Find a cable in DC circuit

[Cor van Houtum]

hello fellow solar friends,

recently I came to a site where there are about 10 DC strings on the roof and brought down with 20 cables
ALL Black

It took me a while to find out where all these cables went to , and where ended.
this made me wonder why there is no tool to find these cables,
even why there is no easy way to measure continuity in a string with only one cable.

That would make life mutch easier for a technician to locate a continuity fault in a string.
or even find a panel that is not connected at all , but hopped over in the process of building.

Or even a tool that helps the "non electrician" on the roof to see if the panel he just mounted is part of the string and the connection is done in a good way.
without touching any electrical parts at all.

This would make a lot off sense , so the guy's that come mount the inverter next day , do not have the surprise of non continues strings.

So I mean testing with only one cable starting with the minus of the string and knowing all the way that the panels are contacted .
without use of a return cable or a inverter.

I think I found the solution.

Do you think this would be a handy tool ?

let me know your opinion please

Cor van Houtum
Draaistroom Nederland

[Ralph Day]

In the late 1970's I worked with a telecom contracted company (digging holes) and they had something they could clip onto a customer's phone that would send a signal they could locate at the massive junction box in the neighbourhood. Maybe there's something available like that.

Ralph

[Cor van Houtum]

Thanks Ralph
i find out

[Brian McGowan]

something like this is what they use at work.

https://www.amazon.com/Extech-TG20-Wire-Tracer-Generator/dp/B00APD16D2

[Cor van Houtum]

I have try'd this but that does not work when there is voltage on the line
the present voltage on the strings can be even higher then 500 volts
the beep is then fading away directly after connection,
when you want to detect the cable and allready know what to look for then it seems to work a little sometimes.

So my opinion about these beepers is that the detection is bad and to wide.
in a way it is a open microphone with a bad connection that pickes up any disturbance
like in a audio system with a unearthed connection.
an this effect is used to find a cable.

When there is also a ac line in the neigbourhood it does not work very reliable.

do you have a other way to find a solar dc cable when there are panels connected ?

Cor

[Brian McGowan]

I will have to try a science experiment at work once one of the installers is there to borrow their tester.
Perhaps you cannot directly connect the sender end to the wire and might be better wrapping a wire around the line you are looking for so there is no direct DC connection and inductively couple the signal to the line.
I have to see if the black and red wires on the sender unit are positive and negative of the signal. If so then connecting the clips to the coiled wire might work better.
If you can measure the voltage on each string then it should be a simple matter to cover a few of the panels on that string with some opaque material and you should see the voltage drop on that string and it should be a fairly predictable amount.
Short of that the only thing I can think of is to disconnect the wires an put a resistor across one set of wires and you should be able to measure that amount with an ohm meter at the other end.

[Cor van Houtum]

Hello Brian

Thank you for your input , but i know offcourse how to measure this kind of wires
That is not the purpose of this discussion.

i wanted to know if there is a easy way to follow a unknown dc wire in a solar setup that has multiple wires in a bundle.
all the not so easy way's of testing and following the wire I found my self.
and generaly it is all the time needed to have a loop or both ends of the wire
and that is sometimes not easy to do.

this is for controll purpose in the building state of the solar setup not easy enough
especially not for roofworkers that are not electric skilled.

So I started to build a easy tool for doing this.
and i wanted to know if there is a demand for this kind of tool.

The way it is working is based on a modulated sinewave that is put on the cable.
The sinewave is compatible with a normal penlike field detector.
The sinewave is on the start of the cable and goes also trough the connected panels.
this makes the use more diverse.

What can I do with it,

Disconnect all the panels on the inverter by removing the MC4 connectors
before doing the measurement

Then use the tool transmitter to connect it with a mc4 from the wire that goes up the roof.
Now it is easy to follow the wire with the field pen.
also by putting the fieldpen against the glass of the panel , it wil light and buzz when this panel is connected on the tested wire.
also the next panel in this string can be found easy , and so on.
But this is in away not why I made this thing.

I made it because i wanted a tool to check if the panel that is just connected in the string has a continuity towards the beginning without knowing anything about electricity.
In the future there will be more and more solarpanel tiles that are small and have a lot of wiring and connectors.
the risk of not connecting a tile or a broken connector or cable wil be more and more.
so I wanted to give the carpenter a tool that he can use to check if the panel is connected or not , before he goes to the next panel.
And I did not want to give him a second cable and a multimeter because this can be dangerous having both poles of a high voltage string in the hands of a woodworker. (and he also needs to have his hands free and not carrying all kind of stuf around while mounting)
Also when he droppes his pen or looses it , its just 15 dollar
and all the colleagues have also one.
please respond

Cor

[Brian McGowan]

I am not aware of anything that will do this function at this time. Mind you I do not get to see installations from an up close point of view.

