3.7V Power Supply with Battery Backup

Benjamin Scott's picture

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Joined: Nov 03, 2020

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3.7V Power Supply with Battery Backup
November 3, 2020 - 9:04pm

Hi,

I have a temperature probe that operates using exclusively a 3.7V Li-ion battery. This is very inconvenient when the battery dies, and temperature data is no longer recorded until the battery is replaced. It would be much more convenient if this operated using a constant power supply that also had a 3.7V Li-ion battery as a backup for power outages. I'm uncertain of the current draw of the temperature probe but I believe it's less than 5A.

I know literally nothing about circuitry and I assume that this is not terribly difficult to do. If someone could point me in the direction of basic resources for designing a simple circuit, or help me along the process of what's needed to accomplish this. 

Also as a note, these are primary 3.7V Li-ion batteries so there is no need to include recharging in the circuitry.

Any help would be greatly appreciated.

Sourav Gupta's picture

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Joined: Feb 12, 2018

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Lithhium batteries required many precautions during charging. A simple 3.7V will not charge a 3.7V lithium battery. You need atleaset 4.2V and proper Constant current and Costant voltage charge profile.

However, it is certainly possible to use a 3.7V adapter, but since the temparature probe is using a lithium battery, my best guess is the temparature probe has some sort of power input options for charging the battery. If not, then you need a basic 3.7V lithium battery charger module board that requires 5V usb, could be directly connected with the battery holder.

Thus,

In conclusion -

If the temparature probe supports charger, use it. You need nothing. If not, then surely the battery is removable, do not remove the battery, connect a lithium battery charger module board that supports 5V input as USB, and connect the module output with the battery holder. Problem solve. You apply an USB voltage the charger will charge the battery and tun the temparature probe. The battery will act as a backup. (Same charging concept of a laptop).

 

 

However,

The temparature probe maybe not under 5A. 5A is a huge current for a lithium battery. My best guess is the current could be something between 500mA (0.5A). If so, 1A of charge current will be adequate.

Benjamin Scott's picture

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Joined: Nov 03, 2020

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Thanks.

I have no intentions of charging the batter. These are primary cells. This means they are not intended to be rechargeable, and the temperature probe does not recharge them. The temperature probe does not have a charger because it operates exclusively on battery power. I would like to, however, continue to use these batteries as a backup when power is out. Otherwise, I would like a power supply that replaces the battery. I have no intentions of charging this battery.

Is this clear? Like I specifically said in my original post, I do not want to charge the battery.

Sourav Gupta's picture

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Joined: Feb 12, 2018

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Use a 3.7V output charger with 500mA rating. Here it will not charge the battery but will run the temparature probe. When the power will be shutoff the battery will provide the power.

Since, it is quite difficult to find out 3.7V 500mA adapter, use a lithium battery charger module (Here it will not use as a charger). The module will take input from a 5V SMPS (Mobile phone charger specifically) and the output 3.7V will power the circuit. Connect the charger module output (positive and negative) in the place of the battery terminals.

In this way the job will be much easier and will solve the purpose.

Debashis Das's picture

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Joined: Dec 02, 2019

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As sourav said you can always use those TP4056 based lithium battery charger module.