Parameters defining the charging rate

[Electroenthusiast]

I was charging my cellphone from a wall wart, and through the USB cable, and through a low rated wall wart. What i find was that the speed of charging was different with different wall warts, and one charging cable doesn't seem to charge so fast when i connect it to the PC.

On what does the charging time depend on? Does using a cheap cable increase the charging time? If so? How? Since voltmeter always show zero resistance.

 

[Nigel Goodwin]

Perhaps you knew as I did from Battery University long ago that time spent during CV mode after CC severely reduces life cycles. This remaining capacity is < 20% and if the charger and phone is used simultaneously, this may extend the time during CV mode.

Basically, fast charging provides less charge in the battery (it cuts off sooner) and also reduces battery life - personally my designs use more gentle slow charging, and charge to a higher percentage.

However, I appreciate the requirement for devices like phones to charge quickly, at the expense of how well the phone is charged, and reduced battery life.

 

[Electroenthusiast]

rjenkinsgb All i knew was USBs use 4 terminals, utmost 5 terminals if it was USB 3.0. Where did so many terminals come from? Don't understand that.

My question was the top pins and bottom pins of plug/socket should be symmetrical.

Nigel Goodwin Most of my engineer friends know that fast charging reduces the life of battery, but i doubt slow chargers are available in the market to buy and use them for overnight charging.

I have a old one, which came with some mobile phone (rated 1A max.) which i use for overnight charging. It charges up the mobile mostly to the fullest at the time of sun rise/ wake up. How can anyone make sure that they are buying slow chargers, since the market is now mostly filled with fast chargers?

Tony Stewart Can you explain CV mode and CC mode? I mean especially the abbreviation.

 

[Nigel Goodwin]

rjenkinsgb All i knew was USBs use 4 terminals, utmost 5 terminals if it was USB 3.0. Where did so many terminals come from? Don't understand that.

My question was the top pins and bottom pins of plug/socket should be symmetrical.

Nigel Goodwin Most of my engineer friends know that fast charging reduces the life of battery, but i doubt slow chargers are available in the market to buy and use them for overnight charging.

I have a old one, which came with some mobile phone (rated 1A max.) which i use for overnight charging. It charges up the mobile mostly to the fullest at the time of sun rise/ wake up. How can anyone make sure that they are buying slow chargers, since the market is now mostly filled with fast chargers?

Again, it's down to the phone to set the charging current - just don't buy a high current PD type supply.

The phone will still fast charge regardless, just not overly fast.

Tony Stewart Can you explain CV mode and CC mode? I mean especially the abbreviation.

Constant Voltage and Constant Current.

Charging Li-Ion starts with CC, then switches to CV once the voltage threshold is reached.

 

[rjenkinsgb]

My question was the top pins and bottom pins of plug/socket should be symmetrical.

They are rotationally symmetrical in the sockets.

The D+ & D- are for compatibility with four pin USB, those are the two data wires. They are cross-connected in each socket, so it does not matter which way around the plug is.

For the others, look at the socket - they are always the same or equivalent signal, whichever way around the plug fits.

USB-C has multiple separate ground and power pins, separate contact pairs for configuration control and either two (like USB3.x) or four extra high speed data pairs, capable of supporting either 5 or 10 Gigabit data throughput.

If it's used with a cable that does not support all the signals, it will fall back to the best mode that works, down to basic two power and two data pins for basic USB if that's all that is available.

With anything above that, the two ends of the link will negotiate which pin pairs to use for best throughput.

It's not a fixed pin-to-signal system, like older USB - the same USB-C socket may be multiplexed with eg. DisplayPort or Thunderbolt devices, with it switching modes dependant on what type of device is on the other end of the cable.

 

[Tony Stewart]

The CV mode starts after the CC mode reaches 4.2V then the current reduces to a low % of the CC to determine the cutoff. But if the screen is on max brightness and under a heavy load, this may extend the time the charger supplies 4.2V. So it is not a matter of slow vs fast charging during CC mode that I made this comment, but deferring the time to use CV mode until overnight when the user is less likely to have the phone active in order to minimize the time spent charging at CV. After the CV current drops below 5% of the CC rate. this is the most common threshold to say the charge is complete. But after the battery gets loaded, it quickly drops from 4.2 to 3.8 to 3.7V while at 100% capacity. So this voltage range is not useful for measuring Sate of Charge (SoC). it is important to do some current or coloumb counting method to compute the SoC calculations so that this voltage hysteresis does not trigger the charger to keep turning on and boosting the voltage to 4.2V again then cycling back to 3.8V when the phone load is active. This causes more chemical degradation of the cell than and is not as useful for restoring charge near the top 10% capacity. It gets complicated due to the many ERS*C time constants that describe battery storage behaviour with the double-electric layer effects. This is one of the reasons why charging rates often use a 80% limit for time because the last 20% is slower but the time must be minimized and this software change is necessary to know when the phone is not active from the user history is one step to extending battery life.

