How do you know that it's the internal resistance that's limiting the current and not internal charging circuitry? I think that you jumping to the simple/easy conclusion while the reality is much different.
There is nothing else between my voltage source and cell. When connected, the voltage is at 4.3V, when separated, the cell voltage is at 3.8V. There is no other internal circuitry.
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Most USB chargers didn't stick to the standard.
Typically they could output currents up to their capability and would indicate that to the device by doing things such as shorting the data lines or using resistors to set a specific voltage.
Samsung and Apple did it differently.
kw
Except that the cell itself can have circuitry.
No, they are bare cells. I opened up some just to be sure.
If the cell cannot store more charges and turn them into heat, then by definition is the internal resistance. Most chargers avoid it by lowering the voltage or current, but doesn't mean the IR limitation is not there.
Are cars driving at 55MPH because the cops are there, or because there is a speed limit?
Default dumb USB chargers are typically 5v nominal at 1A or 2A current limited by the supply PSU.
Anything beyond that and the client device has to negotiate with the charger to get either higher current or higher voltage or both. I have lost track of which combinations are allowed and accepted these days.
I have various USB "fast" chargers in various Android and Apple flavours and some will do fast charge with certain devices and not with others. It is a bit suck it and see but the worst you are ever likely to see is a warning "device is charging slowly - use original lead and charger".
On Thursday, 18 November 2021 at 09:14:08 UTC-8, Martin Brown wrote: ...
The usual approach is to use resistors on the D+ and D- lines at the charging end to signal to the device the capability of the charger. There is no negotiation.
You do this all the time. You completely muck up the topic as if you knew nothing at all about electronics. What current will flow into your battery at 4.4V? How about 4.5V? How about 5V? There is nothing that says the voltage is set to a single value. As I've said, batteries are often initially charged at a rate set by current rather than voltage.
No one cares what you are doing. Normal devices use an internal charger matched to the battery so as to not overcharge it either by voltage or current. I've always heard that 1C is optimal (low wear and yet fast) meaning 1 hour, but that is a current setting and only provides a portion of the charge before it is switched to voltage control. In the voltage control stage the current drops off asymptotically and so can take a larger share of the charging time compared to the current controlled phase for the amount of charge provided. Lithium batteries suffer most of their wear in the final 10 to 20% of the charging cycle, so not topping off not only saves time it gives the batteries a longer life.
No one cares what you are doing. You are not a phone or other electronic device which is what was being discussed when you made your erroneous statement.
USB "chargers" are not chargers, they are powersupplies, the charger is integrated in the device
Fine. Nobody needs to follow what i do. All i am saying it that beyond 60% SOC, internal resistance is the thing limiting charging rate. It doesn't matter what voltage you are setting. The charging rate is limited by IR. You are saying charger is the limiting factor, but in fact it is trying to avoid the real limiting factor: internal resistance.
On Thursday, 18 November 2021 at 11:06:35 UTC-8, Ed Lee wrote: ...
Yes, beyond about 50-60% SOC the charger would typically use constant voltage charging where the internal resistance does control the charging current. However, the current is still being measured by the charging circuit and if it attempted to go above the limit set by the battery or the source the charger it would go back into constant-current mode.
The ultimate limit is not the current determined by the internal resistance but that determined by the battery characteristics, temperature, and power source etc. For example, at low temperatures, the charger would dictate a lower charging current and reduce the terminal voltage to meet that current limit.
kw
"It doesn't matter what voltage you are setting." Now you are showing ignorance of Ohm's law. I can't help you. You literally won't listen to anything anyone says that doesn't agree with you.
Often people forget that Ohm's law is just a relationship between the current and voltage in a circuit. We define the resistance by the ratio of voltage and current. The battery internal chemical operation is what defines the current flow at a voltage. We like to think we can describe this by Ohm's law, but for batteries it is a poor fit and is much more complex as you indicate by the variation with temperature for example. It will also vary significantly over time, not just as the battery charges, but when the battery is resting. Charge and measure the parameters, let it set and measure again and they will be different. That's why the internal resistance is not so useful. A battery is not a voltage source with a resistor. It is a chemical reaction with electrical properties.
Battery internal resistance is a function of SOC and temp, not a fixed resistor. Resistance is defined as turning voltage and current into heat, rather than charge storage. Fine, if you want to call it something else, but i see it as internal resistance to charging.
On a sunny day (Thu, 18 Nov 2021 11:16:46 -0800 (PST)) it happened " snipped-for-privacy@kjwdesigns.com" snipped-for-privacy@kjwdesigns.com wrote in snipped-for-privacy@googlegroups.com:
I usually charge batteries on my lab supply (set voltage and curent limit), for example with eneloop 1.5V AAA charging at 1.6V 1C you will see a clear temperature rise when the cell is full. Normally one should measure that and switch the charger off.
There are charging ASIC that will fully charge cells to 100% with auto shut-off, but problem is that it only charge at maximum of 300mA and it would take hours to charge.
My current device must be charged in 15 minutes or less; so, just a fixed voltage source using 40% capacity of the cell. Beyond that, the "Internal Chemical Resistance to Charging" limits the charging rate. Don't call it Internal Resistance, as per Internet Police.
You can never try to understand what someone is telling you. The internal resistance does not limit the current absolutely. You said you were charging at 4.35V or something. Up the voltage and you will see a faster charge rate. You may not like the accelerated wear, but it will charge faster. Even a 15 minute charge rate is likely to wear the cells faster unless they are specially designed to charge fast.
The voltage source is not easily adjustable. Increasing voltage also runs the risk of overcharging the cell. At 4.3V, it will fully charge the cell after days, if left connected accidentally. The device will not be cycled often; so, wearing it out at 2C or 3C should not be a problem.
I'm not suggesting you should do anything. I'm trying to get you to understand that what you are saying is not factual. You are trying to tell others wrong information. You can never get your head out of your own details to understand the conversation you are in.
That's all I have to say on the matter. Enjoy.
On a sunny day (Thu, 18 Nov 2021 12:07:38 -0800 (PST)) it happened Ed Lee snipped-for-privacy@gmail.com wrote in snipped-for-privacy@googlegroups.com:
OK, what I forgot to mention is the volatge drop (when charging current limited) that happens when the cell is full (there is a name for that, delta V or something?) and normally used by chargers to detect 'battery full'. Get your battery cherging curves from the internet (google). I have made charge curve pictures for all my battery types. nimh_charge_curve.png eneloop_800mAh_AAA_charge_discharge_curve.gif lifepo4_charge_curve.jpg etc
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