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Rechargable LED Torch Hand-Cranked Dynamo
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LED Flashlight Hand Cranked Dynamo with a rechargable NiMH battery pack - using Lego Education's Renewable Energy Extension Kit Energy Meter X1
About this creation
This is my third prototype of a hand crank dynamo LED torch - the new feature being that it can now store energy. Because it is a proof of concept model - only one 2-LED assembly(8870) was connected to the Lego Energy Meter output connector(next to the green button in the photo). The LEDs run on 9 Volts DC @ 0.001 Amperes taking 0.009 Watts (1 watt = 1 joule/second). The light output is not very bright. The electricity is generated by the cranking a handle which turns a 40 tooth gear which powers an 8 tooth gear connected to the axle of a Lego Power Function M-motor (8883) which acts as the electrical generator. The electricity generated goes into the Lego Energy Meter Display unit (W979668) that restricts storing more than 100 joules of energy (this conveniently prevents overcharging and damaging the NiMH battery inside) into the Lego Energy Storage unit(W979669) which is rated at 8.4 VDC. Within a few minutes of cranking the Lego Energy Meter blinks that it has "100J" when it reaches 100J internally; however, only after the Energy Meter LCD shuts down automatically has this charge fully transferred into the NiMH battery. The NiMH battery must be fully recharged and discharged THREE TIMES via a battery pack before being used (this is called battery conditioning). It may takes from one to three hours to fully recharge the NiMH Battery AND it takes 30 minutes to 90 minutes to initially a discharge sequence- this means that each Lego Energy Meter needs up to 13.5 hours to prep before using! If you use the flashlight immediatly after getting to flashing "100J" - the Energy Meter has only stored 4 joules temporarily (in a capacitor?): 100 joules @9.3 Volt to 96 joules @ 8 Volts. The Lego Energy Meter green button must pressed once to switch it *on* before it can save the electricity into the NiMH battery (pressing it a second time will turn the meter *off* ). When the orange knob is centered then the electricity is saved into the battery but no electricity is powering the LEDs. If the orange knob is turn to the right (or left - which reverses the current flow direction) then electricity will also flow from the Lego Energy Meter output connector to the LEDs ( while still accepting electrical power from the hand crank dynamo). If there is not a constant input of electricity from the dynamo, the Lego 2-LED assembly will drain the battery in about 7 minutes ( 420 seconds ). A fully charged Energy Storage unit will fully discharge even with no electrical load or even when the Energy Meter is turned off. The Energy Meter display unit requires a minimum current/load to remember the status of the battery which acts as a *Phantom energy loss* which drains the power from the NiMH battery even when the unit is turned off. If the Lego Energy Storage Unit is detached and reattached to the Lego Energy Meter Display, then the energy is reset to 0 Joules; thus one cannot remove the battery to prevent the *Phantom energy loss.* Lego Energy Storage units cannot be combined in series or in parallel to one Lego Energy Meter Display unit. Torque on the crank axle causes the axle to slip/twist off ( in the real world a cotter pin and washer could secure the axle from falling off but there is no Lego solution like this) - the Lego solution would be to lower the torque on the crank handle axle by replacing the 40 tooth gear to a 24 tooth gear OR/AND swapping the M-motor with the E-motor. The clutch power of the electrical power input socket in the rear of the Energy Meter is weak and clumsy to access - extra lego pieces were used to secure it. This prototype is difficult to hold because it does not have a handle. A hi capacity ultracapacitor would have been more useful than a slow charging NiMH battery in this particular prototype.

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By Walter Lee
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Added September 1, 2011

LEGO models my own creation MOCpages toys shop Rechargable LED Torch Hand-Cranked DynamoTechnic

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