diy solar

diy solar

Fuses / disconnects / breakers for 2 LV6548 system

There's nothing wrong with stacking extra protection.
As long as you don't mind spending the money.
 
smoothJoey said:
Is this your topo?
If yes, the short as shown would not be interuppted by the class_t fuse.
Code: 
positive
|<->class_t_fuse<->rest_of_system
|->dead_short------------------------------>|
|<->mrbf_fuse<->breaker<->battery.1<->bms<->|
|<->mrbf_fuse<->breaker<->battery.2<->bms<->|
                   rest_of_system<->shunt<->|
                                     negative
Click to expand...

I understood it to be:

[Battery #1 <-> internal 125A breaker] <-> MRBF <-> Busbar
[Battery #2 <-> internal 125A breaker] <-> MRBF <-> Busbar
Busbar <-> Class T fuse
Class T fuse <-> 250A breaker as switch
250A breaker as switch <-> system

Busbar (and any cables to it) must be immune to shorts. Maybe a sandwich of insulating sheets above/below so whip cables from MRBF to busbar and busbar are protected from contact. Be very deliberate about turning off all internal 125A breakers and testing for voltage before exposing.

Class T per battery would be same architecture but higher AIC. By the way, how do you mount them to prevent shorts? Whip of cable from battery "+" to fuse holder mounted to insulating support, out of reach of chassis? Careful work with a wrench when changing fuse, or do you disconnect battery negative? (Seems to me a switch on negative cable would facilitate this. One switch after negative busbar, and busbar "double insulated" against faults.
 
Last edited:
timselectric said:
There's nothing wrong with stacking extra protection.
As long as you don't mind spending the money.
Click to expand...
Agree, and since I don't trust the bms, breaker or MRBF fuse I would put an overcurrent device in that position that I do trust.
Since the breaker can serve as a switch I would choose a class-t fuse as its the least expensive option.
If there were no breaker I might choose a breaker with sufficient specs.
If @RichardfromSignatureSolar says that Signature Solar is confident that their breaker can quench a dead short then I would not require the class-t fuse.
 
There is one downside to stacking over-current protection.
Every bit of over-current protection adds resistance and more joinery which also add resistance.
 
Last edited:
smoothJoey said:
Agree, and since I don't trust the bms, breaker or MRBF fuse I would put an overcurrent device in that position that I do trust.
Since the breaker can serve as a switch I would choose a class-t fuse as its the least expensive option.
If there were no breaker I might choose a breaker with sufficient specs.
If @RichardfromSignatureSolar says that Signature Solar is confident that their breaker can quench a dead short then I would not require the class-t fuse.
Click to expand...
So just a heads up, I personally went to test this on a few batteries. 100% of the time, using the terminals the BMS shut off before the breaker (which makes sense because it's programmed for a slightly lower voltage). Manually bypassing the BMS, we were able to trip the breaker. We also have the breakers as a stand alone product (for replacements etc) and was able to duplicate that on those as well. I'd stand confident behind these breakers at this point.
 
RichardfromSignatureSolar said:
So just a heads up, I personally went to test this on a few batteries. 100% of the time, using the terminals the BMS shut off before the breaker (which makes sense because it's programmed for a slightly lower voltage). Manually bypassing the BMS, we were able to trip the breaker. We also have the breakers as a stand alone product (for replacements etc) and was able to duplicate that on those as well. I'd stand confident behind these breakers at this point.
Click to expand...
@RichardfromSignatureSolar that is great news!
Thanks for taking the time to test that and for reporting back.
Apologies for doubting you and your companies' product.
Class-t fuse not required :).
UPDATE: class-t fuse still required.
 
Last edited:
RichardfromSignatureSolar said:
So just a heads up, I personally went to test this on a few batteries. 100% of the time, using the terminals the BMS shut off before the breaker (which makes sense because it's programmed for a slightly lower voltage). Manually bypassing the BMS, we were able to trip the breaker. We also have the breakers as a stand alone product (for replacements etc) and was able to duplicate that on those as well. I'd stand confident behind these breakers at this point.
Click to expand...
Awesome
Thanks, for testing this.
 
