Charge rates
Conventional advice recommends charg- ing your lithium polymer batteries at a rate equal to their capacity in amps. Thus a 1000 mAh battery should be charged at 1 amp, a 2200 mAh battery at 2.2 amps, 3500 at 3.5 amps, etc. This ratio is commonly referred to as a 1C charge rate. Recharging a pack that is fully depleted at this 1C rate will take roughly an hour. Multiplying these current rates by the total voltage of the pack when fully charged will let us deter- mine the minimum charging power needed. The nominal fully charged voltage of a LiPo cell is 4.23 volts. Thus a fully charged 2S pack will measure 8.46 volts and a 3S pack would be at 12.69. Most chargers are programmed to consider 4.2 volts per cell a full charge, offering a little safety margin. Because of this, you are more likely to see charging cutoff occur at 8.4 and 12.6 volts respectively.
I used Hitec’s X4 to keep this large Grumman Albatross flying boat airborne (facing page) at Joe Nall 2013. It carries a pair 3S 3200 mAh packs, one for each motor. Making several flights a day meant a lot of charging and the four charge ports of the X4 easily kept pace with that demand. The 97-inch Albatross is available as a laser-cut kit from Park Scale Models. Shown with the Hitec H4 charger (above), balancing boards connect your battery to your charger’s balancing port allowing both you and the charger to monitor the individual cell voltages for maximum battery performance and life. Hitec offers these boards to match any commonly used battery.
Take a look at the batteries you are cur- rently using in your models, and any up- grades you might be considering in the near future. Of interest is not only the cell count, but also the overall capacity. Just for exam- ple, let’s say that you are flying smaller to midsize electric sport models up to about
X1 AC Plus
three pounds or so. These typically use 2- and 3-cell LiPo packs, commonly referred to as 2S and 3S packs. Your packs probably have capacity values between 1200 and 3300 milliamp-hours (mAh). That, along with a very little bit of simple math, will tell us what you need.
Power is measured in watts, derived by multiplying volts and amps. To make the math a little easier, I round the 2 and 3S pack values up to 9 and 13 volts. In round numbers, charging a 2S 2000 mAh pack at 1C requires 9V × 2A, for a total of 18 watts. Similarly a 3S 3,300 mAh pack will require 13V × 3.3A, or about 43 watts.
Based on these quick numbers, I would recommend a charger with 50 watts of out- put capacity for someone using packs simi- lar to these. By the same token, if your packs are larger, say 6S 5000 mAh, you will want 130 output watts from your charger, (5A × 26V = 130W). It should be obvious by now that as the cell count and capacity in- crease, so too do the power requirements of your charger. You can charge higher cell
H4
The X1AC Plus is an affordable and flexible AC/DC charging option that makes a perfect upgrade from the chargers included with many ARF/RTF models. It is priced right, charges all bat- tery types and is easy to use. It also features charge/discharge cycling and an automatic current setting feature, preventing you from over charging your battery.
Lithium:
NiCd/NiMH: Pb:
Charge Range:
Max Charge Power: Discharge Range:
Max Discharge Power: AC Input: DC Input:
FLYING MODELS 1–6S
1–15 cells 6–12 volts
0.1–6.0 amps 55 watts
0.1–2.0 amps 5 watts
110–240VAC 11–18VDC, 20A minimum
Beautifully designed, the H4 features a sleek aluminum design, large backlit display and four independent 120-watt charging ports. You can also bridge two adjacent ports to provide a single 240-watt output port and increased support for larger capacity batteries.
Lithium:
NiCd/NiMH: Pb:
Charge Range: Max Charge Power: Discharge Range: Max Discharge Power:
AC Input: DC Input:
1–6S
1–15 cells 6–12 volts
0.1–8.0 amps 120 watts
240W with ChannelBridge 0.1–2.0 amps 4 watts
8W with ChannelBridge 110–240VAC
11–18VDC, 30A minimum 53
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