Hey Guys,
I have an 80,000L concrete water tank located about 150m away from my shed.
I want to preferably hard wire communication between some type of level sensor in my tank to my shed which has a Victron Cerba GX in it.
I dont want to rely upon any type of solar set up at the tank.
Has anyone done this before and how was it done?
Thanks
Matt
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Hi Matt
For a start just what is a “Victron Cerba GX” and how does it fit in.
Cheers Bob
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Are you planning to use the tank inputs or the digital inputs? I presume that the digital inputs will allow you use the pump on/off, while the tank inputs will measure the level. I can’t tell if measuring a level is enough to turn a pump on and off - that will depend on options in the software. If you use the tank inputs, what is the specification for that input? It might be difficult to use that input with your required length of cable. For instance, you might have to encode the measure at the tank for transmission to the Vectron, and then decode it for input to the tank input. On the other hand, if the specification is suitable, it might be possible to avoid running any power to the tank. It depends on the details of the Vectron.
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Hi Matt
Just had a quick (and I mean very quick) look at the Manual for that device. Smart piece of work I must say.
The way I read it this supports resistance type level sensors only for tank monitoring. If you have anything else it has to be converted to resistance type to work. I might be completely wrong here as I did not go into too much detail.
This should not be a problem in itself. the device supports 2 different systems. BUT your biggest problem could be the actual wiring distance. You state 150m. the resistive round trip will be 300m. The problem arises because the resistive systems supported are dealing with quite low actual resistance, <300Ω. With low values like this if your connecting wiring is too small the wire resistance will become a significant part of the circuit as a whole with the associated errors.
The way to overcome this is to select a gauge which is practical and have a low enough resistance not to be too much bother. There are lots of charts on the internet if you enter “wire gauge chart” in your search bar you will get lots of results. Note that these days sizing is AWG (American Wire Gauge) as such the spelling might be “Gage”. I think Google is smart enough to pick this up. There are lots of info in these charts like actual diameters, stranding, resistance (usually ohms / km) etc.
Cheers Bob
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Cerba GX is the brains of a victron solar system
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I think I’m going to connect the Victron Tank 140, this allows me to communicate with a current read sensor… what I have found, I could use this
And then just running a 150m cable… unsure of AWG? Plugging into the Tank 140 and hoping for the best lol
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That device provides the measurement as a current between 4 and 20 mA. The Victron tank inputs are capable of measuring a resistance. So you can’t connect that device to the Victron tank inputs. This is an example of the type of level sensor needed for the tank input. Converting the reading from a current to a resistance would be difficult. If you are using the tank level information to turn a pump on and off then you could use a digital input by converting the mA reading to a digital signal using a current sensor and a MCU.
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Over that distance I suggest using a RS485 interface.
You would need a MCU on the USB port of the Victron Tank 140 that converted the data to UART serial output, connected to a RS485 convertor. The serial data rate at 9600 baud for RS485 can be reliable sent about 1km. At 150M a higher rate would be possible.
Another convertor at the other end of the line and a PC capable of UART serial input.
Software would then need to adjust the data from human readable information.
These are some RS585 interface devices I have working reliable now. You would need two.
Normal telephone cabling (not used anymore) would work, if you can find any today. CAT5 cabling would work too, just use 1 pair.
Cheers
Jim
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Hi James
I wonder what that funny looking stuff connecting my Modem to the NBN node is then. I always thought it looked like telephone wire.
Bit of a funny statement Jim.
Cheers Bob
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Hi Matt
That is the impression I got from my quick look at the Manual. Looked to be heavily biased toward solar management with a few handy add ons.
As Jeff says the tank level inputs are designed to handle a physical resistance. Apparently 2 different systems but still an actual resistor. I think anything else is going to be very complicated. Pity it wasn’t a corrugated metal tank as then all you need to do is tap the sides. Just joking.
Cheers Bob
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Thanks Jim… something to think about, I think I’ll just try running 2.5mm the total distance, if this doesn’t work then look at a 485 converter of some sort
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I believe that if I get the Victron tank 140, this will talk to the 4-20mA sensor and then then convert that to talk to the Cerba GX
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Haha I have an external visual inficator that I can see from the house with an old gun scope but I want to be able to check remotely when I’m not home
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Hi Matt
I am assuming here that you are intending to run cable from the sensor and co-site the Victron 140 close to the main Cerba GX unit and communicate via USB.
If that is the case and you are using 4-20mA loop signal the cable AWG is less important. As long as the size is reasonable like 20 or 22AWG. Being a current loop the current will be adjusted by the sensor irrespective of external resistance like cable resistance etc. as it is the same current flowing around the loop. The sensor will adjust the applied voltage to allow the correct current. That is why the operating voltage for this type of signal is so high, to allow enough head room for external resistances.
Cheers Bob
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Yeah so much of Australia is yet to get fibre to the house. Ours included.
Its frustrating because I saw them run the fibre cable to a Telecom pit at the front of our unit complex. NBN Co is offering a discounted connect, but all units need to be connected at the same time. Body Corporate does not have enough money to do that at this time.
Anytway, point taken.
cheers
Jim
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Perfect, thanks Bob…
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Hi Matt
Tip:
If you are running 150m 4-20mA loop to the sensor use twisted pair cable to reduce any common mode interference. If it is screened earth the screen AT ONE END ONLY. Usually at the “receiver” end, in your case at the Victron 140/Cerber GX end.
Cheers Bob
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Rule of thumb I learnt long ago.
Digitise the analog signal as close to the sensor as possible or accept the line interference and other stuff the cable run will introduce distorting the signal. Theory is this will produce the most accurate measurement of the sensor. In this case it may not matter.
All the best
Cheers
Jim
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Hi Jim
Screened twisted pair done properly interference in a domestic or rural environment would be negligible.
Have used such a system with no bother in Broadcast and TV studio and TX site. Also HF transmitting station with up to 0.5 MegaWatt of HF out in the aerial farm. No problem and believe me the specs in some of this sort of installation are pretty tight. Has to be done properly though which is no hassle really. The main thing is multiple grounds like only ground a cable screen AT ONE END. With the exception of Co-Ax of course but that is a different can of worms.
Not quite right. With a 4 - 20mA current loop THE SAME CURRENT is flowing around all the elements in the loop and the “accuracy” or the 4 - 20mA signal current will be the same at both ends.
Cheers Bob
PS: I put the bit about Co-Ax in because someone would be sure to pick up on that.
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Thanks guys… I’ll keep you posted… will be doing this in a few weeks
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