Odd charging with a WF-139?

[bagman]

I got a couple of WF-139's the other day and was trying them out last night charging one of AW's protected 18650's.

When I took it off charge after going green the 18650 was only reading 4.01v

I ran the 18650 down a bit in my 18650 Scorpion (10-15 mins) and tired it again, same result.

I ran it down again and charged it back up in my Pila charger( in case it was the battery), upto to 4.20v??????

Tried the other brand new WF-139 with the same result, the wierd thing is the 18650 read 4.08 before charge and then down to 4.01 after the light went green??

Any ideas please?

 

[SilverFox]

Hello Bagman,

Charge your cell in the WF-139 until it indicates full charge. Next put the charged cell into your light and "flash" the light on and off. We are looking for a flash duration of around 0.1 seconds, or whatever you can manage. Don't turn the light on and leave it on, just flash it.

Now, remove the cell and let it rest for 15 minutes, and check the voltage again. What did you get?

Tom

 

[bagman]

I'll give it a go and let you know

 

[bagman]

I'll give it a go and let you know

Spooky, now at 4.20v???

Pray tell the secret?

 

[SilverFox]

Hello Bagman,

:devil: MAGIC... :devil:

You bumped up against the protection circuit while charging. When it kicks in, it shows as a lower voltage. By flashing the light, you reset the circuit and now you can measure the actual cell voltage.

Tom

 

[bagman]

Thanks Tom, I take it there isn't any issues with the batteries/charger when it does this?

 

[SilverFox]

Hello Bagman,

Other than poor cycle life...

The protection circuit is set to kick in at a voltage above 4.2 volts. When you charge to the level that it takes to have the protection circuit kick in, you are doing more damage to the cell than you would be doing with normal charging. This additional damage results in reduced cycle life.

Also, if you use your charger to charge unprotected cells, you may run a risk of experiencing a rapid vent with flame incident, depending on how high a voltage the charger charges to.

Protection circuits kick in at around 4.3 volts (+ - 0.05 volts). This means that in the worst case your cells may have been charged to 4.35 volts. While this is below the "danger" point, it will result in lower cycle life. AW had some protection circuits made up with a set point of around 4.25 volts (+ - 0.05 volts) if I remember correctly, if this is what you have then the maximum charge voltage would be reduced to 4.30 volts.

It is best to use a charger that only charges to 4.2 volts, and does not subject the cell, at any time during the charge cycle, to a voltage above 4.2 volts. Unfortunately, chargers that do this are initially more expensive. People who define "value" by initial cost rather than by performance, usually find that they end up spending more money overall because of early battery deaths.

Tom