Checking Li-Ion battery voltage under load?

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Pete7874
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Checking Li-Ion battery voltage under load?

I’ve been re-reading HKJ’s article on Measurements , specifically, checking battery voltage under load. For alkaline cells, he adds a resistor to simulate load condition. I get that. But for Li-Ion he specifically states:

Quote:
The voltages for a LiIon must be measured without load

Why is that? Is it considered unsafe to measure Li-Ion cell voltage under load presented by a resistor? I guess you would need a fairly high current to see voltage dip on a Li-Ion cell? Is it just not necessary to check voltage under load for Li-Ion cells?
Edited by: Pete7874 on 01/12/2018 - 08:23
WalkIntoTheLight
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He’s saying if you want to estimate remaining capacity, then you have to check the lithium-ion resting voltage. A voltage under load won’t give you much information about capacity.

pennzy
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While we are talking lithium-ion , is it alright to fast charge 18650 at 3 amps ?

sbslider
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WalkIntoTheLight is correct. However, measuring the voltage of a LiIon under load can be useful. You can tell something about remaining capacity if the cell is near no capacity remaining. The voltage will begin to drop off very quickly down to 3V and below. If you see this, then you should remove the load and charge the battery back up again. If the voltage drops much below 3V, (below 2.8 maybe, 2.5 definitely) then it would be wise to understand more about the specific battery chemistry being tested prior to recharging the battery. Discharging a LiIon battery to too low a voltage can be dangerous.

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HKJ
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WalkIntoTheLight wrote:
He’s saying if you want to estimate remaining capacity, then you have to check the lithium-ion resting voltage. A voltage under load won’t give you much information about capacity.

That is because the remaining capacity tables are based on no-load measurements.
It would be a lot more work to make a table based on a specific load for a specific cell chemistry and wear of the cell.

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bilakos10
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pennzy wrote:
While we are talking lithium-ion , is it alright to fast charge 18650 at 3 amps ?

Yes, most modern cells (INR, IMR chemistries) should be able to handle a charging current of around 1C.
Though, before doing anything you should try looking at the manufacturer’s specifications.

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pennzy
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Thank you .

Pete7874
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Thanks all!

WalkIntoTheLight
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gauss163 wrote:

Not true. One can get compute very precise information about SOC from voltage under load if one has access to sufficient data – as do some fuel gauges (e.g. see TI’s impedance tracking algorithm).

However, it is much easier to do this when the battery is relaxed.

The cited remarks in HKJ’s article are (as often) misleading. Maybe he will explain what he thinks he is achieving by measuring alkaline under load but not measuring Li-ion under load.

Well, okay, but given nothing other than a “lithium-ion” battery description, I think HKJ is correct in saying measure it at rest. It won’t give you a perfect measure of capacity, but it will be better than trying to guess what the discharge curve looks like under a specific load.

Besides, if you’re going to go to all the trouble of measuring it under load, and having to know all the variables involved, you may as well just do a discharge test and measure its capacity with 100% accuracy.

Pete7874
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WalkIntoTheLight wrote:
Well, okay, but given nothing other than a “lithium-ion” battery description, I think HKJ is correct in saying measure it at rest. It won’t give you a perfect measure of capacity, but it will be better than trying to guess what the discharge curve looks like under a specific load.

But then why measure alkalines under load? How is that more useful if we don’t know their discharge curves either?
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But he does do discharge curves under loads.
Those are (i.m.o.) the most useful of the graphs
(or am i missing something?)

Q

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gauss163 wrote:
WalkIntoTheLight wrote:
[…] Well, okay, but given nothing other than a “lithium-ion” battery description, I think HKJ is correct in saying measure it at rest. It won’t give you a perfect measure of capacity, but it will be better than trying to guess what the discharge curve looks like under a specific load.

But that doesn’t answer the OP’s question as to why HKJ is (apparently) attempting to infer capacity/SOC of Alkaline differently from that of Li-ion – one under load and the other unloaded. Nothing is said there about that. As we see here – this may prove confusing to novices.

It is not only me that is doing that, but just about everyone in the world.
For some batteries it is easier to get an estimate of remaining capacity when they are measured under load.

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WalkIntoTheLight
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gauss163 wrote:
But that doesn’t answer the OP’s question as to why HKJ is (apparently) attempting to infer capacity/SOC of Alkaline differently from that of Li-ion – one under load and the other unloaded. Nothing is said there about that. As we see here – this may prove confusing to novices.

