Ultrafire WF-138/WF-139 LiIon chargers

[coppertrail]

I've had the Ultrafire WF-138 for about 2 weeks now. I charged a couple Ultrafire 3.6V 14500 cells last week and the cells terminated charge at 4.29V. I did a top off charge on one of these cells this evening with the same end of charge voltage.

In a thread under the Ultrafire WF-139 charger, folks are reporting the same results with non-protected cells.

It seems as though these chargers are designed to cut off at 4.29V. From what I've read on batteryuniversity.com, this is "pushing the limits" with LiIon cells. According to the Charging Lithium Cells article, venting can occur at voltages above 4.3V, which could be dangerous. It also appears that the life cycle of these cells will be reduced by charging to 4.29V. Another member mentioned that he removes the cells when they hit 4.2V.

These cells work great, even at these voltages, in the Jetbeam MKII and MKIIx lights. They still regulate at this voltage.

As it stands, I'm happy with this charger and cells, but disappointed that the life cycle of the cells will suffer at these voltages. The cells don't become even "slightly warm" to the touch, which is also reassuring.

 

[DM51]

They will work quite well if charged to 4.3v, and in fact they will have taken a lot more charge (maybe 10% more) and you will be pleased with the run-time you get.

BUT!!! As you note, the life cycle will be substantially reduced if you keep charging to 4.3v. I don't think you are risking a nasty runaway reaction - you'd probably have to exceed 4.4v before that might happen - but you are definitely doing some damage. You should always terminate charge at 4.2v. Better still, use protected cells that cut out at 4.2v, then you don't have to worry so much.

I hope Silverfox will chime in here and give you a more definitive answer to this.

 

[coppertrail]

DM51 - And I have indeed found that to be the case, my Jetbeam MKII lights are incredible with these cells. I also agree about the runaway, and it's clever that they terminate charge at 4.29V and not 4.3V To date, I've not read any reports concerning cells venting with these chargers.

Again, to sum it up, I'll most like see much fewer charge cycles with these cells IF i continue to let them charge up to 4.29V. While I'd like to say I'll pull them at 4.2V every time, I just don't know that I'll be able to baby sit them during every charge.

I did forget to mention in my last post that folks using the protected cells in these chargers are seeing them term at 4.2V, so I may well invest in a couple sets of protected cells.

The Jetbeam MKIIx says it will regulate up to 4.2V. It seems to be regulating fine at 4.29V, as I'm able to switch modes. But, the cell voltage may be dropping to or below 4.2V upon turning on the light.

 

[SilverFox]

Hello Copertrail,

The cell phone industry did a study looking at the effects of ending charge voltage on cycle life.

Under laboratory conditions, and with an 80% depth of discharge, terminating the charge

at 4.1 volts, you get over 2000 cycles.
at 4.2 volts, you get roughly 500 cycles.
at 4.3 volts, you get under 100 cycles.
at 4.4 volts, you get less than 5 cycles.

The RC people have seen similar results, and one test that is ongoing is at roughly 800 cycles with a charge termination of 4.15 volts. This seems to be the sweet spot for performance and cycle life.

In normal use, you can extend the life of your battery by limiting the maximum charge to below 4.2 volts, and limiting the depth of discharge.

Tom

 

[coppertrail]

Thanks Tom, this precisely the information I was looking for.

 

[DM51]

Yes, very useful info.

The WF-139 charger is worrying, although it least yours doesn't go any higher than 4.3v. I was staunchly defending the WF-139 the other day, saying mine always terminated at 4.2v, until I realised it was the cell's protection circuit doing the terminating! Doh! The WF-139 cannot really be considered safe with unprotected cells.

 

[coppertrail]

DMF - In your previous post, you said that runaway wouldn't occur until 4.4-4.5V? Other than only getting 100 cycles at 4.29V, why would you deem this charger as unsafe for unprotected cells?

 

[DM51]

You can't really tell for sure when you are going to get a problem. In fact I think it is highly unlikely you will have one, and maybe some cells will go way over 4.4v before erupting, but I was really making the point about this model of charger in general. If some terminate at 4.3 when it is supposed to be 4.2, who's to know there aren't some of them out there that take it up to 4.5++? That's the point I meant to make - sorry, I didn't express it well and I hope I didn't alarm you.

 

[coppertrail]

Understood, I get it now. My point is that if all chargers terminate at 4.29 - 4.3, things should be safe. But you're right, if there are chargers terminating at 4.4, we're dancing on the verge of a problem. And unfortunately we won't know that unless folks who own these chargers report that.

