When pilots look for ways to upgrade performance of a quad, the battery connector is hardly the first component that comes to mind. But when it comes to tiny whoops, BetaFPV believes the current standard leaves performance on the table. The BT2.0 connector from BetaFPV promises higher current, less sag, and longer flight times.
What is BT2.0?
The BT2.0 battery connector was introduced by BetaFPV on the Meteor65 Brushless Whoop in late 2019. So far, only the Meteor65 and BetaFPV’s HX100 “toothpick”-style quad use the connector, but there are sure to be more in the future.
BetaFPV released a host of other BT2.0 components, such as batteries, bare connectors, pigtails, adapters, and a battery charger/voltage checker.
Does the connector really matter?
Physical connectors are often the weakest links in delivering power, so their design matters a lot.
Every part of an electrical system introduces some amount of resistance. This happens within all wires, components, and traces on the circuit board. Most of these resistances are so small that they have almost no effect on the circuit. Soldering components and wires together effectively makes them one solid piece, and this keeps the resistance near zero when electricity moves from one component to another.
Our batteries aren’t soldered in place. Instead of welding them together, we rely on electrical conductors to physically touch each other. This offers us a great deal of convenience—there’s no need to solder batteries to change them—at the cost of greater electrical resistance. In electrical systems, this is referred to as Contact Resistance and is often a major source of headache for system designers.
The amount of resistance in a connector comes from many factors such as electrical and chemical properties of each material. The total surface area of a connector plays a big role, and a smaller role is played by the amount of pressure between the two sides. Resistance also increases when oxidation occurs on the surface of a connector. Finally, the more current you put through a connector, the higher the resistance will become.
A higher resistance means that more of the power being drawn through the connector is lost (converted into heat). Losing power this way causes a drop in voltage, and when less voltage is available motors can’t produce as much thrust. This loss in power also reduces flight times.
BT2.0 vs. JST-PH
The original Blade Inductrix used a JST-SH connector for its battery. This is an extremely small plug with only 1.25mm spacing between the two pins. It quickly became obvious that the tiny connector was restricting power to the quad, so pilots began upgrading to the larger JST-PH connector. Now, JST-PH is the current standard for micro quads. This connector has 2mm pin spacing, so it’s sometimes referred to as the “PH2”, “PH 2.0”, or “Powerwhoop” connector. Even though this was a big step forward, JST-SH was designed for “high-density connection of internal wires to PC boards”. Data transmission is a low-current application, so the connector only has a current rating of 2A.
The BT2.0 connector was designed specifically for micro quads. BetaFPV rates the connector at 9A. (Though worth noting here is that BetaFPV rates the JST-PH connector at 4.5A.) The BT2.0 has a similar shape to the Amass XT30 and XT60 connectors that are common on larger models. When I first brought the Meteor65 to a local event, one pilot remarked: “Is that like an XT10?” The comment is not far off the mark.
The JST-PH has 0.5mm-wide square pins, and an inserted contact depth of 4mm. This calculates out to a surface area of 8.0mm² (0.5mm width × 4mm depth × 4 sides). A BT2.0 connector uses 1mm-diameter rounded pins, and also has a 4mm inserted contact depth. At 12.6mm² (1mm diameter × π × 4mm depth), the BT2.0 connector has an advantage of more than 50% additional surface area.
While JST connectors generally use crimped pins for easier machine assembly, the BT2.0 has solid pins that require soldering. While this makes BT2.0 harder to assemble, it reduces contact resistance by eliminating a friction connection at the wire junction.
The thickness of the material plays a role as well, similar to how thicker wires are rated for higher current. A JST-PH pin has only 0.25mm² (0.5mm × 0.5mm) of thickness along its cross-section. Sometimes the JST pins are folded from flat metal sheets; the result is a much thinner hollow pin that has even less ability to carry current. The BT2.0’s pin thickness is over three times that size at 0.79mm² ((π × 0.5mm radius)²).
