Inverter fuse

[Bluewatersailor]

I have a Chinese 3000W-6000w inverter in reality it never going to give me any thing like 3000w, batteries bank 400Ah .
am I correct in saying a 250A fused will be fine ? 3000/12v 250A
Also where best to fit the fuse, V+ next to the battery terminal? Or by the inverter?
The inverter came with 4 ( 2v+ 2v- ) 2/0 cables with one cable connector joining the cables together making two pairs,
the cables are 2 mts long which is much more then I need would it be better to shorten them or would the voltage drop within that size wire be fine .
If I can help it I rather not shorten them as they have a nice connection.

Thanks

 

[Hedges]

Fuse should be located before any short circuits you expect the system to suffer. Certainly before passing through any metal bulkheads. Right at the battery positive terminal is best.

2/0 as single wires (not bundled in a cable or conduit), if 90 degree C insulation, can handle 300A
What is efficiency of the inverter at 3000W output? 3000W/12V/<efficiency> = amps

250A fuse is reasonable if continuous load will always be below 3000W.

2/0 is 0.00032Ω/m
Was that 4 cables, each 2m long? 8m x 0.00032Ω/m = 0.00256 ohms
0.00256 ohms x 500A surge current = 1.28V or 10%. At 250A, half that

"with one cable connector joining the cables together"
Connectors have voltage drop too.
If you don't need a connector, and could get away with two, 0.5m cables, do that for minimum voltage drop.
But you can get away with leaving it as 8m total. The difference would only really matter starting a motor.

FLA wet cell? SLA? Lithium?
If FLA, corrosive gasses, so have battery in separate compartment from inverter and vent.

Single battery or several in parallel?
A single car battery can supply 3000A into a short circuit. 100 Ah AGM about 4000A.
ANL fuses are shown as 3000 AIC by some sources, 6000 AIC by others.
Class T are 20,000 AIC
Midnight Solar has DC breakers rated 50,000 AIC
With your 12V system there are more choices than for people running 48V
Select a fuse or breaker with AIC (amps interrupt current for faults like a dead short circuit) high enough for what your battery bank can produce.

 

[Pappion]

Fuses generally are sized to protect the wiring, which reduces fire hazard. A smaller fuse at the appliance, protects the appliance, and reduces fire hazard.

 

[Zil]

Fuse must be as close to the battery positive as you can fit. You need to have the cables as short as possible. Why did manufacturer supply doubled cables. Not a good idea. Bet they are sub-standard wire, maybe aluminum. I would replace them with quality marine grade tinned copper with quality crimped lugs. You can get the cables made to custom lengths. I would use 2/0 with 300 amp fuse. https://www.genuinedealz.com/products/custom-battery-cable-marine-grade-by-the-foot or here https://baymarinesupply.com/wiring/custom-battery-cables.html These fuses are good for lead acid chemistry, https://shop.marinehowto.com/products/blue-sea-marine-rated-battery-fuse With LiFePo battery I use Class-T fuse. https://shop.marinehowto.com/products/class-t-fuse-holder-225a-to-400a

 

[Hedges]

These fuses are good for lead acid chemistry, https://shop.marinehowto.com/products/blue-sea-marine-rated-battery-fuse With LiFePo battery I use Class-T fuse. https://shop.marinehowto.com/products/class-t-fuse-holder-225a-to-400a

Do you have a good reference for short circuit current of various battery types and sizes?
I've only come across a couple data point, plus calculation based on CCA (which is simply current from a 12V battery pulled down to 7.5V)

Is "internal resistance" as measured/reported for a LiFePO4 battery suitable to calculate short circuit current?

One more fuse type for batteries, ANL

ANL Fuses - Blue Sea Systems

Use with ANL Fuse Blocks for many applications with 35-750 Amp loads

www.bluesea.com

 

[Bluewatersailor]

Fuse should be located before any short circuits you expect the system to suffer. Certainly before passing through any metal bulkheads. Right at the battery positive terminal is best.

2/0 as single wires (not bundled in a cable or conduit), if 90 degree C insulation, can handle 300A
What is efficiency of the inverter at 3000W output? 3000W/12V/<efficiency> = amps

250A fuse is reasonable if continuous load will always be below 3000W.

2/0 is 0.00032Ω/m
Was that 4 cables, each 2m long? 8m x 0.00032Ω/m = 0.00256 ohms
0.00256 ohms x 500A surge current = 1.28V or 10%. At 250A, half that
4 cables in all two for - two for +

Don't quite understand the maths.

"with one cable connector joining the cables together"
Connectors have voltage drop too.
If you don't need a connector, and could get away with two, 0.5m cables, do that for minimum voltage drop.
But you can get away with leaving it as 8m total. The difference would only really matter starting a motor.

FLA wet cell? SLA? Lithium?

Lithium batteries

If FLA, corrosive gasses, so have battery in separate compartment from inverter and vent.

Single battery or several in parallel?

Two batteries in parallel

A single car battery can supply 3000A into a short circuit. 100 Ah AGM about 4000A.
ANL fuses are shown as 3000 AIC by some sources, 6000 AIC by others.
Class T are 20,000 AIC
Midnight Solar has DC breakers rated 50,000 AIC
With your 12V system there are more choices than for people running 48V
Select a fuse or breaker with AIC (amps interrupt current for faults like a dead short circuit) high enough for what your battery bank can produce.

 

[Zil]

Problem with ANL fuses. Interrupt of only 6000 amperes. Also there are so many junk ANL out there, not every one will score a quality fuse. Most automotive parts discounters and audio shops have garbage for ANL fuses. I'm not going to list every reference I use, it is very easy to find the information on your own. Google might be your friend. Or even Blue Sea Circuit Wizard But I don't care much anymore. You all can do whatever you can live with. I want to protect my clients.

