sim_tcr
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Power rpi 4 using 18650 question

Tue May 05, 2020 12:05 pm

Hello,

I am getting a rpi 4 4gb version.
I have several good quality 3000mah 18650 cells lying around which can discharge up to 10A easily.

Should I be using 1 cell and boost the voltage to 5v? Or use 2 cells and step down to 5v?
What is the best way to achieve either of the method? Any ready made regulator available?

Thanks.
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Raspberry Pi Model B x 2, Raspberry Pi 2 x 2, Transcend 32GB Class 10, Transcend 16GB Class 10, Transcend 8GB Class 4, Custom 12V 1.5A (stepped down to 5.5V)

Brandon92
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Location: Netherlands

Re: Power rpi 4 using 18650 question

Tue May 05, 2020 12:12 pm

How long do you want it to run on the battery?

sim_tcr
Posts: 331
Joined: Tue Nov 06, 2012 1:01 pm
Location: Bangalore
Contact: Website

Re: Power rpi 4 using 18650 question

Tue May 05, 2020 12:16 pm

Brandon92 wrote:
Tue May 05, 2020 12:12 pm
How long do you want it to run on the battery?
May be 1 or 2 hours and then I will charge the batteries.
I will monitor the battery voltage and make sure never drop 3v.
http://raspisimon.no-ip.org
Raspberry Pi Model B x 2, Raspberry Pi 2 x 2, Transcend 32GB Class 10, Transcend 16GB Class 10, Transcend 8GB Class 4, Custom 12V 1.5A (stepped down to 5.5V)

Brandon92
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Location: Netherlands

Re: Power rpi 4 using 18650 question

Tue May 05, 2020 12:27 pm

Depanding on the load on the Rpi 4, it could maybe not last that long. You can measure how much current the Rpi 4 needs in you application, or your test it how long it wil last.

I will place the two batttery in series and use a buck converter that is set to 5V to power the Rpi. Often it is easier go down in voltage that rather going up and more efficient. However it is not impossible. Note that you will need a buck converter that can deliver the maximum amount of current that the Rpi 4 needs. And often a bit more if its from ebay ect..

And it is indeed important that the battery voltage wil not drop below 3V, there are special IC for that (BMS).

sim_tcr
Posts: 331
Joined: Tue Nov 06, 2012 1:01 pm
Location: Bangalore
Contact: Website

Re: Power rpi 4 using 18650 question

Tue May 05, 2020 12:36 pm

Brandon92 wrote:
Tue May 05, 2020 12:27 pm
Depanding on the load on the Rpi 4, it could maybe not last that long. You can measure how much current the Rpi 4 needs in you application, or your test it how long it wil last.

I will place the two batttery in series and use a buck converter that is set to 5V to power the Rpi. Often it is easier go down in voltage that rather going up and more efficient. However it is not impossible. Note that you will need a buck converter that can deliver the maximum amount of current that the Rpi 4 needs. And often a bit more if its from ebay ect..

And it is indeed important that the battery voltage wil not drop below 3V, there are special IC for that (BMS).
I was thinking something like https://robu.in/product/dc-dc-4-5-40v-5 ... ter-modul/
But it says out put is 2A. I guess rpi 4 needs 3A.
Or this https://robokits.co.in/power-supply/dc- ... 7DEALw_wcB
http://raspisimon.no-ip.org
Raspberry Pi Model B x 2, Raspberry Pi 2 x 2, Transcend 32GB Class 10, Transcend 16GB Class 10, Transcend 8GB Class 4, Custom 12V 1.5A (stepped down to 5.5V)

Brandon92
Posts: 847
Joined: Wed Jul 25, 2018 9:29 pm
Location: Netherlands

Re: Power rpi 4 using 18650 question

Tue May 05, 2020 12:45 pm

The one with the LM2596 could work, but it is a little bit short on the output power and you certainly need a heatsink to get that amount of power. When you place the battery in series and they are almost empty the voltage the input voltage is 6V. The IC needs 1.5V higher than 5V to operate correcly. So if you detect that the battery voltage is around the 6.5V you need to disable your system. And this includes to cut the power from the battery. Otherwise the buck converter could still discharge the battery.

I think I will look at a power supply that can deliver at minimum 5A.

emma1997
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Re: Power rpi 4 using 18650 question

Tue May 05, 2020 8:53 pm

I agree with Brandon that 2 or more cells with step down is best. IME direct from lithium cell is good for minutes (ie emergency shutdown) but not hours. Unless you parallel the 18650s but then there will still be major wasted energy. Counter-intuitive because direct should do better considering converter losses but in practice I found opposite to be true.

Also note that if you depend on human monitoring to stay above 3v you will be replacing cells often. Unless using the very expensive type with built-in BMS.

Also agree that LM2596 can be marginal for Pi4. May be ok for older Pi but XL4015 modules with toroid much more reliable for the new power hungry Pi models.

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