Yes, that’s a good point. I don’t know the answer as to why he uses a load-method for alkalines.

IMO, you can easily tell if an alkaline has full capacity: it measures 1.6 volts. Empty, it measures 1.0v or less. In-between is tougher, but most devices use a linear approximation between those values. It might not be highly accurate, but it seems good-enough for most purposes.

Well, it’s probably most accurate in low-drain applications. Maybe it doesn’t scale well to higher-drain applications like flashlights.

Yeah, I don’t know why he’d use a load for alkalines and not for lithium-ion, or vici-versa.

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gauss163 wrote:
Popularity has little to do with accuracy of science. The majority of “the world” has little knowledge of battery electrochemistry,

The majority of manufacturer that make battery testers may know something about the chemistry.

gauss163 wrote:
Please explain what you think you are achieving in the cited page by measuring Alkaline under load but Li-ion unloaded. Are you simply blindly following someone else’s techniques or do you have some logical (scientific) explanation for doing so?

If you have a “logical (scientific) explanation” then post it, instead of hunting me.

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If you believe you know something, why not post it, instead of you silly antics.

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gauss163 wrote:
HKJ wrote:
If you believe you know something, why not post it, instead of you silly antics.

Scientific methods are far from “silly”. Doing the analogous tests for Alkaline cells will allow you to learn the answers to these questions – with hard data to back up the conclusions. Moreover it will provide much useful information to your readers.

Since you do not post the answers, it must be you that do not know why (If you know why it is “silly antics” from you).

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hIKARInoob
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What is up HKJ?

gauss163 wrote:
The cited remarks in HKJ’s article are (as often) misleading. Maybe he will explain what he thinks he is achieving by measuring alkaline under load but not measuring Li-ion under load.
gauss163 wrote:
Please explain what you think you are achieving in the cited page by measuring Alkaline under load but Li-ion unloaded. Are you simply blindly following someone else’s techniques or do you have some logical (scientific) explanation for doing so?
gauss163 wrote:
I cannot possibly explain the unwritten logic behind your methods since I cannot read your mind. The best I can infer from what you wrote above is that you are attempting to blindly mimic some battery testers, but you don’t understand why the battery testers use this method for Alkaline vs Li-ion. Is that correct?

It’s quite unfortunate that gauss163 does not contribute to this topic. It really does look like he just wants to attack you.

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gauss163 wrote:
hIKARInoob wrote:
It’s quite unfortunate that gauss163 does not contribute to this topic. It really does look like he just wants to attack you.

Scientists attacks pseudoscience. It’s the nature of the beast. If you can’t explain why you believe something is true then you are pulling rabbits out of hats. But magic is not science.

Scientists do not attack pseudo science.
Scientists conduct science (so why aren’t you sharing your thoughts about this topic?)
HKJ is not a pseudo scientist because he does not answer your questions.
Following protocols is part of science. Following protocols is not the same as “simply blindly following” something.

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While no-load voltage is needed to estimate the remaining capacity, voltage under load would still be useful information, as it relates to the battery’s performance under load. Voltage sag is often talked about when comparing similar batteries, and lower voltage sag is one of the reasons people prefer the Sony VTC6 over the Samsung 30Q, and the 30Q over the LG HG2. But people always talk about it in a general sense, without much in the way of data to back it up.

I have no idea how you would collect or display the data, but hard information about the voltage under, say, 5, 10, 15, and 20A loads would be useful for comparing similar batteries, particularly high drain batteries intended for demanding applications.

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Delta_V wrote:
While no-load voltage is needed to estimate the remaining capacity, voltage under load would still be useful information, as it relates to the battery’s performance under load. Voltage sag is often talked about when comparing similar batteries, and lower voltage sag is one of the reasons people prefer the Sony VTC6 over the Samsung 30Q, and the 30Q over the LG HG2. But people always talk about it in a general sense, without much in the way of data to back it up.

I have no idea how you would collect or display the data, but hard information about the voltage under, say, 5, 10, 15, and 20A loads would be useful for comparing similar batteries, particularly high drain batteries intended for demanding applications.

HKJ already does all that in his reviews.

