Having conceptual trouble with charging speed.

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Yes, "CC/CV"(-ish) algorithm largely accounts for the difference

Check out its charging curves, here ...

https://lygte-info.dk/review/Review Charger Nitecore Digicharger D2 UK.html

... if you like

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Yes, everything is a trade-off ... features, flexibility, power, heat, reliability, cost, etc, etc

Isn't CV/ CC for charging li-ion ....shouldn't the eneloops be charged at .5 amps the whole time?

jimbo231 said:

Isn't CV/ CC for charging li-ion ....shouldn't the eneloops be charged at .5 amps the whole time?

Click to expand...

A lot of it depends on how full the batteries are when you place them in your charger.

If they're partially full, whether li-ions, or NiMH, they might be in the slower stage of the charging algorithms.

Chris

Oops, didn't notice you were referring to 'loops, sorry

Still, looking at the graphs at the link is instructive ... looks like that charger is generally delivering a bit less than "rated" current.

There is also a fair bit of "noise" / pulse / fluctuation that may be slowing things down some.

And, of course, heat losses and other inefficiencies.

I haven't tested anything of the kind, and haven't seen tests done, but I presume, perhaps in error, that the losses in the system as a whole would increase with increasing charging current as well. Whether it's linnear or following another scale, I don't know.

Almost tempted due to lack of nothing better to do, to do some tests with charging a cell on my C9000 starting with very low charge current, and ramping it up to see the various time differences as compared to the ideal situation with no losses.

I'm sorry to tell you. . . In order to get 1900 mAh out of a battery, you always have to put more than 1900 mAh in. We're bump up against the laws of thermodynamics here.

c_c

Curious_character said:

I'm sorry to tell you. . . In order to get 1900 mAh out of a battery, you always have to put more than 1900 mAh in. We're bump up against the laws of thermodynamics here.

Click to expand...

This is indeed true for NiMh chemistry, i.e. unlike Li-ion, its charge (Coulombic) efficiency is not 100%, so you need to put more charge in than you get out. Actually they are 100% charge efficient below 90% SOC, e.g. see AA Cycler's NiMH Charge and Energy efficiency graphs for Eneloops.

Gauss163 said:

This is indeed true for NiMh chemistry, i.e. unlike Li-ion, its charge (Coulombic) efficiency is not 100%, so you need to put more charge in than you get out. Actually they are 100% charge efficient below 90% SOC, e.g. see AA Cycler's NiMH Charge and Energy efficiency graphs for Eneloops.

Click to expand...

Thanks, I stand corrected. The energy efficiency must be less than 100% but in some cases as you say, the Coulombic (amount of charge) efficiency can be 100%. At 100% Coulombic efficiency, energy efficiency is less than 100% because the average charge voltage is greater than the discharge voltage.

c_c

hap124 said:

I figure this is one of those simple things where I am missing a fundamental understanding. I have a Nitecore D2 that charges 2 channels at 500mA each. When I put 2 AA 1900mAH Eneloops in it takes them 5.5 hours each to charge. Is it not as simple as dividing the capacity by the charging rate? I expected 4 hours max given the math. Is the extra hour and a half some ramping up and down thing that the charger doesn't display?

Click to expand...

No battery expert but the rate of charge seems to slow down near the end. Maybe those electrons are scrambling to reach their nose bleed seats. So the math never works out in my experience. I have tested this with my USB detector and it also applies to powerbanks, lithium ion batteries and other USB chargeable devices. Guessing the same is going on there as well.

jimbo231 said:

Isn't CV/ CC for charging li-ion ....shouldn't the eneloops be charged at .5 amps the whole time?

Click to expand...

Seems most of my chargers are doing 1/4 amps for NiMH. Some even lower. Again no battery expert just going by what the readings say. Some pulse charge NiMH. For example the O-light UC charges all Lithium ion batteries at a max of .75 amps but pulse charged eneloops at .25 amps. The Lii200 does .5 amps for 2 LSD NiMH. The goal zero guide 10 plus does around .80 amps for 4X NiMH.

Chargers slow down as they approach the max battery capacity, both for safety and also to fit as much energy as possible in it.
You can get faster chargers, such as the new BQ-CC55 from panasonic which is a lot faster than most nimh chargers I've seen around.