Unexpected iMax Charger settings? (Chemistry Question)

[HKJ]

@gauss163

It would be nice if the nominal (i.e. label) voltage was precisely the average voltage. But this is simply not how it is used nowadays. So deeming it “wrong” is meaningless.

The Sanyo NCR18650GA has a 3.6V nominal rating and if you calculate the average voltage during a 0.2C discharge .my guess would be that the result is very close to 3.6V.
Because I only discharge to 2.8V I could not verify that. The average voltage I got at 0.5A was about 3.65V and 3.63V at 1A (0.2C is 0.67A).

[Jerommel]

@gauss163

@Jerommel

@Texas_Ace

It will charge to 4.2V as we desire.

But why do ‘we’ desire this?
Judging by the test results it’s not really worth it, a Li-ion cell drops from 4.2 V to 4.0 V in seconds, and from 4.0 V to about 3.3 V it’s got the actual capacity, and under about 3.3 V there’s also not much left

You’re comparing apples vs. oranges, i.e. open-circuit (no-load) voltage vs voltage under load. The voltage under load includes a voltage drop I*R due to internal resistance R. As soon as you remove the load (I=0) this component equals 0 and the voltage quickly rebounds back to the open circuit voltage.

Of course, but i was referring to the discharge graphs.
They show a steep voltage decline from 4.2 to 4.0 Volts, which is not because of the internal resistance, because then it would be immediate, not a decline over a short amount of time.
Or am i wrong?

[Jerommel]

@gauss163

@Jerommel

[…] They show a steep voltage decline from 4.2 to 4.0 Volts, which is not because of the internal resistance, because then it would be immediate, not a decline over a short amount of time.
Or am i wrong?

Yes, you are wrong, I explained how this works in the post above with the graphs. If you need further elaboration to understand that then please explain what points are not clear to you.

Those graphs didn’t ‘speak to me’ earlier, but now i see (better).
Still, there’s a ‘knee’ there, but it’s around 4.1 Volts.
I’m not sure about the recovery after charging cuts off, but i usually measure 4.15 V on a freshly charged cell, but that could be my charger…

Let’s consider the data in that post. It shows that at a 3A load the the decline from 4.2V to 4.0V uses only 2% of the cell capacity. But this does not imply that charging to 4.0V (vs 4.2V) loses only 2% capacity. Instead, as we saw, it loses about 15% capacity.

This has to sink in yet somehow… (in my mind that is…)
But thanks for explaining so far.

[Joshk]

Would you guys like to see the same cell capacity tested from 4.1 to 3.1 and then 4.2 to 3.0 on this charger?

[Texas_Ace]

If you really want full control of your new charger look into the Cheali Charger firmware

I talked about it in this thread, I love it: Serious battery charging station setups on a budget

[Joshk]

I don’t know that that is made for the version 2 charger.

[Texas_Ace]

@Joshk

I don’t know that that is made for the version 2 charger.

If it has the Atmega MCU it should work, thats the only sure fire way to know.

[Joshk]

@Texas_Ace

@Joshk

I don’t know that that is made for the version 2 charger.

If it has the Atmega MCU it should work, thats the only sure fire way to know.

Nope, a look at the Google group says in the V2 charger “the chip is megawin MA84G564”

[Texas_Ace]

Well, I guess that is your answer. You could get a basic version of the Imax and flash it, I keep thinking I should order another one while I can get them just to have around.

[Joshk]

What are the benefits of that firmware?

[Texas_Ace]

@Joshk

What are the benefits of that firmware?

Full control for one thing, you can also calibrate it to be exact, much more accurate, the ability to use external “probe” to sense actual voltage after the wire voltage drop allowing for internal resistant measurements that actually work and better charging. Plus just general improvements.

It is not a must have but if you like full control over all the details of your batteries charging, then it is lightyears better.

I like having full control lol.

[Joshk]

If you guys are curious to know - I had charged the batteries from my old laptop to only 4.1v out of caution many days ago. Today I decided I wanted 4.2 or flames. Each cell took another 110 mAh.