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I'm running a Supernova E3 PRO 2 of my dynohub. However I would like to use my non-dynohub front-wheel whilst still being able to use the same lights on battery power.

The lights have an internal AC/DC converter, so I can't just go around that. Would is be possible to just hook up a couple of AA batteries or an USB-powerbank?

UPDATE

Turns out you do need a DC inverter. It works for a few minutes, after which the light turns off. After connecting it to the dynohub it was working again.

  • Now that you know DC batteries don't work, could you disapprove the answer that suggests them? – ojs Feb 1 '18 at 21:19
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If the AC/DC convert is a simple rectifying bridge plus filter and voltage stabilizer, it should work with a direct current source as well. The only question is how many batteries connected serially you will need to reach the minimum acceptable voltage. Given that specifications for your lamp say to use 6 V A/C you can go with four AA batteries or two 18650 accumulators.

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    18650 is a 3.7 volt lithium battery - so 1 is likely not enough and 2 in series would possibly be too much. 4x AA at 1.5V is about 6V so closer. – Criggie Jan 21 '18 at 19:29
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    Oops, for some weird reason it appeared to me that 18650 had something closer to 2 V. Must have confused them with Li-Ion stuff. However, having input 3.7 V × 2 = 7.4 V might be OK if the lamp's circuitry has a stabilizer. And it has to have one, as dynamos generate higher voltage with higher rotational speeds, and that excess has to be suppressed to prevent lamps/LED blow-out. – Grigory Rechistov Jan 21 '18 at 21:08
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    @Criggie, Gary E suggests that it will lose .6 to .7 volts, so maybe the over voltage of using 2 18650 might be just the way to go. Or am I wrong there? – Wijnand Jan 22 '18 at 8:34
  • @GrigoryRechistov I'll give the 4xAA a try tonight! And the light does have a stabilizer of some kind yes. Whenever I go > ~10km/h the light is on full power already. Curious to see how long it will last and whether there lights will have the same output. – Wijnand Jan 22 '18 at 8:37
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You can't just put the batteries in parallel with the DC coming out of your hub. The hub output voltage will attempt to light the lamp AND charge the batteries, which are not designed to be charged that way. You need to put a diode in series with the batteries to isolate them from the hub power.

The series diode on the battery line will also drop the battery voltage by .6 - .7 volts.

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  • Thanks Gary, I wasn't planning on running them side by side though! It's really meant as an alternative power source. – Wijnand Jan 22 '18 at 8:32
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    I would say this discussion has moved more to the electronics side of the question rather than to a bicycle one... or it was like that from the beginning — not much about bicycles but more about circuitry and schematics. – Grigory Rechistov Jan 22 '18 at 13:48
  • There is more about electronics here, but with a dynamo hub the light stops when you stop moving. With a battery (and diode) in parallel with the hub the light will stay on when you stop. Need a switch on the batteries to turn this off and on too. – Gary E Jan 23 '18 at 2:59
  • Bicycle dynamos actually generate AC. – ojs Feb 1 '18 at 21:20
  • LED lights run on DC. The AC in the dynamo is converted by internal circuitry to DC. – Gary E Feb 2 '18 at 4:54

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