In this post I will be reviewing the Gemini Dual-Channel (2x)80W balance charger. I would like to thank Banggood for providing this charger for review. Before this, my primary charger was a cheap IMAX B6 clone so when I saw the RCGroups thread on this product it seemed very interesting. This charger can charge all common battery chemistries, has a nice form factor, twice as much power as your average 4-button charger and a built in power supply. You can buy this charger at Banggood.

Technical Specs

  • Dual channel; 80W charging per channel
  • 5W Discharge (per channel)
  • Supported Battery Chemistries: Lipo, Lilo, LiFe, NiCd, NiMH, Pb
  • Input: 100-240V AC / 11-18VDC
  • Temperature probes supported (not included)
  • Weight: 930g
  • Size: 96x138x192mm

Here is what you get in the box (apart from the charger):

  • 4mm banana to XT60 male cable (to charge XT60 equipped packs)
  • 4mm banana to Deans male cable (to charge Deans equipped packs)
  • Alligator clips to XT60 female cable (to power the charger from a DC source like a car battery at the field)
  • Alligator clips to barrel jack (this is used to power chargers which have a barrel jack for DC input. Useless for this charger)
  • 2 x balance boards (to connect the balance plug as the charger only has one balance input to save space)
  • 2 x balance board cables.
  • Travel Adaptor for the AC input cable (this was in the package but not in the same box as the charger)
  • Instruction manual

First Impressions

My first impressions of this charger were not too positive. It arrived with 2 buttons jammed and also the LCD would not come on when I powered it up (even though there was a startup beep). The build quality was also a bit disappointing as the two case halves did not align properly, causing the LCD to appear a bit crooked and the buttons to be jammed/ sticky.  It also looked like the case halves had been forced together as the plastic was partially cracked where they join. When I tried to loosen up the jammed buttons, one of them ended up breaking off

3 buttons broken off from the control panel

3 buttons broken off from the control panel

Teardown/Repair

As I enjoy soldering and DIY electronics, I decided to take the charger apart and fix it myself. One important thing to note here is that the charger seems to have been designed so that the button caps are put on after assembly (and thus must be removed to disassemble it). I did not realize this and ended up breaking another button while taking the charger apart. This charger uses standard 6x6x14mm push buttons. However, I was not able to find them locally so I had to make do with regular push buttons soldered vertically with a little hot glue on the button caps. Also, the power lead to the control board (the one with the LCD) as well as the cable connecting it to one of the charging modules were disconnected, explaining why the LCD was not turning on. One interesting thing I noticed was the presence of programming pads, meaning there is a chance that firmware updates/ open source alternatives can be flashed. There is a SWIM pad, suggesting this charger uses one of the STM8 series of microcontrollers. Soldering quality appears pretty good. However, internal build quality is also pretty disappointing. The lower power supply in my picture is held in by 2 small screw while the upper one was not screwed in at all!

The insides of the charger. 2 plugs are disconnected

The insides of the charger. 2 plugs are disconnected

Fixed the buttons

Fixed the buttons

Charging

No complaints here. The charger seems to be working well. Switching between channels is seamless and the LEDs reduce the potential for confusion.The charger does not heat up much even while charging 2x3S packs at 4A (which would make my IMAX B6 VERY hot). The fans are quite effective but for some reason they seem to come on at the beginning of every charge (even if it is at 0.1A) which is a bit unnecessary. They then shut off and come on again once the temperature crosses 48°C.  I will do some more testing at high charge rates (the full 80W per channel), along with some internal temperature readings (there is a an option to view the internal temperature, which is very nice, but I would like to verify them) and will update this post soon. I also need to test whether the LM35 temperature sensor works with this charger.

UPDATE: The LM35 does not work with this charger. It reads a constant 16°C when the actual temperature is closer to 30°. The same sensor works on an IMAX B6 though. I have also used this charger some more and it definitely works well. It is very convenient to be able to charge batteries simultaneously.

Verdict

This charger has several positives:

  • Twice as much power as a standard 4-button charger.
  • Very simple interface. Anyone who has used a 4-button charger before will have no trouble with this.
  • Nice form factor making this charger compact and portable.
  • 2 independent charging circuits letting you simultaneously charge different battery chemistries, cell counts etc.
  • AC + DC input for easy charging at home or at the flying field

There are a few negatives as well:

  • Mediocre build quality. The sticky buttons seem to be a common issue and the misalignment of the case halves doesn’t make this charger look very good.
  • Constant references to the Venom Pro Duo – This charger seems to be either a rebranded or a cloned Venom Pro Duo. The instruction manual mentions the Venom charger several times and the Gemini even shows Venom on the startup screen. This does not look too good.
  • The biggest letdown for me – no LiHV support. I’ve been wanting to pick up some LiHV packs for a while now but neither of my chargers support it. A small tweak in the firmware to allow charging up to 4.35V per cell would really make this charger a winner (if the build/ QC issues are sorted).
  • No extra adapters included (such as JST or even the servo plug for my Tx pack).
  • No internal resistance checker (would have been a nice feature but is not a strict necessity)

Overall, this seems like a nice charger for those who want more power without sacrificing the ease of use of 4-button chargers. It is almost like having two IMAX B6s + the power supply in a nice convenient box.

The table below summarises the Watts per $ you get with several popular chargers (factoring in the cost of a power supply). This is a pretty approximate figure as some chargers require a particular voltage input to get the max charging power and some people may be used hacked server/PC power supplies which can be significantly cheaper than the ones I’ve listed. However, the table does show that the Gemini offers good value for the price point.

Screen Shot 2016-04-09 at 11.19.30 AM

Get your Eachine Gemini charger here.