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

[tslibertan]

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

 

[dlgoff]

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.

 

[ravenprp]

.

Hi T.S.L.,

Thank you for sharing your setup and diagram. It seems like you are using a LM7805 voltage regulator to power your 5v front LED light and a LM317 voltage regulator to power your 10v rear LED lights. The issue you are facing is that the headlight is hogging the current and causing the rear lights to not work unless the headlight is disconnected. This could be due to an impedance mismatch, as you mentioned.

One solution you could try is using a current limiting resistor in series with each LED light. This will help to balance the current and prevent the headlight from hogging it all. You can calculate the appropriate resistor value using Ohm's law (R = V/I), where V is the voltage drop (12v - 5v = 7v for the front light, and 12v - 10v = 2v for the rear light) and I is the desired current for each light. This will help to partition the current evenly and prevent unnecessary power wastage.

Another option is to use a separate voltage regulator for each light. This would eliminate any potential impedance mismatch and allow each light to receive the appropriate voltage without affecting the other.

I hope this helps and good luck with your setup! Let me know if you have any further questions.