Of course, a slow 8W USB port charger is also effective but not if the phone is in use during the SoC>80% AND the phone is in use AND does not have this software upgrade. If you are not mobile, it might make more sense to use a low-capacity charge part while the phone is in use, so that the phone effectively runs off the USB port while you are at a desk and keep it charged at 70%. This way the battery would never be used but then how would the phone know the user's habits to predict when he/she needs 100% capacity or prefers to get longer battery life and just stay at 70% with float charge just to power the phone. This is just above the ideal long-term storage capacity of 66% which is the SoC most often shipped from the factory.

So smart charging depends not only on voltage, SoC, load rate, time of day and usage history to figure out how to choose a method that trades off between capacity for lifespan, or convenience and inconvenience. These smart parameters will evolve to minimize temp rise in the cell, idle screen blank times, and notification sleep rates while advertisers continue to suck up all your extra life with an unwanted waste of energy.

 

[Electroenthusiast]

Nigel, Is 25W PD a high power/current PD supply? Almost all the chargers nowadays come with rating of 3A. How do i choose the Charger now? How will it fast charge if i had 5V 1A charging adapter? Just don't understand the exact point. Again, a 25W PD adapter means that it can deliver current upto 5A at 5V (under constant Voltage).

Tony, CV mode or CC mode is not in my hands. It depends on the software and and the state of the battery/battery charge at the moment. I never knew that chargers acted so differently. Now, my question is do all chargers start with CC mode and end up to CV mode, or are these most advanced chargers specially designed for Li-ion batteries. I'm sure this is a latest development, and was not there few years ago.

In regards to the choosing the right charger, i am still not sure how i can buy one which is safe charger and not fast charger. I think in a few days, it would be hard to find a adapter which is not a fast charging type. Specifically, how do i understand that at someone's place, a mobile charger of theirs is safe for use for my cell phone device (just by looking what is mentioned on it)?

 

[rjenkinsgb]

Specifically, how do i understand that at someone's place, a mobile charger of theirs is safe for use for my cell phone device (just by looking what is mentioned on it)?

If it has a USB socket, it is safe to use with anything that has a USB plug; that's the whole idea - compatibility.

As with any set-voltage power system, the current rating or capability of the source does not matter, as long as it is adequate for the load.

The load will draw the same current weather the source can only just match that or is capable of 5 x or 500 x as much

The phone internal charge system handles the battery control regardless.

 

[Nigel Goodwin]

Tony, CV mode or CC mode is not in my hands. It depends on the software and and the state of the battery/battery charge at the moment. I never knew that chargers acted so differently. Now, my question is do all chargers start with CC mode and end up to CV mode, or are these most advanced chargers specially designed for Li-ion batteries. I'm sure this is a latest development, and was not there few years ago.

All 'chargers' for Li-Ion batteries work this way - it's simply how Li-Ion is charged, for serious safety reasons.

You're still confusing yourself by referring to the power supplies as 'chargers' - they aren't chargers at all, the charger is inside the phone. As long as the power supply can supply the correct voltage (5V by default) then the phone will sort everything out.

If you don't want fast charging, first off don't buy PD supplies, and look for something that says '5V 1A' or '5V 2A' on it.

 

[Electroenthusiast]

Thanks. I now understand this, and it is the charger that is present inside the phone that controls the charging of Li-Ion battery no matter what power supply (old/new/PD/USB) it is fed with. So, even with a normal USB power supply, the CC and CV does work (?).

So, if i buy a 5V 1A power supply, which doesn't mention anything as PD, i can use it for overnight charging(?). Just asking, does the Power Supply units mention whether that is PD or normal one?

 

[rjenkinsgb]

So, if i buy a 5V 1A power supply, which doesn't mention anything as PD, i can use it for overnight charging(?). Just asking, does the Power Supply units mention whether that is PD or normal one?

You can use any, PD or not. It makes no difference.

