Teardown of a HomePlug Adapter


Hello Mr Holm

a great job all the stuff you exposed on powerline over copper pair
if you want to go 1000m and even more coax cable is a better choice.
also very easy to do is power over coax in order to inject 48v one side
If you need working sample easy to use contact Xingtera.com they have ready to use product based on G.hn chipset ( similar to powerline but ITU standard)
but you can also use coax cable on Tenda and buy power coax injector for 2$ an extract other side
that standard technology used in TV cable distribution.
but it probaby better to use 60V AC on coax on long distance … used in Cable TV and Docsis industry
By the way I learn a lot reading your post and it gave me some ideas



OFDM over copper like adsl vdsl2 have a reach of 1000m but high frequencies are to much attenuated and speed drops.

I suggest to use coax cable even they poorest is many times better than copper
1000m link over coax is not a problem

have a look coax adapter with remote power used in video surveillance business.
I suggest to have a look www.xingtera.com


Oh man, this is awesome info… really it is!
i appreciate your whole effort to compile custom power adapter article with detailed info.
Cheers to that!


Is there any specific information on which of the six power header pins for the Tenda P200 V2 require to be used to power it? I can’t get mine to power up when applying power when it is separate from the it’s supplied mains power, even although I know they are still working.


According to Sheet 2 of the 2.8 Controller Board Schematic, the Tenda P200 V2 is supplied 3.3vdc, by U5, from J18-5 on the Controller Board. If you can match the correct Tenda P200 V2 pin to the J18-5 connector socket then you will have identified the power pin.
Also, you must provide a dc return path (gnd) to the Tenda P200 V2 and that gnd is on J18-1 on the Controller Board.



Here’s an old forum post you can use for pictorial guidance- see the topside photos at the bottom of the post. The controller board schematic is a good place to start, but unfortunately trying to figure out the correct orientation of header blocks based upon schematic pin numbers tough chore.



@Walt_Holm, Hi Walt, I read your posts and I found very useful for my project (not related to openrov).
Hoping you can help me, here my question.

I need to inject 24VAC into the tether line.
Should I add some components (in one or both the TENDA V2 units)?

Thank you very much


@Walt_Holm et al.

Network loss due to draw from thrusters… Can anyone advice? Thanks :slight_smile:

I’m mentoring a team of high school students competing for their third year as an underwater ROV team. We are trying to eliminate our network cable and so we got the Tenda pair and two interface boards from the OpenROV store and are able to stream IP cams to a surface laptop over a 100ft 12 gauge +ve/GND tether which powers the ROV with 12V and 20-25A. We pulled the resisters on the interface boards on both ends so that powering of the tether line is isolated from the powering of the Tendas, as instructed by the OpenROV support team. We are using Blue Robotics T100 thrusters with their Basic ESCs. These can pull up to 11.5A each. We use algorithms to make sure we don’t fully power more than 2 at once.

The problem is that when we power on a single thruster (even gradually) there is occasionally some temporary network packet loss (over 1-2s) - noticeable video frame drop/lag, and increased ping time. We haven’t yet hooked up the Raspberry PI controller. The indicator lights on the Tendas stay on.

As an A/B test, we connected a network cable straight from the laptop to the IP camera, while still powering the cameras over the tether, and this eliminated the issue, therefore the issue is definitely related to the network going over the tether in some way.

I assume the current draw or the power pulsing from the ESCs is throwing off the Tendas.

Is there a way to buffer this power draw and/or prevent the power pulsing of the ESCs to the thruster coils from affecting the Tenda connection?

Note that we are not allowed in the competition to use any on-board batteries, or voltage up-converters, but capacitors and voltage regulators are allowed.

Thanks for any help.



Based on the specs in your post I’ve calculated the cable voltage drop using http://www.calculator.net/voltage-drop-calculator.html

Voltage drop: 7.94V
Voltage drop percentage: 66.17%
Voltage at the end: 4.06V

This is calculated with the full load of 25A going through the cable, so with a lower load you would get a higher voltage.
Real world conditions may be different.
I would suggest using a shorter cable with thicker conductors. A big electrolytic capacitor or a super capacitor at the ROV end would help to buffer this voltage too.


Hi Brendan.

The thrusters need 12V to run and are in fact still running up to full speed so we don’t appear to be losing too much through tether resistance.

We did the test with 10AWG cable too and had the same problem. Ultimately we’ll operate with 60ft - we just had 100ft unwound from a reel. 25A is the fuse with some overhead. We’ll likely only ever draw up to 15A based on measurements with a meter from the last ROV built using the same thrusters. Last year we had that 15A running 60ft and still working, but with a network cable rather than network over power.

I should mention that the power for the Tenda circuits (which is isolated from the tether power) was not tapped off the tether for the test - they were powered from a separate power supply.

Is there a good equation and suggested model for a electrolytic capacitor?


Btw, the IP cameras ‘require’ 12V to run. They contain a little RTSP board. They take time to boot up, and do not reboot when the thruster surge happens, but an ongoing ICMP ping to them drops inline with frame drops and the flashing network port on the end of the camera cable is seen to stutter. That’s plugged straight into the Tenda.


