Heavy duty busbar advice (+600A)

[FilterGuy]

I suspect joining resistance is quite variable.

That is an understatement!! In addition, my experience is that joining resistance is a LOT higher than the other parts of the system.

 

[John Frum]

This doco talks about "selective coordination" -- https://diysolarforum.com/resources/bussman-selecting-protective-devices.72/

Littelfuse has a roughly equivalent document, from memory that is where I got the term "fault isolation".

The concepts are approximately synonymous.
Actually "fault isolation" is probably better described as a subset of "selective coordination"

 

[OzSolar]

The first reason I wonder this is that Victron does not use them and I have not heard of issues.

We're on the same page on those points.

Victron does seems to be oddly quiet about what type of fuse from what I've seen. I've never seen them mention Class T per se. Going from an iffy memory I think that sometimes the picture in their quick start guide looks like a class T and sometimes it looks like a Mega but if they've ever printed "Class T" in a manual, I've not seen it. Keep in mind that's a sample size of less than 4 Victron inverters so I'm a babe in the woods on Victron.

View attachment 106854

Another example that I'm curious about is that many BMS' will go into an error mode when pre-charge is ignored. I suspect the that the in milliseconds (fraction of a ms?) that the BMS is first powered on it sees the inverter as a dead short and acts accordingly. I suspect that subject had already been talked about ad nauseum.

 

[John Frum]

Another example that I'm curious about is that many BMS' will go into an error mode when pre-charge is ignored. I suspect the that the in milliseconds (fraction of a ms?) that the BMS is first powered on it sees the inverter as a dead short and acts accordingly.

I thought that was established fact.

 

[FilterGuy]

This doco talks about "selective coordination" -- https://diysolarforum.com/resources/bussman-selecting-protective-devices.72/

Littelfuse has a roughly equivalent document, from memory that is where I got the term "fault isolation".

The concepts are approximately synonymous.
Actually "fault isolation" is probably better described as a subset of "selective coordination"

It looks like a good article..... but it will take me a while to chew through it.

 

[FilterGuy]

Another example that I'm curious about is that many BMS' will go into an error mode when pre-charge is ignored. I suspect the that the in milliseconds (fraction of a ms?) that the BMS is first powered on it sees the inverter as a dead short and acts accordingly. I suspect that subject had already been talked about ad nauseum.

I thought that was established fact.

Yes, the BMS overcurrent protection is an interesting wrinkle in the discussion. It can probably act faster than a fuse in a short circuit situation, but how reliable is it? For it to work, there is a *lot* of complex circuitry that has to be functioning correctly.

 

[John Frum]

Yes, the BMS overcurrent protection is an interesting wrinkle in the discussion. It can probably act faster than a fuse in a short circuit situation, but how reliable is it? For it to work, there is a *lot* of complex circuitry that has to be functioning correctly.

If I trusted the fets I wouldn't sweat the fuse.

 

[OzSolar]

I thought that was established fact.

Is it? Only one post is revealed when I search for your so called "established fact" and it is almost two years old. Way before I got here. Don't take cheap shots at people.

 

[John Frum]

Is it? Only one post is revealed when I search for your so called "established fact" and it is almost two years old. Way before I got here. Don't take cheap shots at people.


View attachment 106866

No shot intended.

 

[John Frum]

Yes, the BMS overcurrent protection is an interesting wrinkle in the discussion. It can probably act faster than a fuse in a short circuit situation, but how reliable is it? For it to work, there is a *lot* of complex circuitry that has to be functioning correctly.

I see a FET or contactor based bms as the second last line of defense.
It should trigger well before the fuse can blow on a dead short but both fets and contactors can fail closed so I don't trust them.

 

[FilterGuy]

I see a FET or contactor based bms as the second last line of defense.
It should trigger well before the fuse can blow on a dead short but both fets and contactors can fail closed so I don't trust them.

I had not thought of it before, but when you look at the total system, the BMS is another reason fuses are not a bad way to go when you need a high current OCPD. Here is my thinking:

1) Depending on the system and where the short is, the BMS will cut the current before a fuse blows. In these cases, the reason for the OCPD is if the BMS fails in a short. (If it fails 'open', it is not good but the OCPD does not help and it won't be a cascading problem) (Note that the largest OCPD in the system is almost always near or at the battery)
2) Consequently, the chance of the fuse blowing and needing to be replaced is reduced...
3) and that means the convenience value of a breaker is also reduced because it is less likely to ever be needed.

Hmmmm..... maybe I am stretching it a bit.... but it is still true.


BTW: I am OK with breakers for low current applications..... the cost, convenience and reliability can make small DC breakers a good decision, particularly for something like a DC distribution panel in an RV. It is the big-ass OCPD devices where I think the fuses are the clear winner. (I will always pick a fuse for anything at 100A or more. Below 100A, the decision gets into many other factors and is situation-dependent.

 

[John Frum]

I suspect the bms will trip before the branch circuit fuse will blow.

 

[FilterGuy]

I suspect the bms will trip before the branch circuit fuse will blow.

Maybe..... it depends on a lot of things. The further 'downstream' the branch circuit is from the BMS, the harder it is to predict.

Of course, when you have a lot of parallel batteries, everything changes because the total current can get quite large before the BMSs start turning off.

