Yes, it has both of them. The output will automatically shut off after 15 seconds when charging begins. I've no idea though whether it's safe to connect the adapter to both the input and the output of the battery and the Pi all at the same time. If that's safe the relay and capacitor are not necessary.Burngate wrote:It should work ...
Provided the battery has separate 5v In and 5v Out - and in fact that the battery has its own charging circuit built in, and a DC-DC converter to make sure the output is really 5v
Which may mean it already does what you want!
OK, thanks. Those buggers seem to have the same price as the PiBurngate wrote:As for the capacitor ...
Assuming the relay could take 10ms to switch, and you want the cap to provide 1A during that time while keeping the voltage within 0.25v of the nominal 5v ...
C = It/v
1 * 0.01 / 0.25 = 0.04F or 40,000uF
That's rather clever - but a tad irritating!poing wrote:The output will automatically shut off after 15 seconds when charging begins.
Probably not!poing wrote:I've no idea though whether it's safe to connect the adapter to both the input and the output of the battery and the Pi all at the same time
Not going to work... 2 reasons:poing wrote:
In the mean time I thought of diodes, like this:
That would be simpler than the relay circuit and without mechanical parts. I happen to have a strip of 50 diodes that have a max current of 200mA, so I think it would be possible to replace diodes D1 and D2 each by 5 parallel diodes of the kind I have lying around for a total max current of 1A. Correct? (not the most elegant solution but the cheapest option at this point).
will not matter that much as the battery output switches off about 15 seconds after 5V is placed on the charging input. But the voltage drop is the real killer of course, as the voltage right out of the battery is just perfect for the Pi.Ravenous wrote:With the battery and the power supply both at 5V, current will flow through both diodes. (Your battery will have to keep charging, which might reduce its life.)
Why do you say that, do you think the circuit with the relay won't work?Ravenous wrote:That won't work either.
Ah no I didn't mean that. I meant the diode switching. But as you say, if the battery's controller is smart enough to stop charging itself, then the two diode arrangement probably will work.poing wrote: Why do you say that, do you think the circuit with the relay won't work?
Happy to say the above method works; I received a bunch of 10,000uF capacitors yesterday thinking I'd add capacity until I reached the right value. The first try was immediately successful, meaning the Pi with only Ethernet and HDMI attached survived numerous changes between battery and adapter, even several times a second, using a single 10,000uF capacitor. Of course this was only using around 350 mA (while the design goal was 1A max) and I'll have to see if added peripherals make more 10,000uF capacitors necessary.poing wrote:
The site it refers to no longer exists, you are reacting to a two year old post.wizard2072 wrote:Hi. Is there a circuit schematic for this? The image in the first post is broken.