Protected batteries...

[justinjja]

This is probably a stupid question, but Im going to ask it anyway :crackup:

Is overvoltage of the things a protected battery is protected from?

What happens when you hook up 5v to a protected battery?
Will it burn out a fues? lock down until the overvoltage is resolved?
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I ask these questions because I am curious about this:


Some lithium ion battery has 200 mOhm internal resistance and a max voltage of 4.2v.

So I wonder if it would be ok to charge it at 1A until the voltage was 4.4v.
Take off the 1A load and the voltage would drop to 4.2v
and the battery is fully charged, quicker than cc/cv could have charged the battery?

 

[Sigurthr]

You should never charge a Li-Ion cell to higher than 4.19V because at above that point the battery can explode and catch fire. As little as 4.21V has been reported to cause this issue.

What the protection circuit protects against, and how it accomplishes what it does, depends on the circuit used, which depends on the brand and make. Not all are the same. AFAIK there are no hard fuses though.

Safe charge current depends on the capacity of the cell. Generally 2/3C is the accepted safe maximum charge current. For example a 1000mAh cell can be charged at 666mA safely. Some cells can take as much as 0.8C charge rate with no issue at all, but if you don't know your cell's charging dynamic it is safer to use 2/3C.

 

[justinjja]

From what I have read, some of ultrafires chargers actually charge at over 4.2V to speed up charging.

 

[Sigurthr]

That is possible, ultrafire is utter crap. I have an Ultrafire 16340 with 790mOhm Ri (internal resistance). It came this way new, sealed in plastic.

I use a Tenergy brand dual universal Li-ion charger. Voltage is locked at 4.19V and current is limited to 600mA/channel.

 

[piferal]

Now you have Li-Ion batteries that can be charged to 4.35V, and the Samsung ICR 18650-30A is an example of this.

 

[Hiemal]

Yeah, some Li-ion batteries are rather finicky about the way they're charged.

Typically the charging cycle starts by constant current, anywhere from 1/C (c is capacity of the battery) to 1 full C. So lets say we have a 1000 mAh li ion; 1 / c would be charging it at 100 mA, while 1 C would be 1000 mA.

After the constant current is done, it usually switches over to constant voltage. This usually happens around 4.00 volts. Chargers that do this are "topping" the li-ion. Chargers that don't do this will cause the voltage to drop once you take it out of the charger...

I think most chargers stick to constant current all the way up to full charge; however this doesn't really give the full 100% charge a li-ion usually needs... as said above, the voltage will drop as soon as you take it out.

 

[BShanahan14rulz]

Every protection circuit is different. They are supposed to protect against overcharging, overdischarging, and discharging too quickly.

Charging should be at charging rate specified by manufacturer of the cell, constant current until the cell reaches 4.2V. At that point, charge at constant voltage and let the current taper off. Once the cell charging current reaches about 5% of the specified rate, the cell can be considered full.

 

[piferal]

Every protection circuit is different. They are supposed to protect against overcharging, overdischarging, and discharging too quickly.

Yes, In general the most common protective circuits for Li-Ion battery, are for.

voltage overcharge, voltage overdischarge and overcurrent discharge.

May have more or less, or different types of protection, but the 3 mentioned above are usually the most common,
and generally implemented in almost all battery protection circuits.

But they can also have in the same circuit, these other protections.

Overcurrent protection during the charge, Short protection, etc.....

 

[Elektrotechniker]

You should never charge a Li-Ion cell to higher than 4.19V because at above that point the battery can explode and catch fire. As little as 4.21V has been reported to cause this issue.

What the protection circuit protects against, and how it accomplishes what it does, depends on the circuit used, which depends on the brand and make. Not all are the same. AFAIK there are no hard fuses though.

Safe charge current depends on the capacity of the cell. Generally 2/3C is the accepted safe maximum charge current. For example a 1000mAh cell can be charged at 666mA safely. Some cells can take as much as 0.8C charge rate with no issue at all, but if you don't know your cell's charging dynamic it is safer to use 2/3C.

What? Really? Now that is interesting or I know too little about batteries.

 

[justinjja]

What? Really? Now that is interesting or I know too little about batteries.

It is probably exagerated,
but I could see it being true for a lipo,
Those things are ridiculous.

 

[BShanahan14rulz]

The chemistry doesn't like going above 4.2V. 4.25V is generally the extreme maximum I see referenced in datasheets.

 

[LarryDFW]

You should never charge a Li-Ion cell to higher than 4.19V because at above that point the battery can explode and catch fire. As little as 4.21V has been reported to cause this issue.

The standard charging voltage for most common lithium-ion cells is stated as:

4.20 VDC to 4.25 VDC .

Any brand name cell will work with these charging voltages.

Newer high-capacity 3000mah cells utilize a 4.35 VDC charging voltage.

LarryDFW

 

[jasonck08]

The standard charging voltage for most common lithium-ion cells is stated as:

4.20 VDC to 4.25 VDC .LarryDFW

It should be 4.20v +/- 0.5v. Meaning anything within 4.15v - 4.25v is still within spec and is considered "acceptable" according to the industry standard for most LiCo cells. As you mentioned this doesn't apply to ALL cells, but it does apply to most cells that are not 2800 and 3000mAH cells with 4.3 and 4.35v charge specifications.

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To respond to the OP. All protection circuits should have overvoltage protection. This is usually set about 0.1v higher than the recommended charge voltage of the cell.

Basically the cell's protection circuit has an IC, when this IC detects over voltage, it will trigger the onboard mosfets and stop allowing energy to flow in and to further overcharge the battery. The battery must then be discharged (e.g. put in a laser or flashlight etc) before these mosfets will allow it to be charged again.

You should never rely on the protection circuit's overvoltage charging feature to terminate the charge cycle, but should instead use a proper CC/CV charge method that tapers off the current as the cell's voltage rises, then terminates the charge at ~50mA.