Problem with Lipo Amigo Pro - voltage drop

I’m having a problem with a Lipo Amigo Pro when using it on a RPi 3B+ with zero2go (both purchased via the Pimoroni website)

I observe the following behaviour:

  • when running just from the Battery on Input B ( C disconnected ) the Pi runs just fine, zero2go shows it’s using Input B. System runs stable.

Battery → Zero2Go Input B → Pi

This works with a 13400 mAH or 2000mAh Lipo, even doing a cpu stress test on the Pi.

  • when both inputs are connected the zero2go switches between B and C regularly as the voltage changes (batteries are rather similar charged). Every time the input is switched to C the voltage on C drops and it’s switched to B immediately. System runs stable

Battery – Lipo Amigo → Zero2Go Input C → Pi
Battery → Zero2Go Input B /

When unplug Input B the system restarts. (probably because of a voltage drop)

  • when running from Input C (Battery via Lipo Amigo) the Pi reboots during the boot process. Voltage measured on the Amigo (VDEV to GND) drops to ~ 2.25V and then goes up again.

Battery – Lipo Amigo → Zero2Go Input C → Pi

The same behaviour occurs when the Amigo is plugged into USB

Battery – Lipo Amigo → Zero2Go Input C → Pi
USB -/

I tried different things (different Pi, different zero2go, different Lipo Amigo Pro, different batteries) but the issue is pretty much reproducible. The Battery used is a high capacity one with 13400mAh .

Am I using the two products in the wrong way? Help would be highly appreciated.

Many thanks.

If it was me, the Amiga Pro “Device” connector would be plugged into the Zero2Go 2 pin JST-PH connector for plugging in a LiPo/LiIon battery. I wouldn’t use two batteries. My Amiga Pro’s came with the required cable.

Not familiar with the zero2go, but after a quick glance, it’s basic function is the same as the lipo amigo pro… namely to supply uninterrupted power (with some nice extras) and only lacks the battery charging capacity

it could just be that the combined switching time from chaining both together is to long, or the boot draw from the pi is too high at startup to get a fast enough response.

for the first you might try modifying the zero2go’s switching behavior (you’ll need to make sure the supplied power is all above, or all below the zero2go’s output range).

alternatively, playing around with the setting on the pi may allow you to lower boot up power draw (best place to find that out is the official RPi forums)

I’d also modify the setup to a single battery on the amigo, and if you plan to run an constant power also do that through the amigo, that way you should only be dealing with one potential switching delay (the amigo’s) assuming the goal is to have in line charging of the battery as an extra feature. A nice improvement would be to get a couple of jst-PH female headers to put on pig tails to connect to the bare wire and jstXH headers to make battery swapping less of a PITA

the other way to go would be just one battery direct to the zero2go, and use the amigo as an offline charger for the other as a spare. that way when you add the spare back the zero2go will cleanly switch to it (because of the higher voltage) and you can remove the previous one without interrupting power. you could even do it with a single battery if you supply usb power to the zero2go and take the battery off to be charged.