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I purchased an Infinisolar Super 4kw hybrid inverter and 4 Pylontech 2.4kw lithium batteries from Full Circle Solar.

I want to use the system as a battery backup for now and add panels later. 

I have no idea what I’ll get from the system as far as usage is concerned - the inverter can charge 4 lithium batteries (which I bought after reading all the discussions).

The installation was fairly painless into a custom tall cabinet also supplied by FCS. Being black it is quite conspicious but can be painted a nicer colour later as it is next to a pool table. The original position was moved due to it being taller (by 60mm) than the description on their site.

However, I am still waiting for a quote from 3 electricians for the splitting of the db.

If this is because it is Dec I don’t know - two definitely did not even bother although they took the time to inspect my db. And this is not rocket science.

I told all of them I will get all the parts and they only need to do the labour and coc.

In the mean time I’ve ordered the parts for the inverter battery setup (dc isolator, dc thermal circuit breaker instead of fuses, ac 2 way switch) from Amazon of all places. These will be mounted on the cabinet. I could not find these parts locally and gave up looking. Also a nice clamp meter for a price that you cannot get locally. I (and swambo of course :-)) like the look where everything is hidden from sight behind a heavy metal cover.

So much for supporting the locals.

I have some more questions and replies will be appreciated.

the inverter, although a 4kw, can go to 8kw which it can import from the mains.

How do I accomodate this with the recommended 20 amp mcb connecting it to the db? Does not make sense to me.

Has anyone done this before with similiar inverters?

And why must the switches going to the inverter be 6k instead of the 3k? This is info from the electrician.

I really need this info before purchasing the parts for the new split db.

 

 

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2 hours ago, Johandup said:

How do I accomodate this with the recommended 20 amp mcb connecting it to the db? Does not make sense to me.

I think the fundamental question is always exactly what the job of that breaker is. Normally the job of the breaker is to protect the cable (primarily) and protect against fault conditions (which usually heats up the cable, so this is secondary). The inverter itself would usually have its own overload protection, so my gut feeling is that you don't size this breaker to protect the inverter, rather, you size it for the cable size and the total expected load.

It probably depends on what they mean by 8kw total. Is that continuous or surge? If continuous, does it mean it will combine 4KW from the battery and 4kw from the grid, or does it mean it will (sometimes, say the batteries are too low) take the full 8kw from the grid?

I suspect they recommend 20A because the 8kw figure is a kind of surge capacity. To understand this you must look into the so-called "curve" of the breaker (see attached picture I stole from the interwebz). A C-curve breaker will trip instantaneously only if you put about 5 times more current through there than its I_n (current nominal) rating, but if you go only slightly over (say 10%) it takes a bit of time to heat up before it finally trips. A 20A C-curve breaker (good for 4.5KW continuous) would do 8KW for a full minute before it trips, and it would do 6kw for a good 5 to 10 minutes.

curve.png.3667298db4143d3932f7e727599e7c5f.png

So if I have to guess, that is why they recommend a 20A breaker.

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7 hours ago, plonkster said:

I think the fundamental question is always exactly what the job of that breaker is. Normally the job of the breaker is to protect the cable (primarily) and protect against fault conditions (which usually heats up the cable, so this is secondary). The inverter itself would usually have its own overload protection, so my gut feeling is that you don't size this breaker to protect the inverter, rather, you size it for the cable size and the total expected load.

It probably depends on what they mean by 8kw total. Is that continuous or surge? If continuous, does it mean it will combine 4KW from the battery and 4kw from the grid, or does it mean it will (sometimes, say the batteries are too low) take the full 8kw from the grid?

I suspect they recommend 20A because the 8kw figure is a kind of surge capacity. To understand this you must look into the so-called "curve" of the breaker (see attached picture I stole from the interwebz). A C-curve breaker will trip instantaneously only if you put about 5 times more current through there than its I_n (current nominal) rating, but if you go only slightly over (say 10%) it takes a bit of time to heat up before it finally trips. A 20A C-curve breaker (good for 4.5KW continuous) would do 8KW for a full minute before it trips, and it would do 6kw for a good 5 to 10 minutes.

curve.png.3667298db4143d3932f7e727599e7c5f.png

So if I have to guess, that is why they recommend a 20A breaker.

Thanks plonkster,

I’ve placed the mcb order on 6ka and curve c. That should cut out nuisance trips.I received a massive quote of R10k for the db work so its time to go to another plan. That would work out R150 per connection. People aspire to become rich quickly. 

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9 hours ago, plonkster said:

I think the fundamental question is always exactly what the job of that breaker is. Normally the job of the breaker is to protect the cable (primarily) and protect against fault conditions (which usually heats up the cable, so this is secondary). The inverter itself would usually have its own overload protection, so my gut feeling is that you don't size this breaker to protect the inverter, rather, you size it for the cable size and the total expected load.

