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I am experiencing voltage drops with the following setup and I hope someone with mad electronics skills can explain my mistake to me:

When I boot this system up, the RasPi gets stuck in a boot loop. Which means the screen turns on for a couple of seconds and then the lights of the TFP401, as well as the screen, turn off and restart again. This setup draws around 0.7A, which should be no problem for the PowerBoost as well as the battery. If I only connect the RasPi without Display the system boots up, drawing around 0.2A.

I have researched this topic already and found the following post to describe almost the same problem. Unfortunately I don’t have an Oscillometer to see what is happening. The PowerBoost however features a LED light, that will light up if voltage drops below 3.2V.

In my first setup (all components) the light is almost constantly on, which indicates massive voltage drops. The second setup (only RasPi) does not show the LED most of the time. However, even there the LED will flicker for very short amounts of time.

Doing research on the battery I bought, I saw that it is rated for 0,3C continuous and 0,5C peak (which should still suffice for the test setup). My end goal is to have a continuous draw of around 1,4-1,6A, so I will probably have to get a battery with higher rating.

Again, can someone with electronics knowledge explain to me what is happening and how I can prevent this from happening?

I append two pictures. First, is the safety circuit of the battery. Second, is the wiring of my setup.

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EDIT: So what I have found out so far is that you should not try to boot a RasPi 3 with less than 2A. I believed the battery to have a 0,5C rating (as it was described in an eBay description), which turned out to be false. Furthermore, I did not consider any loss due to stepping up the voltage. So the power draw coming from the PowerBoost I describe in my post, is roughly 1.5 times higher for the battery.

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  • What operating system does boot the system up? Is it Raspbian?
    – Ingo
    Mar 9, 2019 at 19:52
  • It is Raspbian.
    – SuperTasche
    Mar 10, 2019 at 14:00

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In addition to what your edit says about insufficient LiPo current rating, there are several other aspects which may have a negative impact:

  • Boost converter have significant reaction time. Unlike buck converters which can pass current directly from input to output (dropping the voltage) under heavy loads, boost converters first need to generate that current internally, because the input voltage is lower than output voltage. During this time, the load is only supplied by whatever capacitors are present on the 5V line, which don't last long. That's why 3.7V LiPos are great for powering 3.3V devices, but less so for 5V.

  • Voltage drop in the path of highest current. It's hard to say from your photo what kind of wires and connectors you have between the LiPo and the boost module, but they should be something that can handle 4 Amps of current easily. Meaning there should be thicker and shorter wires, more soldering and fewer connectors.

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  • So if I understand you right, could something like a strong 4000mAh 7.4V battery plus a step-down regulator like this be a solution to my problem? Or will I experience different problems?
    – SuperTasche
    Mar 11, 2019 at 20:43

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