I have a 12kw Deye inverter which has a max charge and discharge rate of 240A. 

I will be installing 4 x 5.5kw Hubble batteries. 100a each. 

The batteries will be connected in parallel

Do I install a 250A disconnect switch or a 400A disconnect switch? 

Edited March 1, 20224 yr by Deeos
Incorrect battery connection stated

Good question.  I have the same question.

*I'm sure you mean the batteries will be connected in parallel, and not series.

Edited March 1, 20224 yr by JayN

My view, was to go with a 250a and limit the charge and discharge to 210a.

The difference in price between the 250a and 400a fuse disconnector is significant.  

Also depends on the number of panels you have and name plate capacity.  If nameplate capacity is less than 10000w+your normal demand, then there should be no issue.  

You will loose about 2000w by derating the inverter charge/discharge.

 

 

The price is not the concern as I buy them directly from Electro Mechanica. 

I want to put the correct one. 

If they all in parallel that means I have a capacity of 400amps. But I am still limited to the inverter which can do a max 240A. 

 

So I think the correct way is to install a 250A which protects the inverter. Since the disconnect switch has fuses. By the time it blows the 400A fuse it more than likely would have damaged the inverter 

1 hour ago, Deeos said:

I have a 12kw Deye inverter which has a max charge and discharge rate of 240A. 

I will be installing 4 x 5.5kw Hubble batteries. 100a each. 

The batteries will be connected in parallel

Do I install a 250A disconnect switch or a 400A disconnect switch? 

You will need a 250A fuse holder which can also be used as a disconnect switch. 

Your battery does not dictate the size of the fuses. Your inverter rating does. However, you need to consider surges above the nominal AMPs for the inverter, which it can handle safely. So, if the rating on the inverter is 240A, you can multiply that by about 1.5. 240A x 1.5 = 360A rated fuses and holder. If 360A size is not available, you can put the closest to it - maybe 320A.

I would go with Keto size 2 (rated to 400A) and 320A or 360A fuses - whichever ones are available.

Otherwise, if the Deye has surge current rating in the datasheet, rather stick to that number.

Edited March 1, 20224 yr by PowerUser

You should also consider the current rating of the cable and spec the fuses to protect the cable too.

The manual says Max 240A, so 250A fuse will be fine (providing of course that you have used a minimum of 95mm^2 wire).

No need to worry about surge rating, as these are slow fuses.  They will handing double the current for around 30s, so great for protecting the inverter from prolonged surges.

If you follow some other advice, and go for 320A fuses, remember that the minimum wire size goes up to 150mm^2 (on the CoC, the fuse is determined only by the wire size).

(Double check those wire sizes though, I do not have the SANS table handy.)

8 hours ago, JustinSchoeman said:

The manual says Max 240A, so 250A fuse will be fine (providing of course that you have used a minimum of 95mm^2 wire).

No need to worry about surge rating, as these are slow fuses.  They will handing double the current for around 30s, so great for protecting the inverter from prolonged surges.

If you follow some other advice, and go for 320A fuses, remember that the minimum wire size goes up to 150mm^2 (on the CoC, the fuse is determined only by the wire size).

(Double check those wire sizes though, I do not have the SANS table handy.)

For my 120A spec SunSynk 5kW inverter, Steve from the PowerForum store advised me, that the correct fuse size is 160A and not 125A because of surge currents. That is approx. 120A x 1.35 = 162A.

And my fuses have rating gG - which means they are FAST ACTING fuses. Not sure, why do you use slow fuses for your installation...

Do you think, he is giving wrong advise and I should be using 125A fuses instead?

Edited March 1, 20224 yr by PowerUser

Would be nice if someone can post a video demonstrating a Sunsynk going into its surge capacity rating. I'm yet to see it. 

I dont understand why x = max dc charge/ use x 1.35

 

If max is 240 should one not have a fuse for said max to protect items?

26 minutes ago, Deeos said:

I dont understand why x = max dc charge/ use x 1.35

 

If max is 240 should one not have a fuse for said max to protect items?

As a general rule of thumb for electrical circuit, the fuse rating should be 1.25 times higher than the nominal load.