It probably depends on what they mean by 8kw total. Is that continuous or surge? If continuous, does it mean it will combine 4KW from the battery and 4kw from the grid, or does it mean it will (sometimes, say the batteries are too low) take the full 8kw from the grid?

I suspect they recommend 20A because the 8kw figure is a kind of surge capacity. To understand this you must look into the so-called "curve" of the breaker (see attached picture I stole from the interwebz). A C-curve breaker will trip instantaneously only if you put about 5 times more current through there than its I_n (current nominal) rating, but if you go only slightly over (say 10%) it takes a bit of time to heat up before it finally trips. A 20A C-curve breaker (good for 4.5KW continuous) would do 8KW for a full minute before it trips, and it would do 6kw for a good 5 to 10 minutes.

curve.png.3667298db4143d3932f7e727599e7c5f.png

So if I have to guess, that is why they recommend a 20A breaker.

Thanks plonkster,

I’ve placed the mcb order on 6ka and curve c. That should cut out nuisance trips.I received a massive quote of R10k for the db work so its time to go to another plan. That would work out R150 per connection. People aspire to become rich quickly. 

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14 hours ago, Johandup said:

.I received a massive quote of R10k for the db work

A year ago I paid 6k. That included some materials (a new surface-mount DB, and a little bit of cabling, maybe about 1k materials). But I basically bought a full day of the sparky's time to be safe, because there was a lot of specialist equipment involved (anti-islanding is external with the multi). I also asked him to neaten my DB up a bit, something yours can definitely do with (it's not bad per se, and it's not dangerous, but it could be better). So yes, agreed that 10k is a bit much... but it's not too far out for the right kind of expertise.

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On 12/18/2017 at 7:12 AM, Johandup said:

I have some more questions and replies will be appreciated.

the inverter, although a 4kw, can go to 8kw which it can import from the mains.

How do I accomodate this with the recommended 20 amp mcb connecting it to the db? Does not make sense to me.

Hi Johan

Page 7 of the manual says a 40A breaker. 

On the load side I would have a 16A breaker Max Overcurrent is 52A for 1ms.

On 12/18/2017 at 7:12 AM, Johandup said:

 

And why must the switches going to the inverter be 6k instead of the 3k? This is info from the electrician.

I really need this info before purchasing the parts for the new split db.

6kVA switches are industrial class switches whereas 3kVA switches are residential (based on their short circuit capability). Since you have a 4 kW unit 3kVA switches are not going to  do.

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4 hours ago, Chris Hobson said:

6kVA switches are industrial class switches whereas 3kVA switches are residential (based on their short circuit capability). Since you have a 4 kW unit 3kVA switches are not going to  do.

Hang on... mixed up unit here. I believe it is a question of 6 kiloVOLT vs 3, not KVA. That's the impulse withstand voltage, ie how much you can put across it under test conditions without failure. Some googling around says 3kV is good enough for domestic purposes, but if there is a higher probability of such surges in your area go with something higher. If you live in an area with heavey weather and lightning strikes, you should apparently go with the higher voltage. I have no experience, this is just some google-fu and the basic knowledge that breakers do have such a big number that they test them at.

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Guys,

Thanks for taking the time to reply. 

Much appreciated. 

I’ve googled far and wide to research distribution boards and solar wiring and am really not much wiser. 

It is not addressed in the SANS regulations currently (?).

This will probably happen in future - same as with electric fencing, and we will have to jump. So the best is to do a db with future changes in mind. Especially taking sparky labour costs in mind. Then the component costs pale in comparison. 

What is the experience with the neutral wires in split db’s? Must it be earthed before or after the earth leakage? Must one create a separate neutral away from the mains?

Anyway, I was informed that my order will only be delivered next year. So I will have a peaceful time with my family. 

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3 hours ago, plonkster said:

Hang on... mixed up unit here. I believe it is a question of 6 kiloVOLT vs 3, not KVA. That's the impulse withstand voltage, ie how much you can put across it under test conditions without failure. Some googling around says 3kV is good enough for domestic purposes, but if there is a higher probability of such surges in your area go with something higher. If you live in an area with heavey weather and lightning strikes, you should apparently go with the higher voltage. I have no experience, this is just some google-fu and the basic knowledge that breakers do have such a big number that they test them at.

The true story of ka ratings. 

Worth reading. 

Two earth leakages fused in my home during electrical storms and caused damages as it was not detected. 

http://www.mandrelectrical.com.au/karatings.php

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2 hours ago, Johandup said:

Must it be earthed before or after the earth leakage?

Before! Otherwise it doesn't work :-)

Earth/Neutral bonding is a topic that comes up every now and then. You are not allowed to make your own bond. This is done either at the transformer (in a TN-S setup) or there might be a second bond where it enters the premises (TN-C-S or PME). But when the inverter is running on its own (grid is disconnected), there must be an earth/neutral bond in place otherwise the earth leakage doesn't work (or sensitivity is significantly reduced). That means the inverter must bond earth to neutral if it disconnects the grid. Most of them do, but it is something to check. On some it is configurable (Victron Multiplus).

