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suitable regulator for battery powered system
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

suitable regulator for battery powered system

by Workaholic on Wed Jul 24, 2019 5:19 am

Hey guys I am using 5 lithium ion cell (18650) in parallel config to get 4.2V 10Ah supply. However, I am having a problem in finding suitable regulator that can provide 3.3V as the battery pack voltage drops from 4.2V. Any module from adafruit will be good. Or any IC that can be hand soldered. Or any solution which is good.

I was first using an approach where I was boosting the voltage to 5V and then regulate to 3.3V but the boost converter was consuming 50mA which was very high for our application. So any suggestion will be appreciated.

Regards,

Workaholic
 
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Re: suitable regulator for battery powered system

by adafruit_support_bill on Wed Jul 24, 2019 6:00 am

I am using 5 lithium ion cell (18650) in parallel config to get 4.2V 10Ah supply.

Unless this is a factory assembled 5P pack, that is not a good idea. Small manufacturing variations between cells can result in an unbalanced pack which can be hazardous. Factory assembled packs take cells from the same production run, then further test and bin them by charge/discharge characteristics. Only cells that match precisely are assembled into multi-cell packs. The rest are sold as loose cells.

I am having a problem in finding suitable regulator that can provide 3.3V

3.3v at what current level? We have a 3.3v buck converter which will efficiently regulate inputs from 3.5v to 5.5v down to 3.3v at up to 600mA. https://www.adafruit.com/product/2745

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Re: suitable regulator for battery powered system

by Workaholic on Wed Jul 24, 2019 7:16 am

Thanks for your reply. I look forward to buy the module. It seems good. My current level is 300mA. So the module is sufficient.

But my concern is that the lithium ion cells discharge up to 2.7V or atleast 3V safely. So if I use the module it will only regulate up to 3.5V. i want to use my battery pack capacity to 80-90%. How do I know at 3.5V how much battery capacity has been consumed, provided the current is 300mA max that my circuit takes when it wakes up. And the rest it is in sleep mode.

Regards,

Workaholic
 
Posts: 15
Joined: Thu Mar 28, 2019 6:23 am

Re: suitable regulator for battery powered system

by adafruit_support_bill on Wed Jul 24, 2019 7:39 am

my concern is that the lithium ion cells discharge up to 2.7V or atleast 3V safely.

Overdischarge protection is typically a function of the protection circuit in the battery pack. Most are set for a low-voltage cutoff of around 3v. All the packs we carry have built in protection circuits. Loose cells or packs intended for RC airplane use often do not have protection circuits.

So if I use the module it will only regulate up to 3.5V.

All regulators need at least a little bit of headroom or 'dropout' to regulate. 0.2v of dropout for this device is quite low. Many regulators need 2v or more. If you want 3.3v output for inputs both above and below that voltage, you need a combination buck/boost converter.

How do I know at 3.5V how much battery capacity has been consumed,

Voltage is not a very good indicator of charge level for LiPo cells, since the curve is pretty flat for most of the discharge cycle, and there are many other factors that can affect the voltage (temperature, discharge rate, etc). There are 'fuel gauge' chips that monitor the actual current flowing into and out of a cell that can provide a better estimate of the charge level.
https://www.analog.com/media/en/technic ... EN-SOC.pdf

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Re: suitable regulator for battery powered system

by Workaholic on Thu Jul 25, 2019 3:40 am

So what I understand is that I need to have single cell fuel gauge for measuring state of charge of the 5P battery pack as voltage is not a good indicator.

Thank you adafruit_support_bill for your quick response and crystal clear answer. You have been very helpful recently.

Best Regards,

Workaholic
 
Posts: 15
Joined: Thu Mar 28, 2019 6:23 am

Re: suitable regulator for battery powered system

by adafruit_support_bill on Thu Jul 25, 2019 5:48 am

Looks like SparkFun has a LiPo fuel-gauge breakout board here: https://www.sparkfun.com/products/10617

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Re: suitable regulator for battery powered system

by Workaholic on Thu Jul 25, 2019 10:08 am

Thanks a lot adafruit_support_bill for your support and cooperation.

Best Regards,

Workaholic
 
Posts: 15
Joined: Thu Mar 28, 2019 6:23 am

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