However for different types of load, various oversizing formulas apply:

https://www.electrical4u.net/basic-accessories/fuse-rating-calculation-chart-fuse-sizing-formula-for-motor-transformer-capacitor/

 

Thank you 

I will set the inverter to 200A since I'm going with the 250A fuse

16 minutes ago, Deeos said:

Thank you 

I will set the inverter to 200A since I'm going with the 250A fuse

A fuse should never be sized based on settings but rather on the technical specification and capability limits of a device. But anyway, it's your installation and money - you can do as you wish.

Fuses are specified based on the wiring.  Same as circuit breakers in a house.  Your fuse should be such that

1. The batteries do not self destruct.  Since they can supply thousands of amps, it is unlikely you can "over-size" a fuse such that the batteries are in full short-circuit without the fuse blowing
2. The wires do not heat up sufficiently to melt the insulation/catch fire/melt the wire
3. The fuse is able to break the circuit safely (determined by the kA breaking rating).  A fuse that is too small will explode.  That in itself can cause a fire or spew metal piece that cause a short.  If a person is close when it explodes they can catch shrapnel.  A lot of systems in SA I've seen seem to use puny undersized fuses in terms of breaking capacity.

Fuses aren't sized for the device.  The device will have its own internal fuse.  But obviously if you undersize your fuse, you are going to be replacing a lot of fuses.  If you think the fuse is protecting the device you are deluding yourself.

Disconnectors mentioned above should be as large as you can afford.  With most inverter systems you'll find it hard to find a disconnector for the high voltage range with suitable current rating.

Edited March 2, 20224 yr by Gnome

7 minutes ago, Gnome said:

Fuses are specified based on the wiring.  Same as circuit breakers in a house.  Your fuse should be such that

1. The batteries do not self destruct.  Since they can supply thousands of amps, it is unlikely you can "over-size" a fuse such that the batteries are in full short-circuit without the fuse blowing
2. The wires do not heat up sufficiently to melt the insulation/catch fire/melt the wire
3. The fuse is able to break the circuit safely (determined by the kA breaking rating).  A fuse that is too small will explode.  That in itself can cause a fire or spew metal piece that cause a short.  If a person is close when it explodes they can catch shrapnel.  A lot of systems in SA I've seen seem to use puny undersized fuses in terms of breaking capacity.

Fuses aren't sized for the device.  The device will have its own internal fuse.  But obviously if you undersize your fuse, you are going to be replacing a lot of fuses.  If you think the fuse is protecting the device you are deluding yourself.

Disconnectors mentioned above should be as large as you can afford.  With most inverter systems you'll find it hard to find a disconnector for the high voltage range with suitable current rating.

Yes what is said above!

The fuse/breaker should protect the wires used. If your wires are not thick enough they will heat up, melt and cause a fire. The breaker/fuse should disconnect before the wire reaches its max capacity.

You size the wire according to the expected max currrent of the application, and the breaker/fuse according to the wire.

 

Just my opinion your draw from the battery ie you cable  and fuse/breaker should be spect to the maximum draw from the battery, so if your battery can deliver 200amp put in 95mm cable with 250amp fuse depending on your needs.

15 hours ago, PowerUser said:

For my 120A spec SunSynk 5kW inverter, Steve from the PowerForum store advised me, that the correct fuse size is 160A and not 125A because of surge currents. That is approx. 120A x 1.35 = 162A.

And my fuses have rating gG - which means they are FAST ACTING fuses. Not sure, why do you use slow fuses for your installation...

Do you think, he is giving wrong advise and I should be using 125A fuses instead?

Firstly, gG is a 'general' fuse.  It will happily take 50% overload for 30s without blowing.  There is no need to up-rate the fuse to accommodate the inverter surge rating.

Fuses should not run continuously at or near their rated current. Most recommend continuous operation (that is, more than 1 hour) at max 75% of rated current.  So if you are going to be running for extended periods at more than 88A, then you may want to consider uprating the fuse (and everything that goes with it).

Secondly, you CAN install a bigger fuse if you want - but it gets expensive...

If you have used the recommended 35mm² cable, then the largest fuse you may legally install is 125A. If you want to install a 160A fuse, then you need to change the wire to 70mm². Depending on the disconnect being used, you may need a larger one too.

Personally, I prefer limiting currents to the minimum required, so I would go with 125A. But there is nothing stopping you from going bigger, as long as everything else is up-rated to match.

4 minutes ago, JustinSchoeman said:

Fuses should not run continuously at or near their rated current. Most recommend continuous operation (that is, more than 1 hour) at max 75% of rated current.  So if you are going to be running for extended periods at more than 88A, then you may want to consider uprating the fuse (and everything that goes with it).

