Oversized wire and breaker?

I recently bought a 2000 watt 24v magnum inverter and in the manual it says: Maximum DC fuse size 150 amps. Would it be okay for me to use my current 2/0 cable and a 250 amp DC breaker from my previous 12v system? I don't want to buy a new breaker and new inverter cables if possible.
Comments
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
I found this breaker used on Ebay for $25. My inverter cables have 3/8 lugs on them and this breaker has 5/16 studs but thats the only problem that I see with it.
Here is another breaker I found with 3/8 studs, it says 12v but in the description it says Max 48v
https://www.ebay.com/itm/12V-DC-150-AMP-Circuit-Breaker-for-Race-Car-Trunk-Mount-Battery-Switch-3-8-Studs-/351998833465 Would either of these work? I would rather use a breaker because if it trips I can just reset it and wont have to buy a new fuse. I am open to suggestions on which breaker to buy if anyone has any.
KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada
This is just another reason why I always use the exact product that the manual specifies.
I do not want to be sued and I want my clients to be safe
http://members.sti.net/offgridsolar/
E-mail [email protected]
My question is: How do I figure the short circuit current of all my batteries? I don't really plan on going much bigger with my system, seeing as how I just doubled it (overall system voltage/ batteries and solar modules). I may go bigger with my next battery bank in a few years, seeing I have 1600 watts of solar modules going to just the 8 golf cart batteries but I will not be adding any more PV
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
For example, all house hold circuit breakers (in North America) have an AIC rating of 10,000 Amps. That is also the maximum current rating of a "typical" pole mount transformer and some resistance of the electrical drop from the pole to the house.
Lead Acid batteries output huge amounts of short circuit current. If you have a large bank and heavy copper cables, then there coudl be high short circuit current.
-Bill
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
Second system 1890W 3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
The following types of fuses are included in the Samlex Kit:
***UPDATE*** I emailed Magnum, my inverter manufacturer and blue sea. Blue sea told me this fuse rarely blows unless a major problem has occured and I should go with the class T seeing my inverter manual recommends it. Magnum tech support told me the MRBF fuse WILL work with this inverter... Now I am totally confused. I think I will go with the Class T before the inverter and MRBF fuse on my second string of batteries.
"With all the info you should be fine with 3/8’ on 5/16” posts. I would suggest using a good 5/16” ID hole washer on each side of the cable flats to provide a bit more support and to prevent slippage. Several customers have reported doing that and it works fine for them."
As for your other questions, maybe someone else with more knowledge will chime in.
With properly sized breaker and wire, fusing the battery side would normally not be needed. There are exceptions though, for example if more than two parallel strings/batteries in the bank each parallel connection should be fused.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
http://www.littelfuse.com/products/fuses/industrial-power-fuses/class-t-fuses/jlln.aspx
http://www.littelfuse.com/~/media/electrical/datasheets/fuses/industrial-and-ul-fuses/littelfuse_fuse_jlln_jlls_datasheet.pdf
JLLN
Voltage Ratings AC: 300 V
DC: 160 V (1 - 60 A)
125 V (70 - 1200 A)
Ampere Range 1 – 1200 A
Interrupting Ratings AC: 200 kA rms symmetrical
DC: 50kA (1 - 30A)
20kA (35 - 1200A)
Approvals AC: UL Standard 248-15, Class T
UL Listed (File: E81895): 1 – 1200 A
CSA Certified (File: LR29862): 1 – 600 A
DC: UL Listed (File: E81895): 1 – 1200 A
Material 1-30 A: Melamine body, Bronze caps
35-1200 A: Melamine body, Copper caps
Environmental RoHS Compliant
JLLS
Voltage Ratings AC: 600 V
DC: 300 V
Ampere Range 1 – 1200 A
Interrupting Ratings AC: 200 kA rms symmetrical
DC: 20kA
Approvals AC: UL Standard 248-15, Class T
UL Listed (File: E81895): 1 – 1200 A
CSA Certified (File: LR29862): 1 – 600 A
DC: Littelfuse self-certified
Material 1-30 A: Melamine body, Copper caps
35-60 A: Melamine body, Bronze caps
70-1200 A: Melamine body, Copper caps
Environmental RoHS Compliant
Took a bit of searching, but found MRBF fuse specifications:
http://www.cooperindustries.com/content/public/en/bussmann/transportation/products/circuit_protection/fuses/marine_rated_batteryfuses.resources.html (not much here)
http://www.peerlesselectronics.com//files/MRBF-100.pdf
applications. Break in capacity meets the requirements of conventional
vehicle batteris and 42V electrical networks
Voltage Rating: 58Vdc Maximum
Amperage Rating: 30A - 300A
Ingress Protection: IP66
Ignition Protected: Per SAEJ1117
Interrupt Rating:
10000 AMP @ 14Vdc
5000 AMP @ 32Vdc
2000 AMP @ 58Vdc
Color Coded (see next page)
Torque Rating: Maximum 12 Nm (106 in-lbs)
Material:
Body - Ceramic
Housing & Cover: UL-rated 94V0 Thermoplastic
Ring Terminals - Tin Plated
Compliances: ISO 8820-6
Rating
30A - 300A
100%
> 100 h
135%
Max 900 sec
200%
max.