RichardfromSignatureSolar said:
So just a heads up, I personally went to test this on a few batteries. 100% of the time, using the terminals the BMS shut off before the breaker (which makes sense because it's programmed for a slightly lower voltage). Manually bypassing the BMS, we were able to trip the breaker. We also have the breakers as a stand alone product (for replacements etc) and was able to duplicate that on those as well. I'd stand confident behind these breakers at this point.
Click to expand...
Follow-up, what is the over-current trip amperage and time for the BMS?
 
RichardfromSignatureSolar said:
So just a heads up, I personally went to test this on a few batteries. 100% of the time, using the terminals the BMS shut off before the breaker (which makes sense because it's programmed for a slightly lower voltage). Manually bypassing the BMS, we were able to trip the breaker. We also have the breakers as a stand alone product (for replacements etc) and was able to duplicate that on those as well. I'd stand confident behind these breakers at this point.
Click to expand...
smoothJoey said:
Follow-up, what is the over-current trip amperage and time for the BMS?
Click to expand...

What is AIC rating of the breaker?
What is spec and tested IR of the cells?

What load current did you apply to cause the trip?
Did you try a dead short, a "bonded fault" with as short and fat a connection as possible?

I happen to have a 3-pole 200A knife switch. I would wire 3 poles with 3 separate 2/0 or 4/0 cables to battery "+", 3 separate 2/0 or 4/0 cables to battery "-". Cables as short as possible. Put a clamp current probe or current transformer around 3 cables, wire to scope. Then close the switch and watch what happens.

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If I wasn't feeling lucky, I would put the largest class-T fuse I could find in series with each cable. After the test, confirm fuses didn't blow and current was interrupted by battery system.
 
Hedges said:
If I wasn't feeling lucky, I would put the largest class-T fuse I could find in series with each cable. After the test, confirm fuses didn't blow and current was interrupted by battery system.
Click to expand...
To be explicit, by the breaker not the bms.
 
Hedges said:
[Battery #1 <-> internal 125A breaker] <-> MRBF <-> Busbar
[Battery #2 <-> internal 125A breaker] <-> MRBF <-> Busbar
Busbar <-> Class T fuse
Class T fuse <-> 250A breaker as switch
250A breaker as switch <-> system
Click to expand...
Yes. With the addition of a third battery.

I'm returning the MRBF blocks and fuses. Eating the one I modified to fit the terminals. Ordered (3) 150A Class T kits.
 
smoothJoey said:
@RichardfromSignatureSolar seems I was too charitable.
I guess we still need class-t fuses.
Click to expand...
I don't know if need is correct. Other than I need to get on with this build. I don’t think too much criticism can be levied for having a little extra piece of mind with those Class T fuses installed at each battery. I can live with "you probably didn't need those 3 Class T fuses."
 
CamoGreg said:
I don't know if need is correct. Other than I need to get on with this build. I don’t think too much criticism can be levied for having a little extra piece of mind with those Class T fuses installed at each battery. I can live with "you probably didn't need those 3 Class T fuses."
Click to expand...
If we can't be certain that chint breaker can quench a dead short I say we need to add over-current protection that can.
 
I accidentally tested my chint breaker, today. lol
I wasn't paying attention to what I was doing. And when I went to switch off my solar breaker, my thumb was behind the handle. Instead of a fast break of the power. It was a slow motion arc drawing (315v/14a) disconnection. I heard the ark happening, and then it quenched. It freaked me out for a second. But, it did its job. And, there was no heat generated. So, while I would never do it on purpose. I'm happy to know that it works.
 
CamoGreg said:
I don't know if need is correct. Other than I need to get on with this build. I don’t think too much criticism can be levied for having a little extra piece of mind with those Class T fuses installed at each battery. I can live with "you probably didn't need those 3 Class T fuses."
Click to expand...

Without those Class T fuses, you just might be giving someone a piece of your mind.
 
Hedges said:
Without those Class T fuses, you just might be giving someone a piece of your mind.
Click to expand...
:ROFLMAO:

When I stopped and looked at it, I paid around $1500 for each battery. If it was offered at $1560 with the difference being a guaranteed protective fuse against a catastrophic event. Would I pay the extra?
No doubt.
 
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