Powering 4 Bela Minis on Battery

violapwr

I'm attempting to power 4 Bela Minis using a 10,000mAh battery with a battery management chip capable of a 2A discharge. When I try to power them all on at once via p2.12 (https://forum.bela.io/d/5046-power-button-for-embedded-bela-mini), I typically get inconsistent results. Usually, only two of the Minis will power on, while the other two remain inactive.

If I turn off the two using p2.12, the remaining two still don’t respond to the power switch. However, if I disconnect the two that initially powered up and then activate the power switch again, one of the previously inactive Minis will power on. Disconnecting that one and re-activating the switch then allows the final Mini to power on.

Interestingly, if I switch each Mini on one at a time (bypassing p2.12 and directly connecting VIN), I’m able to get all four running simultaneously.

For power connections, I’m using p1.05 for VIN and p1.16 for ground (https://forum.bela.io/d/1166-bela-mini-usb-host-power-only-on-usb-supply).

Any suggestions?

giuliomoro

It sounds like the inrush current from 4 units at once may be exceeding the peak current available from the battery?
Or something more complicated along those lines.

violapwr If I turn off the two using p2.12, the remaining two still don’t respond to the power switch. However, if I disconnect the two that initially powered up and then activate the power switch again, one of the previously inactive Minis will power on. Disconnecting that one and re-activating the switch then allows the final Mini to power on.

Not sure how to explain this, it may be due to some problematic internal state it is put it in when powered up.

I assume you are using some long wires? You could try to add some large-ish capacitors (e.g.: 470u) between the incoming GND and +5V lines very close to each board.
Alternatively, you could try to sequence the powering up of the different units so they are a few hundred ms apart.

violapwr

giuliomoro i think that was it! i had to use 2 x 1000uf caps but it did the trick. thanks @giuliomoro

giuliomoro

violapwr e 2 x 1000uf caps but it did the trick

2x1000uF on each board? The important thing - I believe - is that the bulk capacitance is placed close to each board. I think the closer it is the lower the values you need - if that's of any help.

violapwr

giuliomoro 2x1000uF for all 4 boards. each board's vin + ground is connected to the (+) and (-) rails of of the breadboard, so i just added the caps to those rails. perhaps i could position them closer to the battery jumper cables though... i'm open to any suggestions!

giuliomoro

violapwr so i just added the caps to those rails

that's good enough

violapwr

thanks @giuliomoro