12v DYNAMO driving 5v front & 10v rear LED lighting + DIAGRAM

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SUMMARY

The discussion centers on using a 12V dynamo to power both 5V front and 10V rear LED lighting. The setup employs LM7805 and LM317 voltage regulators to drop the voltage appropriately. The issue arises when the headlight operates, causing the rear lights to fail due to current hogging, likely stemming from an impedance mismatch. A solution is sought to balance the current distribution without wasting power.

PREREQUISITES
  • Understanding of voltage regulation using LM7805 and LM317
  • Basic knowledge of LED lighting specifications and requirements
  • Familiarity with electrical impedance and current distribution
  • Experience with dynamo systems and their voltage outputs
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  • Research methods to balance current distribution in parallel circuits
  • Explore alternative voltage regulation techniques for LED lighting
  • Learn about impedance matching in electrical circuits
  • Investigate the specifications and limitations of LM317 voltage regulators
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Electronics enthusiasts, hobbyists working on LED lighting projects, and engineers designing systems using dynamo power sources.

tslibertan
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Hi,

I'm wondering how to drive front and rear lights off one dynamo. See diagram for current setup.

Lights are hooked up to dynamo in parallel.

The LM7805 and LM317 are voltage regulators which drop the voltage from 12v to 5v and 10v respectively.

Currently only the headlight works, the rear lights only work if I disconnect the fheadlight.
Basically it seems as though the headlight is hogging the current, and I assume this is due to some kind of impedance mismatch.

Is there something I can simply add to partition the current nicely? By 'nicely' I mean that I don't want to unnecessarily waste power.

I'm using a 5v headlight (1w heatsinked white LED module, from ebay) because it shares the LM7805 with a USB jack that is used for recharging ipods etc. Obviously there's wastage here, dropping from 12v to 5v, but that's just what USB requires.

Many thanks for any insight,

T.S.L
 

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Have you measured the LM317s input voltage when the front light are on? According to the specifications, it needs an input of 3 volts or greater than the output (10v). Thats 13 volts and your dynamo is 12 volts.
 

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