18650 battery care and usage

Other Hardware General Electronics
1

Hi,

Recently, I've become interested in running Arduino with these batteries / using them to upgrade existing battery powered items that previously took NiMh cells etc.

If I look on instructables, I see plenty of projects using these devices but also lots of comments about people creating "bombs" because they're not using the proper precautions.

Perhaps someone here can help clear things up?

I can see that it's possible to charge these devices either with a dedicated charger (e.g. https://www.gearbest.com/chargers/pp_365133.html), which deals with individual cells, or something like a TP4056 which, again, I think is only for charging individual cells.

Some people appear to be "paralleling up" 18650 cells and charging them with something like a TP4056 but I'm thinking that this isn't how it should be done.

So, what happens if I want to charge 2x 18650s in series? I think I need something like this: 2S 3A PCB Protection Board Li-ion Lithium Battery 18650 Charger Module 7.4V 8.4V | eBay which appears to allow connections to the anode and cathode of each cell connected in series which is then suitable for charging this pair of cells "individually."

Now, I also understand that discharging these cells too far can damage them or render them inoperable. This means that they shouldn't be discharged below 3V (?)

In this case, this needs a battery management circuit which looks at the voltage of each cell and, presumably, cuts off the output of the pack (if 2 batteries are in series) when this occurs (?) Again, something like that "2S 3A PCB Protection Board Li-ion Lithium Battery 18650 Charger Module 7.4V 8.4V | eBay" could be used for this providing that 8.4V is put onto the P+ P- pins ?

And those very same P+ and P- pins, once the battery pack has been charged, can presumably be used for the battery's load ?

Are those assumptions correct?

Is it also possible to pair up cells for these BMS boards or is that just asking for trouble?

Also, how do you know that these BMS boards have "charged" the battery pairing? There is no indication so it is a case of monitoring the current?

Thanks for any replies.

2

Hi,

MOST 18650 type cells have internal protection circuits that disconnect them when the voltage gets too low, and prevents the charging voltage from going too high. There are also overcurrent and pressure-relief parts. Amazingly complex but now easy to use.

Here's some info:

A protected battery will (hopefully) include the following protections:

  • PTC, protect against over temperature and indirectly over current and will automatic reset.
  • CID or pressure valve, will disable the cell permanently if the pressure is to high in the cell (Can be due to over charge).
  • PCB will protect against over discharge, over charge and over current, depending on design the PCB will reset automatic or when placed in a charge

Inside it looks like this:

800×240 16 KB

See This Page

Tesla uses 18650 type/size cells in their cars. Thousands of them. They do NOT have the individual protection shown here, but TEsla has complex protection systems and fireproof foam etc..

3

Theres no problem in paralleling 18650 cells as long as they are all of the same type and brand.
This is commonly done to increase the AH rating of a battery bank without increasing the voltage.
The paralleled cells can then be simply charged as 1 cell.
Most laptop computers have paralleled cells , with usually 3 sets in series to give 11V.

4

briscaF1:
Now, I also understand that discharging these cells too far can damage them or render them inoperable. This means that they shouldn't be discharged below 3V (?)

In this case, this needs a battery management circuit which looks at the voltage of each cell and, presumably, cuts off the output of the pack (if 2 batteries are in series) when this occurs (?) Again, something like that "2S 3A PCB Protection Board Li-ion Lithium Battery 18650 Charger Module 7.4V 8.4V | eBay" could be used for this providing that 8.4V is put onto the P+ P- pins ?

Did you check what is the lowest cut off voltage of the device you posted the link for ?

5

terryking228:
Hi,

MOST 18650 type cells have internal protection circuits that disconnect them when the voltage gets too low, and prevents the charging voltage from going too high.

I beg to differ.

I VERY rarely see protected cells. I only encounter them when i see high-powered LED-flashlights with "idiot proof" batteries, where the electronics in the flashlight does not employ any over-discharge function.

Protected cells are harder to manufacture, more expensive and are longer, and won't fit into many battery holders because of this.

So saying that "MOST" cells are protected, are downright incorrect.

// Per.

6

So saying that "MOST" cells are protected, are downright incorrect.

You're right in that I was talking about 18650 typically sold in USA which has strong regulations. Where are you located? To be more correct and help readers here let's try to show more detail on this.