If you have a device and it works I could see it being useful in this industry. If you have not developed this device and are only thinking about it I would attempt to make a working model.

[Cor van Houtum]

Hello all,

After testing and trying to find a tool that can identify cables in a DC bundle of black wires
I found the solution at allmost no cost.

If you have a tool that can find a live AC wire like a Active finder
just such a pen with a light or a beep on the top
it is easy to find a AC cable in a bundle (when it is live)

But in the DC world this is a other story
You need to put a signal on the wire and try to trace it with a special tracer
Some of these can cost even a small fortune and work so-so in long distance cables


SOMETIMES THE SOLUTION IS SO SIMPLE !!

If the installation is connected to a TL inverter the AC site is also visible on the DC site
when the inverter is working !

So if you put a known String of panels on the inverter and let it work
you will see that you can measure the DC cables easy with a AC tracer

In this case the inverter is working
we have a bundle of cables
and it is easy to pick out the two cables that go to the connected string
(ALL THE OTHER STRINGS ARE DISCONNECTED FROM THE INVERTER)

It is also easy possible to go to the roof and hold the AC live finder against the glass of some panels and find out what panels are connected to the string that is working right now.

if you know this , then connecting a new cable to the inverter wil also be discovered easy.
It does not make a difference , this new wire you try to find is connected on the other end or not ,
The AC tracer pen will find it.
I tested this with a cheap laserliner , but others will work also

I am sure that this info will make your day,

Have a great 2017


Cor

[Rob Beckers]

Very smart idea Cor!
This is something I'll keep in mind for future reference. It's been more than once that I've been staring at a bunch of black PV-wires on a roof, wondering which string is which...

-RoB-

[Dave Schwartz]

That really does make sense when you think about it...

The inverter cannot pull a constant DC current - it has nowhere to store it when the AC waveform is not at maximum (either positive or negative).

Therefore, the waveform of the DC current will look like the AC coming out of an AC full-wave bridge rectifier: 0 when the AC is at zero (crossing from positive to negative and vice-versa), maximum at either AC positive or negative peak and following the sine waveform in between. And that would be enough field variation on any conductor in the circuit to set off an AC circuit-alert device.

So obvious!

[Cor van Houtum]

Sometimes the "obvious" does it Dave

But what now if there is not yet a inverter connected ?
I toke a inline 220 volts earth fault automatic of 10 milliamperes (such a thing to put between a extension cable
just for safety)


and just plugged it into the mains (the L should be the same as the connected output, and be L on the mains socket)
(DO NOT CONNECT THE N or zero)

on the output site I connected a small resistor 22k in series with the L , ( DO NOT CONNECT THE N or zero) so the current on the L lead can never go up to a dangerous level for safety , (the resistor prevents this)
then I connected a mc4 female plug to the resistor on the L leg of the output , and I made a small cable male-male (for testing the other gender cable when there are plugs on the cables that I want to find on the roof or in the way to it )

guess what ?

Now I can plug in a single solarcable into our self made tester and trace it with a ac detector
even when solar panels are connected .
Also all the connected panels in the string , can be traced with the ac tracer , just by holding it against the glass.
AS LONG AS YOU ONLY USE ONE LEG AND THERE IS NO INVERTER CONNECTED. (there is no circuit)
AS LONG AS YOU ONLY USE ONE LEG AND THERE IS NO INVERTER CONNECTED. (there is no circuit)
now you have a tool to easy trace solar cables and also test continuity in the string you are building.

basically this does the same as what the inverter does with its Riso detection.

FOR ALL WHO ARE READING THIS DO NOT PLAY WITH ELECTRICITY IF YOU DO NOT KNOW WHAT YOU ARE DOING !!!

This could be a product that is yet not for sale and that can be used by every roof installer to check if continuity in the string is available
if the start cable is connected to the tester and the roof people have a ac low cost test pen..
Now it would seem that this is not so important with systems that contain a few panels, then you are right,
but with the upcoming Tesla roofs where every tile is a panel, there will be hundreds of connections,
and think about the result when one of the workers did not connect a single tile probably,
you be a serious good engineer and circus guy , to find out where the wrong or no connection is.
I think it would be better to give a tool to the "not electric roof workers" that gives them an easy check of their work .
So the engineers that install the inverters and power walls are not surprised .
(Mr Musk , do not forget who's idea it was)

[Alton Root]

it's really helpful for me Cor..