Installing a DC Shunt - Using a Thermocouple module + PLC to read it
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In this video, I install a 2000 amp deltec shunt on the buss bars feeding to my LiFePO4 battery bank. The purpose of the shunt is to create a small voltage drop, which I then measure and scale to an amperage value in the PLC. This will allow me to add some new control features to the PLC!
Current shunts are ALMOST always installed on the negative battery terminal so that there is negligible DC offset voltage. Check your PLC's specs to make sure it handles 50-60v offsets.
Imagine if you were using a Tesla battery pack at its full 350 volts, that would mean you have a 350v DC offset on the sense lines. Very dangerous and also requires fusing both lines at the shunt.
PLC max i/p is +/- 50v
Yeh, low side current measurement to avoid common-mode voltage issues is a standard consideration for PLC's?
A couple hints for you. Would be a good idea to add some series resistance say around 50-200 ohms or larger to BOTH of shunt sense lines directly at the shunt. If the CO-04THM fails or the sense cable some how gets shorted this will limit the current to less than an amp and prevent a fire. Just heat shrink the resistors at the fly leads directly at the shunt. The 50 ohms will have no effect on the reading because the module's 5meg input resistance is so much larger, a fuse is another options. Always be thinking about what happens to wires if they get shorted when you have shit loads of battery current available.
The second thing to consider is the "Common Mode Range" input specification on the CO-04THM module. It's listed as -1.3 to +3.8V. relative to the COM terminals This is telling you that the TC1+ and TC1- inputs must remain in this range. See the note on the data sheet wiring diagram for TC4+ . Obviously you have violated this by your shunt being at 50V, I assume nothing bad has happened, most likely because the module has some internal isolation and you have not connect the COM to any other part of your system. Watch for phantom paths where the COM could get referenced to BAT- or an un-powered item with leakage to BAT-. It's very easy to blow out the inputs with 50V signals, doesn't take much leakage current. This is why you usually see shunts in the negative bus bar. I suspect the Common Mode Range also applies between TC1+/- and the other TC inputs. Ie. don't want TC1 on a positive BAT shunt and TC2 on a Negative BAT shunt. There are likely internal protection diodes between the TC inputs and the COM and the ADC power rails. What you really need is a module that has a common mode input range of >60V.
Good luck
Craig
That is a huge Shunt good job Chris for giving you that Shunt
That's awesome! Good job! :)
Woww thats a Boss set up you've got.
At 5:14 it looks like you had a little arching and a sparking on that back bus bar.
Nice vid! And sweet power room setup! They suggest you short out all unused TC connections; I noticed you didn't. How much capacity did you used to have with your lead acid setup compared with what your current LiFePo test/trial setup has?
Awesome job brother.
Nice work as always
HighTechLab's worst nightmare, An M-80 in a jar of powdered graphite.
As always.... I want one, but I am too stupid. Jim
Is that thermocouple module electrically isolated? Those lines coming off of your shunt might was well be connected directly to your battery. Watch out for ground loops! I would recommend putting two 0.1 amp fuses right on your shunt before going to your shielded cable. One for each wire.
RingingResonance I think this is why manufacturers typically utilize the negative as its safer
+ one for small fuses at the shunt-end.
but than again, the wires are so thin and the current so high, that the wire it self would turn into a fuse if something happened...
Since the battery Bank positive and negatives are not bonded to ground, if it were to short to ground there would be no current flow.
Cool. I'm sure you tested this. An unforeseen ground loop would fry those wires should your isolation barrier break down for any reason!
That is wat you get by using the impirial system 👻👻👻👻 i like youre vids
Copper bus bars would be a big improvement
How do you figure? The aluminum is so oversized for the application it's actually insane.
@@HighTechLab ...copper is a much better conductor, less resistance, less loss than aluminum, yes your thick aluminum bar can take the amps so can a thick iron bar too, but copper is much more efficient, since your system is state of the art. Aluminum has 61 percent of the conductivity of copper. Big improvement with little money. Of course lithium batteries more important. Just saying since everything else is first class.
Great job! Some brain farts aren’t so forgiving 🥴
Always be thinking about what happens to wires if they get shorted when you have shit loads of battery current available.
Yes, those exposed buss bars direct from the battery banks are just asking for an explosion or fire.
Kinda wondering why you are trying to copy industrial Panel layouts, when you won't buy the single tool that every qualified Panel Wiring Technician has. A ratchet crimp tool. Without a stable termination for those wires your mV readings are going to drift in time.
And please get some rubber sleeving for that shunt cable end, I don't know your wiring layout but it seems a dubious idea to have the shield grounded at one end and flapping about near a positive rail at the other.
How much current does all the automation and monitoring equipment use? I don't think I could spare the power with my small system, well I could, but I have other uses, a couple amps at 24v 24/7 adds up, my system is alot closercto home, I don't really need such equipment, I need a mppt controller for wind power , for lithium ion, the midnite classic150 is out of my price range, great video...
Draw on the 48v battery Bank for the automation is less than an amp. The idle draw from the inverter far exceeds this draw.
Does the thermocouple module have built-in linearity corrections? Or does it simply report naked millivolts to the CPU? If the latter, then you're good. If the former, how do you compensate for the non-linear signal reported by the module to the PLC's CPU? The shunt will be 100% linear. Also... does the TC module have internal cold-junction compensation? If so, then again, how do you plan to map the mV signal of the shunt to actual Amps in the software?
It can do both CJ comp and raw input over a few ranges
Why not use a drill punch to mark the holes you need?
Typically the shunt lands on the negative with the plc does it specially call out positive placement
The PLC is isolated so it doesn't call out any placement for a shunt because it's designed for a thermal couple module
HighTechLab cool I also want to add a Plc to my off grid place, have you seen my system?
I am subscribed to you, my understanding is there are few systems you have going. Is that correct? What is your approximate location?
Does sheilded wire make a difference ? Does it work when ac and dc lines run together or just for dc to dc wiring?
Aluminium is nice to work with 100%. I have a lot of Al busbars
Is that grey voltage regulator in the control box just hanging by the wires?
Which control cabinet are you referring to, the big one or the small one?
@@HighTechLab The one you installed the thermocouple module in
@@jschroedl983 ah. That is a DC to DC converter to run the solar tracker. It is temporary as my plan is to build my own tracking logic. It will be removed as soon as I make that happen.
@@HighTechLab Ah, thank you.
I want one, but haven't got the money
Yea Need More Copper on them Buss lines..
Electronics are flashy but extra cost for not much
Not having proper monitoring equipment can kill a battery Bank. Some electronics are cheaper than replacing abused batteries excessively
I usually use a multimeter. So the system will turn off if there is a problem?
There is a handful of fail safe options depending on the situation
Man that buss Is ugly