Hi Colinizer,

Interesting… Given the thrusters run at full speed, and while using a network cable it functions correctly; it could be noise related or possibly due to inrush current???

I would suggest a 0.1uF 50V mono / ceramic capacitor for filtering noise. It’s highly likely the tenda adapters (and other components in your system) will already have some filtering across the tether and / or voltage supply. If it’s inrush current to the motors I would suggest an electrolytic capacitor 1000uF (or greater) rated at 25V.

You can experiment with the placement of these caps, and also use of multiple capacitors; e.g. at each end of the tether, across voltage supply to tenda, across voltage regulators, on power to ESC’s and see if it makes any difference.

Are the thrusters submerged for these tests? And is the cable a twisted pair or figure 8?


The thrusters are water-lubricated so they are in a bucket of water for these tests. We tried it with them moving around freely and holding the mounts in place. The 8 and 10 AWG cable is figure 8 zip cable from PowerWerx.

Once a thruster is eased on, I can turn them up (PWM controller) and down gently with no interruption for the most part. Occasionally when starting them in either forward or backward direction, the network interruption appears to happen, sometimes.

From your last response, I was looking at these super capacity packs mentioned before on the basis there was some momentary voltage drop which was confusing the demodulation on the tenda:

This one is .78F which I thought may help to cover some momentary power draw.

Would the filter capacitors potentially strip out the signal?


A filter capacitor attenuating or removing the signal is a possibility, but it can usually be fixed by substituting a different value capacitor.

From your further descriptions of your setup and the fault, a momentary voltage drop due to motor inrush current is starting to sound much more probable than a noise related issue.

The capacitor bank in the link would be an excellent choice for preventing said voltage drop. I would suggest installing it as close to the ESC’s as possible. It may power the ROV for a while after the power is removed from the tether, and it will probably increase the time it takes the ROV to boot up.


Hi Colinizer:

There are two potential problems here, and you’ll need to do some homework to figure out which is the culprit.

The first possibility is that turning on the motors drops the DC voltage at the payload enough that the network circuitry has problems. The second possibility is that the motor controllers (ESCs) create electrical noise within the communications bandpass of the homeplug adapters (2 MHz - 30 MHz), which interferes with the operation of the homeplug adapter. You first need to perform a test to see which issue it is. You can do this by rigging up a test to run your ROV networking and CPUs off a battery pack, but sharing a common ground with the ESCs (which will still be powered over the tether). If dropouts still occur with the battery power, then it’s not an issue with voltage drops over the tether.

If the issue is RF interference with the homeplug signal, then you’re going to need to get some big ferrite beads that can handle the current of the ESCs, and place them on the power leads going to the ESCs. This will keep RF energy from making its way from the ESC back to the tether.

There’s a lot going on here that can’t be explained in a simple forum post. You may very well need to find an electrical engineer to advise your group, and round up an oscilloscope to take a detailed look at what’s happening on the tether.

Let us know how things work out.




If you’re just using the Tenda units on their own, you don’t need any extra components, as they use capacitors and a transformer to isolate themselves from DC and low-frequency AC on the tether.

If you’re plugging the modules into OpenROV topside adapters, then you need to pull off one or more resistors from the topside unit to make sure that the USB 5V power is not placed onto the tether. Get the schematic for the topside adapter off of our Github site and read the notes.



Thanks @Walt_Holm & @Brendan

It will take a week or two to get the capacitor packs from Hobby King which I already ordered. I only have a couple of 1000uF on hand. We actually have a Voltera PCB printer that we haven’t got running yet, so we could make our own with the right caps. I wouldn’t think a temporary breadboard setup would be good to handle the current?

In the meantime, we’ll experiment with isolating the source of the issue.

As mentioned, we currently have the Tendas powered by a separate USB-power hub (plugged into the wall) since we are waiting for some USB-mini connectors (that the tenda topside interface board uses), and so there’s also currently no shared ground.

One other query I have in mind for later is whether HomePlug signal is susceptible to general RF. If someone operated an ROV nearby perhaps using a similar system, is their use, or any other noise on the 120V AC power in the building likely to mess things up?



@Walt_Holm Just to stay ahead of the possibilities while waiting for other pieces, do either of these ferrite beads (available from DigiKey) look suitable?

From their datasheets they appear to provide impedance nicely over the 2MHz to 30MHz range and can handle 10A - so one per motor controller +12V line - all on a single custom PCB.

I assume there are no suitable snap-on beads for this frequency range and that snap-on is not as effective as in-line?

I’m wondering if it would also be good to have one on the surface to prevent any interference from the power supply or mains power, but that would need to be rated to 20-25A which is harder to find.


There are plenty of bare cores available, that you can just slip on the power lead of the ESC. You just need to search differently within DigiKey. Here’s an example:


Note that the core impedance drops as a function of DC bias current, which in this case is going to be quite high, maybe 10A or more with the motor running on full. The datasheets for the beads don’t show impedance under load. I’d just select a bead that is as large as is practical in your design, hoping that the large mass of ferrite minimizes saturation problems.



Thanks @Walt_Holm

Any wrapping/turns or just straight through?

So only the +12V or both +12V and GND leads?