2 hours ago, Johandup said:

Must one create a separate neutral away from the mains?

Inverter side has its own neutral bar. Your changeover switch must switch both Live and Neutral. Refer to SANS regulations for installing a UPS. If the output of the inverter feeds sockets, it must have its own earth leakage on the output side too.

1 hour ago, Johandup said:

The true story of ka ratings. 

Exactly. Unit confusion. Breakers have a voltage rating, a current rating (max it can break safely), and then it has a working rating and a curve. Lots to consider :-)

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To specify the required KA rating of the breaker you have to determine the maximum fault current at the point of the breaker installation. This maximum fault current is called the Prospective Short Circuit Current and it is the current that will flow if you have a dead short on the load side of the breaker. (Phase to phase will generally give you the highest fault current.) Only the impedance of the upstream network will restrict the current flow. The Ka value can be determined by measurement or calculation.

To do the calculation you will need to know the transformer details (KVA rating of the transformer, Rated short-circuit impedance voltage of the transformer (%) and Phase to Phase voltage) and the cable details (Cable size, material and length). 

It basically boils down to ohms law I = V/ZTotal where (ZTotalTotal impedance of the upstream network in Ω).  ZTotalZTransformer ZCable

A smaller transformer will have a higher impedance resulting in a lower fault current. Also a long cable will have a higher impedance resulting in a lower fault current.

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  • 4 weeks later...

Hi Johandup

About your question on cb's . I will not get too technical.

This all depends on what the battery charge is going to be for the input cb.

I do not think anyone has mentioned this before.

The output of the infisolar is 4kw about 18amps  So the cb will have to close to that value (20amps). Also the wiring has to be of a higher value (25amps).

I always wondered why the input cb and wiring suggested was 60amps and this is what I concluded after thinking about it for quite a while.

 

The input cb has to be the output kw plus the battery charge kw plus loss kw. This is why the input power is higher .

You can limit the input amps by seting the battery charge current down. I am sure you can damage your batteries if you charge at too high current.

For lead acid batteries this is the formula.

The maximum charging current = Battery capacity (Ah) x 0.2

 

I have two infinisolars in parallel and protect the input for each of them with 40amp cb's and wiring and have no problems.

 I only have one bank of 4x 12v 180ahr batteries so I have set the battery charge current down to 18amps each (36amps total).

I  have split the charging current between the two inverters.

For me this adds about 8amps to the input. ( 4amps for each inverter ) without losses.

18amps + 4amps + loss = about 25amps x 2 input current (50amps mains input)

A normal household is protected by a 60 amp single phase breaker .

It does not make any sense to proctect the input to the inverters with 60 amp breakers unless you have or going to fit a huge battery bank and have to charge them with high current.

The maximum input current for the infinisolar super 4K is 40 amps and will allow you charge batteries at 80amps max and this is about 18amps on the mains side.

If you had two infinisolars in parallel and charge at max current a 60amp home breaker will trip.

 

The input cb has to be the output kw plus the battery charge kw plus loss kw.

18 amps + 18amps + loss  X2 = > 72 amps.

This will only apply if you are charging from mains power and not  from solar panels.

 

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Hi Peter,

Thanks for the reply.

I bought 6ka mcb as they were only R10 more than a 3ka mcb with far better short circuit protection. Peanuts really.

It is amazing that a 3ka isolator costs R109 and a far better 6ka goes for R279.

I went for 10mm wire as I could buy it per meter whereas the 6mm wire comes per 100m rolls. Less cash this way.

My whole setup is planned not to exceed 18 amps at a time. So a lot of discussions were done with my wife.

We are only two in the house so it makes it easier by far.

I bought a clamp meter to measure all the current consumption.

I am currently busy splitting up the distribution board into a low amp inverter supply side and a high amp mains supply side.

I am replacing all the mcbs to the right size as my old farm house db setup is not right.

I hold thumbs that all will work as planned when I commision this.

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3 minutes ago, Johandup said:

Hi Peter,

Thanks for the reply.

my setup is with an infinisolar 4kw with 4 pylontech  2,4kw batteries. I chose this system so my wife can look after when I’m not around.

I bought 6ka mcbs as they were only R10 more than a 3ka mcb with far better short circuit protection. All with level C curve trips.

It is amazing that a 3ka isolator costs R109 and a far better 6ka goes for R279.

I went for 10mm wire as I could buy it per meter whereas the 6mm wire comes per 100m rolls. Less cash outlay this way. I only needed 10m per colour.

My whole setup is planned not to exceed 18 amps at a time. So a lot of discussions were with my wife.

We are only two in the house so it makes it easier by far.

I bought a clamp meter to measure all the current consumption.

I am currently busy splitting up the distribution board into a low amp inverter supply side and a high amp mains supply side.

I am replacing all the mcbs to the right size as my old farm house db setup is not right.

I hold thumbs that all will work as planned when I commision this.

 

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