Here’s the quickie…
1. Cool LCD screen that shows the status of all the batteries.
2. 4 cell charging is done with a time-share system where only 2 batteries are actually being charged at the same time.
3. It can charge LiFePO4!
4. Cooling is a bit of a problem (for in depth, read the whole review)
5. Overall this is a charger with a good warranty. If you got a flashlight or ecig that goes through batteries like a mad man, this is a good candidate.
Full review:
The looks:
The Nitecore D4’s outer appearance is quite amazing. The curves tapers off the edges leaving the charger with an elegant look and feel, not that you will be holding the D4 like a phone watching the bars slowly move up. Since when it is fully populated with 3400mah Panasonic 18650’s this D4 becomes a brick, a charging brick?
The usage:
The D4 can charge pretty much any battery you can find, with the exception of the 9v. (I wish Nitecore made a 9v battery adapter…) For the lithium groups, you can either have it cut off at 4.20v for Lithium ions/IMR. Or if you have LiFePO4’s you can have it cut off at 3.60v. The charger can’t automatically detect a LiFePO4 from a Lion battery, but all you need to do is hold the mode button until it switches over to LiFePO4. FYI, Holding the MODE button also puts it into “Low” speed charging, but keep holding it and it will switch over it LiFe. For NiMH and NiCD batteries, the D4 uses delta Voltage and delta Time (-dV/dt on the LCD), the D4 measures the change in voltage over the change in time to detect when the battery is full.
Charging 101
Lithium batteries:
When charging a lithium battery, you use a constant current (CC) to bring the cell to a voltage of 3.6v/4.2v/4.35v. When the max voltage is reached, the processor of the D4 will switch over to constant voltage (CV) and it will wait until the current drops below a certain amount. When that current is reached, the D4 cuts the power supply and it will show the “Charging Finished” icon. On this particular charger, it doesn’t do a continued float charging where it keeps the batteries topped off. So that means if you leave the charger plugged in and powered, after 1 year the battery voltage will be lower than the charge voltage, but the charger will still say “Charging Finished”. The same goes for all “common” Lithium batteries in all shapes and sizes. Notice I wrote “common”, so no charging Lithium-Air or Lithium perchlorate batteries in the D4…
Just FYI, Lithium batteries when over discharged will be damaged, because the cathode and anode of the battery will be destroyed and cannot be reverted back to its original state, thus losing capacity on a massive scale. Over charging Lithium batteries can be catastrophic, because the cell will heat up and go into thermal runaway. (When the battery self-destructs, like a diesel engine burning motor oil, runaway diesel). It’s quite fascinating how lithium batteries symbolize our own DNA. Every time they get charged, their “ends” are damaged a little bit losing capacity just like how our DNA loses its telomeres every time it replicate.
For NiMH/NiCD batteries:
The D4 uses a –Delta Voltage over Delta Time, or in English, the change in voltage over the change in time. So when the D4 receives a dead Eneloop AA for example, it will begin to supply power and take down notes of the time. It will also start a virtual graph with slopes, plotting down many voltage measurements along the time axis. So now you have a timer, memory, and a virtual graph. Seem quite complex just to charge a battery right? Without going too deep into the charging algorithm, let me finish off this off. When the processor detects a sudden drop of voltage at the terminals, the charger will terminate the charge and call it complete. Because of the close relationship of temperature and voltage in the chemistry of the battery, having a thermal sensor right under the battery is not necessary.
END CHARGING 101
The bads about the D4:
The thermal design of this charger is horrific. Despite the time-share charging system, it still uses mosfets with close to none heat sinking. I had to make custom copper heat sinks and fill the whole charger with thermal pads. Although we are at a state in tech where even at 100C these PN junctions still operate happily for a while. But for long-term durability, the heat created is never good. I can safely say that the charger will last a good year or two, but with that amount of heat produced, you can question the efficiency of this charger. Granted, it only uses 12v 1amp, 12 watts, but it is only charging at 1400ma (750ma x2) @ 4.2v.
Bottom-line is this charger is a must have, if you have Skyray kings or Supfire m6’s. Even their own TM06 uses 4x 18650s. I have had this charger for almost a month already. Gave me no problems, I have charged all my Eneloops and my whole collection of unprotected 18650’s, 32 of them!
Wasn’t paid for this, nor was I given a free product. Just a good product that deserves a good review.
They sure do think a lot of themselves, but pretty sure they don’t manufacture their own caps. I’d rather see a top brand cap like Nichicon, Panasonic, Rubycon than some unknown cap labeled with their name.