Split feed for house

[crappy]

Hi Folks,

I have a couple of 2KW sine wave invertors I want to use in the house. To start with, I want to run all the light circuits and a couple of rings (low usage ones) off them. There are of course a few issues.

My idea is to have a second (4 way?) CU and move the circuits to it. It would be fed from a contactor (40A) which would be fed from either the invertor (only ever one invertor to a circuit(s)) or the original CU. The contactor would be energised by the invertor so any overload, low battery etc, would cause it to drop out and switch back to the main supply.

From the original CU, I will be feeding the contactor with meter tails (overkill but...) and contactor to new CU would also be with meter tails.
The feed from the main CU would be via a breaker (40A) and the second would have its own isolator / RCD in it.

There would be a similar setup with the second invertor when I get round to it.

My issue with all of this is "hassle" and bulky. Is there a neater way I could do it? Split load CU? (for a single invertor only) or do you get CUs where I can split the load as many times as I want?

I have a lot of slack on the circuits coming into the CU so to move them is simple and no joining required. Space is a bit of a premium in the "cupboard" as I a solar invertor, the 2KW invertor, CU and various isolators etc so compact is better but not essential as I can grow the cupboard

Any suggestions or comments welcome

 

[ban-all-sheds]

I will be feeding the contactor with meter tails (overkill but...)

So why use them?

It's only a 40A circuit - 6mm² will be OK.

My issue with all of this is "hassle" and bulky. Is there a neater way I could do it? Split load CU? (for a single invertor only) or do you get CUs where I can split the load as many times as I want?

1 main CU, and one split - one inverter per side?

Space is a bit of a premium in the "cupboard"

I'll bet it is if you've got enough batteries in there to deliver 4kW for a meaningful amount of time.

 

[crappy]

So why use them?

It's only a 40A circuit - 6mm² will be OK.

I "thought" anything feeding a CU would have to be those? Thanks for the tip.

1 main CU, and one split - one inverter per side?

urm, had not thought of that
So a split does not have to be a RCD in between each load, they can be fed as you wish? A RCD on each for the incoming (Do I need an isolator or does a DP RCD count?)

I'll bet it is if you've got enough batteries in there to deliver 4kW for a meaningful amount of time.

Currently a sore point in my life. The lack of a garage means I have to find space in study. Currently, have one 270AH battery weighing in at 60Kgs. More to come.


if I relocate the invertors and batteries to an outside "cupboard" I plan to build (soley for this, water proof etc etc) would there be any issue with running the feed from invertor to CUs? It would be from within the cupboard, through the wall into the house so no armoured would be needed(?)


Thanks -
Crispin

 

[bernardgreen]

Two points

[1] Do you really want a generator of hydrogen and oxygen inside your house.

Gassing batteries produce these gases in the precise mixture for an explosion. One spark and the battery and surrounding area suffers damage.

[2] A simple change over contactor selecting mains or invertor as supply to the CU will work. But it is not safe unless the contactor is specifically designed for the purpose and cannot under any fault / damage situation allow mains and invertor inputs to become connected together.

If the invertor fails do you really want to unconditionally fall straight back to mains ? If you were on invertors due to a problem with the mains supply then it might not be advisable to re-connect to the mains until you were sure the fault with the mains had been cleared.

 

[crappy]

The battery is a valid point. While it is a sealed one and recombines the gases internally, it would still vent if something was going very wrong.
Having said that, the "cupboard" which it is in actually has a vent to outside. This will be forced as well for cooling for the invertors.



The contactor point is very sound! I feel a bit daft that I did not remember that they do burn and leave contacts closed. I've changed a few burnt out 3 phase motors from that.
Anything I should look at for a "special" one? I'm being fussy but I would like one with very rapid switching so that most appliances would not "notice"

I don't see a problem with the automatic failover. The invertor will drop out if there is an overload or low battery. Seeing as it is _only_ a 2KW invertor, if someone plugs a kettle into the study or lounge, it would trip out. 2+KW is an overload for the invertor but not outside of the circuits capability.
One of the safety features is a 5 minute delay before resetting so there would not be any chatter.

Cheers,
Crispin

 

[bernardgreen]

it would still vent if something was going very wrong.

The charger has to be one that cannot over charge under any circumstances including a dead cell ( voltage below 12 ) which may be interpreted as a battery so depleted that it needs full or boost charging.

Having said that, the "cupboard" which it is in actually has a vent to outside. This will be forced as well for cooling for the invertors.

Essential when charging at a fast or boost rate.