The CC/CV charging is nothing new, pretty much all battery charging systems newer than the old fixed-charge-time setups use that in some variation.

The battery life things you can control are:
Trying to reduce the "span", eg. keep it in the 20% - 80% range rather than 0-100%

And even more important, not leaving any lithium battery device on charge after it is fully charged.
Charge it then run it on battery so it's at 100% for as little time as practical.

 

[Nigel Goodwin]

And even more important, not leaving any lithium battery device on charge after it is fully charged.
Charge it then run it on battery so it's at 100% for as little time as practical.

Surely any Li-Ion powered device will stop charging once it's full?, they don't trickle charge like NiCd or NiMh, they stop charging completely. Certainly all the ones I build do.

 

[rjenkinsgb]

Surely any Li-Ion powered device will stop charging once it's full?

Yes, but simply being left at or near full charge causes lithium cells to degrade far faster than if the average charge state is around 50%

From the Battery university page on prolonging the life of lithium cells, underline added:

Lithium-ion suffers from stress when exposed to heat, so does keeping a cell at a high charge voltage. A battery dwelling above 30°C (86°F) is considered elevated temperature and for most Li-ion a voltage above 4.10V/cell is deemed as high voltage. Exposing the battery to high temperature and dwelling in a full state-of-charge for an extended time can be more stressful than cycling.

For real-world examples, I know several people who insist on using laptops almost permanently on external power, that have had me get new batteries for them.

The batteries are typically useless again within a few months.

In comparison, mine typically last a good few years - I've only this year stopped using one I bought in 2009. (I write the year on each battery I buy & by newest machine uses the same battery as the previous one).

 

[Electroenthusiast]

Usually at work, when we use workstation, the issue of overcharging will be common.
At workplace, once we plug the laptop to the workstation stand, the laptop keeps on charging till the end of the day.

So, i think a lot of them would have the issue with it. But, with the latest OS upgrade, i think there are measures inculcated so that the battery doesn't get charged so fast after a certain extent.

 

[Tony Stewart]

CC>CV>Cutoff < x% of CC is standard in mobile phones and power tools. The difference is mobiles can be used while charging.

So it is critical to have dual current sensing. One for the battery, and one for the load. If the SoC is > 90% and the mobile is being used, how much should it apply for CV or CC just to the battery when the load is in high demand yet connected to the charger?

If the unit keeps cycling below 100% to 100% with CV, this will age the battery faster so some hysteresis algorithm may extend battery life.

 

[Electroenthusiast]

Well, i believe that the adapters use 7805 ICs to limit the output voltage. When you think of the normal old adapters, do they deliver constant voltage, or constant power? Because this would be important to know how they deliver current to the devices.

So, in that case, no matter the charging time (in old adapters), the power consumed will be constant for a constant power delivered adapter, regardless of the changeability of the electronic device.

 

[Tony Stewart]

Std USB Hubs for mobiles are 10 W or 12 W. Some have USB C for higher power as well. Some 4 or 8 port hubs might be 65 W limited total with 12W (2.4A) but all CV=5V but all current limited.

The loads still regulate demand.

 

[rjenkinsgb]

Well, i believe that the adapters use 7805 ICs to limit the output voltage. When you think of the normal old adapters, do they deliver constant voltage, or constant power? Because this would be important to know how they deliver current to the devices.

Even the cheapest ones are switched-mode PSUs, to minimise power dissipation and cost.

The output voltage is fixed. The power taken is down to the connected device, as long as it does not overload the 5V source.

As has already been mentioned, the battery charge control and load regulation, is within each device.

PD-type units can switch to different voltages IF the device that's connected is also PD compatible and requests that, but they also default to 5V for compatibility.

 

[Electroenthusiast]

I asked this because the multimeter shows sometimes a voltage reading such as 9V on no load (meaning reading through the terminals of adapter with no resistance (though doing this might seem ridiculous for electronic engineer).

 

[Nigel Goodwin]

I asked this because the multimeter shows sometimes a voltage reading such as 9V on no load (meaning reading through the terminals of adapter with no resistance (though doing this might seem ridiculous for electronic engineer).

If it's a non-regulated PSU, then it could very well read 9V without any load, but most now are light weight regulated supplies, using switch-mode technology.

 

[Electroenthusiast]

Yes. But, i think all AC to DC convertors have a zener diode at the load side to regulate the output voltage, or to provide a DC voltage across it. I did check the circuitry about both, and found that both had diodes at the load side.

Please do explain it if that is not the case.