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Charge a 7.4 Li-ion battery through micro USB port

Veld73

Jun 24, 2022
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Hello! I want to create an electric toy which includes a motor that works with a 7.4 V Li-ion battery. The battery needs to be charged and I want to use a micro usb-c port/board for that.

Question 1: the 7.4 V batteries that are typically used for these toys are between 500 mAh and 1800 mAh. The higher the mAh the larger the capacity = the longer the duration? What else should I consider?

Question 2: I want the loading of the li-ion battery to be safe and but quick enough. What should be the specification of the micro-usb c charging board? Would this board work: TP4056 Micro USB 5V 1A 18650 Lithium 3.7 V Li-Ion Battery Charging Board or as the battery consists of 2x3.7 V Li-ion batteries (see atatchment) should I find something else ?

Thank you for your help,
Peter
 

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Alec_t

Jul 7, 2015
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Welcome to EP!
Would this board work: TP4056 Micro USB 5V 1A 18650 Lithium 3.7 V Li-Ion Battery Charging Board
No. USB is 5V; not high enough for charging a 7.4V lithium battery. That's a 2S battery which should be charged with a dedicated 2S balanced charger for safety. Such a charger will need a supply of at least 8.4V, typically 9V, able to handle the required charging current.
 

Martaine2005

May 12, 2015
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The higher the mAh the larger the capacity = the longer the duration?
Yes, generally. Obviously depends on the load. If a 500mAh battery is used for a 500mAh load, expect less than an hour. If 500mAh load and 1800mAh battery, expect 3 hours. But of course, nothing is written in stone and battery specifications do over estimate.


Martin
 

Veld73

Jun 24, 2022
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Welcome to EP!

No. USB is 5V; not high enough for charging a 7.4V lithium battery. That's a 2S battery which should be charged with a dedicated 2S balanced charger for safety. Such a charger will need a supply of at least 8.4V, typically 9V, able to handle the required charging current.

Thank you very much for your input - I will be looking for a 2S balanced charger then.
 

Veld73

Jun 24, 2022
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Thank you very much - I will look for the 2S1A model here in the EU.
 

Audioguru

Sep 24, 2016
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Buy a "power bank" and use its USB-input charger, its single battery cell and its output voltage boost circuit.
 
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