Hello,
I have a 3 phase system with 3x Multiplus II 48/15000 200-100. The DC cables are about 5 meters long and 70mm2 thickness (2 negative and 2 positive per multi).
The cables reaching about 61 celcius at high amps (not at the connections, in the run)
The Victron manual says 2x 150mm2 for over 5 meters, the installer says 70mm is more than enough. The cable is high amp flexible welding wire.
thank you
@offgrideu
Not easy to answer over the internet as the physical set up affects the design alot. The cables are also rated open air so must be sized up if in trunking.
It is 5m return trip in the manual. In other words one way is 2.5m to the bank/bus bar. Never go under min spec. Which for the MP2 15kVa is actually 2x95.
Go bigger if the bank is further away (or cables in trunking). Or if the bus bar is close then use 2C 95mm² and make sure the battery bank can supply the current (without voltage drop to the bus bar) with the correct gauge and number of connections.
Anything less then that you will have problems
15kVa at max load pulls way more than 250A BTW
Hi!
The cables are 6 meters away one way, and they are in a closed plastic conduit, which the manual says not to use. 250 amps is the max I’ve hit in our use case so far.
Whst kind of problems should I be looking for? Other than a fire and melting wires… Lol
Your voltage drop is probaply high right now
Temp of 61 degree C. is also pretty high,
as alexandra suggested you need to have bigger cables, at least 95mm2,
The manual says to use 150mm2 with that lenght…
When the cable length from A to B is 6 meters, then you need to calculate with 12 meters for the complete current path.
When the maximum current can reach 250A over 12 meters, then 95mm2 is the advised cable thickness. And when cable is locked up in a closed cable duct, so that the cable can cool less good, maybe 120mm2 is n’t a bad idea.
Next to the cable thickness, also the cable connections are important. Bad or insufficiënt connections can also give hot spots, causing the cable to warm up also. In this case, when you feel the cable in the middle and at the terminal ends, then you can feel there is a clear difference in temperature.
For example: when the connection path of cables and connections have a voltage drop of 0,2V only, but the current is 250A, then 0,2V x 250A makes 50 Watt of heat (loss).
I understand and agree, I am just hoping others agreed and I can convince my authorized vicrron dealer /installer to fix it, so far they said it’s fine and per specification. And the victron sales manager is utterly useless they alwsys side with the dealer and ignore the end users concerns.
Specifications are in the manual. So i am not sure what negotiation needs to be done there. Its either right or wrong.
And a 15kVa in overload (and this can happen for a number of reasons - not just normal load conditions.) can draw twice its rating. The volt drop would be awful and so would DC ripple.
Then I would ask if your loads aren’t that high why have they sized your inverter so large?
I am not saying your system wont work, longevity would be called into question and it would be horribly inefficient. Prone to issues.
By hey if they want to handle warranty and all that jazz then its on them. I wouldn’t be happy with it is all i am saying.
This system if done right is a 10 year investment. Its either 10 years of pain or 10 years of no issues.
the system was sized large, as there is a possibility of further large loads, so the wiring should be sized properly for a max load and potential overload situation.
Look at this:
The contract from the installer said our system load capacity is: 45KVA. 90KVA for 30 minutes, and 135 KVA for 20’ minutes and the installation specifications meets those requirements.
How many amps would be running through our DC cables to the MULTIs at 135 KVA or 90 KVA, and how would a 70mm2 cable handle it? Probably not well.
Keep in mind there are copper bus bars, and the wires from the Multis to the bus bars are 70mm. Then there are 12 batteries (52v x 168 AH) in parallel, the wiring to each battery is significantly smaller diameter.
135kVA is over 2100A, 2x 70mm2 does not like that, they wont last 20 min…
What is the battery wiring size? I would recommendt 35mm-50mm if they are wired separate to the busbar, if smaller that could be an issue too
Are you grid connected running ESS or is this meant for the hybrid generator system off grid or backup essential loads system?
Are you planning on inverting all 90 or 135kVa?
If so it is undersized by far.
100% off grid. Yes all the loads via the multi
So the system is too small unless you plan on having heavy generator support as well.
To run 90kVa for half an hour requires larger than 90kVa of inverter and you have some big air conditioning in the room.
135kVa for 20 minutes inverting requires a bigger battery bank as well (unless there is use of generator - but 1 unit per phase 15kVa wont even pass through the current (100A passthrough) required to aid that load. 135kVa require 200A passthrough.
Thanks for the feedback. The system can’t perform per the contract that’s clear, but our needs aren’t that intensive either. I can see a peak of 60 kw for a few minutes as the absolute max
So the question is what do I as the end user do? I bought a turnkey installed system through one of 3 authorized Victron dealers in Greece, and they insist the wiring is correct. The regional sales manager doesn’t respond to emails or calls. Its a new install.
Send a picture of the manual? I have no idea.
Have you paid everything that is due? If not explain it wont be cleared until they bring it up to min spec?