"Solar Charger" as USB UPS

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zandr
 
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"Solar Charger" as USB UPS

Post by zandr »

Why are you hiding your MCP78371 board under "solar"?

I'm experimenting with CHDK to shoot long timelapses, so I'm powering Canon Powershots from external power. The only way to power an S100 is with a dummy battery, so if there are any glitches, the camera turns off.

I was trying a USB battery pack as a sort of UPS, but all the ones I have shut off the outputs to try to save power. If they've been turned off for some reason, you often have to hit a button to wake them up again. And removing input power turns them off.

I'd like to build a battery pack that acts more like a UPS: Keep the load powered if at all possible, and use the battery to soak up transients. An S100 needs about 500mA to run and shoot, but the zoom motors need >1A. The MCP78371 looked like the right chip, and a quick search brought me to your solar board. For straight USB power use, I guess I'd need to add the MintyBoost circuit to the output, but the Canon cameras are designed for a 3.7V Lithium, so I don't need that here.

So, do I understand how the load sharing works on the 78371 correctly? Will I be able to connect and disconnect power input without losing output power?
Do I need the giant cap if the input is a USB wall wart, rather than a solar cell. (and given my goals, would I be better off with it on the output?)

Thanks!
-Zandr

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adafruit_support_bill
 
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Re: "Solar Charger" as USB UPS

Post by adafruit_support_bill »

The power sharing should give you an uninterrupted supply (subject to battery capacity of course). The capacitor is probably not necessary, but it shouldn't hurt to install it either. One possible issue for your application is the load-sharing output voltage. You will need an input voltage of about 5v minimum to charge the LiPo. When connected to input power, the load-sharing output will be just about 5v also. When running from battery power, it will be at battery voltage. If you do not already have voltage regulation between the charger and the camera, you will probably want to add a low-drop-out regulator.

zandr
 
Posts: 2
Joined: Fri Aug 16, 2013 1:04 am

Re: "Solar Charger" as USB UPS

Post by zandr »

Bill-
Thanks for the reply. You're right about the output voltage, though I'm currently running the camera from a 5V USB supply and it seems fine. I'll see if I can find a suitable LDO regulator, there's probably room for that inside the dummy battery, which would be the best option.

EDIT: Well, maybe not the *best* option... trying to dissipate 2W inside the battery compartment is probably not the brightest idea.

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