pilotfish

The following is cut from the Victron Multiplus User guide; "The MultiPlus is a safety class I product (supplied with a ground terminal for safety purposes). Its AC input and/or output terminals and/or grounding point on the outside of the product must be provided with an uninterruptible grounding point for safety purposes"

I cant think of a situation where earthing a metallic housing of an electrical appliance wouldn't be acceptable - in fact if it has grid power anywhere near it then it is a requirement, and if it doesn't then you should do it anyway.

I have had a cheapie lying around for a while so I took it now and measured boiling water through the transparent glass kettle, which in Joburg will be around 96C. My results varied from 85C to 56C depending on the measuring angle (85C when square on).

Can you post a spec sheet or full set of pics?

That is why I have previously tried to get a common naming format going on the forum; If it can feed back into the grid; Grid-Tie If it can use grid for charging and pass through but not feed back; Grid-Connected or Grid-Assisted (I like #2) If it can operate with or without batteries; Hybrid Type of ECC; MPPT PWM I am sure that there are other main categories which could be added to the above, but the above list would put an end to a lot of confusion. This new Axpert VM III should be called a Grid Assist (not grid-tied) Hybrid (can function with/without batteries) MPPT Inverter/charger. If you read the description you should have a basic understanding of the capabilities without having to delve into the manual.

Great to see someone getting a DIY pack up and running, well done. My only issue with laptop batteries (and please correct me if I am wrong) is that you are using Li-Ion (3.7/4.2V) and not Li-Iron (LiFePO4 - 3.2/3.7V) - My problem with Li-ion is that the average life expectancy is 300-500cyc when the battery is new. The laptop batteries that you are using are used, and although I assume that you are testing them and discarding the dodgy ones, the ones being used are probably 1/2 life by now. So have you allowed for the fact that the pack may die within 150-250 days, or am I getting this all wrong?

If you decide to go this route may I make a suggestion; the 24V version of the inverter that you have been sold is a bit limited in that it has a maximum PV capacity of 1500W, if you trade up to the 48V version of the same inverter then your PV capacity goes up to 3000W which is far more versatile if you decide to add panels in future (which you probably will) - or better yet the MKS 5k which is the 5kVA version if your budget allows. The reason that I suggest this is that you have 11kWh of battery capacity and a panel that will probably average around 6kWh/day if well aligned, you may well find that you would like to increase panel capacity in future as budget allows and it would be nice if your inverter was able to accept it.

Your MPPT section of the inverter has operating voltage range (PV input) of 60V - 115V and an absolute maximum open circuit voltage of 145V Your panels have an operating voltage of Vmp = 37V and an open circuit voltage of Voc = 46V 2 panels in series will give operating voltage of 74V and open circuitr voltage of 92V 6 panels in series will give operating voltage of 222V and open circuit voltage of 276V Read through the above twice. I cant say if the MPPT section of your inverter has been blown but if you connected 6 panels in series I would be amazed if it wasn't (I have never tried this personally so not speaking from any kind of experience in this regard). If on the other habd you have connected the 6 panels in parallel then your voltage at the PV imputs would be less than the 60V required for the MPPT to switch on.

This is your 1st mistake that I can see, you should have 3 sets of 2panel in series (for 72 module panels as 320W panel would normally be). By connecting 6 panels in series your open circuit voltage will be about 270V where your MPPT is max 145V - I think you may have toasted your inverter. The Axpert 3kVA+ comes in both 24V and 48V version - are you sure that yours is the 24V?

Like having an articulated truck with the engine in the horse and the gearbox in the trailer - I like it

I don't believe it has any ability to feed back, which is what I call grid-tie - this inverter is what I think should be called hybrid grid-assist.

I see R32.5bn in claw back has just been approved, probably split over three years, claw back tariff is over and above the Nersa approved tariff. So 2018 tariff increase for example would be Nersa approved 5% + Claw back of about 6% = 11%.

Because the PC at the end of long lead will see rectification sag + cable drop - close pc sees only sag.

Above and beyond! I guess that is a definite proof that it is the voltage regulation delay in the inverter and nothing to do with cabling.

The situation where neutral is not referenced to earth is dangerous, but unlikely to cause flickering. The neutral to live voltage will remain stable at around 230V from the Axpert inverter, it is neutral to earth that will be floating.

But no parallel mode

This Inverter looks awesome, I WANT! Had a quick glance at the user guide, 5kVA version adds the following; 5000VA / 5000W inverter 4000W 500V MPPT BMS comms for LiFe04 61V max charge voltage for the Royal's Trojans battery EQ function built in bluetooth with android app, detachable LCD control for remote up to 20m and for the battery-phobes....... you can run grid/PV only with NO Batteries I think @plonkster got a tough job on his hands now Axpert VM III_DS.pdf

That sounds about right to me, don't change anything.

Well the ROI is still 15%, but it is better than your alternative investment by a margin of 7% (if all goes according to plan) - still sounds bloody marvelous!

If your calculation is correct (it differs for each individual) then a payback of 7 years translates to an ROI of 15% pa - that would be difficult to achieve anywhere else. With unknown Eksdom increases in the future that is likely to improve.

Normally you would use a mechanical interlock - so contactor 1 must have opened before contactor 2 can close and vice-versa. This is normally accomplished with an auxiliary contact.

Quite right, but that is not what I was talking about although my use of the word BOND may have confused the issue. I meant JOIN (rather than bond) an un-switched grid neutral to inverter neutral. Grid neutral is at earth potential, if you connect grid neutral to inverter neutral then your inverter voltage will always be referenced to earth as 0v. Without this your voltages can float around, often with "earth" being the midpoint between live and neutral, so you will measure [N/E/L =115v 0v 115v] whereas you should measure [N/E/L = 0V 0V 230V] Hope that makes sense.

As an electrical contractor I would have no problem with bonding [neutral in/neutral out] at the inverter from a safety perspective. This will ensure that that your neutral is always bonded to earth potential as it should be and as it is by grid provider. Some municipalities may have some B/S requirement about isolating the alternative energy source from the grid, but this actually compromises safety in my opinion and there is absolutely no good reason for this that I can think of.

It is more than likely a standard PT100 type sensor, wire one in there (while closing your eyes) and see what happens Just kidding use a meter 1st to check for voltage on the sensor terminals, if 12V or less then I reckon you could connect a PT100 and see if it gives sensible info - if not then you have wasted about R100 or less.

A [phase failure/sequence relay] and a [3ph over/under voltage relay] are commonly available at any electrical wholesaler. You would need both connected to 2x contactors, one wired straight through and one wired to reverse rotation. If [phase failure/sequence relay] registers an anomaly then it will switch contactors from direct to reverse rotation, but if [over/under relay] also registers an anomaly then it will cut both relays. Not cheap!