Anything I should look at for a "special" one? I'm being fussy but I would like one with very rapid switching so that most appliances would not "notice"

Using two contactors each with an auxilary contact such that if the armature is stuck for any reason in the operated postion then the coil of the other contactor cannot be energised. The contactors should be the type where a welded contact prevents the armature from moving from that position. Or you could use forced break on de-energise and hope the return spring remains powerful enough to break apart any welded contacts.

If you want the equipment to "not notice" the break during change over then run them on small ( 15 second ) UPS units.

I don't see a problem with the automatic failover. ~~~~ One of the safety features is a 5 minute delay before resetting so there would not be any chatter

You may find problems when you look carefully how it copes with a short break in the mains. With delays to prevent cycling between mains and invertors a 5 second breal in the mains might become a much longer 5 minute delay.

 

[ericmark]

1) Star / Delta contractor should have all the required bits to stop two sets on contacts being in together.

2) See all problems I had with 3kW inverter go for 24 volt not 12 volt and don't buy from china.

3) Temperature senders on battery is only way to detect faulty cell. Look at Ford tractors they were fitted as standard on them.

4) The regulator used are switched mode power supplies and convert all DC from solar panel to AC then back to DC so that the opium voltage can be presented to the solar panel and also three stage so to start with charging flat out, until at around 14.8 volt (For 12 volt lead acid), then are voltage fixed until the current drops to around 10A then drops voltage to around 13.2 volt.
This is a problem when using the battery as easy to stop the voltage dropping because of current used local.

5) With consideration of 4) why use batteries? Using grid tie inverters you can use the mains as the storage battery which removes many of your problems.
a) Reduced current at 12v we needed twin 35mm cables from battery to inverter. That's 4 cables in all two + and two -.
b) No batteries
c) Government system pays you loads of money.
d) No change over contactors.

With the narrow boat we had no option as not always connected to mains and also wanted to use supply from the 2 x 70A alternators on main engine. The 4 x 147Ah batteries one engine start and 3 domestic were good ballast so less concrete blocks were required.

But for house grid tie must be the way forward. Unless you want to guard against power cuts.

The switch mode charge units cost a lot of money depending on size of course and to use the old system of converting any extra energy to heat and not correcting voltage to opium level will be 60% less efficient.

 

[crappy]

thanks for the replies.

The battery and invertor setup is to run the various bits at night.
The PV panels are connected to a 2KW grid tie during the day and I get the FIT for that. While there is sun , the batteries will charge with a normal “intelligent” charger (which has a temp sensor) straight from the mains so, indirectly, albeit with a bit of loss, the PV panels will be charging the batteries. Only difference, I get paid for charging them
By night, which is when you use the most, they will run the various bits. Not much seen the point of spending on PV to run the fridge by day.

As for the invertor, I would love 24V ones but as I get the 2KW mastervolt for around £100 each, I cannot refuse them. Cabling, bus-bars, fuses, oh-F**k emergency switches etc etc for the 12V side are all rated for (min)320A (max is bus-bar @ 500) while the batteries are fused at 200A each, the feed to invertors is 200A. As each invertor will only take ±180A at full tilt, I am pretty safe. (me thinks…?) Fuses are SB so should handle any in-rush. If not, I could bump them to 250A
Each panel (everything less bus-bar) will service a single invertor.
I’ve had a battery go very bad on me as well as heard the first hand horror stories from an old friend who lost someone one a mine due to a shorted bank (spanner).
On the 12V side of things, I have done everything I can think off in terms of fail-safe.

Thanks for the contactor info!

Eric – any hints on where I can read about your issues?


Cheers,
Crispin

 

[ericmark]

Running a washing machine from an inverter
What is a "connecting starter"
Power on boats
Inverter no load power requirements
Cable size and inverter?
The main problem was the useless inverter. Rated 3kW with 6kW peak it started to burn out with a 2kW kettle.
The inverter had build in fuse bank one blade type auto fuse for each FET but there was nothing to show fuse had blown so once first one went then other FET's would heat up quicker and would not trigger the cooling fans. Never really sorted. Boat was sold so no longer my problem.

 

[crappy]

Thanks Eric,

seems though that all the invertors were MSW invertors. I have an 800W and a 1KW of them and never found them much good. Anything with a motor got really annoyed or stalled, they too seemed to bail out before they should have.

The ones I have are MasterVolt (Dutch?) and are pure sine wave. A friend who has the same one, loaded it up with a big angle ginger (around 2KW) and was pretty mean to it. Made the grinder work hard through a concrete block, lots of stop starts (was not able to stall it though ) and all was well.

His setup was simplier than mine, it's in the back of his Landcruiser and wired straight to the battery via a single fuse.

Thanks for the posts, will continue to read.