Review of / Measurement on Xtar MP2 charger

[HKJ]

[SIZE=+3]Charger Xtar MP2[/SIZE]

This is a small dual RCR123 charger, that can handle multiple battery types.

The charger has a switch that can select between 3.0 and 3.7 volt, the 3.7 volt is for normal LiIon and the 3.0 volt is a 3.2 volt position for LiFePO4 cells. The charger has a small led for each channel, this led will be red when the charger is charging and green at all other times.

The charger is supplied with two spacers, making it possible to charger smaller cells (Remember: only charge cells that can take a 250 mA charge current!).

The charger is powered from a mini usb connector.

The charger is supplied with a standard usb power supply with universal voltage (100-240VAC 50/60Hz).

As extras it is possible to get a car adapter.

The charger can handle 35.6 mm long batteries, I checked my collection of 16340 cells and they all fitted in it (The long cells was a bit tricky to put in).



[SIZE=+2]Measurements[/SIZE]

Below 1.5 volt the charger does not charge, it discharges with up to 80 uA.
Between 1.5 and 2.8 volt the charger charges with about 80 mA.
Between 2.8 volt and 4.2 volt the charger is applying regular charge current (See curve below).
When the charge current goes below 90mA the charging is stopped and it will discharges with 200 uA.
The charger will restart charging when the battery voltage goes below 4.06 volt (3.4 volt on 3.0 volt charger setting).
When charger is disconnected from power, but with a battery in, it will draw below 360uA from the battery.
Two batteries will reduce the charge current with 10%.
Because each channel is independent, the different voltage and currents varies between the channels.

The charge curve looks like a CC/CV charger, and it stops at a rather high charge current. This is not a real problem because the charger measures the voltage with charge current turned off, this means that the charging is not a real CC/CV charging, and the batteries is filled completely, even when the current is turned off at 90mA.

Same battery, but on another channel. There is a good match between the channels.

My old RCR123 IMR cell.

Here I am charging a LiFePO4 cell on the 3 volt position, the low capacity (due to LiFePo4) cell is charged in under two hours, but the charger has some problems with termination, it keeps restarting charging because the voltage falls below 3.4 volt.

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.



[SIZE=+2]Conclusion[/SIZE]

The charger has a CC/CV like charge profile, the termination is not according to manufacturer recommendations, but works fine in practice. I like the small size and the ability to also charger LiFePO4 cells. The usb power connector makes it possible to get power from a lot of sources, even a battery power pack. No charging at low voltages might give problems activating a tripped protection.



[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.

 

[45/70]

The charger has a CC/CV like charge profile, the termination is not according to manufacturer recommendations, but works fine in practice.

Again, I disagree here.

The purpose of the CV stage when a proper, recommended charging algorithm is used, is to allow fully charging the cell without causing unnecessary damage to the cell. Oxidation within the cell during charging increases as the voltage increases. As a Li-Ion cell nears the fully charged state (~4.05 Volts OC cell voltage for a LiCo cell), the charging current should start to taper down, minimizing excessive oxidation, which would otherwise damage the cell.

The XTAR chargers do not begin tapering the charge current until the cell OC voltage is ~4.20 Volts. This negates any advantage of the CV stage of a proper charging algorithm, and likely causes some degree of cell damage. Most of the other inexpensive chargers also do this, but in a slightly different way, such as the WF-139. Does this method allow fully charging cells faster? Yes. Is it good for the cells? No.

As pertains to LiFePO4 cells, this "CC/CV like" algorithm probably causes little damage, as this chemistry is more forgiving to charging anomalies. My concern would be primarily with charging LiCo and LiMn cells with this method.

We've been over this before, but again, I disagree that this shortcoming "works fine in practice", as it likely causes damage to cells. I'm not really saying that this looks like a bad charger, as compared to most others available it seems pretty decent, but it still "ain't right".

I still say ditch the voltage checking and utilize a proper CC/CV algorithm.

Dave

 

[Dances with Flashlight]

... it stops at a rather high charge current.

I have two of these chargers. Both seem to function consistently and reliably. However, one terminates at 4.21/4.22v and the other at 4.24/4.24v. This second charger definitely terminates at far too high a voltage. So although these chargers are very modestly priced and nicely built with useful features, there is a price to pay in reduced battery life. For those only occasionally using 16340's (or other batteries that fit) they may be a good value, but Flashaholics are likely going to steer clear until Xtar cleans up this termination issue. This is rather frustrating since Xtar had promised in earlier posts that it was going to produce a dedicated 16340 charger that not only charged but terminated properly.

 

[jsj42]

I don't really understand all the technical talk, but since you guys do, maybe you can help me out.

I have Tenergy rcr123a 900mah batteries that I need to charge. I'd like to be able to charge them via a USB input. The other priority is that the charger be as tiny and lightweight as possible.

The XTAR seems to fit the bill... will it work for these batteries?

Thanks!

 

[tobrien]

Thanks for the review, I'm gonna pick one of these up!

 

[rebar]

Again, I disagree here.

The purpose of the CV stage when a proper, recommended charging algorithm is used, is to allow fully charging the cell without causing unnecessary damage to the cell. Oxidation within the cell during charging increases as the voltage increases. As a Li-Ion cell nears the fully charged state (~4.05 Volts OC cell voltage for a LiCo cell), the charging current should start to taper down, minimizing excessive oxidation, which would otherwise damage the cell.

The XTAR chargers do not begin tapering the charge current until the cell OC voltage is ~4.20 Volts. This negates any advantage of the CV stage of a proper charging algorithm, and likely causes some degree of cell damage. Most of the other inexpensive chargers also do this, but in a slightly different way, such as the WF-139. Does this method allow fully charging cells faster? Yes. Is it good for the cells? No.

As pertains to LiFePO4 cells, this "CC/CV like" algorithm probably causes little damage, as this chemistry is more forgiving to charging anomalies. My concern would be primarily with charging LiCo and LiMn cells with this method.

We've been over this before, but again, I disagree that this shortcoming "works fine in practice", as it likely causes damage to cells. I'm not really saying that this looks like a bad charger, as compared to most others available it seems pretty decent, but it still "ain't right".

I still say ditch the voltage checking and utilize a proper CC/CV algorithm.

Dave

Holy thread resurrection

Any suggestions on a quality IFR charger? Or one thats "right" with the proper CC/CV algorithm?

 

[45/70]

Holy thread resurrection

Any suggestions on a quality IFR charger? Or one thats "right" with the proper CC/CV algorithm?

Hi rebar. I've been out of the loop for a few months but as I said above, most any charger that is setup for charging LiFePO4​ cells will probably work OK. As long as the actual maximum charging circuit voltage is in the 3.6-3.8 Volt range, damage will be minimal, if any, when charging IFR cells regardless of how well the charging algorithm is executed. Again though, this only applies to IFR cells, as this chemistry is more forgiving concerning charge voltage.

I occasionally use a WF-138 (set to "3.0 Volts") for charging IFR 123 and CR2 (with spacers) cells. The only drawback is that the cells do not quite fully charge (when the LED goes green). They charge to about the same level as when charging with the "fast charge" option on a hobby charger. The difference is actually minimal between "fast charge" and a regular charge however, so it really doesn't make much difference.

Anymore though, I use one of two hobby chargers for 99+% of my Li-Ion cell charging needs. Since I have an acceptable, and easy to use charging cradle setup, it's not difficult to charge 1-8 cells (in parallel) and the cells are assured a proper charge. Also, concerning some IFR cell sizes, due to the different voltage requirement, hobby chargers may be the only option, along with a DIY charging cradle.

Dave