Review of / Measurement on Xtar WP2 II charger

[size=+3]Charger Xtar WP2 II[/size]



This charger is an update to the WP2 charger, the update includes a switch that can change between two different charge currents and a usb power output. The charger has two channels, i.e. it can do two cells independently of each other.



It comes in a cardboard box with a view to the charger and specifications on the back.




The charger is powered from a single 12 volt DC connector, this connector can be powered from either the supplied AC adapter or supplied car adapter. The AC adapter I got is a universal voltage adapter (100 - 240 VAC 50/60 Hz) with a plug for European use.



The switch select between usb power (position: 0), 0.5 ampere charge current (position: 1) or 1 ampere charge current (position: 2). This is not the best marking, something with USB, 0.5A and 1A would have been much better. I would have preferred that the switch was somewhere on top of the charger, to make it more visible. The usb connector is a usb power output, that can be used to power or charge small usb devices. it can supply up to about 500 mA.



There is a charge led for each channel, this led will be red when the charger is charging and green at all other times when the charger is powered and charge selected. If the usb power function is selected, when power is connected, the led on the left channel (the channel used for usb power) will flash red.
The centre led is red and will be on when usb power is selected, no power is connected and a charged battery is in the left channel, i.e. when there is power on the usb connector.





The charger can handle 69.5 mm long batteries, including flat top cells. (See my 18650 LiIon comparison for length of different brands).



[size=+2]Measurements charger[/size]

Below 2 volt the charger charges with about 0.5 mA, this is enough to reset a protection pcb (Note: The led is green).
Between 2 volt and 3 volt the charger charges with about 80 mA.
Between 3 and 4.15 volt the charger is applying regular charge current (See curve below).
When the charge stops the current is between 60 and 75 mA in my test, when the charger is finishes the current goes down below 100uA (This is a insignificant current).
The charger will restart charging when the cell drops to 4.0 volt or after a power loss.
When charger is disconnected from power, but with a battery in, it will draw about 550 uA from the battery.
Two batteries will not change the charge current.
Because each channel is independent, the different voltages vary between the channels with a small amount.



The charge curve shows a good approximation to a CC/CV charger, but the charger stops to early, the voltage has not reached 4.2 volt. This means that the battery is not fully charged, but will have a longer lifetime.



Same battery on the other channel, there is not much different in terminating current and voltage compared to the first channel.



My old 16340 IMR cell.



The first curves was done with old cells, but this one is a new cell with low resistance. The voltage rises slower and the charger uses full charge current for some time, before switching to constant voltage (CV) charging.



In the above curve I am charging a cell in both slots, there is very little difference in performance between this and the above with a single cell. I.e. the charger can run both channels at full charge current simultaneous.



A closer look on all the noise in the current shows that the charger stops charging each time it want to measure voltage. This has the advantage that all connection resistance can be ignored and noise from the charger is eliminated.



The first curve did not show much noise in the charge current, but that was because I used a filter. Without a filter it can be seen that it contains a lot of noise.



In this chart I have zoomed in on the noise.



[size=+2]Measurements on usb power[/size]

To use the usb power output a charged battery must be placed in the left slot, the switch must be in the usb power position (0) and the 12 volt input must not be supplied with power.

USB specification says the voltage must be between 4.75 and 5.25 volt.

All curves are made with Xtar 18650 2400mAh cells.



The first curve is with a 20 ohm load, this gives a load current of 250 mA, the usb output stays exactly at 5 volt, until the battery is empty. It keeps a good efficiency at about 80%.
When the battery is empty the charger does not turn fully off, but continues to drain the battery for some time, to keep the battery voltage at 2.8 volt. It does not drain the battery below 2.8 volt.



Reducing the resistor and increasing the current to 417 mA also shows a good 5 volt output for more than 2½ hours. With the higher current the efficiency goes down, especially when the battery is nearly empty.



With 455 mA current it can keep the voltage within usb specifications for two hours.



With 500 mA in current the voltage is only within specifications for one hour.



[size=+2]Conclusion[/size]

The charger is very close to a CC/CV charging profile. The charger does charge to a little below 4.2 volt, this might put slightly less energy in the battery, but will increase the lifetime of the battery a little. Because the charger does supply a small current at 0 volt, it can reset any kind of protection. The possibility to select two charge currents makes it much better for both 18650 and smaller cells, the 18650 can be charge faster and the smaller cells can be charged safer.
The usb power is a nice addition, but would have been even better if it always worked when 12 volt was connected to the charger.
All in all a good charger and a nice upgrade to the old WF2 charger.



[size=+3]Notes[/size]

Here is an explanation on how I did the above charge curves: How do I test a charger

The charger was supplied by XTAR for a review.

Thanks HKJ! I love this charger.

Thanks for the review!

*Sigh* I observed similar "noise" when I was testing the LTC-4054-4.2 when that IC was overheating. I suspect that this IC is constantly overheating and that is why the current and voltage is constantly pulsing up and down.

VIN - cell voltage x current = watts dissipated by the IC. I wonder if someone can open it up and install some resistors prior to the IC's VIN pin. This would cause the resistors to dissipate some heat, rather than the IC doing all of it. I don't know what IC they are using, but in my experience little SOT-23-5 IC's can only take about 0.5 watts until they kick into thermal limiting mode and reduce the current (due to reaching 120C).

jasonck08 said:

*Sigh* I observed similar "noise" when I was testing the LTC-4054-4.2 when that IC was overheating. I suspect that this IC is constantly overheating and that is why the current and voltage is constantly pulsing up and down.

