Blue sea class T VDC?

[MartyByrde]

Using a growatt SPF 3000TL LVM-ES. Would this fuse be too large at 110 A? Using 80amp output * 1.25 = 100 amp fuse recommended.

Also this fuse shows max 125 VDC. Would this work with a 48v system?

https://www.bluesea.com/products/5112/Fuse_A3T___Class_T_110_Amp

 

[timselectric]

That should be fine. It's a tad large. But, it still protects against a dead short. And the inverter will protect itself from over current.

 

[rmaddy]

Where is this Class T fuse meant to go? Normally you only need a Class T fuse as the main battery fuse between your batteries and the main bus bars. It would be sized for the max total current draw being pulled from the batteries or for the max total charge current going to the batteries, which ever is larger.

 

[MartyByrde]

Where is this Class T fuse meant to go? Normally you only need a Class T fuse as the main battery fuse between your batteries and the main bus bars. It would be sized for the max total current draw being pulled from the batteries or for the max total charge current going to the batteries, which ever is larger.

Between the inverter and busbar to give a higher AIC protection. Is that necessary?

 

[rmaddy]

The Class T should be between the battery and bus bar, close to the battery. Having it near the inverter doesn't really help much.

 

[MartyByrde]

Where is this Class T fuse meant to go? Normally you only need a Class T fuse as the main battery fuse between your batteries and the main bus bars. It would be sized for the max total current draw being pulled from the batteries or for the max total charge current going to the batteries, which ever is larger.

If I had two 120A charge controllers would it need to be sized to 250A?

 

[rmaddy]

You have two 48V 3000W all-in-ones, correct? So the inverters can pull 6000W / 48V / 85% = 150A from the batteries. If the charge controllers are 120A each then that's 240A possible going into the batteries. Since 240A is bigger than 150A (obviously) then fuse based on 240A. 240A x 125% = 300A. So you need a 300A fuse.

I have to admit, this is the first time I've seen a setup where the charge current is higher than the load current. I think with this setup you need the 300A Class T fuse close to the battery but you should also put a 150A fuse close to each all-in-one. Those two 150A fuses don't need to be Class T since you need nearly as high of an AIC as you do with LiFePO₄ batteries.

Are you going to have 12kW of solar panels? That's what it would take to end up with 240A of charge current.

 

[MartyByrde]

You have two 48V 3000W all-in-ones, correct? So the inverters can pull 6000W / 48V / 85% = 150A from the batteries. If the charge controllers are 120A each then that's 240A possible going into the batteries. Since 240A is bigger than 150A (obviously) then fuse based on 240A. 240A x 125% = 300A. So you need a 300A fuse.

I have to admit, this is the first time I've seen a setup where the charge current is higher than the load current. I think with this setup you need the 300A Class T fuse close to the battery but you should also put a 150A fuse close to each all-in-one. Those two 150A fuses don't need to be Class T since you need nearly as high of an AIC as you do with LiFePO₄ batteries.

Are you going to have 12kW of solar panels? That's what it would take to end up with 240A of charge current.

Yes 18kW of solar. Also 4 16S 3.2v 280Ah battery packs. So I need a high charge coming in to charge the 4 batteries.

 

[rmaddy]

You're 50% over paneled with 18kW on a system that can only support 12kW.

Do your batteries each support 60A of continuous charge current?

 

[MartyByrde]

You're 50% over paneled with 18kW on a system that can only support 12kW.

Do your batteries each support 60A of continuous charge current?

So it’s one growatt 3000TL LVM-ES (4000w PV)
and 2 growatt SC48120 (7000w PV each)

4 LiFePo4 3.2v 280Ah batteries configured 16s. So 4 48v LiFePo4 battery packs.

 

[rmaddy]

Your other question is tightly related to this one:

Does adding extra charge controllers increase the size of busbar needed?

Keeping the load the same but want to speed up battery recharge time by adding another SCC. Does adding extra charge controllers increase the size of busbar needed? Since more amps will be flowing in.

diysolarforum.com

 

[MartyByrde]

Your other question is tightly related to this one:

Does adding extra charge controllers increase the size of busbar needed?

Keeping the load the same but want to speed up battery recharge time by adding another SCC. Does adding extra charge controllers increase the size of busbar needed? Since more amps will be flowing in.

diysolarforum.com

That one was regarding busbar size. This one was regarding fusing size

 

[rmaddy]

So it’s one growatt 3000TL LVM-ES (4000w PV)
and 2 growatt SC48120 (7000w PV each)

OK. You effectively have 1 inverter and 3 charge controllers.

That's a 3000W inverter and (120A + 120A + 80A) 320A of charge controllers.

Then you need a 400A Class T fuse at the battery, and a 150A non Class T fuse at each of the two SC48120.

