Charging with low power

Question

If I charge a LiIon 500 mA 3.7 V battery with a charger that has a 100 mA power only, the battery will be charged in a longer time or not charged at all ? Thanks in advance to solve this doubt. Enrico

crjeder · Accepted Answer

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.

amgalbu · Answer

The charge processo of a LiPo battery has two phases

Constant current: the voltage is kept to 4.2 V and current flows into the battery. The charger tries to keep current constant

Constante voltage: when the battery voltage reaches the applied voltage, current drops

So to answer tour question: to fully charge tour battery it would take a shorter or longer time depenfing on the current tour charger fan supply ad far the charger voltage is 4.2 V

Cheers

Ambrogio

crjeder · Answer

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

jc2048 · Answer

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.

jonivanart · Answer

Hello Enrico!

First off, the rating of mA on the battery is the max discharge rate.

Secondly, the LiIon battery has to be charged with a monitoring and balance charger built specifically for LiIon batteries. Please "DO NOT" use just any power source to charge any batteries. LiPoly's. NiMh, NiCad, etc. all require specific types of chargers and methods. The charger will ask to set the voltage due to the balancing feature if the battery has multiple cells or just one. It will also ask for the mH of the battery pack. This is also to charge at a specific rate that is required for that type of cell.

Lastly, the rating on the power source is also the max power output rating.

Side note: If you want to get the most out of your battery packs look up "Storage Voltage" of that type of cell. When you want to put them on the shelf for a while, make sure you bleed them down or charge them up to that voltage to make them last or they will go bad on the shelf.

Charging with low power

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