Hello!

I have an idea for a project that sounds fun, but I’m not sure how to proceed (or if it's even possible). I have an Aaxa pico projector that I would like to power off of an Anker 20100 portable USB charger on backpacking trips. I know the anker charger is capable of outputting 4.8A total (2.4A from each port) and that the aaxa projector has input requirements of 5V at 3A. Is it possible to build a circuit that will plug into both ports on the Anker charger, negotiate those power requirements, and then output them to the projector?

I did try building a circuit from a similar project I found on the internet, but the circuit doesn't power up. This other project took batteries and stepped the voltage and current down to USB levels (link: http://www.instructables.com/id/Universal-Portable-USB-Charger/). I've included a picture of the original circuit, my modified circuit drawing, and the physical circuit I built (please forgive the horrendous soldering job; It's been a while and I need a new soldering iron!).

Originally I tried splicing the power cable that came with the projector to a USB plug to see what would happen. It does provide power, but far below the requirements, which isn't good for the bulb or the projector. I then tried to splice it into a USB Y split (similar to what external hard drives use to draw more power), but it didn't affect the output much. I suspect it's the negotiation piece I'm struggling with, since the Anker powercore has a bunch of safety features and this projector was never designed to run off USB power.

So what do you guys think? Doable, or should I walk away from this one? I took Physics 2 in college (E & M) and have dabbled in circuits before, but nothing like this. If someone can help me with the design bit, I'm excited to build it and share my results.

Thank you,

Tom

Materials:
http://www.aaxatech.com/products/p3_pico_projector.htm
https://www.amazon.com/gp/product/B00X5RV14Y/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

 

Another idea I had was to try and wire a USB port in where the internal battery connects to the board inside of the projector. I measured the battery at 3.7V. Maybe that would be easier than trying to match what the wall outlet would normally provide?

 

Bump? Would anyone mind chiming in? I tried soldering the circuit again but I still can't get it to power on. I'm thinking maybe I have a defective DC-DC step down converter.

 

Too many uncertainty factors. The Anker says it can do 2.4A per port and the Pico says 11.5 watts at 5 volts which is 2.3 amps, but the Anker seems to negotiate with phones, not projectors. Theoretically, the amps and watts seem to work, but you are not getting results.

Then the pico says it wants 3 amps, not the 11.5 watts it said on the same page. What's up with that? A start surge that the Anker will not tolerate?

Too many uncertainty factors.

 

Follow up question. Is it possible to build a circuit that will connect the anker battery to the battery inputs in the projector? That way I don’t' have to worry about the higher power requirements. I pulled the projector's battery and measured it at 3.7v, not sure the amperage though (battery is unmarked and my volt meter blew a fuse). Assuming I can figure out the amperage, couldn't I tweak the circuit in my original post to work? Also, could someone help me determine why that circuit wouldn't work at all?

 

I read this on their site; "Please note that the projector will not charge while in use and only when it is turned off. When the projector is charging, the LED indicator will be red. Once the P2-B is fully changed, the LED indicator will turn green." So unless you hack the firmware/software I suspect that is why it won't work. If you want longer run-time maybe look at replacing the battery with a higher amp hour unit.

 

Oh I meant why the circuit I built won't power up. I tried charging a cell phone through it, but it doesn't work. : )

In a way, that's what I'm trying to do. I'm wondering if I can replace the internal battery with a USB port that connects to my giant anker battery pack and run it directly off of that. My current thinking is maybe I can build a circuit that "negotiates" with the anker battery pack for whatever the voltage/amperage requirements are and leave it at that.

 

Bypassing the input on the projector is a bad idea. Try putting the appropriate voltage divider resistors on the USB data pins. Google for this.

You blew the current fuse in your meter because you tried to measure voltage with the meter set up for amperage.