Click to expand...

No, overheating would not look like this "noise". Overheating would not be present the same second the unit starts charging and work on a regular 1 second schedule.
The charger is not using a LTC-4054 or any other linear regulator, it is using some sort of switching regulator, this can be seen from my oscilloscope traces.

I originally posted this in the wrong thread, but......Nice job HKJ. You know how I feel about chargers that almost charge correctly, why can't they simply make one that works properly? So I'll just say, it's an improvement, anyway.

Dave

45/70 said:

I originally posted this in the wrong thread, but......Nice job HKJ. You know how I feel about chargers that almost charge correctly, why can't they simply make one that works properly? So I'll just say, it's an improvement, anyway.

Click to expand...

I do not really believe that the manufacturer recommended way to charge is the only way to charge a battery, but any charger has to stay within the limits specified by the manufacturer.
These limits are:

1. Maximum charge current, the charger must not charge with more than this, but almost anything lower is ok.
2. Minimum charge current or termination current, the charger must not continue charging at near maximum voltage with a lower current than this.
3. Maximum voltage, the charger must not charge the battery above this voltage, but I do not know if it is ok to measure it with zero charge current.

The WP2 II charger stays within these limits, it never goes above 4.2 volt, even measured with charge current on. The minimum current is a good compromise between large and small batteries and the maximum current is selectable, I believe it is to high for 10440 cells and I did not put them in my list of supported batteries, even though Xtar specifies them on the charger.

Why is it unable to charge 14500?

Girryn said:

Why is it unable to charge 14500?

Click to expand...

? I did put 14500 in the table of supported sizes and wrote "no" to "Requires spacer".

I'm interested in picking up one of these as a travel charger for my li-ion batteries. The USB output is major selling point for me. Sorry if this is a n00b question, but if I am charging my phone with the USB output function, will the USB output stop when my phone is fully charged? Or will it continue to charge and potentially overcharge the battery?

hazna said:

I'm interested in picking up one of these as a travel charger for my li-ion batteries. The USB output is major selling point for me. Sorry if this is a n00b question, but if I am charging my phone with the USB output function, will the USB output stop when my phone is fully charged? Or will it continue to charge and potentially overcharge the battery?

Click to expand...

A usb charger is just a power supply, the phone has a internal circuit to handle the charging. I.e. the phone is controlling its own charging and you can use any usb charger/power supply without any risk of overcharging. There is just one restriction, the usb charger must follow the usb standard (WP2 II does), some usb power supplies are specified to give 5.5 volt, that is not safe.

The WP2 does not present itself as a high speed usb charger, i.e. equipment will not charge faster than when connected to a computer.

HKJ said:

? I did put 14500 in the table of supported sizes and wrote "no" to "Requires spacer".

Click to expand...

I am dumb.

I got one.....
Everything seems nice, but there's problem on flat head battery.
It would got poor contact on the anode.
By add a cd-rom screw would solve the problem, but that way 18700 battery might be not support on the same time.

Try the little magnets. They act as the "head" to the battery and give you a better contact.

Panasonic 3100s consistently come off my wp2 at between 4.19v and 4.21v. The paint is also slightly different -- the current/usb switch is labeled slightly better. Maybe there is a revision 2. The WP2 II 2?

finn said:

Panasonic 3100s consistently come off my wp2 at between 4.19v and 4.21v. The paint is also slightly different -- the current/usb switch is labeled slightly better. Maybe there is a revision 2. The WP2 II 2?

Click to expand...

There was some rumors about a upgraded version, it was probably in November.

Would you guys say this is one of the best chargers out there for the price?

I am new to Lithium but I have some good condition (I hope) 18650 unprotected Sanyo's that would like to safely charge and use.

I read an entire thread on the Shekor charger but it appears they are no longer made.. This looks like a great $20-$25 charger.

Also do you know if the USB mode can use both battery banks? I noticed in your review you mentioned only the left side.

Thanks

koocuz said:

Also do you know if the USB mode can use both battery banks? I noticed in your review you mentioned only the left side.

Click to expand...

Yes, the USB output does only work with the left slot.

HKJ said:

Yes, the USB output does only work with the left slot.

Click to expand...

Thanks for your review. I bought this charger based off of your test results and while it has some minor quibbles, I like it so far with the EagleTac 3100s I bought.

The first battery #1, I charged in the first slot and right off the charger, it was 4.19v. The second ET was marked #2 and placed in the second slot and charged at the same time. It read 4.16v. On the next charge, I switched bays and battery #2 measured 4.14v and the battery #1 charged again to 4.19v in bay #2.

I thought well...maybe one battery was 'iffy', but on the third charge, going back to the original slots, battery #2, charged to 4.19v in bay #2 and battery #1 charged to 4.19v in bay #1, so things seem pretty kosher to me.

I'm using these items for a Fenix PD32 and a Zebralight SC-600, for the record.

Can't complain for $18 delivered for the XTAR and $20.39 delivered for the two ET 18650s.

Thanks again HKJ!

Chris

Thanks for the reply's, I am new to the lithium world so I just want to be sure I get a safe charge. The cutoff is important to me in case I forget about a charging cell. And of course no one wants to overcharge them. Seems like this XTAR is a good pick.

I need to pick one up soon, anyone else have any comments on chargers? I noticed someone reccomended the Accucell 6 charger but they are also hard to find now...