Charge a 7.4 Li-ion battery through micro USB port

[Veld73]

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

 

[Alec_t]

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]

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

 

[Bluejets]

2 out of 3 requirements........

https://www.ebay.com.au/itm/403577748670

 

[Veld73]

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]

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

 

[Audioguru]

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