How do I power a 1.5 volt, 25 ma light bulb with a 1.5 volt dc motor/generator?
My Daughters "Wind Farm" Science Project: She has 12 1.5 volt DC motors with fan blades that are connected in series. They spin under a fan and generate 1.8 volts, ~30 ma. Why won't they light a 1.5 volt 25 ma light bulb?
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I dont know, maybe try to put them in parallel,If you put 12 -1.5 volt batts in series you would get 18 volts.maybe you blew out the bulb. or maybe in series they create too much resistance though each motors winding? let me know im curious now! ————–12 batts in parallel would produce 1.5 volts w/ more amps
Series is the way to go with this system. Parallel will cause all the generators to spin at the same speed and ruin the efficiency. The ones generating power will end up spinning the weaker ones.
As for the power output. This really depends on how you measured it. When you said that it generates 1.8V, is this referring to the open circuit (ie. no load) voltage or the voltage under load (ie. connected to the light). When you measured the current at 30mA, did you just hook your multimeter to the terminals? If so, this is a dead short.
To properly measure the output, you need to put the ammeter in SERIES with the load (bulb) and a voltmeter in PARALLEL with the load. This will tell you the true power output (Watts = Volts x Amps). In your case, it sounds like you need 37.5 milliwatts to drive the light bulb. Anything short of this may not power the bulb as expected.
With that said, I have a few suggestions as to why the system isn’t working as expected:
1) bulb is burnt out. check the bulb by connecting it to a AA battery.
2) if the bulb is an LED, check the polarity. hooking it up in reverse will cause it no to function. again, check it with an AA battery.
3) you have your ammeter hooked up in parallel with the load. this is a dead short and will cause no current to pass through the bulb
4) the system is just not powerful enough. Remember that just because the generators will output 1.8v without a load that doesn’t mean that they will output anything when you put it under load (ie. connect it to the bulb). Also, just because the generator will output 30mA in a dead short doesn’t mean that it will output 30mA at a higher voltage. Again, it is the combination of volts and amps that drive the bulb.
hope that helps