It used to be that for us to charge our battery packs for our RC gear we had to wait hours to charge just one pack on a simple DC power supply and would check to see if the battery was warm to see if it was ready to go. Gone are the days of heavy nickel cadmium battery packs and simple chargers that gave little or no feedback on the status of the battery. Now with Lithium Polymer batteries we have many choices in pack size and even more choices in chargers. You can spend plenty of time and money trying to find just the right charger for your needs and there are just as many accessories for them as the airplane. Does it have a power supply? Will it support different battery types? Can I charge at different rates? What more do I have to get for it to work properly. It can be a mess trying to find the perfect charger for everything and often there is not one charger to meet all needs but sometimes we can find a good middle of the road option to cover 90% of our needs.
In our search for a good overall charger we stumbled onto the Eachine Gemini 2100 dual balance charger. Banggood.com was kind enough to send us one for review so in this article we’ll give it an overview and a rundown of it’s features and put it through some tests.
To start off lets look at the product details from the manufacturer
Size: 96x 138 x 192mm
Voltage Level: 1.2V/cell
Allowable Fast Charge Current: 1C~2C depends on the performance of cell
Discharge voltage cut off level 0.85V/cell(NiCd),1.0V/cell(NiMH)
Voltage Level: 3.6V/cell
Max. Charge Voltage: 4.1V/cell
Allowable Fast Charge Current: 1C or less
Min. Discharge Voltage Cut off Level: 2.5V/cell or higher
Voltage Level: 3.7V/cell
Max. Charge Voltage: 4.2V/cell
Allowable Fast Charge Current: 1C or less
Min. Discharge Voltage Cut off Level: 3V/cell or higher
Voltage Level: 3.3V/cell
Max. Charge Voltage: 3.6V/cell
Allowable Fast Charge Current: 4C or less(eg. A123M1)
Min. Discharge Voltage Cut off Level: 2.0V/cell or higher
Voltage Level: 2V/cell
Max. Charge Voltage: 2.46V/cell
Allowable Fast Charge Current: 0.4C or less
Min. Discharge Voltage Cut off Level: 1.5V/cell or higher
Can be powered by AC100-240V or DC 11-18V
Dual Charge Circuitry
High Power Charging Circuit
A powerful 80-Watt charging circuit. The charger can safely charge or discharge up to 15 cells of NiMH or NiCd batteries and up to 6S LiPo batteries.
Multiple Chemistgry Charging
Will charge NiMH, NiCd,Lilo,LiPo,LiFe and Pb battery types.
1 x Alligator Clips Cable
1 x Deans Plug Cable
1 x XT60 Female Cable
1 x XT60 Male Cable
2 x Balance Block
2 x Balance Cable
1 x Charging Cable
Physical FeaturesThe dual charger is bigger than two single 50w chargers however what you gain is the built in AC power supply. It requires fewer cables than multiple chargers and it’s upright design keeps the footprint small so you have more room on your workbench or pit table for more support gear. The LCD display is up top and is bright enough for daylight use. The buttons have a distinct clicking feel to them when pressed. The banana plug ports on the front hold the plugs tight and are lower on the charger for easy out of the way access for your charging leads. The balance plug ports were a little recessed which made it a little tough to get the cables seated all the way. Once they are seated the plastic plug ends are inside the surface of the charger case. This makes me not want to unplug them very often as you have to pull on the wires instead of the cable ends. The overall weight of the charger is surprisingly light making it easy to pack away for use at the field or racetrack.Charger OperationThe charger is very simple to operate. To power it on you either connect the AC cable to the charger and then plug it into the wall outlet or you connect the DC input cable to a 12V source. Once either one is connected the charger will power on. (You never want to have both connected at the same time) If you have had any experience with the common 50w chargers on the market you’ll be right at home with the simple menuing systems in place. The difference with this charger is it has two channels. There is a channel button that allows you to switch between the two channels and an LED light will help identify which side you are currently working with. Both channels are completely independent so you can start one charging and then switch to the other side and start a completely different battery.Our initial tests with charging a variety of lipo battery packs from storage charge went well. The charger was easy to setup for each pack. The chargers fans came on at the beginning of each charge but they were not too loud and shut off quickly. At the end of the charge the cells were all within .01v after resting for a couple minutes. We verified this with a Fluke mutimeter on each of the individual cells. We will continue to monitor the charger and hope to get some testing of it off the workbench and at the field soon
So what do you get with 80 watts of power?
Watts are measured using the formula of Volts multiplied by Amps. So knowing this we can figure out the maximum charging rate of a pack based on its nominal voltage. The charger does have a maximum rate of 7 amps so we will limit the rates there. The most common battery used is likely the 3 cell lithium polymer battery or 3S Lipo. It has a nominal voltage of 11.1v so 80w / 11.1v = 7.2amps. (7 amps with the chargers limit) So for the 1cell to 6cell packs this charger supports check out the list below for maximum charge rates.
- 1 Cell / 3.7v | 7 amps
- 2 Cell / 7.4v | 7 amps
- 3 cell / 11.1v | 7 amps
- 4 cell / 14.8v | 5.4 amps
- 5 cell / 18.5v | 4.3 amps
- 6 cell / 22.2v | 3.6 amps
As you can see with the larger packs you’ll be limited in the charge rate so for a person using 6cell 5000mah packs it could still take 1.5 hours to fully charge a depleted pack. However for a person using up to 4 cell packs this charger will complete the charge quickly under normal 1C charge rates.
5 watts of discharge
The 5 watt discharge rating on the Gemini 2100 is one of the disappointing features. This very minimal discharge rating means it will pull less than .5amp on any battery pack which will take a very long time to take a fully charged lipo battery down to a storage charge. This is one downfall of such a compact charger. To discharge batteries your turning energy into heat and that heat needs to be dissipated to not risk burning up the electronics. I imagine to keep the charger compact and fit the dual channel capabilities this was a choice they made. A higher discharge rating would require more space and weight to accommodate a larger heat sink. This is not a deal breaker for me as I prefer to discharge the batteries in the plane and then charge the battery back up to a storage level.
- Dual channel operation
- Both AC/DC inputs built in
- 80 watts per channel (that’s 150% of the average 50w charger)
- Affordable price for all the features included.
- Discharge limited to 5 watts (per channel) – but I understand the engineering challenges
- Limited shipping protection
When helping someone get started in electric RC the issue of what charger to get is always a hard one to address. You don’t want it to be too expensive but you also want enough features and usefulness that they won’t end up turning around and buying a new charger once they expand to more batteries. There is also the issue of support gear. Most chargers are DC input power only and require a power source. This adds to the complexity and the chance you’ll forget something at home.
The Eachine Gemini 2100 addresses most of these issues. It’s economical with its sub $100 price point. It’s a dual charger so right off the bat you can charge more than one pack at once. It’s 80 watts per channel power means it has more room to grow with larger batteries. Perhaps it’s biggest feature is the AC/DC power inputs built in. You won’t need a separate power supply with this charger.
We will continue to test out this charger and try to follow up with any hits or misses we find after more intensive and field testing. If you would like to check one out for yourself you can find it here:
Be sure to check out our video review for this charger as well.