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Thread: Jetbeam i4 PRO Intellicharger Review: Current/Voltage Comparisons for Li-ion & NiMH

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    May 2006

    Popcorn Jetbeam i4 PRO Intellicharger Review: Current/Voltage Comparisons for Li-ion & NiMH

    Since Jetbeam and Nitecore/Sysmax have gone their separate ways, Jetbeam has apparently come out with its own branded version of the popular Sysmax/Nitecore Intellicharger i4 battery charger. It is called the Intellicharger i4 PRO in Jetbeam's hands.

    As an aside, I'm sorry to say Jetbeam has apparently misspelled the unit's name as "Interllicharger" on both the packaging and unit itself.

    As before, the i4 PRO continues to "intelligently" handle both Li-ions and standard NiMH/NiCd rechargeable batteries. Has anything changed from the previous i4 V2, other than the color of the unit and its packaging? Scroll down to find out …

    Please see my previous Sysmax Intellicharger i4 V2 review for more background info on this model.

    Note that I am not as well versed in electronics or circuitry as some of the other members here, so I suggest you consult with the experts if you want to know more than just the basic current/voltage runtime relationships presented here (which are all that I can produce). If you are looking for more information on how to perform similar measurement/testing on chargers, please see HKJ's excellent Measurement on flashlight page.

    Jetbeam i4 PRO Reported Specifications
    Note: as always, these are only what the manufacturer report. And further note that these specs are identical to the earlier i4 V2.

    • Li-ion: 26650, 22650, 18650, 17670, 18490, 17500, 17335, 16340 (RCR), 14500, 10440
    • NiMH / NiCd: AA, AAA, C
    • Input Voltage: AC 100-240V 50/60Hz or DC 12V
    • Input power: 10W
    • Output Voltage: 4.2V +/- 1% / 1.48V +/- 1%
    • Output Current: 375mA x 4 / 750 mA x 2
    • Capable of charging 4 batteries simultaneously
    • Each of the four battery slots monitors and charges independently
    • Automatically identifies Li-ion, Ni-MH and Ni-Cd rechargeable batteries
    • Features three charging modes (CC, CV and Trickle Charge)
    • Automatically detects battery status and selects the appropriate voltage and charge mode
    • 3 Color LED displays charging progress for each battery
    • Automatically stops charging when complete
    • Features reverse polarity protection
    • Certified by both RoHS and CE
    • Dimensions: 139mm x 96mm x36mm
    • Weight: 156g (without batteries)
    • MSRP: ~$26

    As with my Nitecore i4 V2, the Jetbeam i4 RPO comes with just a standard 110 AC power adapter (North American-style plug, in my case). The unit supports 100 – 240V AC, 50/60Hz, so those outside of North America can use it fine (with the appropriate terminal plug). A 12V DC car adapter is available separately, as before.

    Stylistically, the unit is now white instead of black, with more rounded edges. But there are two obvious physical changes that are significant – and welcomed, in my view.

    The first is the battery channel springs now seem to sit in a metal rail. Spring action is definitely improved on the i4 PRO compared to the earlier i4 V2s I've handled – nice and smooth now, with no need to add extra lubricant any more.

    The second change may seem minor – the cut-outs on the sides of the charging bay are now deeper near the top of the unit.

    This means that you can now fit oversized cells (like the green NiMH C-cell shown above) comfortably in slots 1 and 4. Previously, on the i4 V2, I found these could only fit well in slots 2 & 3, which meant you could only charge one at a time. By allowing the greater space at the edges, you can easily charge two such cells at once.

    There are some label changes, but these are unfortunaltely not for the better. Much like the "interllicharger" labeling issue, there has also been some sort of mangling of the charge and current specs on the back of the unit. As was clearly labelled on the original Nitecore i4 V2, the current levels (350mA x4 and the 750mA x2) are independent of the voltage support for 1.4V and 4.2V cells. For the i4 PRO, it looks like someone confused these as being linked in some way by "criss-crossing" the entries without clear dividers. And in any case, the currents are both listed wrong now on the i4 PRO - it is still 375mA x4 (not 500mA), and 750mA x2 (not x4), as you will see in my testing results below.

    Here is a quick video overview of the physical build of the new i4 PRO charger, and how it compares to the original:

    Video was recorded in 720p, but YouTube typically defaults to 360p. Once the video is running, you can click on the configuration settings icon and select the higher 480p to 720p options. You can also run full-screen.

    There are a couple of very minor changes in how the circuit operates, but these do not significantly affect performance (as long as you are aware of them).

