# Tethered UAV power supply from vehicle (boat)

#### ssboatworks

Joined Jan 14, 2020
7
As briefly as possible… My goal is to have a UAV on my boat that is connected to a power tether and provides a bird’s eye view. Basically just fly straight up and follow the movement of the boat. Maybe 100-150 feet height max.

I’m aware of tethered systems out there and they range in the $20k to$50k price range… I don’t need this that badly lol.

Ideally, I would be able to use the boat’s alternator as the initial source of power, even if I have to upgrade to a higher output alternator.

The issue that I need to solve is sending power over a long cable that is also as thin as possible.

My initial thoughts are some kind of converter to boost the 12-14V DC way up at the base and then convert it back at the drone itself. This is where I am stuck… Trying to get some help from people who have a bit more expertise in this area.

#### Sensacell

Joined Jun 19, 2012
2,908
Yes - that's the idea.

Build an inverter that runs at some high frequency - puts out a higher AC voltage.
At the drone end, a small ferrite-cored transformer reduces the voltage, followed by a rectifier and filter stage.

The high frequency keeps the magnetics small and light- but not too high or you have too much skin-effect loss in the cable.
You can send up high voltage DC too- but then you need more heavy stuff in the drone to reduce the voltage.

The FCC be dammed! you might end up with a great radio transmitter too!

#### ssboatworks

Joined Jan 14, 2020
7
Yes - that's the idea.

Build an inverter that runs at some high frequency - puts out a higher AC voltage.
At the drone end, a small ferrite-cored transfomer reduces the voltage, followed by a rectifier and filter stage.

The high frequency keeps the magnetics small and light- but not too high or you have too much skin-effect loss in the cable.
You can send up high voltage DC too- but then you need more heavy stuff in the drone to reduce the voltage.

The FCC be dammed! you might end up with a great radio transmitter too!
Thanks for the response. You're saying to convert the DC from the boat's alternator to AC first, but you lost me at 'build an inverter'. I'm willing to spend some money to get this thing figured out, but building an inverter is outside of my pay grade. There has to be something out there that I can re-purpose for this use case?

#### Sensacell

Joined Jun 19, 2012
2,908
Unless you have some real electronics chops- this project is not an easy one.
Can you reference any of the expensive systems here?

They might provide good design clues.

#### ssboatworks

Joined Jan 14, 2020
7
The Fotokite Sigma is one.. here's some more interesting info too: project appa

#### MisterBill2

Joined Jan 23, 2018
9,485
What current does the flying device require and what voltage. The simple way would be to use higher voltage motors, except that such an option is not available. Keep in mind that l0ong thin wires will have quite a voltage drop. There is no way around that problem.

#### ssboatworks

Joined Jan 14, 2020
7
What current does the flying device require and what voltage. The simple way would be to use higher voltage motors, except that such an option is not available. Keep in mind that l0ong thin wires will have quite a voltage drop. There is no way around that problem.
Average is around 200-300 watts at hover, with peak around 450 watts max. The drone in question runs on a 3-cell lipo battery, so around 12 volts.

#### MisterBill2

Joined Jan 23, 2018
9,485
Average is around 200-300 watts at hover, with peak around 450 watts max. The drone in question runs on a 3-cell lipo battery, so around 12 volts.
OK, now that voltage, power, and current are known the design can begin. 360 watts at 12 volts =30 amps, while at 120 volts it equals 3 amps. A 120 volt high frequency inverter is a reasonably simple device, and that current and voltage would allow fairly thin wire, given that it is in the air and wire heating would not be a huge issue. At the UAV end a simple transformer, rectifier, and simple filter for the smarts part may not be heavier than the batteries it replaces. The remaining concern is the weight that the UAV can lift, versus the weight of the required length of wire.

#### ssboatworks

Joined Jan 14, 2020
7
OK, now that voltage, power, and current are known the design can begin. 360 watts at 12 volts =30 amps, while at 120 volts it equals 3 amps. A 120 volt high frequency inverter is a reasonably simple device, and that current and voltage would allow fairly thin wire, given that it is in the air and wire heating would not be a huge issue. At the UAV end a simple transformer, rectifier, and simple filter for the smarts part may not be heavier than the batteries it replaces. The remaining concern is the weight that the UAV can lift, versus the weight of the required length of wire.
Thank you very much for the help. I thought I understood this stuff a little better than I actually do apparently. If you are interested in helping me a bit more in detail, is there a way I can contact you? My email is (REMOVED).

MOD NOTE: E-mail address removed. Please do not put contact information in posts -- it attracts spammers to both you and the forum.

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#### MisterBill2

Joined Jan 23, 2018
9,485
Thank you very much for the help. I thought I understood this stuff a little better than I actually do apparently. If you are interested in helping me a bit more in detail, is there a way I can contact you? My email is (REMOVED).
I am not an expert on inverters, there are a whole lot of published inverter circuits around, and the acceptable weight of wires and the high frequency transformer will be decided by the lift capacity of the UAV that is selected for the project. To contact me you click on my name and follow the selections to "start a conversation."

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#### ssboatworks

Joined Jan 14, 2020
7
I am not an expert on inverters, there are a whole lot of published inverter circuits around, and the acceptable weight of wires and the high frequency transformer will be decided by the lift capacity of the UAV that is selected for the project. To contact me you click on my name and follow the selections to "start a conversation."
Thanks. Heck, the battery on this thing is around a pound. I figure on putting a much smaller backup battery on it just for an emergency, but only enough to get it to the ground. With the current setup, this thing has a lot of lifting power. It's one of these that I've modified to run on a better flight system, PX4.

#### MisterBill2

Joined Jan 23, 2018
9,485
OK, now you need to locate a source of wire that will work and not be excessively heavy. For 3 amps it should work with #24 wire, and for 100 feet up it will take 200 feet of wire, plus a bit more. Then a high frequency transformer with a 10: 1 turns ratio and a secondary of #12 wire, the primary can be #24, like the feed line, with varnish insulation. If those 2 weigh less than a pound it is fine, because it still needs a rectifier and a bit of filtering.
Then all that remains is the inverter for powering it from the boat. Probably ten kilohertz will be a good guess for a running frequency. It will need a high frequency core and at that point I am not the one to ask. Ferrite or powdered iron will be the choices.

#### ssboatworks

Joined Jan 14, 2020
7
OK, now you need to locate a source of wire that will work and not be excessively heavy. For 3 amps it should work with #24 wire, and for 100 feet up it will take 200 feet of wire, plus a bit more. Then a high frequency transformer with a 10: 1 turns ratio and a secondary of #12 wire, the primary can be #24, like the feed line, with varnish insulation. If those 2 weigh less than a pound it is fine, because it still needs a rectifier and a bit of filtering.
Then all that remains is the inverter for powering it from the boat. Probably ten kilohertz will be a good guess for a running frequency. It will need a high frequency core and at that point I am not the one to ask. Ferrite or powdered iron will be the choices.
Thank you. I will get to work and update you soon!

#### Sensacell

Joined Jun 19, 2012
2,908
Sounds like a reasonable plan.

I would caution that typical drone batteries have a very low impedance and produce very stable voltages.

The tether system may need additional regulation to keep the drone's PID systems happy - the resistance of the lead wires increases the impedance of the power supply- while the transformer 'dilutes' the effect, its still present to some degree.