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A lot of Gaussian noise in this thread.. Wink

But i’m confused right now.
I always look at the discharge curves, which i assume are V/t diagrams (or rather V/Ah diagrams) made of measurements under load.
Or did i miss something?

Q

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Jerommel wrote:
Or did i miss something?

Only who is doing the posts.
Information level will increase when gauss163 leaves, he has something against posting knowledge. He probably believes it is better for you to spend a couple of hours searching for information, than it is if he post it.

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Jerommel wrote:
A lot of Gaussian noise in this thread.. Wink

But i’m confused right now.
I always look at the discharge curves, which i assume are V/t diagrams (or rather V/Ah diagrams) made of measurements under load.
Or did i miss something?

That’s how I interpreted them too.

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gauss163 wrote:
hIKARInoob wrote:
Scientists do not attack pseudo science.

They have no choice but to when they are attempting to teach the general public. But not every scientist has the extreme patience and thick skin needed for debunking popular pseudoscience.

Again: scientists do not attack pseudo science. Scientists do not teach the general public; scientists conduct science and publish their findings. For example teachers teach the general public. Scientists do not need extreme patience and thick skin for debunking popular pseudo science. That is because it is not their job to do so. Again, a teacher for example could need extreme patience and thick skin to teach a class.

So basically you do not understand the role of a scientist.

gauss163 wrote:
IKARInoob wrote:
Folllowing protocols is part of science. Following protocols is not the same as “simply blindly following” something.

It seems you are misunderstanding something. Above “blindly following” refers to believing that Alkaline cells must be tested under load only because (some) battery testers do it that way. That does not constitute scientific proof that it must be done that way. Nor does it shed any light on the underlying science governing the matter, e.g. why Alkalines are any different from Li-ions in this regard..

Oh no gauss163 I’m not misunderstanding! It is not up to HKJ to give you any scientific proof that Alkaline cells must be tested under load! It is not up to HKJ to shed any light on the underlying science governing the matter.

gauss163, it looks like your background is not science, as you’re making a lot of false statements. Nevertheless you accuse HKJ’s work as pseudo science.

This is how it’s done in science:

You accuse HKJ of pseudo science as you severely imply, then you deliver the unambiguous evidence it is so. It is certainly not up to HKJ to answer your questions.

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gauss163 wrote:
How very sad, instead of explaining your beliefs you instead post unfounded ad hominem attacks on those who try to enlighten you – just as you did when I tried to teach you about Tesla’s and Philips fast-charging algorithms. Keep behaving like that and you’ll soon have no more scientists left here to learn from. But maybe that’s what you desire. Be careful what you wish for ….

If you try to enlighten me you hide it very well.
I do generally not count snide remarks or “use google” as enlightenment.

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Guys….

Let’s give it all a rest for now.
Start over next time, without the attitude, anger and frustration. (you know who you are)
This sucks.

Q

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gauss163 wrote:
On fast-charging I gave you many links to scientific literature

Not many and many of the links you posted where behind paywalls. You also posted links that was only google searches.

What you obvious never understood was that just because a scientist succeed in fast charging a battery, it is not the same as every charger on the market can ignore the manufacturer specification for all batteries and fast charge them.

What I post is usual backed by research and often done by me.
I do not see any reason to explain anything to you, you have never posted any research you have done, but you frequently complain about my postings, without showing any research against it.

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Follow-up question: Can voltage under load be measured in a flashlight? Another words, using the flashlight and its LED as an alternative to a resistor?

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Yes. How easy it is depends on your light. The Olight S1R ( and a few other similar lights) bring the battery voltage to the outside of the light. This makes it very easy. I did some test on my light / battery, see this post

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Pete7874
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Thanks. One question about this: when measuring voltage under load in a flashlight, I do not see the LED light up, so where is all the energy going? What is absorbing it if there is no dedicated resistor?

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Measuring voltage of a li-ion is only a estimate of what capacity is in the battery unless you have already collected data on the particular cell you are using. li-ion’s usually dont have the same discharge curve. You can take two li-ion’s of a different make and compare them in HJK’s graph’s. Say a Sony US18650VTC6 at a 5 amp load, cell voltage at half capacity is around 3.65v. Compare a NCR18650A, at the same 5 amp load half capacity is 3.25v a .4v difference. Using HKJ’s graph’s has data to improve the guessing of your capacity of a cell. Even resting voltages vary between cells, that’s why it has always been considered a estimate.

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