Ultrafire WF-139 Charger

[FatTony]

I finally bought one of these to charge the growing number of 18650 cells I have harvested from laptop packs but from all of the stories I hear about this over charging I have kept a close eye on it. I have charged about 20 cells now, protected and unprotected and I haven't experienced any over charging at all.

Using unprotected cells if I pull them from the charger when the lights turn green they read exactly 4.20v, however if I leave them on the charger for several hours after the green light (monitoring heat and voltage) the cells return to room temp and steady themselves at 4.18v.

Has Ultrafire released a new version of this charger that completely stops charging when the lights go green?

 

[DM51]

You should carry on monitoring all charges closely, and always take the cells off the charger as soon as the light goes green, not leave them there.

The charger is not recommended for unprotected cells because it can carry on trickle-charging after the light has turned to green, and this can result in damagingly high over-charging.

There appear to be inconsistencies in the manufacture of these units, with some giving different results to others. You seem to have a good one if it is not taking any cells above 4.20 volts.

Ultrafire have not released a new version of this charger AFAIK.

 

[FatTony]

Thank you. I will continue to treat it as a risk and monitor all charges very closely.

 

[j3bnl]

I finally bought one of these to charge the growing number of 18650 cells I have harvested from laptop packs but from all of the stories I hear about this over charging I have kept a close eye on it. I have charged about 20 cells now, protected and unprotected and I haven't experienced any over charging at all.

Using unprotected cells if I pull them from the charger when the lights turn green they read exactly 4.20v, however if I leave them on the charger for several hours after the green light (monitoring heat and voltage) the cells return to room temp and steady themselves at 4.18v.

Has Ultrafire released a new version of this charger that completely stops charging when the lights go green?

I dont leave the charger unattended and always check voltage when the batteries come off. I have never had any protected cells go above 4.2v they are usually always about 4.18v-4.19v when the light turns green.
Having read a lot of threads about this particular charger it would appear that I also got a good one thankfully.

 

[falconx]

I have ordered one of these chargers and was wondering how long on average it should take for it to fully charge a cell so i can set a timer and not forget about it. The batteries I bought are protected 3.7v 18650s (sku 6979) I was told this should charge fine with this charger.
Btw, I would just like to verify that the negative side of the battery faces the head of a WF-600 and makes contact with the spring? This is the first light I have that hasn't got the spring in the tail so I thought I'd make sure before something blows up. Cheers

 

[DM51]

I have ordered one of these chargers and was wondering how long on average it should take for it to fully charge a cell so i can set a timer and not forget about it. The batteries I bought are protected 3.7v 18650s (sku 6979)

If you divide the capacity of your cell in mAh by the output of the charger, you will get an indication of how long it will take. If your 18650 has a capacity of 2,250 mAh and the charger an output of 450 mA, the cell would in theory take 5 hours to charge from empty (5 x 450 = 2250).

In practice it is not quite like that, as Li-Ion charging utilises a constant current followed by constant voltage charging cycle, so the charger's output will vary. But it gives you an approximate idea.

To get the maximum life from your cells, you should not run them down to empty each time - it is better to top them up after each use.

You should never leave Li-Ion cells charging unattended.

 

[indycrucible]

My WF-139 terminates charging at 4.2V also. So far, it has never gone higher than that.

 

[WadeF]

While everyone is on the topic of this charger, this charger will safely charge AW's 14500's?

 

[FatTony]

Yes it will as long as they are 3.7v cells.

 

[Yenster]

Btw, I would just like to verify that the negative side of the battery faces the head of a WF-600 and makes contact with the spring? This is the first light I have that hasn't got the spring in the tail so I thought I'd make sure before something blows up. Cheers

I'm thinking you probably already figured this out, but I briefly had a WF-600 (sent back because it wasn't the "18650 Only" version) and the positive battery terminal faces the head. Check to see if the tail is also spring loaded by pressing down on the brass terminal (the spring may be underneath it).

 

[mrQQ]

i'm sorry for a stupid question, but since everyone keeps telling how dangerous LiIon is, i'll better be stupid than sorry should wf-139 be making a "hiss" sound when charging batteries? the sound is in sync with red flashes - when they turn green for a split second the sound turns off, and comes back?

