DC breaker size

[J0livier]

Hi, 

I'm also new to the solar system environment. I hope someone can advise me here. 

I have a Growatt 5Kw inverter paired with 3.5kwh pylontech battery. (plans to upgrade storage later) and connected to 6x 380w solar panels, the setup is mostly aimed at load shedding and power interruptions. 

I found that my DC breaker between the battery and inverter trips when the loads exceed 2500W. It's a 150A three way CBI DC breaker. (see picture) 

1. What size DC breaker is recommended  between the battery and inverter for this combination?

From what I understand, the grid should kick in and pick up the increase in load if the battery can't handle it. (which it should be ) 

2. Is there a specific setting that I need to change in order for the grid to assist automatically with heavier loads. 

The inverter setup is as follows. 

1.SOL, 4.SdS, 5.LI_L02, 14.OSO. 

Everything else is set to default and seems to work just fine. 

Thanks Joe. 

 

 

Edited August 4, 2020 by J0livier

[RikH]

150A fuse should be ok. 2500W at 50V means 50 Amps so something else is going on I'm afraid.

[Coulomb]

I've never seen a proper DC rated 150 A breaker that small before. I'm suspicious that it can do what it says it can.

Most installations have fuses for that reason. And a 150 A DC rated fuse is still a lot bigger than that breaker appears to be (but I don't have anything to judge size by). It looks like a standard AC 17.5 mm wide breaker... how big is it really?

[J0livier]

3 hours ago, Coulomb said:

I've never seen a proper DC rated 150 A breaker that small before. I'm suspicious that it can do what it says it can.

Most installations have fuses for that reason. And a 150 A DC rated fuse is still a lot bigger than that breaker appears to be (but I don't have anything to judge size by). It looks like a standard AC 17.5 mm wide breaker... how big is it really?

 

[J0livier]

9 hours ago, Vassen said:

If you have a single us3000, then the recommended charge / discharge current is 37A, max is 74 and 15sec peak is 100A. 
 

The fuse should depend on the cable size more importantly. 
 

5kw inverter should have dc current of around 100A. I use a 125A fuse on mine. 
 

 

Hi Vassen, 

The cables are AWG4 1000v. The normal cables that comes with the US 3000 battery. 

[RikH]

9 hours ago, Vassen said:

If you have a single us3000, then the recommended charge / discharge current is 37A, max is 74 and 15sec peak is 100A. 

Of course this is completely true but it doesn't explain why the fuse is tripping.

3 hours ago, Coulomb said:

I've never seen a proper DC rated 150 A breaker that small before. I'm suspicious that it can do what it says it can.

Most installations have fuses for that reason. And a 150 A DC rated fuse is still a lot bigger than that breaker appears to be...

Very sharp!

[J0livier]

3 hours ago, Coulomb said:

I've never seen a proper DC rated 150 A breaker that small before. I'm suspicious that it can do what it says it can.

Most installations have fuses for that reason. And a 150 A DC rated fuse is still a lot bigger than that breaker appears to be (but I don't have anything to judge size by). It looks like a standard AC 17.5 mm wide breaker... how big is it really?

Hi Coulomb, 

 Is the 150A rating for a single cable or split 3ways, so it becomes 50A per connection going through the fuse/breaker? 

If it's 50A per line and only positive & negative passing through, does it mean that it can only handle 2400w. (50A x 48V=2400W) and it's tripping if it exceeds the watts? 

[___]

2 minutes ago, J0livier said:

 Is the 150A rating for a single cable or split 3ways, so it becomes 50A per connection going through the fuse/breaker? 

To me it looks as if CBI made a 150A breaker by slapping together three 50A breakers. The picture on it shows the internal wiring, or at least how you are supposed to wire it. It's "single pole" in other words.

(At this point in the message, imagine I'm going off to google a bit and make sure of my facts..)

Aaah yes. Here is the spec sheet.

And this is how you're supposed to wire it:

If you're not actually using all three contacts in parallel, then it explains your tripping point. Each contact is 50A. 50V*50A = 2500. Spot on.

A bit of googling shows that the U2 curve indicated there will trip after around 10 seconds if you go 30% over.

So yeah... open up the box and check how it was wired.

[Coulomb]

2 hours ago, J0livier said:

 Is the 150A rating for a single cable or split 3ways, so it becomes 50A per connection going through the fuse/breaker? 

It looks like it is 50 A per section. I didn't realise that the three levers were joined together. The symbol on the middle section looked like something to do with 3-phase to me.

If you continue to use this breaker set, you'll have to get something like in the photo above that carefully splits the current 3 ways evenly. If you ended up with an 80/10/10 split, say, then you're only a little better off than you are now.

[phil.g00]

I've not seen that before.