 

Now we are talking 🙂  The inverter is capable of pulling 240A nominal power. That mean, for extended periods of time. Even hours if required. Then, in order to run the fuse at that same extended period of time at 75% comfortably, you multiply 240 x 1.25 = 300A. That stands with my recommendation for the closest fuse of 320A and Keto 2 rated for up to 400A.

12 minutes ago, PowerUser said:

Now we are talking 🙂  The inverter is capable of pulling 240A nominal power. That mean, for extended periods of time. Even hours if required. Then, in order to run the fuse at that same extended period of time at 75% comfortably, you multiply 240 x 1.25 = 300A. That stands with my recommendation for the closest fuse of 320A and Keto 2 rated for up to 400A

Well, if you follow the fuse manufacturer's recommendations, then multiply by 1.33 (not 1.25), as you want the final continuous load to be 75% of the fuse rating...

But in reality, this is pointless for virtually any battery system, as most batteries would be dead in an hour or two if the inverter ran continuously at max rated draw. Generally solar battery systems run at peak loads for a few minutes at a time.

Unless you have a massive battery and a truly pathological load profile, there is no need to up-rate the fuse and wiring from what is specified.

2 minutes ago, JustinSchoeman said:

Well, if you follow the fuse manufacturer's recommendations, then multiply by 1.33 (not 1.25), as you want the final continuous load to be 75% of the fuse rating...

But in reality, this is pointless for virtually any battery system, as most batteries would be dead in an hour or two if the inverter ran continuously at max rated draw. Generally solar battery systems run at peak loads for a few minutes at a time.

Unless you have a massive battery and a truly pathological load profile, there is no need to up-rate the fuse and wiring from what is specified.

I personally have an 8kw Sunsynk with 2 x 6.4kwh BSL and 160A fuses and 50mm cable. Been operating like that for almost 2 years with not a single issue. Max I have seen is around 140A. Still yet to see an 8kw Sunsynk delivering more that 185A from the battery bank when it surges. 

Thank you guys

I'm using 95mm cables and plan on using the 250A fuse with limiting the inverter 

In the future I might add 1 or 2 more batteries. Would I need to upgrade the cable for this to get the most efficiency of the system 

Edited March 2, 20224 yr by Deeos

A 12kW inverter has a max discharge of 240amps.  That is 240 * 48 = 11 520kW.  So either they are lying about the 12kW rating, you are misreading the manual or their own manual sucks.  Even at 100% efficiency you are looking at 250 amps.  And let's not forget that most inverters can sustain a surge for ~1->10 seconds.

Your fuse sizing is completely wrong but I see a lot of bad advise on the thread about sizing based on demand/"good enough for me"/etc.  So YOLO I guess.

23 hours ago, JustinSchoeman said:

If you have used the recommended 35mm² cable, then the largest fuse you may legally install is 125A

35mm² for a 12kW Inverter.  So 12 000 / 48 = 250 amps... On 35mm² that is crazy.  I have no idea who recommended that but they don't know what they are doing.

18 minutes ago, Gnome said:

A 12kW inverter has a max discharge of 240amps.  That is 240 * 48 = 11 520kW.  So either they are lying about the 12kW rating, you are misreading the manual or their own manual sucks.  Even at 100% efficiency you are looking at 250 amps.  And let's not forget that most inverters can sustain a surge for ~1->10 seconds.

Who said 48V?  The manual has a Voltage range of 40-60V, so theoretical max output only attainable at the higher DC voltages. Go over 240A, and the overcurrent alarm will come on. Sustain it for 10s, and the inverter will turn off. No need to spec for higher currents than what the inverter will use.

36 minutes ago, Gnome said:

35mm² for a 12kW Inverter.  So 12 000 / 48 = 250 amps... On 35mm² that is crazy.  I have no idea who recommended that but they don't know what they are doing.

That was in reply to someone talking about the 5kW inverter...  Obviously not applicable to 12kW.

18 hours ago, Deeos said:

I'm using 95mm cables and plan on using the 250A fuse with limiting the inverter

Obviously only legal if you are running open cables.  If they are in a conduit, you probably require a 230A fuse.

Is a 200A fuse holder/fused isolator designed to continously carry 200A? If seen a couple of fuse holders melted due to hot connections so why not buy the bigger one? Everything is designed on the limit with zero room for safety.