Review of the GT Power A8 Battery Charger

In the realm of intelligent battery chargers, there are far too many choices. Prices range from about $50USD to some in the $300 range and come with a whole variety of features. The problem is that the new emerging market is for cheap products that don’t perform, or don’t have the durability and quality expected for a complex device.

Most new intelligent battery chargers can charge, discharge, and cycle Pb, NiCd, NiMH, Li-ion, LiPo, and more recently LiFePO4. These chargers feature control over charging/discharging current. Contrast this to your ‘dumb’ chargers that are essentially trickle charge wall warts that push in around 0.5C that can overcharge NiCd/NiMH, or slow LiPo balance trickle chargers that come with RC helis sometimes.

The GT Power A8 charger sells for about $80USD + S&H, I got mine from HobbyCity.com. It features:

• NiCd and NiMH charging, discharging, multiple cycling
• Pb charge/discharge
• Lithium battery mode: charging, balance, fast charge, storage charge, discharge
• Settings menu: lithium battery type, NiMH/NiCd sensitivity (to detect dV/dt peak), temperature cutoff, timer cutoff, etc (more settings exist, but those are the only noteworthy ones)

The first thing out of the box, was the charger, followed by the instruction manual, CD, and several cables with Deans ultra connectors on them that even had little grips moulded (for anyone that uses deans connectors, you know how hard it is to connect/disconnect). The charger also includes a temperature sensor, and a short USB A to USB mini cable. My first impression of the charger is that it seems to be built solidly and has a few useful accessories, but my opinion will wait until I see what it can do.

One useful feature that this charger has is that it features a USB connection and allows for software monitoring of charging/discharging, etc. Most of the really cheap crappy intelligent chargers (in the $50-70 range) have a USB port, but because of incorrect design and lack of testing, it actually ended up being a serial UART port on a USB connector.

USB to serial UART IC

The GT Power A8 charger has a proper serial UART to USB adapter IC inside, and works properly. Unfortunately the supplied software does not work, however a different software called Logview does work (requires that you select the e-Station BC8). For the most part alot of these cheap Chinese chargers are electrically identical in design, with minor variations in component quality, assembly, and firmware (the moral of the story is you get what you pay for).

LiFePO4 Discharge & Charge

NiCd Discharge & Charge

So I ran the charger through its paces and did a discharge/charge cycle on a 900mAh NiCd and a 1350mAh (probably closer to 800mAh) LiFePO4 battery. You can see from the discharge curve (only relevant traces shown) that the batteries have different characteristic curves, but more importantly that the charger can monitor the voltage and prevent over-discharge. Also the temperature sensor shows the charger how hot the battery is, and you can set a cutoff point for the device to prevent overheating. During the charge cycle the charger seems to be programmed to turn off at intervals to check charge state, and recognizes the negative dV/dt value as the end of the charge cycle for NiCd cells.

So for a quick summary:

Pros:

• Its somewhat cheap, you get good features for a affordable price, but its not *too* cheap.
• Comes with different adapter cables, and a temperature sensor.
• Cooling fan and multiple transistors with proper heatsinking inside mean that it is unlikely to fry

Cons:

• The software doesn’t work (fortunately you can use Logview)
• Temperature sensor only works for batteries with ferromagnetic materials (ie: steel battery cases), a separate battery sensor meant for LiPo batteries that could strap on would be better.
• The input power leads aren’t the same length because a snap on ferrite bead was added, and they wrap one of the leads around it to get more supression.

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