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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.
 

ScooterR

Oct 7, 2023
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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.
The part about the USB 5v not high enough for charging a 7.4v lithium battery isn't necessarily accurate. For instance I've got two 9volt batteries I just removed from their charger sitting in my lap. They are EBL 6F22 9V 600 mAh Lithium-ions. Their charger is an EBL 6F22 charger. The input voltage is 5v 1.0A supplied with a micro USB to USB cable and wall adapter for my phones. The output of the charger is 8.4 v 1500mA*2 MAX meaning it has two output charge stations that do so simultaneously. Depending the actual output of your charger it may very well get you where you need to be. Most 9v batteries have a nominal voltage of 7.2 to 9.4 and anywhere in between. I hope this helps.
 

Alec_t

Jul 7, 2015
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The part about the USB 5v not high enough for charging a 7.4v lithium battery isn't necessarily accurate.
That part related specifically to the TP4056 Micro USB 5V 1A 18650 Lithium 3.7 V Li-Ion Battery Charging Board, not to USB powered chargers in general. As this thread is over a year old I expect the TS's battery is fully charged by now :) .
Welcome to maker.pro ! Please check thread dates before posting.
 
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