# Power over Tether Considerations

Powering the Manifold 5S  over a tether is more complicated than one would suspect at first blush. A tether is essentially a long cable, and it uses wires that are as small as practical to save weight and cost. The combination of these two factors means that the tether will dissipate power and lose voltage between the tether's home base and the Manifold 5x .

There are two primary factors to look at to see if a power-over-tether (POT) system will work for you:

* The total power consumed at the Manifold 5x end of the cable
* The voltage available at the output of the tether interface

The loss in the tether depends entirely on the current through the tether. It is a bit counter-intuitive, but the lower the voltage at the Manifold 5x end, the more power will be lost in the tether. This is because the power supplies in modern electronics are quite efficient, and use less input current if the input voltage is higher, holding power (volts x amps) nearly constant. If the power supplies were 100% efficient, the current needed would be the device's power consumption in watts divided by the supply voltage. Of course, the efficiencies are less than 100%, but still quite high so the principle is directionally correct.

A typical Blue Robotics 1-twisted-pair [thin tether](https://bluerobotics.com/store/cables-connectors/cables/fathom-rov-tether-rov-ready/) 100 meters long has a resistance of about 30 ohms. At 300 meters, the resistance is about 90 ohms.

The Manifold 5S with no hotel load and a brain installed consumes about 7.5 watts, which is about 500 mA at V-in of 15 volts. This would require you to supply the head end of the tether with 30 volts, and the tether  itself would dissipate 7.5 watts. Using 7.5 watts in the tether gets close to the point where if the tether is on a spool, it can get warm or hot.

You can mitigate the tether power loss by either shortening the tether, or decreasing the resistance of the tether, or both. Decreasing the resistance can be done by using a tether with larger wires or by using more wires in the tether to carry power.

{% hint style="info" %}
Note: Powering the tether requires you to have a tether power injector for the head end.
{% endhint %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.ceruleansonar.com/c/manifold-5l-and-manifold-5s-ethernet-switch/power-over-tether-considerations.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.