 

[Hedges]

Don't quite understand the maths.

Lithium batteries

Two batteries in parallel

If an inverter is 90% efficient, it will draw 1.00/9.00 times as much current to produce the same power.
3000W/12V/0.90 = 278A

OK, lithium may be able to produce higher short circuit current than lead-acid. I don't have a good source for figures, though.

Two in parallel, so whatever short-circuit current one can produce, you bank can produce twice.

The fuse should be rated to interrupt that short circuit current.

 

[Hedges]

Problem with ANL fuses. Interrupt of only 6000 amperes. Also there are so many junk ANL out there, not every one will score a quality fuse. Most automotive parts discounters and audio shops have garbage for ANL fuses. I'm not going to list every reference I use, it is very easy to find the information on your own. Google might be your friend. Or even Blue Sea Circuit Wizard But I don't care much anymore. You all can do whatever you can live with. I want to protect my clients.

For any decent fuse, I am able to get interrupt ratings.
It is the batteries I typically can't find short circuit ratings for.

Here's the battery I use:

http://sunxtender.com/datasheet/PVX-4050HT.pdf

The only info I have is one independent report of a different brand 100 Ah battery, for which they measured 4000A.

For OP's battery bank, he needs a suitable fuse. Likely the class T you recommended is sufficient.
But do you have a source for data or a method to determine what short circuit current is for a given battery?
For some size bank, maybe it would be necessary to separately fuse parallel strings of batteries. Need the short circuit current value to determine.

 

[Zil]

Blue Sea Circuit Wizard sizes fuses by CCA of lead acid battery. Li is a whole different worm. Every engineer specifying LiFePo and other Li battery recommend Class-T or MRBF. Most suggest to not use ANL fuses because of the many substandard brands available to DIY. Blue Sea will recommend their ANL fuses. But they are still only 6000A interrupt. Here is a read from Rod Collins, fuses are about 3/4 through article. https://marinehowto.com/lifepo4-batteries-on-boats/
There is not a direct correlation of AH to CCA but with a lead acid chemistry multiply the 20 hour AH by 7.5 to get a very general idea.

 

[Pappion]

I have 2 SOK 206AH batteries on order. Each BMS can output 100A. I might use 150A MRBF at the battery terminals just in case something goes terribly wrong, like a towing accident.

 

[Hedges]

MRBF fuses

MRBF Terminal Fuse - 175A - Blue Sea Systems

Space-saving ignition protected fuse for 30 to 300 Amp loads. Must use with Terminal Fuse Block.

www.bluesea.com

"

Specifications
Amperage	175A
Ignition Protected	Yes
Maximum Voltage	58V DC
Interrupt Capacity	10000A @ 14V DC 5000A @ 32V DC 2000A @ 58V DC

"

That takes care of most lead-acid battery banks for a 12V or 24V system.
OP's system is 12V. If lead-acid not lithium this would be fine.

For someone with 48V system, the 2000 AIC at that voltage would not be sufficient.

Some ANL fuses are rated to 80 VDC, but 2700 AIC so also not sufficient.

https://www.grainger.com/product/BUSSMANN-Forklift-Limiter-Fuse-1DC61

Class T does look like the best way to go. 20,000 AIC up to 125VDC

https://www.grainger.com/product/LITTELFUSE-Fuse-486L86

I have 2 SOK 206AH batteries on order. Each BMS can output 100A. I might use 150A MRBF at the battery terminals just in case something goes terribly wrong, like a towing accident.

Yes, fuses are good. Wouldn't trust BMS to interrupt thousands of amps short circuit current.
A fast fuse might protect it, might not.

 

[Zil]

I could not find a reasonable way to fit MRBF close to the terminals on my LiFePo battery. So I have a Class-T. Further down system I have MRFB on a buss bar for the branch circuits.

 

[orangeminnie]

MRBF fuses

MRBF Terminal Fuse - 175A - Blue Sea Systems

Space-saving ignition protected fuse for 30 to 300 Amp loads. Must use with Terminal Fuse Block.

www.bluesea.com

"

Specifications
Amperage	175A
Ignition Protected	Yes
Maximum Voltage	58V DC
Interrupt Capacity	10000A @ 14V DC 5000A @ 32V DC 2000A @ 58V DC

"

That takes care of most lead-acid battery banks for a 12V or 24V system.
OP's system is 12V. If lead-acid not lithium this would be fine.

For someone with 48V system, the 2000 AIC at that voltage would not be sufficient.

Some ANL fuses are rated to 80 VDC, but 2700 AIC so also not sufficient.

https://www.grainger.com/product/BUSSMANN-Forklift-Limiter-Fuse-1DC61

Class T does look like the best way to go. 20,000 AIC up to 125VDC

https://www.grainger.com/product/LITTELFUSE-Fuse-486L86

Yes, fuses are good. Wouldn't trust BMS to interrupt thousands of amps short circuit current.
A fast fuse might protect it, might not.

For a big ass inverter, or any other load of 200A or more, I sleep much better with a Class-T fuse, than other types. They are massive, and run cool to the touch at full load. I can't say that about the ANL's I've seen. Heat=power loss.

 

[Hedges]

For a big ass inverter, or any other load of 200A or more, I sleep much better with a Class-T fuse, than any other type. They are massive, and run cool to the touch at full load. I can't say that about the ANL's I've seen. Heat=power loss.

How about this one?



250A, 150 VDC, 50kA IR

 

[orangeminnie]

How about this one?

View attachment 33827

250A, 150 VDC, 50kA IR

Those are ultra fast acting semiconductor fuses. $60 a pop. Might be better than T-fuse in protecting an inverter from frying. We've used them in AC circuits that experience dirty line power.