18650 Li-ion Battery Protection Boards

[John Murdock]

I am currently using some rechargeable 1860 Li-ion batteries ( similar size to AA batteries) to be able to use a system remotely without needing the mains in remote locations.

I read up about these online and it seems they are somewhat unstable and have a lot of leakages and short circuit issues. I found some already made protection type circuits online but to be frank, I'm not too sure what I should be looking for ( roughly 5V, 3-4A).

I was thinking of using something like this: https://www.ebay.co.uk/itm/18650-Li...4-CELLS-Circuit-Lithium-Polymer-/152829479052 [2 cells version].

running it into a breadboard with a Potential divider to get the right voltage.


I would appreciate if anyone would know better solutions or a whole new way of tackling this. Many thanks.

 

[Pommie]

What are you trying to power? A potential (resistive?) divider is not a good solution.

Mike.

 

[Nigel Goodwin]

You need to consider what you're trying to do, how many cells you're using, and consider what you're trying to 'protect'.

If you're using one cell, or single cells in parallel, the main 'protection' is to prevent the cells getting over discharged, which kills them.

If you're putting cells in series then a protection board that also balances the charge is a good idea. However, plenty of commercial equipment doesn't balance charge - and as always with batteries it's essential to use identical ones, and not mix old and new.

 

[John Murdock]

You need to consider what you're trying to do, how many cells you're using, and consider what you're trying to 'protect'.

If you're using one cell, or single cells in parallel, the main 'protection' is to prevent the cells getting over-discharged, which kills them.

If you're putting cells in series then a protection board that also balances the charge is a good idea. However, plenty of commercial equipment doesn't balance charge - and as always with batteries it's essential to use identical ones, and not mix old and new.

What are you trying to power? A potential (resistive?) divider is not a good solution.

Mike.

Thank you for your response Nigel and Pommie.

The system:

An arduino taking in 5V -> connected to a driver circuit -> connected to 20 servo motors. [ I made a new design and the servo motors will not all be on all at once, max 2 on at the same time but 99% of the time one on at once max.Hence less current drawn]. It now needs 5V 2-3A.

2 LI-ion cells provide 7.2V and 3A.

I am thinking maybe an SMPS buck converter could do the job but then this would limit the current output?

 

[Nigel Goodwin]

Thank you for your response Nigel and Pommie.

The system:

An arduino taking in 5V -> connected to a driver circuit -> connected to 20 servo motors. [ I made a new design and the servo motors will not all be on all at once, max 2 on at the same time but 99% of the time one on at once max.Hence less current drawn]. It now needs 5V 2-3A.

2 LI-ion cells provide 7.2V and 3A.

I am thinking maybe an SMPS buck converter could do the job but then this would limit the current output?

You could use two in series and a buck converter to give 5V (do the servos actually NEED 5V anyway?), or use two in parallel and a boost converter to give 5V - makes little difference either way, and 2A converters (of both types) are commonplace and cheap.

But for a start check the exact specs of your servos, many were 6V, but were often run on 4.8V (4 NiCd's in series).

 

[John Murdock]

You could use two in series and a buck converter to give 5V (do the servos actually NEED 5V anyway?), or use two in parallel and a boost converter to give 5V - makes little difference either way, and 2A converters (of both types) are commonplace and cheap.

But for a start check the exact specs of your servos, many were 6V, but were often run on 4.8V (4 NiCd's in series).

Thank you for the response. The servos are continuous servo motors (360 degrees). The input voltage has to be rather accurate. since these don't have any feedback, I am using speed and velocity to determine their position and the input voltage has an effect on the velocity. At 5v they run at max speed which all the code is designed for.

 

[Nigel Goodwin]

Thank you for the response. The servos are continuous servo motors (360 degrees). The input voltage has to be rather accurate. since these don't have any feedback, I am using speed and velocity to determine their position and the input voltage has an effect on the velocity. At 5v they run at max speed which all the code is designed for.

So why are they 'servos' rather than just 'motors'? - needless to say they will be terribly inaccurate.

 

[John Murdock]

In terms of accuracy, it is reasonable, not perfect but workable. The 360s are easier to work with as it has more libraries built for it and drivers etc.

 

[Pommie]

Do you have a link to the servos you're using?

Mike.

 

[gophert]

In terms of accuracy, it is reasonable, not perfect but workable. The 360s are easier to work with as it has more libraries built for it and drivers etc.

sometimes, trying to build hardware that uses existing software is more difficult less optimal than using the right hardware and taking the time to write the code.

 

[John Murdock]

Do you have a link to the servos you're using?

Mike.

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