Is Big Clive right about lithium battery charging?

[sleemanj]

There are two competeing considerations at play, and I think this is a large part of why people disagree on this, some people have a focus on longevity of the cell (loss of capacity over time), and some people have a focus on safety of the cell (not setting your house on fire).

"Float charging" if you like to call it that, having a 4.2v supply connected to a cell which is sitting at 4.2v, is perfectly safe, but it could conceivably cause an accellerated reduction in capacity (aging) over time (at least anecdotally, I don't know the actual research).

It gets worse when the "longevity" people think because it's not as good for longevity that it must be bad for safety.  And the "safety" people think that because it's perfectly safe that it must be fine for longevity too.  These two don't necessarily correlate!

Personally, I go for the "it's safe" position, I don't care about capacity loss.

But in any case, a TP4056 is hard pressed to maintain an amp at the best of times anyway.  A P-Fet bypass to provide the load directly from a connected supply is pretty trivial.  It's kinda weird that none of the chinese TP4056 boards include one, and yet for powerbanks almost universally power the load directly from a connected supply.

[IanB]

It's kinda weird that none of the chinese TP4056 boards include one, and yet for powerbanks almost universally power the load directly from a connected supply.

I think power banks have changed a bit since the early days? I thought the early ones with a cylindrical form factor just had one single USB A port? I suppose the newer ones with multiple USB ports can be charged through one port while loaded through the other?

My favorite USB power bank is going to be this one:

https://www.ryobitools.com/products/details/33287177264

It doesn't have all the latest USB standards, but it is powered by a massive tool battery and it is 85% efficient, so a 4 Ah tool battery can provide about 12 000 mAh at the 5 V USB output (4000 x 18 / 5 x 0.85).

If the battery runs out, you can just swap it for another one, no recharging necessary. It is not, of course, suitable for air travel.

[Siwastaja]

"Float charging" if you like to call it that, having a 4.2v supply connected to a cell which is sitting at 4.2v, is perfectly safe, but it could conceivably cause an accellerated reduction in capacity (aging) over time (at least anecdotally, I don't know the actual research).

Yeah, but if the alternative is microcycling the cell between 4.20V and 4.00V, this is (probably, I'm not sure!) going to be even more detrimental to the lifetime.

According to my own tests plus others I have read, you really have to go low enough storage voltage, say 3.90V and below, to get any significant decrease in calendar fading.

In any case, you are absolutely right, and if one wants to design a long-life "float" application, you can choose a tad larger cell and float it at 3.8-3.9V or so.

[Peabody]

A P-Fet bypass to provide the load directly from a connected supply is pretty trivial.  It's kinda weird that none of the chinese TP4056 boards include one, and yet for powerbanks almost universally power the load directly from a connected supply.

Yes I've always thought it was strange that the module makers of the Far East don't seem to know about power sharing.  You even have combination charger and boost converter modules, but they don't have power sharing either.  There are some charger ICs with that feature built into the chip, but they don't come in hobbyist-friendly packages, and few if any modules use them (maybe Adafruit is an exception, but that would not be low cost).

[amyk]

A P-Fet bypass to provide the load directly from a connected supply is pretty trivial.  It's kinda weird that none of the chinese TP4056 boards include one, and yet for powerbanks almost universally power the load directly from a connected supply.

Yes I've always thought it was strange that the module makers of the Far East don't seem to know about power sharing.  You even have combination charger and boost converter modules, but they don't have power sharing either.  There are some charger ICs with that feature built into the chip, but they don't come in hobbyist-friendly packages, and few if any modules use them (maybe Adafruit is an exception, but that would not be low cost).

Because they know it's not necessary and just increases cost?

[SiliconWizard]

Or maybe define "module makers". Or whatever.
Just because there are zillions of modules, mainly targeted at hobbyists, made around the TP4056 (which itself comes in various clones, with slightly different characteristics, fun stuff), doesn't mean that this is the only asian chip available or that it is even relevant. Yes, there is a life beyond the TP4056! Believe it or not.

[Peabody]

A P-Fet bypass to provide the load directly from a connected supply is pretty trivial.  It's kinda weird that none of the chinese TP4056 boards include one, and yet for powerbanks almost universally power the load directly from a connected supply.

Yes I've always thought it was strange that the module makers of the Far East don't seem to know about power sharing.  You even have combination charger and boost converter modules, but they don't have power sharing either.  There are some charger ICs with that feature built into the chip, but they don't come in hobbyist-friendly packages, and few if any modules use them (maybe Adafruit is an exception, but that would not be low cost).

Because they know it's not necessary and just increases cost?

Well, even if power sharing isn't necessary, it would prevent the cycling between 4.2V and 4.1V that occurs when the load current is less than the termination current.  And it would eliminate any potential startup issues if the battery is discharged to below 3V and the load current is greater than the initial float current.  Some might want those benefits.