Xtar WP6 II charger won't charge cells to 4.2V

I have an XTAR WP6 II charger that, for whatever reason, refuses to charge my cells to 4.2V, consistently only charging them to 4.15V, occasionally only to 4.14V. Double charging and/or leaving the cells on charge for an extended period does not raise their voltage either. (I do not do that often)

Granted, this probably is a good thing in that it is not hard on the cells, and I would rather it cut the charge short rather than late. Any ideas WHY this charger is doing this? Is this normal behavior? For reference the cells I'm charging now are AW IMR 164340's and AW RCR123's that are in good condition.

DayofReckoning said:

I have an XTAR WP6 II charger that, for whatever reason, refuses to charge my cells to 4.2V, consistently only charging them to 4.15V, occasionally only to 4.14V. Double charging and/or leaving the cells on charge for an extended period does not raise their voltage either. (I do not do that often)

Granted, this probably is a good thing in that it is not hard on the cells, and I would rather it cut the charge short rather than late. Any ideas WHY this charger is doing this? Is this normal behavior? For reference the cells I'm charging now are AW IMR 164340's and AW RCR123's that are in good condition.

Click to expand...

"Good condition" could be a cell that only charges up to 4.15v.

I have 10 Xtar charger and their USB meters and one is their MP1S that charges any cell, new, or used up to only 4.14v-4.15v and as you note, that's not bad for the cells, but it wreaks havoc on my OCD. Even my first li-ion charger, a WP2 II slightly undercharges, as a rule, to about 4.18v-4.19v, so it happens.

Try another charger and see what you see. I've extensively used AW's IMRs and ICRs for 6+ years and they don't get a lot of cycles out of them, before you start to notice a drop-off. Don't know how hard you bang on them, but I would just blast my cells on high, in the beginning and well...

Chris

No access to another charger. I am going to buy some new cells and see what the result is.

I can live with a 4.15V charge, my only concern is whether this charger is actually functioning normally.

DayofReckoning said:

No access to another charger. I am going to buy some new cells and see what the result is.

I can live with a 4.15V charge, my only concern is whether this charger is actually functioning normally.

Click to expand...

We can't answer that because we don't know the state of your cells. Unless Andrew is back online producing AW cells after the factory flood, even if you found new old stock last month, they could be in a tired state.

You need to start ruling stuff out one variable at a time.

Get a couple of Liitokala Lii 100s, or 202s off of GearBest for cheap. They're single/double bay multi chemistry, multi voltage USB chargers that cost less than a slice of pizza and a Coke, or an Xtar MC1+ ANT and stash them away

Chris

The standard charge is 4.20v +/- 1%. Or sometimes given as 4.20 +/- 0.05v. So, 4.15v might be barely within spec. And given that most cells drop about 0.01v or 0.02v fairly quickly after a charge, your charger may be fully within spec.

Besides, I'd rather have it charge a little under 4.2v than a little over.

This sounds normal as far as I know.

As noted above, there is some allowed variation in the charge voltage, because that's just the way the real world works. Samsung's 30Q datasheet, for example, specifically states 4.20 ± 0.05 V.

Don't worry about 0.05V. It's only going to be 2-3% capacity difference (if even that) for most cells, so maybe a light running at 1A average draw only lasts 2 hours and 55 minutes instead of 3 hours.

Also, there is a little bit of normal voltage drop after the charging stops as the cell equilibrates. As far as I know, 0.05V would be a normal amount for a couple hours after charging, and it will slow down to the pace of normal self-discharge after that.

I believe how large the voltage drop is partially depends on the current that the charger terminates at. During the final part of the charge, the voltage is held constant, and the battery gradually accepts a lower and lower current. The WP6-2 seems to terminate at 150mA, which is pretty typical for 18650's. Some lower capacity chargers will terminate at 50mA, which will fill just a little bit more charge in, but not enough that it's generally worth giving much thought to.

Sounds to me like my charger is just within specification. I am not going to let the 0.5V difference bother me, and I'm actually going to consider it a positive thing, as my cells will likely last longer.