    As before, there are three yellow lights located over each charging bay, and a blue power indicator at the top right hand side of the unit (lights up when AC/DC power is supplied). Previously, on the i4 V2, one flashing yellow LED indicator on the bottom meant the unit was charging, and the battery was less than 1/3 full. One solid on the bottom and one flashing LED in the middle meant the unit was charging and the battery was more than 1/3rd full, but less than 2/3rd full. Two solid and one flashing LED meant the unit was charging, and the battery was more than 2/3rd full. Three solid LEDs meant the battery was fully charged and the unit had stopped charging.

    On the new i4 PRO, the bottom LED is always lit, and the unit cycles through the second and third LEDs to indicate the battery is charging (i.e., they flash on/off, in sequence). Once the battery is 2/3rds full, the bottom two LEDs remain constantly on, and only the third LED flashes. When fully charged, all three LEDs remain solidly on.

    The other change is in regards of the paired charging bays. As before, there remain only two independent charging channels. This means that you can charge two cells at full current (i.e. 750mA x 2), or four cells at reduced effective current (i.e., 375mA x 4). But what has changed is the relative positioning of the paired bays.

    Before, on the i4 V2, the paired bays were #1 & #3, and #2 & #4 (i.e., if you put cells in those two paired bays simultaneously, the charging current was split between the cells). Now, on the i4 PRO the paired bays are side-by-side (i.e., #1 & #2 are paired, as are #3 & #4). Truth be told, I find this new pairing more intuitive (i.e., cells side-by-side are paired, not spaced apart). But ultimately, any such arrangement is arbitrary. What really matters is to have this pairing clearly spelt out somewhere, either in the manual - or preferably - on the unit itself. Unfortunately, there are still no markings as to how the bays are paired. I found out by directly measuring it, but most would only be able to figure it out by noticing that some pairings took longer to charge than others.

    But to clarify – like before, the unit does not just cut the charging in half in paired bays (i.e., 375mA per bay). Rather, the current remains at 750mA for each bay – but it alternates charging by cycling off/on once every second for each battery. This effectively results in the same thing, but the cell is actually being charged at 750mA for a 1sec on, 1sec off, cycle.

    Now, let's see how it performs compared to the i4 V2.

    Voltage/Current Measurements

    To examine the performance of the charger, I have directly monitored charging current and voltage with a data-logging DMM (on separate runs). For these tests, I have used my standard AW protected 18650 (2200mAh) and RCR (750mAh) cells, and Sanyo Eneloop AA NiMH. The cells used here have all had a good number of cycles on them, but are still in reasonable condition. To deplete the cells, I used my regular test bed of a fully-regulated JetBeam Jet-III ST, Jet-II or Jet-I Pro (all IBS models) on Max output – and wait until the cell’s protection circuit gets tripped. The cell is then immediately loaded into the charger for testing and recording (depleted resting voltage typically <3.4V).

    Let's start with something simple: 1x18650 and 1xRCR:

    The i4 PRO charging algorithm looks pretty much the same on 1x18650 as the i4 V2 (keeping in mind this is a different cell being tested). While not a completely proper CC/CV (i.e., it doesn't keep the CV phase voltage entirely constant), it at least approximates it well. The initial charging current remains at 750mA, as before.

    Again, we see a similar pattern on the i4 PRO as the i4 V2 for 1xRCR. The unit does not keep the initial full 750mA CC phase for long, and drops in current fairly soon. Although it seems to stay at a higher current longer on my i4 PRO, that may have more to do with the batteries used than the circuit (i.e., this is a different RCR from the earlier i4 V2 review, but of comparable age and usage).

    The low ~40 mA termination level on Li-ion is very respectable, and means that lower capacity Li-ions can probably be safely charged in the light (e.g. RCR, 14500, 10440, etc.).

    In both the 18650 and RCR tests, my cells show a resting voltage of ~4.19-4.20V, which is good. Note that my testing cells were well used, so it's possible newer cells might terminate slightly higher.

    Note also that although my DMM drops to zero, i4 PRO does not completely terminate when the three yellow LEDs go solid. Although my DMM dropped to zero on my 10A port, when I switched over and re-ran the termination charge on my DMM’s mA/uA port, I measured a low 114 uA current. But this is low enough to be irrelevant. Note that this is also the same as my i4 V2 (which was measured at ~110uA).

    As a side note, I wish the manual would stop referring to this as a "trickle charge." A true "trickle charge" usually involves a regular pulse of mA current, to maintain the fully charged state. This is not a good thing for Li-ions – most "trickle chargers" are set too high, and over the long-term, will slowly cook your batteries (i.e. it gradually over-charges the cell, as long as it sits in the charger). The constant low uA current here is negligible, and will not lead to "trickle-charger" style over-charging. For all intents and purposes, the i4 is close enough to full termination.

