USB Charger Selection for RS2

I just wanted to give people a heads up to select a good quality USB charger for the RS2.

I picked up a 5V/2A charger and it was getting hot so I checked the load. It turns out the RS2 will pull a little more than 2A and then the charger drops to 4.5V and the load rises to 2.5A and the heat begins.

I will replace the charger with a 3A rated block now as I don’t want to risk a fire. Check yours if you notice it warmer than usual.


The iPad and newer Android “fast” chargers work the best for me.

I agree, from what I gather the newer ‘Fast-Charge 3.0’ type charger are rated for 5V/3A.

That is what I would use here… not the typical 5V/2A smartphone charger. Unless there is going to be an option to lower the charge current in the software somewhere.

Just make sure you have a thick enough USB cable, I have to assume the provided cable can safely handle the 2.5A.


Remember that a quality charger getting hot isn’t usually a bad thing. It just means that the unit you are charging are utilizing the full potential of the charger, which the charger should be perfectly capable of handling.

True, it’s only cautionary if the device is pulling more than the rated current… And the charger cannot keep a nice steady 5V.

Any charger that is warm but can keep the 5V supply and under rating is just fine.

Just to follow-up.

I also noted that the USB charge voltage was only at around 3.9V (as reported by ReachView) when I was using the regulat 5V/2A adapter and the battery voltage when charging could not get above 7V.

Once I plugged into a “Fast-Charger” capable adapter that could handle the 2.6A, the USB charge voltage was well over 4V and the battery began to charge up to ~7.2V…

I am starting to think that the anomalies in charging being reported are due to undersized USB adapters that cannot hold the steady 5V out at 2.6A and then the charge voltage into the battery is too low to charge properly…


Makes a lot of sense. In theory a rated 2A charger should hold a steady 5V out, BUT unfortunately there’s a ton of really inferior, poor quality USB chargers out there, produced by the truckload.

I’ve never had any issues when using “laptop grade” USB-C chargers like the 65W rated unit from my ThinkPad or indeed the similar output unit for my MacBook, but these are obviously well and truly oversized for charging a battery that’s in the RS2.

It may be worth the Emlid guys packaging a decent quality USB charger with the units when they ship them…

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Yeah, they can hold 5V at 2.1A but when the RS2 pulls the 2.6A the voltage sags quite a bit.

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It’s not something I’ve paid much (any?!) attention to, but having looked now at the larger laptop USB-C chargers I have that are multi-voltage output, as follows:

The 85W Apple one, made by Delta Electronics (Jiangsu) here is
20.2V @ 4.3A or
9V @ 3A or
5.2V @ 2.4A

The 65W Lenovo, made by Chicony Power Technology (Suzhou) is
20V @ 3.25A or
15V @ 3A or
9V @ 2A
5V @ 2A

Interesting that at the lower voltages, at least on the nameplate, these are capped well below the overall power rating of the chargers.

Interesting explanatory article here on USB-C and USB Power Delivery (PD) from Texas Instruments…

Will try out this Apple USB-C fast charger on the RS2s. It’s rated up to the full 3A at 5V, so shouldn’t struggle and deliver up to a 50% faster charge (in theory at least)…

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In the review app, see what the battery stats are like with this one VS. a regular 5V/2A charger.

This Lenovo USB-C cig-lighter / travel charger also will do 5V output at 3 Amps…

I think you’ll find that RS2 is compliant with the 5V capabilities under the USB-C spec. I don’t believe the higher voltages are of benefit to RS2.

Correct, agreed. The higher voltages are definitely not required for the RS2, just listing them off the charger specs for completeness.

These high output USB-C chargers determine the required output voltage by communicating with compatible devices using the “PD” protocol, otherwise if the connected device does not support PD (like the RS2) then they will default to their standard output which is 5V.

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