How do I select the right external power supply?

If you choose to run with an external DC adapter, we recommend you to pick one from an established supplier. The adapter should be low noise, approved for IEC 60950-1 as a Limited Power Source.

The output from the DC adapter can be in the range 7-9V. We recommend 9V in case you have a voltage drop in the supply cables. Pick an adapter that is able to provide a little more than the output current you will need. Be aware that the voltage drop in most cables at 5A is not negligible.

Otii Arc voltage output range: 0-4.2V, 0-200mA
In most cases, the power supplied by your computer’s USB Host will be sufficient. However, not all computer USB Hosts are created equal, and if you experience problems you might need an external power supply, see the next section. Hint: By enabling ”meters” (Device => Meters) you can see the actual voltage of your Otii. VBUS is the USB voltage. If this goes below 4.75V, you should switch to an external DC adapter. The input voltage from the external DC connector is also monitored (VDC) and this should not go below 7V.

Otii Arc voltage output range: 0-5V, 0-2A continuous current
For this you should use an external AC/DC adapter. There are many good ones available, and we recommend you pick a certified one of good quality with sufficient power rating and 7-9VDC output. XP Power VEL18US090-EU-JA, providing up to 2A, and available through, has received good feedback.

Otii Arc voltage output range: 0-5V, 0-2.5A continuous current, 5A peak current
Again, use an external power supply. However, many AC/DC adapters with a rating above 2A have been found to be quite noisy, so you should really be careful about the quality when looking for good measurements and working in these ranges. We recommend you use a good certified lab power supply. Extech 382260 available through Amazon and others has received good feedback. Make sure your lab supply can handle the maximum peak current your device possibly can surge. Be aware of the + and – signs for the DC input.