@Coulomb is perfectly correct about ensuring a perfect split for measuring.

But what's worse,  it also relies on perfectly synced breaking timing.

And nothing's perfect, the last pole to open even by a mS is breaking the full whack, and yet 1 pole isn't even rated to carry full load.

I don't trust it.

 

[___]

38 minutes ago, phil.g00 said:

And nothing's perfect, the last pole to open even by a mS is breaking the full whack, and yet 1 pole isn't even rated to carry full load.

The contacts do have a 10kA interrupting capability according to the spec sheet, and has VDE and a string of other approvals. So this may be okay.

The spec sheet also allows for wiring in series to up the voltage rating.

I've  never been much of a CBI/Samite fan, but I must admit, they make quite decent stuff.

[J0livier]

6 hours ago, plonkster said:

To me it looks as if CBI made a 150A breaker by slapping together three 50A breakers. The picture on it shows the internal wiring, or at least how you are supposed to wire it. It's "single pole" in other words.

(At this point in the message, imagine I'm going off to google a bit and make sure of my facts..)

Aaah yes. Here is the spec sheet.

And this is how you're supposed to wire it:

If you're not actually using all three contacts in parallel, then it explains your tripping point. Each contact is 50A. 50V*50A = 2500. Spot on.

A bit of googling shows that the U2 curve indicated there will trip after around 10 seconds if you go 30% over.

So yeah... open up the box and check how it was wired.

In other words, the way its connected now, it will never work the way it supposed to. .? 

[J0livier]

Thanks for everyone's input..

I think we found the problem, which i'll get fixed asap by installing proper 160A fuses.

I also  just spoke to my installer, he confirmed that he needs to do a software update on the inverter too.

Edited August 5, 2020 by J0livier

[Louisvdw]

1 hour ago, J0livier said:

In other words, the way its connected now, it will never work the way it supposed to. .? 

This wiring will trip on 50A.
To make it work the positive will have to go to all 3 input terminals and all 3 output terminals, and the negative will bypass the breaker.

Or use fuses  

[___]

2 hours ago, J0livier said:

In other words, the way its connected now, it will never work the way it supposed to. .? 

Uuuh, no, it won't. In fact, this makes me doubt the experience level of your installer.

I'm also concerned about the size of the wire. Those breakers are 12.8mm across. I know you can fit a 25mm^2 to most DIN breakers (16mm wide), so I'm a little concerned about those.

Edit: Also polarity. Positive at the top, negative at the bottom. Check that it is installed correctly.

Edited August 5, 2020 by plonkster

[Ingo]

I must say I don't get a warm and fuzzy feeling from that breaker. Most installations I saw have one of these, either single pole or double pole if you really want to break both + and - legs. They are bomb-proof with up to 160A fuses inside and if you are unfortunate to ever see smoke where it's not supposed to be you have a large handle to pull on - no melted stuff in the DB.

[J0livier]

Thanks guys. I'm definitely changing to  proper fuses. 

[Coulomb]

9 hours ago, plonkster said:

In fact, this makes me doubt the experience level of your installer.

+1. The polarity has to be wrong on one side. The magnetic blowouts (presumed, about the only way they could break DC in that tiny space) will actually work against breaking the arc on one side. This indicates a lack of understanding on the part of the installer.

Confusion on how to wire polarised DC breakers has made them illegal in Australia.

[JustinSchoeman]

Well, its not a polarized breaker, so that at least is not an issue here...

[___]

33 minutes ago, JustinSchoeman said:

Well, its not a polarized breaker, so that at least is not an issue here...

It is, it is on page 7 of the 8-page spec sheet, though not marked on the breaker.

Normally, for a two pole breaker, one side would be reversed so that you don't have to cross-over the cabling to make it work right (battery on one side, loads on the other), but in this case the breaker was clearly not designed to be used in this manner.

Edited August 6, 2020 by plonkster

[JustinSchoeman]

That is only applicable to the 125V breakers.

[___]

11 minutes ago, JustinSchoeman said:

That is only applicable to the 125V breakers.

You're right! Indeed, I stand corrected. Thanks.

[Coulomb]

If you zoom in on the middle breaker with the diagram, you can see minus on top and plus underneath. The opposite of the image above.

Edit: if a breaker doesn't have magnetic blowouts, which are inherently polarised, it generally needs a mechanism that stretches the gap between contacts. In that miniature breaker, I'd say that's impossible. At least, that's my understanding.

Edited August 6, 2020 by Coulomb

[___]

4 minutes ago, Coulomb said:

If you zoom in on the middle breaker with the diagram, you can see minus on top and plus underneath. The opposite of the image above.

You mean this:

 

[Coulomb]

1 minute ago, plonkster said:

You mean this:

Exactly.