 

[half-watt]

i'm sorry for a stupid question, but since everyone keeps telling how dangerous LiIon is, i'll better be stupid than sorry should wf-139 be making a "hiss" sound when charging batteries? the sound is in sync with red flashes - when they turn green for a split second the sound turns off, and comes back?

i have a number of chargers that make a similar sound. a small AA/AAA 4-pocket NiMh one which plugs directly into an outlet w/o using a power cord is going right now is making that noise (sometimes with NiMh chargers hi-current pulse charging might be taking place too).

even my age-degraded hearing can still pick up on the sound that you refer to.

i have to believe that it is quite normal. actually, i'm not sure that i DON'T have a charger that i can't hear some soft sound from when it's operating.

as far as i'm concerned:

sound = 'ok'
sparks = not 'ok'
smoke = not 'ok'
flame = very not 'ok'


still, i always monitor Li-ion charging and have the charger on my coal stove when the stove is not being used; elsewhere (another non-flammable surface) when the stove is in operation. good advice DM51 gives - heed it.

 

[ampdude]

The charger is not recommended for unprotected cells because it can carry on trickle-charging after the light has turned to green, and this can result in damagingly high over-charging.

This can happen just as easily with protected cells, especially at a trickle charge rate in which the protection circuit typically won't kick in.

 

[DM51]

This can happen just as easily with protected cells, especially at a trickle charge rate in which the protection circuit typically won't kick in.

Most over-charge protection circuits are set at 4.25-4.30V, which is higher than a Li-Ion charger ought to go, but still within safety margins.

AFAIK there have been no reports of good-quality protected cells being trickle-charged to >4.3V.

Good Li-Ion chargers terminate properly at ~4.2V, and do not rely on a cell's protection circuit.

The main problem is with the potentially dangerous combination of poor-quality unprotected cells being charged in chargers that don't terminate properly and carry on trickle-charging to >4.3V.

 

[Yenster]

I don't have the WF-139, but I have other chargers that are rated at 4.2V output. When I measure the actual output with my DMM, I see that they measure at 4.24V. So I'm guessing that it doesn't really matter whether the charger trickle charges or not...the battery can't possibly be overcharged to anything greater than 4.24V. Is that right?

 

[DM51]

4.24V is overcharged. The extra 0.04V doesn't sound much, but it is another ~4% of energy that is being forced into the cell, and that will shorten its life because it is not designed to take it.

However, you say you have chargers (plural) that measure 4.24V. It sounds strange that more than 1 charger should register at precisely the same incorrect figure. Are you sure your DMM is reading correctly?

If you can, ask an electrician or electronic engineer to calibrate it against his own instrument, which will probably be more accurate. If your DMM is off by as much as 0.05V, it is not really accurate enough for this sort of work.

 

[mrQQ]

i just charged 2 18650's and 4 RCR123's which were just received from AW.. i measured them all about 5 hours later. all 4 RCR123's came out at 3.97-3.98v, 1 18650 was 4.02v, and 1 was 3.76v. I put that one into charger again, and 10 minutes later it was at 4.02v.

so how come my charger doesnt put them to 4.2 like everyone's? and what's with that one undercharge?

 

[Yenster]

4.24V is overcharged. The extra 0.04V doesn't sound much, but it is another ~4% of energy that is being forced into the cell, and that will shorten its life because it is not designed to take it.

However, you say you have chargers (plural) that measure 4.24V. It sounds strange that more than 1 charger should register at precisely the same incorrect figure. Are you sure your DMM is reading correctly?

If you can, ask an electrician or electronic engineer to calibrate it against his own instrument, which will probably be more accurate. If your DMM is off by as much as 0.05V, it is not really accurate enough for this sort of work.

I agree that 4.24V is slightly overcharged...but at least it's under your 4.25V - 4.30V safe margin.

I actually have 5 chargers rated at 4.2V ... 1 @ 4.22V, 2 @ 4.23V, and 2 @ 4.24V...so they are all within tolerance. My DMM isn't a cheap one (Radio Shack 22-812), so I tend to believe it's the variations of those chargers and not that strange (I think it would be strange if all 4.2V chargers actually measured 4.20V).

However, my assumption is that a battery in a (measured) 4.24V charger will not charge over 4.24V even if left in there for weeks. Is that right, or is there something else that might cause further charging?

 

[Yenster]

i'm sorry for a stupid question, but since everyone keeps telling how dangerous LiIon is, i'll better be stupid than sorry should wf-139 be making a "hiss" sound when charging batteries? the sound is in sync with red flashes - when they turn green for a split second the sound turns off, and comes back?

Interesting....is the WF-139 supposed to flash between red and green? I'm thinking that's not normal behavior and might be the cause of your undercharged batteries.

 

[da.gee]

Mine flashes between red and green. I think this is normal.