to work from 154V DC.

    Even an off-line power supply with "universal" input will have trouble. The widest operating voltage range for universal input power supplies only goes as low as 70V AC, which corresponds to 100V DC. So running it from a battery that could go as low as 86V DC will not work reliably.

    I hope that makes sense now!
     
    hevans1944 likes this.
  16. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Since you made this mod, wiring two 48 V batteries in series, I think it would be simple to connect a 48 V to 6 V DC-to-DC converter to just ONE of these two batteries. Such converters are readily available. You could even get REAL FANCY and arrange a MOSFET switched circuit to alternate the connection between one of the two batteries at, say, fifty or sixty times per second to maintain charge balance between the two series-connected 48 V batteries. Or install an un-fancy DPDT switch that you flip manually each time you ride the bike. I assume, for safety, the lights are always on while riding.
     
    Last edited by a moderator: Dec 2, 2014
  17. wat180

    wat180

    6
    0
    Nov 29, 2014
    well everyone
    I am overwhelmed by all the feed back
    I thought there would be a simple solution to my problem
    I have limited knowledge in electronics and I value all your feed back
    thank you all very much for trying to help me
    wat180
     
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