Handling low-battery situation

Submitted by lars_the_bear on Tue, 02/23/2016 - 09:07

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Hi folks

Does anybody have a feel for how the BattBorg behaves when the battery is getting flat? Does it just kill the power to the Pi immediately, like throwing a switch, or should I expect a period of erratic operation first?

Has anybody tried connecting an ADC or similar to monitor the voltage?

Best wishes
Kevin

piborg's picture

piborg

Tue, 02/23/2016 - 10:26

Typically everything works fine until the battery is basically empty.
At that stage the Raspberry Pi cannot get enough power and resets.
After a few seconds of constantly resetting it gets to the point where the Raspberry Pi gets no power at all.

The only time the behaviour differs is when something else (such as motors) are sharing the same battery supply.
If the other bits pull too much power whent he batteries are getting flat it may dip the voltage low enough that the BattBorg is no able to supply enough power for the Raspberry Pi.

lars_the_bear

Tue, 02/23/2016 - 12:11

OK, thanks. I guess what I need is something that will (a) warn the Pi when when battery voltage drops below a particular threshold and then (b) prevent the Pi being powered at all when it drops below a somewhat lower threshold. I rather suspect I'm going to have to get my soldering iron out for this one; I don't suppose anybody makes anything like that (but do tell me if you know different).

Best wishes
Kevin

cleric boomer

Tue, 02/23/2016 - 13:09

I have been thinking about this too, along with on/off switch and a pi shut-down switch.

The battery issue is something I have considered over the last couple of weeks. I had a look at Adafruit and they have a "fuel gauge battery monitor" for 1S and 2S LiPo batteries.

I have the Red DiddyBorg and I am planning on using 4S liPo battery as a supply.

Texas Instruments who supply the chip, also do a 4S gauge, and I am looking at bashing a monitor. The ultimate aim is to have the Pi monitoring the fuel gauge and shutting down before if drops due to low voltage.

If you want links to the breakout board at Adafruit let me know and I will dig it out

I will keep everyone advised.

Chris

lars_the_bear

Thu, 02/25/2016 - 16:51

Hi Chris

Yes, please -- I'll take any advice or information that's on offer. I'd also be interested in knowing your thoughts on batteries in general. I'm currently running my Pi on a ten-AA-cell LiMH that came out of a toy of some kind. It's fine for the Pi and the attached boards (Reverse, LED displays, sensors), but I suspect that motors will soon exhaust it (I haven't bought the motors yet).

My plan was to use a small sealed-lead-acid battery, because they're cheap. But LiPo, etc, have much better storage for their weight.

Best wishes
Kevin

sigpaw@hotmail.com's picture

sigpaw@hotmail.com

Mon, 03/14/2016 - 21:17

Chris,

Gr8 idea. Your post sent me off to Amazon for at least 20 min! :-)

I have decided to isolate the Pi power/battery from the motors and accessories. Given a full charge on the smaller Pi pack AND the larger motor pack. The motor pack is always guaranteed to die first. This will at least allow the Pi to WiFi a "lost robots" position via camera and/or attached GPS module (my diddy has been assigned to roam our property during the night hours).

rburg

Sat, 07/09/2016 - 15:43

Sigpaw. I think this makes a lot of sense. How does the wiring work for this though?
I kick started PiJiuce and hope to use this to power the Pi whilst using the AA battery pack to power motors.

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