Hi Everyone,
This is my first post here so please go easy on me. My son was recently given a couple of programmable bicycle LED wheel lights which he lost interest in very quickly. I have built a small stand and using an AC to DC power adapter with a 12V DC motor managed to make a rotating image display. The issue is that the programmable wheel lights use 1, 2 or 3 Li-Ion batteries which last between 5 and 15 hours before needing to be recharged (approx 6 hours). Is it possible to use a pancake type slip ring and some kind of power step down after the motor so the entire unit runs from the AC adapter? Here are the specs for the bits I have, Sorry if they are incomplete, I am living in Japan with no Japanese skills! Thanks for any help you can give me on this..
DC Motor
12 V; Speed: 200 RPM, Rated torque: 2.2 Kg.cm
Reduction ratio: 1: 22; Rated current: 0.1 A
No load speed: 5 RPM. Current: 0.04 A.
Load speed: 3.5 RPM. Current: 0.18 A.
Power Supply
AC/DC Power Adapter
Input AC 100V-240V 50/60Hz
Output DC 1-12V 100-2000mA
Light Units
416 Type 3528 LED’s (104 LED’s on four separate armatures)
Powered by 1, 2 or 3 Type 18650 Li-Ion Batteries ( 3.7V 3000mAh) 1 battery gives about 5 hours until depleted
Can be recharged using Micro USB 5V or Mains AC by removing the batteries
Images are programmed onto a MicroSD card

 

Output DC 1-12V 100-2000mA

Your LEDs require about 0.5A at 3.7V nominal, i.e they need about 2W of power, but it's unclear whether your present power supply can provide that. If the motor draws 100mA at 12V that certainly doesn't leave enough power for driving the LEDs as well.
I suggest you use a separate power adapter, with a higher power rating, for the LEDs.

 

Thanks for the help. I'm not sure I really want to have 2 power adapters running into it. Do you think it might be easier to swap the existing power supply for one with a higher power rating to run both the motor and LED's? Guess I'm worried about too much power and burning out the lights. Would they be connected in series…sorry very basic knowledge here

 

If you use a single higher-power adapter providing 12V to the motor, you will be faced with the problem of dropping 12V down to 3.7V at a current of 0.5A. That would involve a linear regulator wasting (12-3.7) x 0.5 = 4.15W (requiring a decent-size heatsink), or else a DC-DC converter.

 

Thanks again, so I am basically looking for a separate AC to DC power adapter with 3.7V output with 0.5A 2W of power? Was just wondering as the LED's are multicolored and depending on the image being displayed some of them are off at times, some on etc. Would this make a difference to the power supply I buy? Is this 0.5A 2W minimum or is it okay to go with something a little higher? Deepest apologies for all the questions..

 

Would this make a difference to the power supply I buy?

You ought to allow for the worst case scenario, i.e. maximum power demand. Bearing in mind that advertised power ratings are, shall we say, optimistic, then allow a generous margin. If 2W is the expected demand then I'd be looking for a supply with a rating at least double that.

 

Great, thanks again for all your help. Regards

 

Final thoughts, Is anyone aware of where I can get a suitable 3.7V DC power supply with approx 4W as above. Looked everywhere but many seem to be 5V or not enough watts. Thanks again for any help on this.

 

Perhaps use a standard 5V 1A supply and drop the volts with a couple of chunky silicon diodes (e.g. 1N5400, or even 1N4000) in series?

 

Perfect, will give it a try. Thanks again for everything.