Pi 3 On The Go

[MYLESV9]

I'm trying to power my Raspberry Pi 3 on the go, with an external battery. I got some help earlier on in the forum, about what I should use. Just as a note, I want it to be togglable (by a switch, not the Pi), and I am using an RFID kit (using about 3.5V.

PowerBoost 1000: https://www.adafruit.com/product/2030

4400 mAh LiOn: https://www.adafruit.com/product/354

Switch: https://www.adafruit.com/product/805

Micro USB Charger: https://www.adafruit.com/product/1304

[adafruit_support_mike]

Those should all work.

[Anthonyfoote]

I was also wondering about those. I'm looking to power a Pi3 and an official 7" touchscreen like in the adafruit project on thingiverse https://www.thingiverse.com/thing:1082431 In the project on thingiverse it was a pi 2. I know the 3 takes a ton more amps. Will the battery pack or the step up converter supply enough? and can you charge through the battery pack?

[MYLESV9]

I know the 3 takes a ton more amps. Will the battery pack or the step up converter supply enough? and can you charge through the battery pack?

Well, I'm powering a 3, with an RFID kit, which uses another 3.5V, or more. I made an earlier forum about what battery I should use, and they suggested this one would be pretty safe for a 3 and some add-ons. There is the PowerBoost 1000 C, but it has load sharing, so it can't run more than 1 core of the Pi, let alone an accessory. So, you'll have to remove the battery and use the charger (Micro LiPo/LiOn) above.

But don't trust me on this! I may be completely wrong, I am horrible with electronics. I would wait for a moderator.

Old Forum: viewtopic.php?f=8&t=137848

[Anthonyfoote]

I think you might be a little confused or maybe I'm a little confused...

The 3.5V isn't the part that is going to be shared, its how many amps it has. Also, you don't want to mix voltages. You wouldn't hook up a 5V device to your car without a step down converter.

Also, I think the load sharing is so you don't need to unhook the battery. There are some chargers without load sharing and you can't have it on while charging. In fact if i read it correctly, the 1000C actually requires the battery while plugged in to reduce power spikes.

Hopefully a mod can chip in and help us really understand if those options work for that much draw.

[adafruit_support_mike]

Boost converters are constant-power devices: to get 100mA @ 5V out of one (500mW), you have to send at least 135mA @ 3.7V in (also 500mW). In practice, no boost converter is 100% efficient, so you have to send more power in than you take out. The chips we use in the PowerBoost are about 90% efficient, so you need about 150mA @ 3.7V of input (550mW) to get 100mA @ 5V of output.

That means the major limiting factor in a boost converter is the amount of power it can take in.

The MCP73871 used in the PowerBoost 1000C has an internal switch whose absolute upper limit is 1800mA @ 3.7V (about 6.7W). That puts the upper limit on the output at 1.2A @ 5V (6W), and you really want to keep it below about 1.1A so the first spike doesn’t kill the board.

The PowerBoot 1000 Basic doesn’t do load sharing, so it doesn’t have that switch as an input limit. The limit in that one is the 4A switch in the TPS61030 boost converter, which puts the output limit at about 2.4A @ 5V. You need a LiPo that can deliver 4A to do that though, and an external LiPo charger that can supply more than 4A if you want to keep the battery from discharging even when the charger is connected and plugged in.