Charging lithium ions

[solar3000]

I have a stack of 18650 cells.

Any charger I put them in will raise the voltage to 4.2 volts. That's great, but as we know, it will kill the cell at that voltage after a few months.

Since I can't find a charger that will charge it to a lower voltage, say 3.7 or 3.8 volts. What do you think of a discharger?

[Externet]

If a single 18650 lithium cell reaches 4.2V by charging; it is exactly what you want. It is like that and it is the way it should be. Calling them "3.7V" cells is not a precise term.
Some lithium cell chemistries stay at 4.2V after charging; some decrease to 3.7V. Both behaviors are normal and OK. Just use them and forget a charger to a lower voltage or discharger.

[dacflyer]

4.2v is typical for charging, some hard core battery guys will suggest 4.1v
But after charging the battery will settle down to it's 3.7v or so. depends on the chemistry.
many of these cells have a really long life if charged properly. I been messing with them a while now.

[haklesup]

search ebay using this term "liion charger module" for a range of solutions at low cost.

Charging voltage is always greater than the operating voltage, you seem to want a charger that will shut down once full charge is detected and come back on periodically for maintenance charging. For maximum life maintain between 80% and 20% of charge capacity as a rule of thumb but you'll find a lot more qualified advice if you search.

Look also at the DC-DC converters, some are pushbutton adjustable with LED displays if you want a more manual/configurable setup,

If you are serious about understanding the charge flow, then a USB current meter is a very useful tool. I mentioned this in another thread but this is a great tool. Look for the one with the color display and extended voltage range, it measures charge and other useful parameters.
https://www.ebay.com/itm/USB-Current-Vo ... 4275005846?

[dacflyer]

i think i found what will be useful to me,, found a few nice meters.
one is an 8s balancer meter, and another is like a watt meter, good for up to 55V, and and i been reading up on active balancing v/s passive balancing.
Active balancing seems to be the better method.
I'll be shopping around now for prices.

[haklesup]

I think I know what you mean. I got a panel mount one I was going to put in my explorer to monitor the battery but it was for charge or discharge only (one way) So I need to get back to that project someday and buy the bi-directional meter or wait for a Bluetooth enabled version so I don't have to mount it anywhere visible.

[dacflyer]

i got one of them Chinese knockoff DROK meters, they are bi-directional and they have a BT version as well.
I'm still trying to get the AMP meter section calibrated.
https://www.amazon.com/Charge-Discharge ... B07YWVCBRN
Have a look.

I scored some free Hybrid batteries yesterday.. 6 modules.. 60V ea.. @ 16 cells ea
they check out good, I think they changed the batteries before they found the real problem. But either way.. they were feebies.

[haklesup]

That's a nice one. I hadn't seen the hall sensor for DC yet. I never was comfortable putting a sense resistor in series with the car battery. Looks like it may be a little less precise than the sense resistor types but that's still adequate for many applications. A little thought needs to go into range and accuracy when a module is chosen.

[dacflyer]

i bought this one with the hall sensor, and i have followed the bad instructions....there's actually a forum on this thing,, the Drok meter forum, even tho this is a knock off unit. it's all the same.
I'm having calibration issues. when i get it like i want, it seems like it'll drift
you have to calibrate the voltage 1st, then the current.
I'll give it another whirl, then i might throw it across the room,
there's gotta be something better and simpler to use.

[haklesup]

Simpler would have been one that uses a sense resistor. Sounds like you found its Achilles heel. What load are you testing, I would expect a hall sensor to do better at high current and a sense resistor to do better at low current and better linearity across the whole range. When I just looked at the photo, I thought it was an AC tool at first.

Maybe there is a way to replace the hall sensor output with the sense resistor?
Which of the 3 hookup diagrams from the amazon ad are you using, self powered or externally powered mode?
Do you know the signals on the white ribbon cable? if you do, I bet you could figure out how to substitute a sense resistor

[dacflyer]

externally powered..
and it has a hall sensor..
no idea on the pin connections..