    As an aside, the frequent "dips" in the i4 PRO and i4 V2 graphs above have to do with how the chargers operate – they actually stop charging once every two seconds to check to see if anything has been inserted into the paired charging bay. I don't have an oscilloscope to show you the exact pattern, but I can estimate from my sampling measures that it takes just under a third of a second to check. This is enough to drop the current/voltage reading in the traces above. My sampling rate is once every 30 secs, hence the why you don't see a continuous "wall of noise", but just sporadic dips (i.e. there is a ~15% chance my DMM will be taking a reading during a charging pause).

    For comparing what happens in paired bays, I had to load things a little differently – for the i4 PRO, the cells are in bays #1 and #2, for the i4 V2 they are in #2 and #4.

    Overall, there is not a big difference - except it again seems like my i4 PRO holds the CC phase longer when two RCR cells are being charged (compared to either the i4 V2, or the 1xRCR charging situation). Again, this may simly have to do with the fact that different cells were tested on the i4 V2 review (of equivalent age and use pattern to ones tested here though). I don't consider this very significant - effectively, the two chargers perform pretty much equivalently. You just need to remember that the specific bay pairings have changed.

    Because the chargers alternate the current between the paired bays (i.e. only charges for one second out of every two seconds, with a ~1/3 sec pause to check the bay status), it takes longer to charge the cells. This means I would continue to expect 10+ hours to charge two 18650 cells in paired bays.

    UPDATE JANUARY 8, 2013: FYI, I've justed tested the i4 PRO and i4 V2 with the same RCR cells, and it doesn't look like there's any real difference between the chargers. Here's a chart showing the same RCR cell (with a matched pair) in both chargers, in direct overlay (i4 V2 in green, i4 PRO in blue). I've increase the sample frequency to 1sec for each run, to allow you to better compare.

    The i4 V2 kept the charge level slightly more stable for longer, and the i4 PRO ran a little longer at the end. But for all intents and purposes, you could consider these charging algorithms as identical - what you are looking is probably just natural variation from sample unit to another.

    So how does NiMH look?

    And once again, nothing really seems to have changed. As before, the i4 PRO charger ran at a CC cycle of just over ~700mA in my testing.

    Note that unlike Li-ion, NiMH chargers don't work by a CC/CV method. Instead, they typically terminate when the battery reaches a particular voltage level, based on a characteristic increase in the positive slope of voltage versus time (i.e., dV/dT). As you can see in my runtime traces, there is a very pronounced uptick in voltage just before the run terminates. I haven't tested other NiMH chargers, so I don't know what to expect for proper dV/dT termination, but the commentary on my i4 V2 review suggests this isn't it. But like the Li-ion algorithm, it seems a reasonable facsimile.

    Oh, and as before, you can charge both NiMH and Li-ions at the same time, even in paired bays. There was some issues in doing this on the original i4 V1 (which was recalled), but there's no problem in doing it here or on the i4 V2.

    Preliminary Discussion

    Ok, I will get right to the point – nothing really significant has changed in how the i4 PRO's circuit charges batteries, compared to the i4 V2.

    The charging currents and algorithms seem to be pretty much the same, for all cells tested (as near as I can). Also, as before, you still have paired bays where the current alternates between the two cells – the difference now is that the paired bays are side-by-side on the i4 PRO (i.e. #1 & #2, and #3 & #4), as opposed to alternating (i.e., #1 & #3 and #2 & #4) on the i4 V2.

    There are some build changes that are appreciated, though. There is a metal rail within each charging bay on the Jetbeam i4 PRO, with better tension on the springs than the early i4s I tested. Spring action is now smooth, with no additional lubrication needed.

    They have also cut-out some of the plastic around the side edges of the unit, where the charging bays are located. This means that you can now fit wider cells – NiMH C-cells – in the outer-most bays. As a result, you can now charge two over-sized cells at the same time, independently (e.g., in bays #1 and #4). Previously, they only fit in bays #2 and #3, and you could only physically fit one at a time).

    Whatever you may think of the charging algorithms, they continue to do the job well. As before, you are not necessarily getting a pure CC/CV for Li-ions, or a proper dV/dT termination for NiMH. But the i4 models have quite reasonable approximations in my testing, with decent performance (e.g., low termination current for Li-ions, etc.). This is better than most of the inexpensive Li-ion-only "budget" chargers I've looked at.

    Despite the "PRO" label on the Jetbeam-branded version of the i4, not much has really changed. The circuit performs the same, although you are getting some build improvements. That said, I don't know what the spring action is like on the currently shipping Sysmax i4s (i.e., it may also have improved from my early models). You should do fine with either one, but may find better spring action on the i4 PRO.


    i4 PRO charger supplied by for review.
    Last edited by selfbuilt; 01-29-2013 at 08:44 PM.
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