# How to power AC bike lights with batteries?

I have a more then decent set of lights on my bicycle link. They are currently powered by a dynohub in the front wheel of my bicycle. The dynohub has an output of 6V AC and the light has a AC/DC converter inside. I'm not looking to open up the casing and removing it!

Is it possible to power the lights with rechargeable batteries or 18650 accumulators that output DC? If so, how?

Thanks in advance!

UPDATE Thanks for all the replies!

I tried hooking up some batteries directly like your suggesting. They turned on, but the light of 2 AA batteries was still quite dim.

I got an old USB cable, cut one end off, put it in a small powerbank (1amp, 5v) and hooked those cables up to the light.

This gave me a better brightness, but after a few minutes the light turned off. The powerbank and lights are still working.

I'll contact the manufacturer for more info.

• Probably.... that's all you get with that limited info. – Trevor_G Feb 1 '18 at 13:51
• If you contact the manufacturer and ask them you might find that they even have a matching battery module. – Andrew Morton Feb 1 '18 at 13:54
• You may not need to change the light at all. Grab a cheap alkaline battery and hook it up and see what happens. – Trevor_G Feb 1 '18 at 14:28
• @Trevor_G I have no real experience with electronics, apart from an ac/dc converter with USB port I soldered together from a tutorial with a circuit diagram. Would it nog be possible to do build a dc inverter? and hook up a power source? – Wijnand Feb 1 '18 at 15:16
• Try a 2.4A USB gang Hub charger 60W LIght only uses 2~3W – Tony Stewart Sunnyskyguy EE75 Feb 1 '18 at 15:23

## 1 Answer

This will probably work. Connect up a DC source to the lights and try it. Start at about 3 V then increase this as far as 6 V until you get the light you need. You need to aim at getting the output you need with the minimum of DC voltage.

The issue that concerns me is power dissipation in the rectifier. Using DC all of the power is going through one (or two) diodes instead of two (or four) diodes with AC. I can not be more precise without asking the manufacturer or having a circuit diagram.

If this works you will need a circuit to avoid overdischarge of your rechargeable batteries. This will disconnect the batteries when the battery voltage drops below their safe threshold. This is particularly important for Lithium chemistry batteries as it is possible to ruin the battery by overdischarging it.

• +1 you may also want to mention the Ac/Dc may well be a buck-boost regulator that will keep the lights at a more constant brightness at a much lower and wider range of voltages. This may be problematic for over-draining the rechargeable batteries. – Trevor_G Feb 1 '18 at 14:42
• @Trevor_G Good point the Lithium type need this protection in particular. – RoyC Feb 1 '18 at 14:47
• @RoyC I tried hooking up the batteries like you suggested and updated the question above. – Wijnand Feb 1 '18 at 15:42