T class fuse rating

[Papote]

I have 2 Orient Power 5Kw @ 100 Amps 48 Volts LiFePo4 wall mount batteries. I plan to purchase more in the future. At the moment, I have a 300 Amp Bus bar to connect all the batteries. The positive and negative 4/0 cables are about 7 feet and go to another 300 Amp Bus bar to distribute positive and negative using 3/0 wire to 2 Orient Power 6.5 Kw inverters. I've been reading up about Breakers vs ANL vs T Class fuses and it seems T class fuses would be best to protect the system.

Can I get away with just one T Class fuse on the 4/0 positive cable between the bus bars or do they need to be on each inverter? What specs do I need to look for? Any suggestions on getting a good deal on one?

Note: all my lug diameter sizes are 5/16.

 

[DIYrich]

Fuse protects the wire. I suggest a separate fuse on each battery. If you accidentally connect a drained battery with a charged one, you can get a lot of amps flowing between them. I think the smallest class t is 150 amps. Next best place is between the two busbars.

 

[Papote]

Aren't the t class fuses supposed to be as close as possible to the positive of each inverter?

I don't think these inverters draw more than 110 Amps. I'm afraid they might blow if they go to surge at 150 amps. Is a 250 amp fuse to high?

 

[Papote]

Thinking of getting this Blue Sea 5502 320a fuse holder and but a couple extra South Bend 250 Amp T fuse.
Would this be fine?
I do notice that the fuse holder is M10 (1/4") and might need to widen the lugs a bit.

 

[Hedges]

I don't like the pinch-to-remove fuse holder, can't seem to open without cracking it.
Consider the one with clips:

Class T Fuse Block with Insulating Cover - 225 to 400A - Blue Sea Systems

Allows use of Class T fuses for high speed circuit protection of electronic equipment and inverters.

www.bluesea.com

Aren't the t class fuses supposed to be as close as possible to the positive of each inverter?

As close as possible to the battery.

I don't think these inverters draw more than 110 Amps. I'm afraid they might blow if they go to surge at 150 amps. Is a 250 amp fuse to high?

250A fuse is allowed if cable ampacity is high enough.
Although fuse can't be depended on to protect electronics, it might. Less likely if higher amperage.

What is inverter wattage? Efficiency at max continuous wattage?

Fuses have a time-current curve which tolerates inverter's 2x surge for a few seconds.

Assuming:
5000W
50V
90% efficient
25% margin (allow heating and avoid nuisance trips)
12% ripple factor (battery doesn't supply DC, it supplies current looking like rectified sine wave)

5000W / 50V / 90% x 125% x 112% = 156A minimum recommended fuse.

In which case, smaller fuse holder and 175A fuse
(150A isn't much smaller, you'd likely get away with it using some of the 25% margin.)

Class T Fuse Block with Insulating Cover - 110 to 200A - Blue Sea Systems

Allows use of Class T fuses for high speed circuit protection of electronic equipment and inverters.

www.bluesea.com

Fuse A3T / Class T 175 Amp - Blue Sea Systems

Use with Class T Fuse Blocks for circuit protection of devices including inverters. high interrupt capacity for large battery banks including Lithium-ion and TPPL batteries.

www.bluesea.com

2/0 cable would be good.

I think the smallest class t is 150 amps.

I found 110A

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

 

[DIYrich]

I don't think these inverters draw more than 110 Amps. I'm afraid they might blow if they go to surge at 150 amps. Is a 250 amp fuse to high?

Class t fuse protect the wire. I would call them "slow blow", so your electronics will be fried by the time it blows if you rely upon them to protect electronics.

 

[Hedges]

Semiconductor Fuses - High Speed Fuses - Littelfuse

www.littelfuse.com

https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/fuses/bussmann-series-high-speed-fuses/bus-ele-an-10507-hsf.pdf

MERSEN | Semiconductor protection fuse

Semiconductor protection fuses are used to protect against overcurrent conditions in power electronic equipment. They are specifically designed to reduce the I2t, peak let-through current and arc voltages during a fault condition. More information on the dedicated website: Electrical Power.

www.mersen.com

 

[Papote]

As close as possible to the battery.

Was confused because in @Will Prowse blueprint he has it close the inverters.

 

[Will Prowse]

Was confused because in @Will Prowse blueprint he has it close the inverters.

View attachment 156444

Yeah I did this because I don't trust the internal fuse on the unit. And the manual recommends it. Especially important if you have 50kWh of batteries connected and the internal fuse doesn't have a aic rating. Not smart

 

[Will Prowse]

Was confused because in @Will Prowse blueprint he has it close the inverters.

View attachment 156444

Each manual is different but all of them recommend some form of overcurrent protection device and it will have a amperage spec. You can use a breaker but I prefer t class fuse when dealing with large battery banks.

 

[Will Prowse]

It also depends on what size battery you are running. If I have a stack of 25 to 30 kWh batteries, I'm going to parallel then into the system with its own t class fuse. And then I'll have a t class fuse for each inverter.

Might be overkill, but I don't trust those internal fuses. And my battery bank is a bit over 100 kilowatt hours right now I think.

 

[Papote]

Thanks for the clarification @Will Prowse !!

I have been reading for hours on the subject and keep going back and forth on either T Class Fuses or Midnight Solar 250A (MNEDC250) Breakers cause of their high AIC.
LOL.

Right now, I only have 10KwH battery bank, but hope to expand in the future. The manual doesn't say anything about fuses, but the inverter did come with an ANL fuse. I asked the manufacturer of the batteries and inverters that I bought (Orient Power) and they said: "Fuse is not required. Inverter inside has fuse"...