Now let me argue against myself.....kinda. If you have a lot of 48V parallel batteries on a moderate to small system, the current from each battery might be small enough that using breakers on the battery circuit might be reasonable. On the inverter side, the same might be true. (A 3KW 90% efficient inverter would not have a sustained draw much over 70A so a 90A OCPD would be appropriate)


The above would even let you take a battery offline and still function well.

I would probably still use fuses, but the idea of using non-polarized DC breakers for the above does not make me cringe too badly.

 

[OzSolar]

Maybe..... it depends on a lot of things. The further 'downstream' the branch circuit is from the BMS, the harder it is to predict.

Of course, when you have a lot of parallel batteries, everything changes because the total current can get quite large before the BMSs start turning off.

Now let me argue against myself.....kinda. If you have a lot of 48V parallel batteries on a moderate to small system, the current from each battery might be small enough that using breakers on the battery circuit might be reasonable. On the inverter side, the same might be true. (A 3KW 90% efficient inverter would not have a sustained draw much over 70A so a 90A OCPD would be appropriate)

View attachment 106891
The above would even let you take a battery offline and still function well.

I would probably still use fuses, but the idea of using non-polarized DC breakers for the above does not make me cringe too badly.

Would you mind checking out post #42 on this thread?

 

[John Frum]

Maybe..... it depends on a lot of things. The further 'downstream' the branch circuit is from the BMS, the harder it is to predict.

Of course, when you have a lot of parallel batteries, everything changes because the total current can get quite large before the BMSs start turning off.

Now let me argue against myself.....kinda. If you have a lot of 48V parallel batteries on a moderate to small system, the current from each battery might be small enough that using breakers on the battery circuit might be reasonable. On the inverter side, the same might be true. (A 3KW 90% efficient inverter would not have a sustained draw much over 70A so a 90A OCPD would be appropriate)

View attachment 106891
The above would even let you take a battery offline and still function well.

I would probably still use fuses, but the idea of using non-polarized DC breakers for the above does not make me cringe too badly.

This brings us round to eg4 batteries.
Or have we been circling them like sharks?
These rack mount batteries have a built in breaker rated for if memory serves 125 amps.

The company rep(can't find him in the forum list atm) tested the breaker and was confident that it would open reliably on a dead short.
He also said that he had to bypass the bms because the BMS would trip on over-current preventing the breaker from opening.
The BMS should trip in microseconds and a breaker or fuse should trip in milliseconds.
So that is expected.

 

[FilterGuy]

Would you mind checking out post #42 on this thread?

I assume you want me to comment on the breaker panel that was linked.

It looks like a nice setpup but:

1) It looks like the fuses are limited to 70A. (I did not research it but the wording implies it)

2) The AIC rating for the breakers is on the low side:

Short circuit current rating is limited to 4,000 amperes (10-30 ampere) or 10,000 amperes (35-70 ampere) when used on 125V dc.

Of course, that gets into the discussion we have had on this thread about the importance of having a very high AIC on a main fuse and or on downstream fuses.

 

[da9el84]

OP I suggest you look for arc flash/blast videos on youtube.
I won't post links here because gore is not ok on this forum.
Yes, I'm kind of trying to scare you.

I have a qualified electrician that works with solar most of his time to size the breakers and wires for me to make sure I am up to code and what not, so I'll just wait and see what he says.

 

[OzSolar]

I assume you want me to comment on the breaker panel that was linked.

It looks like a nice setpup but:

1) It looks like the fuses are limited to 70A. (I did not research it but the wording implies it)

2) The AIC rating for the breakers is on the low side:



Of course, that gets into the discussion we have had on this thread about the importance of having a very high AIC on a main fuse and or on downstream fuses.

Thanks for commenting. Of course that's not a solution for bigger systems but it sure looks like a great way to build complete DC bus for smaller systems.

 

[Sebanavila]

here is another option:

https://www.amazon.com/Electric-Protector-Overload-Protection-Photovoltaic/dp/B09P4RF93Q/ref=rvi_sccl_22/144-6096976-6981325?pd_rd_w=1wpwu&content-id=amzn1.sym.f5690a4d-f2bb-45d9-9d1b-736fee412437&pf_rd_p=f5690a4d-f2bb-45d9-9d1b-736fee412437&pf_rd_r=G4V8SXM9E3B8VDWS07FT&pd_rd_wg=kKeBr&pd_rd_r=31ba9346-d38c-4062-8ef0-71ba3ccf10e3&pd_rd_i=B09P4RF93Q&th=1

Put one of this in between each of the inverters and the busbar or Lynx Power in, or whatever you decide to use. I think this will solve your problems and you don't have to worry about fuses.

 

[FilterGuy]

here is another option:

https://www.amazon.com/Electric-Protector-Overload-Protection-Photovoltaic/dp/B09P4RF93Q/ref=rvi_sccl_22/144-6096976-6981325?pd_rd_w=1wpwu&content-id=amzn1.sym.f5690a4d-f2bb-45d9-9d1b-736fee412437&pf_rd_p=f5690a4d-f2bb-45d9-9d1b-736fee412437&pf_rd_r=G4V8SXM9E3B8VDWS07FT&pd_rd_wg=kKeBr&pd_rd_r=31ba9346-d38c-4062-8ef0-71ba3ccf10e3&pd_rd_i=B09P4RF93Q&th=1

Put one of this in between each of the inverters and the busbar or Lynx Power in, or whatever you decide to use. I think this will solve your problems and you don't have to worry about fuses.

The specs look nice. Thanks for that link! Does anyone have any experience or insight into Dihool? I am nervous about breakers from an unknown company.