Ninja Tam

Hi all, hope your day is well. I have been playing with some small Chinese rc cars, and they came with chargers that are USB plug to balance lead. They seem to work fine, and charge the batteries adequately for the intended use, but the thing that surprises me, and I hope someone can shed light on, is the rated output of the charger. It states 1.3a at 7.4v, with a 5v input, which seem too much for any usb port I know of to supply. Are these specs just nonsense numbers, or is it possible to draw this much froma usb port?

PS, cars are brushless Q903, great little cars, other than crappy shocks. They are super durable, and can run 3s lipo stock (mine has for many packs).

PDR

iTrader: (31)

The power capabilities of USB are many and varied. If it's the traditional USB-A style connector on the charger, the best the standard can offer is around 7.5W. USB-C, which will always have a different connector can conceivably go up to 240W, but special conditions and properly designed equipment must be in play.

Now, there's a lot of cheap gear out there that will simply present a 5V supply with a USB type-A connector, so they can likely go well over the 7.5W the standard specifies. Some of these cheap USB power adapters take too many shortcuts and are potentially lethal, so always be careful with anything going into mains voltage.

The USB specs are not for the faint of hear, but there's a decent summary here: https://en.wikipedia.org/wiki/USB#Lo...-power_devices

Roelof

It is not the meaning you connect it to an USB port of your PC/Laptop but to a simple USB charger adapter which most of the time are 2A rated.

Ninja Tam

Thanks for replying. It just seemed like a large power draw for a usb port. I do always charge it from a 2A power bank, and have made an adapter so I can charge the batteries from a proper ac balance charger.

PDR

iTrader: (31)

As an example, Apple make a 12W charger with the type A plug, which would give you 2A @ 5V. However, currents higher than the standard spec typically involve some "negotiation" between the charger and the device. I use quotation marks, since the negotiation is pretty rudimentary and involves setting/detecting voltages on the data lines. USB-C has much more sophisticated power options. I've made a variety of USB devices (both power side and consumption side) and it's "interesting".