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A system for Charging two separate batteries alternately

Jhnsptr

Mar 16, 2022
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Good day! I am working on a energy harvesting device and I need help.
Do anyone know a system or a module that can help me manage the charging of two separate batteries automatically.
It goes somehow like this, the energy harvester will generate electricity, then it should be charge a battery, but when it is fully charge, it should automatically charge the other one.

Can anyone help me?
 

kellys_eye

Jun 25, 2010
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Two diodes will do it.

Google 'split battery charging' - it's basically two diodes (suitably rated) in a single package. Charging power in on one terminal, one battery connected to each of the other two terminals.

There are many kits available to do this too.
 

Harald Kapp

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@kellys_eye : I'm afraid that is not what the op wants. He's looking for a system that first charges one battery, then switches to charging another battery once the first one is fully charged. The 2-diodes circuit will charge both batteries at the same time.

@Jhnsptr : There are a few open issues you may not have thought of:
  • What kind of battery do you use?
  • Do you have a suitable charger already or is this part of your request, too?
  • What is the circuit supposed to do when the charge state of the 1st battery falls? Should charging revert to the 1st battery or should it continue charging the 2nd battery until this one has reached 100 %, to fall back on charging #1 only then?
  • What is the circuit supposed to do when the charge state of the battery that is not being charged falls below an acceptable (safe) threshold? Should it continue charging the other battery or should it switch over from the battery being currently charged (even if not yet at 100 % capacity) to the battery that has been drained below the threshold?
Why do you need to charge 2 separate batteries at all? Wouldn't it be more effective to charge a single (larger) batery only?
 

Jhnsptr

Mar 16, 2022
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Two diodes will do it.

Google 'split battery charging' - it's basically two diodes (suitably rated) in a single package. Charging power in on one terminal, one battery connected to each of the other two terminals.

There are many kits available to do this too.
@kellys_eye : I'm afraid that is not what the op wants. He's looking for a system that first charges one battery, then switches to charging another battery once the first one is fully charged. The 2-diodes circuit will charge both batteries at the same time.

@Jhnsptr : There are a few open issues you may not have thought of:
  • What kind of battery do you use?
  • Do you have a suitable charger already or is this part of your request, too?
  • What is the circuit supposed to do when the charge state of the 1st battery falls? Should charging revert to the 1st battery or should it continue charging the 2nd battery until this one has reached 100 %, to fall back on charging #1 only then?
  • What is the circuit supposed to do when the charge state of the battery that is not being charged falls below an acceptable (safe) threshold? Should it continue charging the other battery or should it switch over from the battery being currently charged (even if not yet at 100 % capacity) to the battery that has been drained below the threshold?
Why do you need to charge 2 separate batteries at all? Wouldn't it be more effective to charge a single (larger) batery only?

Good day! Thank you for replying
To answer your questions
  • I will use two li-ion AAA batteries
  • I am trying to create an energy harvesting device using piezoelectric materials, so the piezoelectric material will be the charger.
  • The circuit is supposed to fully charge the second battery first. It will only charge the other battery when the one it charges is already full.
  • I am trying to create a self-powered device, so it will be also great if you could also recommend a system that can automatically or manually switch the battery it uses when its battery runs out.
  • I am just trying to consider adding these features to my device, which would be great because it will prolong the life of the battery.
 

Jhnsptr

Mar 16, 2022
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Two diodes will do it.

Google 'split battery charging' - it's basically two diodes (suitably rated) in a single package. Charging power in on one terminal, one battery connected to each of the other two terminals.

There are many kits available to do this too.
Thank you for your reply, but I am afraid that this is not what I need. I appreciate your effort though! Thanks for the help
 

WHONOES

May 20, 2017
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I'm sure that what you are asking for is possible but will require a bit of thought.
How do harvest the energy from your piezo devices?
 

Harald Kapp

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the piezoelectric material will be the charger.
No. The piezo is the supplier of energy. You will need a charger circuit that controls charge current for and state of charge of the batteries. Especially as piezos afaik create high voltages but low currents. If you don't, you risk overcharging the batteries or discharging them below the minimum allowed level and thus risk destroying the batteries.
I still have no clue why batteries and a complicated charging regime would be required.
 
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