What would be ideal would be an ultrafire charger that has selectable termination modes. I'd propose 4.1, 4.15, 4.2, and 4.3.

 

[SilverFox]

Hello Chris,

Keep in mind that as Li-Ion cells age their internal resistance increases. This increase will extend the charging time and limit the maximum voltage.

You may find that after around 10 cycles, your cells may end up at 4.2 volts on their own.

Also, this charger may have been set up for protected cells. The protection circuit adds a little resistance and would also limit the maximum charge voltage.

Tom

 

[bombelman]

at 4.4 volts, you get less than 5 cycles.
Tom

:lolsign:

Great find !!

 

[doc_felixander]

I'll try to set up a simple protection circuit which I'll put in there. Depending on the IC it won't be too hard implementing a switch for various termination voltages.
I've simply too many unprotected cells lying around here, so I won't switch to protected ones in the near future.
And I like the pretty versatile design of the WF139.....

 

[matrixshaman]

I've got a generic 1 cell charger I've been using for Li-Ions that charges at 100ma. I've charged RCR123's RCR2's and 18650's in it (my own setup for fitting other sizes in it) and they all seem to end with the green light at 4.28 to 4.29 volts. Darn - guess I should find another charger or try modding this one to stop at 4.20 volts if it's possible. I wonder if their is a resistor external to the IC in these that can be changed to lower the ending voltage. I think if I had the time or if someone else did that could design an alarm circuit to start the bells and lights going off when a charger hits 4.2 volts (or 4.15 or your choice) they'd make some good money. Or at least so far it doesn't sound like there are many chargers around that are precise in shutting off at a desired voltage (still new in reading about this here so I could have missed some).

 

[doc_felixander]

at least not in this price range.
the WF-139 for instance has no dedicated Li-Ion charging IC, it's built around a LM393 voltage comparator, so tweaking any values would require figuring out the complete schematics and extensive measurements.
setting up a protection circuit is really easy, there are many ICs for that purpose from the bigger semiconductor companies like Maxim, TI etc. which require only few or no external components.
some come with preset shutoff voltages in the 4,15-4,3V range (in 50mV steps), some have an adjustable input (hence the selector switch idea) and they're very reliable. they just cut the power above those values, so you wouldn't really need an indicator.
all you need is some basic soldering skills, many (most?) of these ICs come in the relatively tiny SO8 package.

you might give it a try yourself and get a few samples from TI for instance, you'll see that it's easily done.
if you're still scared, there actually are protection boards for various voltages available , just do a quick search on eBay.

 

[jtice]

I just got my Ultrafire WF-139 the other day.
only charged one 17650 on it so far, it terminated at 4.14V

~John

 

[doc_felixander]

There's already been a thread on this issue, look here: http://www.candlepowerforums.com/vb/showthread.php?t=154222

the individual experiences and shutoff voltages seem to vary, but this thing clearly tends to overcharge.

it would be great if anyone could compare the termination voltages between (different) ext. AC/DC adaptors and the internal switching supply (the latter isn't working in mine).

one more thing i noticed: the tension spring that pulls the contacts has an (ohmic) resistance of ~0.9 ohms. i assume it has at least *some* inductance, this might affect the charging behaviour in some way if the charging current is pulsed.

 

[DM51]

I just got my Ultrafire WF-139 the other day.
only charged one 17650 on it so far, it terminated at 4.14V

Protected cell? If so, that's why it terminated at a reasonable voltage. It's people with UNprotected cells who need to be careful with this charger.

 

[jtice]

ohhhhhhhh
Sorry about that, yes it was a protected cell.

I will stick an unprotected 18650 on it right now...
Cell reads 3.922V at the beginning of charge...

~John

 

[DM51]

ohhhhhhhh
Sorry about that, yes it was a protected cell.

I will stick an unprotected 18650 on it right now...

~John

Keep a close eye on it !!!

Some people have reported these chargers going above 4.3v, which is not doing the cell any good at all and is getting very near a thermal eruption.

 

[jtice]

Just saw that the indicator turned green, I am not sure how long it was green though.
Cell read 4.154 hot off the charger.
I stuck it bad in the charger, after just a minute or two, it turned green again.
I am going to leave it on there a few more hours.
...If I dont report another Voltage reading,,, well, its been nice knowing you all. :wave:

~John