 

[rmaddy]

That one was regarding busbar size. This one was regarding fusing size

Both questions are dependent on the exact same set of details and you must be sure your bus bars are rated higher than the max fuse size you end up with.

Now that we know you need a 400A battery fuse this means you want 450A or 500A bus bars. You do not want bus bars that are weaker than the biggest fuse.

 

[MartyByrde]

OK. You effectively have 1 inverter and 3 charge controllers.

That's a 3000W inverter and (120A + 120A + 80A) 320A of charge controllers.

Then you need a 400A Class T fuse at the battery, and a 150A non Class T fuse at each of the two SC48120.

Do you think it’s more cost effective to have the 4 batteries on their own busbar with the 400A Class T fuse connecting between the battery busbar and inverter/charge controller busbar?

Or have them all on the same busbar with each battery having its own 400A class T fuse?

 

[rmaddy]

With 4 big batteries like that I think it makes sense to have two sets of bus bars. Wire the 4 batteries in parallel to the first pair (battery bus bars).

Wire the all-in-one and two charge controllers to the other pair (system bus bars).

Then run a big wire with the 400A Class T fuse between the two positive bus bars. I would put a battery monitor shunt on the big negative wire connecting the two negative bus bars.

Here's the fun part with the 4 batteries and the battery bus bars - you should put a smaller Class T fuse between each battery and the positive battery bus bar (so that's a total of 5 Class T fuses). Size the 4 smaller Class T fuses to match the max charge current of each battery.

Imagine the scenario where you have a full 320A of charge current. 60A will go to each battery (this assumes each battery is rated that high - you never answered that question). Now think about what happens if one battery fails at this point. Now that 320A will be split between 3 batteries. That's a bit over 100A going to each battery. That might be too much. The smaller fuses for each battery can act as a primary safety before the BMS has to kick in.

 

[MartyByrde]

With 4 big batteries like that I think it makes sense to have two sets of bus bars. Wire the 4 batteries in parallel to the first pair (battery bus bars).

Wire the all-in-one and two charge controllers to the other pair (system bus bars).

Then run a big wire with the 400A Class T fuse between the two positive bus bars. I would put a battery monitor shunt on the big negative wire connecting the two negative bus bars.

Here's the fun part with the 4 batteries and the battery bus bars - you should put a smaller Class T fuse between each battery and the positive battery bus bar (so that's a total of 5 Class T fuses). Size the 4 smaller Class T fuses to match the max charge current of each battery.

Imagine the scenario where you have a full 320A of charge current. 60A will go to each battery (this assumes each battery is rated that high - you never answered that question). Now think about what happens if one battery fails at this point. Now that 320A will be split between 3 batteries. That's a bit over 100A going to each battery. That might be too much. The smaller fuses for each battery can act as a primary safety before the BMS has to kick in.

Thanks for the detailed explanation. I assume the big wire needs to be 4/0.

I had to do some research on charging current. The spec sheet says standard charge current of 0.5C and max charging current of 1C. So 320A would be too high of a charge across 4 280Ah battery banks?

 

[MartyByrde]

With 4 big batteries like that I think it makes sense to have two sets of bus bars. Wire the 4 batteries in parallel to the first pair (battery bus bars).

Wire the all-in-one and two charge controllers to the other pair (system bus bars).

Then run a big wire with the 400A Class T fuse between the two positive bus bars. I would put a battery monitor shunt on the big negative wire connecting the two negative bus bars.

Here's the fun part with the 4 batteries and the battery bus bars - you should put a smaller Class T fuse between each battery and the positive battery bus bar (so that's a total of 5 Class T fuses). Size the 4 smaller Class T fuses to match the max charge current of each battery.

Imagine the scenario where you have a full 320A of charge current. 60A will go to each battery (this assumes each battery is rated that high - you never answered that question). Now think about what happens if one battery fails at this point. Now that 320A will be split between 3 batteries. That's a bit over 100A going to each battery. That might be too much. The smaller fuses for each battery can act as a primary safety before the BMS has to kick in.

Also wouldn’t the 100A Overkill BMS prevent too high of a current flowing into one of the 16s 48v 280Ah batteries?

 

[HRTKD]

Also wouldn’t the 100A Overkill BMS prevent too high of a current flowing into one of the 16s 48v 280Ah batteries?

The over current protection of the BMS should be your last resort. A physical fuse is your best bet to having to replace costly electronics.

 

[rmaddy]

I assume the big wire needs to be 4/0.

For 320A of charge current you definitely need 4/0AWG.

The spec sheet says standard charge current of 0.5C and max charging current of 1C. So 320A would be too high of a charge across 4 280Ah battery banks?

0.5C on a 280Ah battery is 140A and 1C would be 280A.

That's per battery in parallel. So 4 in parallel can handle 4 x 140A = 560A at 0.5C. So you will have no issue with 320A. Even 3 in parallel can handle more than 320A.