While the BT2.0 clearly wins in design, the JST-PH connector has several outside advantages. The most important of these is that JST Manufacturing is an established electronics supplier. JST standards are well-defined and widely distributed; JST-standard parts are easily available from many suppliers. For BT2.0, the only current supplier is BetaFPV.
BetaFPV so far has settled on wiring colors for its BT2.0 equipment of blue and gray. Blue is positive and gray is negative. This goes against years of well-established red/black standard coloration for power wire identification. It looks nice, but it’s sure to cause confusion and result in reversed polarity if not carefully checked.
I ran several trials to put these connectors to the test. I set up two different micro quads each with both BT2.0 and JST-PH connector pigtails and ran many packs through each. There is a definite difference in performance between hollow-pin and solid-pin JST-PH pigtails, so I used only solid-pin JST connectors. I tested a low-end brushed micro (BetaFPV’s 65S) and a high-end brushless micro (Meteor65 22000Kv). I flew the quads with a JST-PH and a BT2.0 battery of identical size and similar age to find out what the most likely practical experience of users will be. But I also went more scientific and used BT2.0 battery with a BT2.0->JST-PH adapter, and then again using the same battery (with a BT2.0->BT2.0 adapter). This eliminated any test bias from differences in battery cells. Another test was to charge BT2.0 and JST-PH batteries to exactly the same voltage, then discharge at the same throttle amount for the same amount of time.
In all of the tests, the BT2.0 performed well above the JST-PH. With the BT2.0, the voltage read at least 0.3V higher under load. At typical 1S flight voltages, that’s a difference of nearly 10%! On the more power-hungry brushless quad, the disparity approached 0.8V—That’s 35% more power with the BT2.0!
The low-end brushed micro didn’t feel significantly different on the BT2.0. The voltage was definitely higher throughout the flight but it didn’t translate into feeling like the quad had much more power to give. Since resistance increases with current draw, it makes sense that a slower machine would not be affected as much. There’s still only so much that this combination of motor and prop could crank out. What BT2.0 does offer is on the brushed micro is an increase in flight time. On the JST-PH the voltage under load at 4 minutes was 3.1V. On BT2.0, a very similar 4-minute flight left 3.4V in the tank. Using BT2.0 unlocked more of the battery’s potential, allowing a longer flight with less sag.
On the other end is the brushless quad with high-powered 22000Kv motors. Surprisingly, this wouldn’t even fly without the BT2.0! Using JST-PH on this quad was a recipe for disaster. Initial takeoff was fine, but after only a few seconds the voltage drop was so great that the flight controller was unable to function. This was true even with the BT2.0 battery used through a JST-PH adapter, so it wasn’t a difference in battery health. The same battery through a BT2.0 to BT2.0 adapter flew just fine, eliminating the extra connector as the problem area. If it weren’t for the BT2.0 connector, the Meteor65 with 22000Kv wouldn’t be a functional machine at all.
It’s obvious that the BT2.0 connector is not simply hype. Getting 10% more of the power out of a battery is impressive.
Our low-end brushed micro quad didn’t really fly differently, but it did fly longer. A high-end quad certainly put the added power to use. Racing pilots can embrace the BT2.0 to get an edge on the course—either from raw power or from a lack of voltage sag toward the end of a pack. Depending on your quad of choice, switching to BT2.0 will either mean longer flight times or increased punch and responsiveness. There’s no doubt that it’s a superior connector and that it has a real, practical, measurable effect.
What would stop someone from upgrading? For one, BetaFPV is currently the only supplier of BT2.0 products. JST-PH equipment is far more available, giving pilots more diversity in supplier choice. Most existing 1S equipment comes with JST-PH. Many pilots have amassed a large collection of JST-PH batteries, and most of them are difficult to resolder with a new connector. Despite the obvious performance advantages, we can’t say if manufacturers will jump on the bandwagon and start producing more quads and accessories with BT2.0.
If you’d like to try it out or make the switch, GetFPV carries most of the currently available BT2.0 products.