tarnis
Posts: 20
Joined: Thu Feb 02, 2017 4:53 pm

Battery Blowup!

Tue Sep 22, 2020 9:10 pm

Ok, nothing really blew up per say...I'm losing cells and not sure why. I'm not a computer science major, just some guy who watches youtube videos.

So I'm working on building a camera out of the pi HQ cam and code-wise it just got ready to hit the streets for the first time...but I also left it on long enough fixing some code to discover maybe we have a problem.

Here's a battery pack I put together out of a battery holder, and some 18650 cells, and this buck converter:
https://www.amazon.com/gp/product/B07PB ... TF8&psc=1
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I've killed two cells now...wishing I was keeping track, but it seems like one will remain at full power while the other fully depletes. I'm also unable to recharge it after it happens. I'm running the pi 4, adafruit 3.2" screen and HQ camera off of the pack...not sure if that's too much. Happens after maybe 5 or so minutes and the screen turns white and starts pulsating.

tarnis
Posts: 20
Joined: Thu Feb 02, 2017 4:53 pm

Re: Battery Blowup!

Tue Sep 22, 2020 9:15 pm

And by the way, these are EBL 3000mah 3.7v cells I bought 3 years ago and never used.

pidd
Posts: 1266
Joined: Fri May 29, 2020 8:29 pm
Location: Birkenhead, Wirral, UK
Contact: Website

Re: Battery Blowup!

Tue Sep 22, 2020 9:46 pm

What are you using to charge your batteries? It needs to be an intelligent charger and the first time they should be charged for a long time.

You could probably do with putting three cells in series, the circuit might stop working long before the batteries are flat because there is not much voltage before the buck converter.

tarnis
Posts: 20
Joined: Thu Feb 02, 2017 4:53 pm

Re: Battery Blowup!

Tue Sep 22, 2020 11:04 pm

This is the charger...I have to pull the cells and put them in so that's probably not the issue.

https://www.amazon.com/dp/B014867612/re ... 3uZekrlBDL

Here are the batteries
https://www.amazon.com/dp/B00DNPT1D6/re ... gNTO6tan8Z

Popping them into one of these...
https://www.amazon.com/dp/B00TK0R5FE?re ... b_ap_share

LTolledo
Posts: 4102
Joined: Sat Mar 17, 2018 7:29 am
Location: Anime Heartland

Re: Battery Blowup!

Wed Sep 23, 2020 9:15 am

no wonder it happens.... maybe because of:
link clicked and this came out.jpg
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:mrgreen:
"Don't come to me with 'issues' for I don't know how to deal with those
Come to me with 'problems' and I'll help you find solutions"

Some people be like:
"Help me! Am drowning! But dont you dare touch me nor come near me!"

User avatar
rpiMike
Posts: 1529
Joined: Fri Aug 10, 2012 12:38 pm
Location: Cumbria, UK

Re: Battery Blowup!

Wed Sep 23, 2020 9:47 am

I believe if using Lithium Ion 18650 batteries you should use some form of voltage cut-off. Each battery should not be discharged below about 3V as the battery can be damaged and possibly be a fire risk.

I would recommend AA Ni-Mh batteries.

alphanumeric
Posts: 2670
Joined: Tue Jan 19, 2016 2:17 pm
Location: Sydney, Nova Scotia, Canada

Re: Battery Blowup!

Wed Sep 23, 2020 11:18 am

Can those cells actually supply enough current to drive a Pi 4 plus display?

pidd
Posts: 1266
Joined: Fri May 29, 2020 8:29 pm
Location: Birkenhead, Wirral, UK
Contact: Website

Re: Battery Blowup!

Wed Sep 23, 2020 4:31 pm

alphanumeric wrote:
Wed Sep 23, 2020 11:18 am
Can those cells actually supply enough current to drive a Pi 4 plus display?
How long do you want it to run for?

I use loads of JCB AA and AAA NiMH batteries for various things but not powering a Pi so far. You would need at least 8 AA NiMH which i would guess should give you over two hours on a Pi4

rhildinger
Posts: 39
Joined: Thu Jun 09, 2016 6:07 pm

Re: Battery Blowup!

Wed Sep 23, 2020 5:36 pm

From what you've said, it seems like you are triggering the protection circuit of one of the 18650 cells, perhaps with the inrush current of the buck converter. That being said, there's nothing wrong with your setup as diagrammed. The buck converter you are using is capable of supplying 5 amps at 5 volts, which should be more than enough to power the pi, screen, and camera. Two 18650 lithium cells can easily supply enough power to keep the buck converter from dropping out, and the inrush current of the buck converter *shouldn't* be enough to cause any problems.

What I suspect is ultimately the problem are the cheap chinese "EBL" brand batteries you used. EBL looks like one of the thousands of cheap battery suppliers that resell batteries of questionable provenance, and I wouldn't trust them at all. Weird charging/discharging issues and vastly inflated capacity claims are the hallmark of these batteries.

Samsung, Sanyo, and LG are all good cell brands and I suspect would work well in your application.

dustnbone
Posts: 395
Joined: Tue Nov 05, 2019 2:49 am

Re: Battery Blowup!

Wed Sep 23, 2020 6:07 pm

You also really want to have some kind of low voltage cutoff for those cells, regardless of their brand/capacity.

Discharging below 3V is generally considered harmful to Li-Ion cells, and some chargers will refuse to charge them if they go too far below that, for safety reasons.

My guess is that for whatever reason one of your cells has substantially less capacity than the other, and is getting pulled way below 3V, causing your buck converter to have insufficient input voltage to output 5V.

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