Help needed, bicycle generator lights indicator

Discussion in 'Digital Circuit Design' started by Mike Ferguson_1472657528, Aug 31, 2016.

  1. Mike Ferguson_1472657528

    Thread Starter New Member

    Aug 31, 2016
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    Hi,

    I'm trying to make a lights board that i can use on my electronic bicycle generator to show students how much power they are generating. My idea is to have a traffic lights style lights board with lights coming on the faster the rider pedals (voltage increases)

    My bicycle generator is a 12 volt system so was thinking of using a VSR to control the lights, for example, whilst peddling really slow and generating 12.2v, only one light one light on the lights boards comes on, then the rider pedals a little faster generating 12.4v, this makes anther light on the board come on, then 12.6, 12.8 etc etc with each voltage increment illuminating another light

    Can anyone help? I haven't got the foggiest of where to start.

    Thanks

    Mike
     
  2. Marley

    Member

    Apr 4, 2016
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    How much do you know about electronics?
    Firstly, you need to connect a load resistor across the generator (which is actually probably an alternator) so that the peddler has to do some real work. This resistor may dissipate 50W or more so needs to be rated to suit. Resistance probably about 2 to 3 ohms. Will be a big wirewound resistor and will get hot so don't let your students touch it.

    Next, because the alternator generates AC, you will need a rectifier. Could be a bridge rectifier but because you only want to measure the average voltage, a single diode will do. Then filter the voltage with some capacitors to get a smooth voltage. Have you got an oscilloscope?

    Then comes the slightly harder bit. I think the simplest way will be to build a circuit that has a number of comparators (see LM339) and compare your generated smoothed voltage with a range of reference voltages derived from a voltage divider chain. These will control some lights. Not directly though. You will need some power transistors or other devices - depending on the power and type of the lights.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    I'd think about using the LM3914 integrated circuit. It contains several comparators and is designed to be used in a "bargraph" display like you've described, allowing an increasingly large load to be applied. It would respond to voltage and turn on a number of lights proportional to the input voltage. Instead of lighting LEDs, which is a typical use of a LM3914, you would turn on another light bulb using a MOSFET switch.

    You would need to use a low-ohms shunt resistor (for instance, 0.1Ω, 20W rated) to get a voltage that is proportional to the total current being generated by the user. You can't use the generator voltage directly, since this will change when the load (number of lit bulbs) changes. But the total current is a good measure of the user's effort. You might also need to use an op-amp to offset and scale that voltage into the right range for the LM3914.

    This is similar to the suggestion in #2, just a different way to go about it. The main difference is that I'd use lightbulbs as both the load and the indicator. The shunt resistor is there only to make a voltage. It doesn't absorb all the power from the rider.
     
  4. Mike Ferguson_1472657528

    Thread Starter New Member

    Aug 31, 2016
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    Thanks for your quick reply Marley :)

    The generator is a DC motor, not AC and I've wired a 300w dump load into the system via a charge controller. I also have a small amp meter wired in however its very small and what I'd ideally like is a display with a big visual impact (like a traffic light).

    My knowledge of electrics is not too bad although I'm no expert.

    Would there be a way to control the sequence of lights via the amp meter? I've been playing with doing this via the volts as I thought one of these (link below) might work but I've not had any luck yet.

    http://www.ebay.co.uk/itm/DC-Voltag...Module-AH8T-/141867498293?hash=item2107f63b35

    Thanks,

    Mike
     
  5. Mike Ferguson_1472657528

    Thread Starter New Member

    Aug 31, 2016
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    Thanks Wayneh for your advice :)
     
  6. wayneh

    Expert

    Sep 9, 2010
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    Yes, there would be some voltage across that meter proportional to the current, just like it's a shunt resistor as I described earlier. That small voltage could feed the LM3914 and create any sort of light show you like.
     
  7. Marley

    Member

    Apr 4, 2016
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    You can use the current instead of voltage to control your display. The LM3914 chip mentioned above is designed to drive a row of small LEDs (like an audio level display). It's not so easy to interface this with larger lamps.

    Don't understand what the charge controller is there for. Why not wire the load resistor directly across the motor terminals?

    Although you can measure the current I think actually it would be easier to measure the actual DC generator terminal voltage. Try looking at that with a digital multimeter set to a DC voltage range. Voltage should be approximately proportional to speed.

    If you want, I could draw you up a simple circuit that will show how to switch some larger lamps depending on the voltage value.
     
