[Solved / Archived] Witty Pi 4 L3V7 I2C read 0x01 0x08 61 failed (result=), and no more retry.

I am confused, why would it lose power immediately?  It actually does not. The 100mHa LIPO battery is the total capacity and not the Amp.  

@andrew-simpson17 Indeed that 100mAh is the capacity, but the ability to deliver current is usually related to the capacity. A LiPo battery with very small capacity usually can't deliver big current, or say its discharge C rate should not be very high.

Let's say it has a rather high discharge C-rate: 5C. That means it can only delivery up to 500mA current.

When Raspberry Pi is shutting down, it consumes higher current than normal usage and 500mA may not be enough. In such case your battery's actual voltage will drop (very quickly) and most probably the MCU has to work undervoltage for a while, which could cause bad things.

Ah, I see. Told you I am a novice. Well, in this case this is a good thing.  I am surprised I have not had all the cameras back then! Well, what minimum and ideal LIPO capacity should I use?  It is just to faciiiate a gracefully exit which takes around 25 seconds.

Many Thanks

@andrew-simpson17 According to my calculation in another topic, the actual current Witty Pi 4 L3V7 draws from the battery is about 1.5 times of the current consumed by your Raspberry. So if you can find out how much current will be consumed by your Raspberry Pi, you know how much current the battery has to deliver.

I'd suggest to actually measure the current consumption of your Raspberry Pi during its shutdown procedure, this could be easily done by a USB current meter. You take the highest current value (and maybe adding some buffer) for next step. Let's say you read 600mA.

Then you know your battery has to deliver at least 600x1.5=900mA. So you should find a battery that can deliver at least 1A current. When you choose battery, make sure to check its max discharge current. Sometimes it is listed directly (like 1000mA, 2A, 3A etc), sometimes it is listed as discharge C rate.

BTW, the battery mentioned in another topic (LP803465) seems suitable for your use case: it can deliver at least 1000mA constantly.

Thank you so much! 

@andrew-simpson17 I took a closer look at another topic and seems his/her use case is the same with yours (Witty Pi 4 L3V7 + RPi Z 2W), and his/her LP803465 is not good enough for this job.

We used 18650 LiPo battery for testing and that we can confirm to work well.

@andrew-simpson17 as promised, the tutorial is here: https://www.uugear.com/portfolio/compile-flash-firmware-for-witty-pi-4/

Thank you very much.

Hi

I checked with the meter after multiplying it all out I rounded up to:

1800.

The actual draw on the Rpi is 1200mHa.

I got this:

https://thepihut.com/products/2000mah-3-7v-lipo-battery?variant=42143258050755

I only just noticed on the data sheet this:

Maximum Constant
Charging Current 1500mA

So, I asuming this is not good?

Hi Again, sorry i had been on holiday and only just got back. I missed something...

"We used 18650 LiPo battery for testing and that we can confirm to work well."

So, i have plenty of 18650 batteries here. But, is there a container that you can recommend for me to insert just 1 18650 battery with  JST plug (already soldered on) so i can make the connection. There is not a lot of spare space in my camera case you see.

Any recomemndations i would be forever grateful.

At least I learnt something here...

The 2000mAh battery you mentioned has similar parameters with LP803465, which are not good enough for this job. It might work when the battery is brand new, but it could fail after some cycles, because the data doesn't have enough buffer.

If you search "18650 battery holder", you can find many. It usually comes with no plug and you will need to connet the PH2.0 cable (included in Witty Pi 4 L3V7 package) with its wires.

Morning.

Thanks for your reply.

sorry to ask you again (only because i have just ordered it) but is this one any better?

https://www.amazon.co.uk/dp/B08215B4KK?psc=1&ref=ppx_yo2ov_dt_b_product_details

Many thanks for all your help BTW.  Things are progressing for us///

@andrew-simpson17 Unfortunately it seems even worse:

Standard Discharge Current: of 0.2C (740mA)

I don't know why they made a battery like this, 0.2C is really small. I really would expect something like 1C with such capacity.

Ok - thanks. will cancel 🙂

Last one I will put to you. Only asking as this is pre-wired:

https://www.ebay.co.uk/itm/404414747979?_trkparms=amclksrc%3DITM%26aid%3D1110013%26algo%3DHOMESPLICE.SIMRXI%26ao%3D1%26asc%3D20201210111452%26meid%3Dd1ed19e61c444848a43962b96acbb95e%26pid%3D101196%26rk%3D5%26rkt%3D12%26sd%3D285581732006%26itm%3D404414747979%26pmt%3D1%26noa%3D0%26pg%3D4429486%26algv%3DPromotedRVIPbooster%26brand%3DMarkenlos&_trksid=p4429486.c101196.m2219&itmprp=cksum%3A404414747979d1ed19e61c444848a43962b96acbb95e%7Cenc%3AAQAJAAAA8CwDxH%252FaslyJlxG5OwCzDVtylcck%252B5sJiuia8Xflas5w3OrV81sUwCuqMcHRuLhFRHHI7Lq0o7iJTfBSb9Bl0OHXz4dWqsRTNEheMzmfrlLNjQkp2SkVL9cpU39ULWFFsr78JT2oVs2YxGYDlzg5km%252BttaeqdFEFPvcbFcNG4Ah9rjf5Sx8NNS0vcPLVmDpLZB14e3Bzp%252BXTztd90I%252FRm3XGvPmQItZ6%252FvD9%252B1P0pdZOELv8R0i1zT3YCVPfTTS8NiELZOYMmE%252B03ySVN49fF00XM9CgsmQkVlA2zpBb2I%252FsQiz%252FcXMQiRKhl84YJeOd0A%253D%253D%7Campid%3APL_CLK%7Cclp%3A4429486&itmmeta=01HWSQ6BFV78GJYZCQWWDGNG12