Good afternoon, could you tell me whether the transformer winding in the new Victron MultiPlus 6k5 inverter is made of copper or aluminum
Aluminium
there is a topic about this
The 6k5 weighs only 29kg whereas the weight of the 5kVA MPII is 30kg! I would question that weight even if the 6k5 has a toroid with aluminium wires. The core has to be of magnetic iron and the size of the core is determined by the magnetic flux required which dependent on the power rating. Aluminium wires can carry less current than copper ones but it is possible that copper coated wire is used exploiting the “skin effect”. The other explanation may be that the 6k5 has two fans and I believe that the 5kVA MPII has only one fan. It is therefore possible that the toroid can deliver more power because of increased cooling. In general, transformers can withstand higher operating temperatures than electronic switching devices such as MOSFETS and IGBTs so a higher internal operating temperature may be acceptable.
Is it possible that 6k5 internals are fundamentally different from the classical MultiPlus designs. Perhaps some sort of hybrid? Has anybody done a teardown?
It is clear that Victron is reacting to the lower prices from the main Chinese competitors. Hopefully that is without degrading their main technical advantages. As these inverters are now made in India the lower labour costs should help. Wages in India are currently still lower than those in China!
Victron should switch to high frequency inverters with ferrite transformer cores. For sure it will be cheaper to manufacture.
That surge advantage of LF inverters is more like a myth from my point of view…
If properly designed, those high frequency inverters could deliver tremendous surge power without any problems.
All EV industry is using high frequency inverters/converters and you know some models are over 1000HP.
That means over 700kW from a 100kW battery for seconds/minutes!! If that is not surge load…
Do you believe they are using low frequency large toroidal transformers?.. 
In the EV industry weight and efficiency are everything, even more so in the electric truck industry. A toroid transformer weighs a ton compared with a PCB with IGBT’s.
In boats and most static solar PV installation weight is generally irrelevant.
I am not decrying transformerless inverters but any electronic switching device is much less robust than a “dumb” transformer. To fatally damage a transformer requires either seriously high temperatures causing insulation to melt, physical damage and/or a short circuit due to water ingress. Thyristors etc are much more easily damaged. I actually have 3 8kW Solis inverters running in parallel. I purchased these rather than the MultiPlus II for the simple reason that running 8kVA and larger MPII’s in parallel is complicated and I was concerned about installing these myself. With the Solis inverters that was child’s play!
See thread above – a transformer with CCA windings is bigger, lighter and cheaper than one with copper windings, and the bigger surface area means it’s easier to keep cool, this is one reason the power output drops off less whan hot than the older models.
HF inverters with ferrite cores are indeed much lighter, see the Multi RS Solar, but there is demand for both types – LF transformer based ones do have a reputation for being more robust, whether this is deserved or not, so many customers still prefer them.
CCA cable is less than half the weight of copper cable but its resistance is 50% higher. Larger diameter wires are therefore required possibly offsetting some of the cost advantages. For a given iron core size a toroid with CCA wire might have a bigger diameter. I suspect that the main reason why Victron has opted for CCA wire is the cost. Weight is perhaps not the main driver. For shipping costs and inverter installers weight is important but weight can also be an indicator of quality!
CCA wires are also more flexible than pure copper wires, this potentially reduces winding costs!
No doubt the Indian manufacturers of the toroids used by Victron have done their homework but having experience with Indian manufacturers of electrical products it pays to watch them for corner cutting! The key is in setting clear specs and continuously monitoring their output.
One further observation. I noted that the fans are in the middle of the airflow.
The cool air is drawn through the bottom of the enclosure and then passes over the PCB’s. The two fans are mounted between the PCB’s and the toroidial transformer and the warm air exits through the top of the enclosure.
This means that the lowest temperature is in the section housing the electronics and the highest temperature is reached over the transformer.
This is a very sensible arrangement. With two powerful fans there is increased airflow over the toroid compared with the 5kVA MPII.
I sometimes wish I had purchased 3 or 4 6k5’s rather than the 3 nos Solis 8kW S6 inverters. Mind you the Solis inverters work like a dream.
Weight is not an indication of quality when you’re the one having to install it… 
The same manufacturer is making the transformers used by APC/Schneider in their UPS products so they should be OK.
That should give confidence to the buyers of the 4k5 and 6k5.
For the same resistance, CCA wires need 1.6x the CSA of copper ones so the winding is thicker, but weighs about half as much (density is only 30%) – which means transformer weight is reduced by maybe a quarter, depending on the core/winding ratio. On top of that aluminium is about half the cost per kg of copper, so the winding cost is about a quarter of copper.
You end up with a bigger but cheaper and cooler transformer, fine for this application but not for a lot of other ones.
Against this CCA wires need a lot more care for termination and connection to ensure low resistance, for example exact-size ferrules correctly crimped on with high-pressure hydraulics – fine for a manufacturer/production line set up to do this, not so much so for the man in the street, or probably quite a lot of electricians…
You are quite correct. Years ago there was a lot of talk about CCA cables being used for industrial and domestic wiring.
I looked at it for busbars but by the time you have considered the extra cost of the connecting materials the savings are not particularly high. Multistranded CCA wires are potentially even more problematic.
I have heard reports of Chinese companies selling multistranded copper wires that are actually just copper coated aluminium wires. I have recently purchased 10mm2 multistranded tinned copper wire via Amazon from a Dutch distributor (the wire was made in China). Other purchasers claimed that it was actually aluminium wire!
As the strands were very fine I soldered the wire ends before crimping the lugs. The wires were definitely made from copper!