60s
350%
min. max.
0.1s 1 s
600%
< 0.2s
And here is a LittleFuse design document... Not a bad place to start if you have detailed questions about how to pick the "right fuse/breaker":
http://www.littelfuse.com/~/media/electronics/product_catalogs/littelfuse_fuseology_selection_guide.pdf.pdf
With fuses and breakers--You really need to go back to the actual manufacturer's specifications to figure out if any particular choice will work for your needs.
And you may never get an "official" answer to questions like can I use an MRBF fuse (58 volt max rated) on a 48 volt battery bank (which can see 60+ volts). My unofficial answer would be (don't sue me for this) is yes because actual battery bank voltage on a shorted circuit would be less than ~58 volts.
HOWEVER, if you have a large Lead Acid (or Li Ion) battery bank and heavy cables, the 2,000 Amp interrupt current may not be high enough... And you then need to look at the Class "T" type fuse with 20,000+ Amp IC rating.
And to make the decision, you need to look at secondary questions. For example, if the DC leads are long enough (and not huge diameter copper), the resistance of the leads may limit the short circuit current (V=IR; I=V/R). For example, to get 2,000 amps at 58 volts:
If you have a 2 AWG cable, that is around 0.16 ohms per 1,000 feet or 0.00016 ohms per foot
http://www.interfacebus.com/AWG-table-of-different-wire-gauge-resistance.html
- 0.029 Ohms / 0.00016 Ohms per foot (2 AWG) = 181 feet round trip (or 91 feet one way)
It appears that for many of our DC off grid System Battery Bank designs, I would guess there is no enough resistance in the copper wiring to limit a short to 2,000 Amps on a fully charged 48 volt battery bank (and using 48 VDC nominal would reduce the one way wire run to ~75 feet for 2 kAmps maximum).To get a feel of what in depth short circuit calculations look like, here is one for AC systems (search for "Cooper Bussman's Point to Point Method of Short-Circuit Calculation" if link is not permanent):
http://www.interfacebus.com/AWG-table-of-different-wire-gauge-resistance.html
Here is a DC short circuit estimate from Schneider:
http://www2.schneider-electric.com/documents/electrical-distribution/en/shared/interactive-catalogue/lvped2080006en/pdfs/page_019.pdf
DB105060
Calculation of the short-circuit current across the terminals of
a battery
During a short-circuit, the battery discharges a current equal to
Vb = maximum discharge voltage (battery 100 % charged)
Ri = internal resistance equivalent to all cells (a function of the capacity in amperehours).
Isc=Vb/Ri
Example
consider a set of four 500 Ah batteries connected in parallel
discharge voltage of one battery: 240 V (110 cells 2.2 V each)
discharge current of one battery: 300 A with a run-time of 30 minutes
discharge current of all four batteries: 1200 A with a run-time of 30 minutes
internal resistance 0.5 mW per cell, i.e. for one battery:
Ri = 110 x 0.5 x 10-3 = 55 x 10-3 W
short-circuit current of one battery: Isc = 240 V / 55 x 10-3 W = 4.37 kA
neglecting the resistance of the connections, for all four batteries discharging the
short-circuit current in parallel, the total short-circuit current is four times that of one
battery, i.e. Isc = 4 x 4.37 kA = 17.5 kA.
Note: if the internal resistance is not known, it is possible to use the following rough
approximation: Isc = kc where c is the capacity of the battery in ampere-hours and k is a
coefficient close to 10 and always less than 20.
Other typical examples
PABXs: Isc from 5 to 25 kA at 240 V DC with L/R = 5 ms
submarine: Isc from 40 to 60 kA at 400 V DC with L/R = 5 ms.
Some numbers measured/estimated for a 100 AH lead acid cell:
https://www.blueboxbatteries.co.uk/blog/battery-internal-resistance-short-circuit-current-47

For standard/typical Lead Acid storage batteries, they tend to have higher internal resistance. For AGM/GEL/Li Ion they tend to have lower internal resistance. And remember that a Lead Acid battery can only out peak current for a few minutes from full charge, and the current quickly drops after that.Has anyone found/done "real life" 12/24/48 volt lead acid storage battery short circuit tests here?
-Bill
Watch a dead short on the power bridge of an XW6848+ and you may do this also. This was a test of a good unit BTW.
http://members.sti.net/offgridsolar/
E-mail [email protected]
the subject of Over Current Protection Devices...
http://www.electricityfromthesun.info/low_voltage_dc_fuse_and_circuit_breaker_applications.htm