  8. Mike Ferguson_1472657528

    Thread Starter New Member

    Aug 31, 2016
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    Hi Marley, Thanks for your kind offer of sending a circuit drawing. I think this would really help :)

    The charge controller I fitted protects the battery and inverter from over charging. With a fast rider the voltage can reach around 35v out of the motor so the controller diverts any additional voltage over 14v to be dumped as heat. This is only when a student really goes for it, usually a steady rider will make around 12-15v on a 5-10min pedal.

    Thanks

    Mike
     
  9. Marley

    Member

    Apr 4, 2016
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    Oh, I see. Did not realise you were actually powering a battery and inverter from it.

    Because we need to monitor a voltage to control the "traffic lights" and this voltage needs to be proportional to the current shown on the ammeter you now need to get a digital multimeter set to the DC voltage range and connect across the ammeter terminals. There should be a small voltage proportional to current in the region of 0V to about 0.5V. Small voltage but this could be used to control the lights.

    There are other ways of measuring the current directly but will make the project more expensive. How much effort do you want to put into this?
     
  10. Mike Ferguson_1472657528

    Thread Starter New Member

    Aug 31, 2016
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    Hi Marley,

    I'm happy to put a lot of effort in if required. Also I'd be happy to pay a person or company to make it for me as I worry the electronics are just a bit beyond me. Would you be able to recommend someone or firm who'd be able to do this for me. Do you do this sort of stuff yourself? I'm based in Manchester but can travel if necessary.

    Thanks :)
     
  11. Marley

    Member

    Apr 4, 2016
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    I do this sort of stuff, yes. And I am in the UK.
    Tell me (us on this forum) a few more things first:
    • How much current passes though your ammeter (what is the range of current the device has to monitor)?
    • How many lights do you want?
    • What sort of lights - exactly? Wattage, voltage, colour, etc.
    I'm not actually looking for work but I could make something. Better still, I can draw a circuit diagram and give you a list of parts so someone else could make it! The electronics part is quite simple really. Actually making a nice job of constructing these things is what takes the time. The total parts for the electronics will be around £50 or so I should think. Not including the lights but I am assuming the lights will be mains powered.
     
  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I think an average rider would produce about 186 W, @ 12 V then 6.5 A into a 1.8 ohm load. For test runs do not connect any other loads other than resistor & measure V across resistor.
    Looks like Marley has it under control.
     
  13. ian field

    Distinguished Member

    Oct 27, 2012
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    Do you know how many poles on the motor armature?

    At low speed the output could pulsate. Gearing up the motor would eliminate that, and make them pedal slightly harder.
     
  14. wayneh

    Expert

    Sep 9, 2010
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    Maybe an average rider, but not an average person off the street. Not for long anyway.
     
  15. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Wasn't the English Channel crossed with about 1/3 hp of man power ?
    About 3 min. is best that I could do now, 1943 maybe 30 min.
     
  16. Mike Ferguson_1472657528

    Thread Starter New Member

    Aug 31, 2016
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    Hi,

    That's great that you can help Marley. We get between 5-13amp across the meter. 13 amps would be going flat out and if you have legs like Bradley Wiggins! on average it's be around 7-8amps. The meter has 0-50amp scale. I'd ideally like either 3 or 5 stages of light increments. I might double this up so each measured increment turns on two lights however I'm guessing this wouldn't effect the controlling system. For the lights I'd like to use either LED lights or 12v halogens which ideally would be powered from the 12v battery within the generator controlling system. Alternatively the lights board could be powered by a separate 12v battery. I'd be happy putting it together if I had a circuit diagram. I'm happy to pay for your services

    Thanks :)
     
  17. Marley

    Member

    Apr 4, 2016
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    OK. 5 stages of 12V lights. I will draw up a circuit and a list of parts. Back soon!
     
  18. Mike Ferguson_1472657528

    Thread Starter New Member

    Aug 31, 2016
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    Its geared to a ration of around 37-1 which means the motor gets about 2700rpm when the bike is being pedalled. I aimed to get 2700rpm as this is what the motor was rated to.
     
  19. Mike Ferguson_1472657528

    Thread Starter New Member

    Aug 31, 2016
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    Thank you very much :)
     
  20. Mike Ferguson_1472657528

    Thread Starter New Member

    Aug 31, 2016
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    Hi Marley, Just wondered if you've managed to have a look into this? it'd be fantastic if you could still do me a circuit diagram :)

    Thanks
     
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