Charging with low power

A good sorce of information is Battery University. The page about charging LiPo does not answer your question, though.

Jan, I was referring to the question marking , not your suggesion. I thin I am one of the best ignorants in power management...

Enrico

Wish a good source for answers like your question.

Clem

I was looking for a good source, but did not find one either.

My gut feeling is that the answer would be "No", though...

This is a Panasonic document that outlines how to do charging of lithium ion batteries:

https://eu.industrial.panasonic.com/sites/default/pidseu/files/downloads/files/li-ion_handbook_22_10_15.pdf

If there's no temperature monitoring of the cell, you wouldn't try to charge (for the constant current phase) at more than 0.5 to 0.7C, though that would depend on the situation of the battery (if it were wrapped in expanded foam you might want to measure the temperature and make sure it wasn't getting too hot). Charging and discharging are both exothermic (some of the energy going in during charging or coming out during discharge ends up as heat in the battery).

Charging at a lower current will just take longer.

Ambrogio perhaps could have added a third state. As well as the constant current and constant voltage phases, the charger needs to know when to stop. That can be done in a variety of ways, but the most usual is to stop when the current falls to a percentage of the C rate - the Panasonic document gives the range 7%-10%, which in the case of Enricho's 500mAh battery is between  35mA and 50mA. If you don't stop, but try to trickle charge it like a lead-acid battery, you'll overcharge the cell. There's some leeway, the manufacturer includes a chemical buffer that means you can go beyond the 100% capacity point without damage, but go too far beyond and you'll seriously degrade the cell. If you can get the data on the charger, look at the data for the end point and see if it's reasonable. If you can't get the data, you maybe could try charging the cell and measuring to see at what current the charging stops (and stop it yourself if it goes on too long, obviously), but you'd need a means of doing that that didn't interfere with the charging; an ordinary handheld meter on a current range has a high enough voltage drop that it interferes with the charging - some of the better bench meters could do this, but you probably don't own one.

By reading a bit more I'd say probably you can charge as long as you can provide a voltage of around 4,2 V. The switchover from constant current to constant voltage might not happen, which leaves you with a battery charged only 75 - 80 %. (if I understand this correctly)

I was not correct, the switchover would happen, but the constant voltage phase might end to early. This is because it ends when the current drops under a threshhold level which might be higher than the provided current. My conclusion was correct, though. The battery might not be charged to it's full capacity.

So my answer would be this:

"Yes, it is possible to charge a battery with a current far less than 1 C, but it might not be charged to it's full capacity"

Hello,

this impact with my initial implied assumption. I see that there are many charger that provide a lower power than the battery power, especially in smartphones and tablets. The same USB charger working on 500 mA full charge a 1500 mA battery. Some ideas what I am seeing under the bad perspective?

Enrico

True, many SmartPhones / Tablets would charge at 1/3 C to 1/12 C. Or in other words 500 mA are 1/3 of 1500 mAh and 1/6 of 6600 mAh (IPad)

But if you provide the IPad charger with something lower than 500 mAh (say 300 mA for example) than it would trigger the end of the "constant voltage" charging phase immediatly because 5 % C is just 330 mA. This is below the above mentioned (by jc2048) 7 - 10 % C.

Hey Crjeder!

finally I am - slowly I admit - reaching the solution with the help of all. What you say is true. So, with the following parameters:

Battery: 3.7V 500 mA

Charger> same voltage (with a limiting resistor) and 100 mA

as the charger is 1/5C should I expect that it triggers correctly when the battery is charged? (that is between your example of 1/3 and 1/6)

Enrico