The more correct answer is "It's Complicated".

18650 is the size: 18mm diameter 65 mm length cylindrical. The protection circuitry in some cells makes them longer.

Button-Top 18650 : This is the typical type of top with a small button like an AA cell. This has protection circuitry.

Flat-Top 18650: We have to be careful here.

  • Cells with no protection circuitry have no button:

    This cell has a flat top recessed BELOW the plastic case. They will not contact when placed in series.

  • Some flat top cells with no protection are not recessed on the top and can go in things like flashlights where they are used in series.

This subject has been covered by many other sites and groups. Click HERE for many more details.

7

Be aware that the cheap 18650s from eBay and the like are nowhere near as good as their specs claim. These commonly are marked for 4000, 5000 or even 9800 mAh- despite the fact that the best cells from top end manufacturers cap out at 3000 (maybe 3500 now). In practice, these knockoffs vary from 1000~2000 at best to under 500 for some batches. Good 18650 cells run around 7 bucks each.

These cheapo cells are often still competitive in terms of mAh per dollar, but they're deceptively labeled and the quality varies widely

8

Hi,

Thanks for the replies.

mauried:
Theres no problem in paralleling 18650 cells as long as they are all of the same type and brand.
This is commonly done to increase the AH rating of a battery bank without increasing the voltage.
The paralleled cells can then be simply charged as 1 cell.

This is good to know. I had expected each cell to have to be monitored individually but I can see your point if you are using matched cells to achieve the aim. Presumably, the more cells you add in parallel to make a "pack", the higher the rating you require of your battery management system (BMS) or....perhaps they just take longer to charge?

srnet:
Did you check what is the lowest cut off voltage of the device you posted the link for ?

I didn't but 3V appears to be a general figure from what I've seen. Are you implying that you have to match the BMS cut off for the particular cells you use?

More generally, the cells that I'd consider would be from a reputable manufacturer but most I have seen have not had any protection built in, hence the questions about the BMS.

From these replies, I'm thinking that if I wanted to use 2 18650s in series, I just need a 2S BMS board to charge and manage the discharge / low level cut off for this series pair. And, for the simple BMS as linked above, this requires a constant current, constant voltage power supply (i.e. bench supply) and the batteries will be charged when the BMS cuts off to a trickle charge.

Would that be a fair conclusion to reach?

Thanks.

9

briscaF1:
I didn't but 3V appears to be a general figure from what I've seen.

So you are not even interested in checking the specifications of the devices you are proposing to use.

What a waste of time.

10

Bit rude, no?

I haven't checked yet because I'm getting general idea of what to do before I drill down into detail.

11

One set LG is 2.5V discharge end voltage.
Another set (Sony) is 2.0 DEV.

There, not a waste of time.

12

briscaF1:
Bit rude, no?

I haven't checked yet because I'm getting general idea of what to do before I drill down into detail.

No, you said;

"I also understand that discharging these cells too far can damage them or render them inoperable. This means that they shouldn't be discharged below 3V (?)"

Now go back and check the detail specification for the part in the link you provided.

13

Indeed. The (?) implies a question or a statement of which I am unsure. And I'm still none the wiser from your replies.

Additionally, the BMS PCB has this specification:

Over Discharge Detection Voltage: 2.3-3.0V±0.05V

2.3 to 3.0V is a pretty wide range so it tells me one of two things:

a. It's pot luck whether the BMS is compatible with any cell having a DEV in the range of 2.3 to 3.0V because, if they were 3.0V, they'd be allowed to discharge too far or, if they were 2.3V, I'd never get the full capacity usage out of the cells as they'd be switched off before they were "flat."

b. It really doesn't matter too much about the DEV as most cells will be OK just so long as you don't go below 2.3V

Since you appear to know plenty about these cells, perhaps you can clarify which is true?

14

You really need to think about what you are going to use the cells for in relation to how they are charged / discharged.
Whats the voltage range of what the cells will be powering?

15

briscaF1:
Over Discharge Detection Voltage: 2.3-3.0V±0.05V

So the cells could be discharged to 2.3V before cutoff.

Does that meet your requirement;

"Now, I also understand that discharging these cells too far can damage them or render them inoperable. This means that they shouldn't be discharged below 3V (?)"