Oversized wire and breaker?
solarpowernovice
Solar Expert Posts: 135 ✭✭
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
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solarpowernovice said: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.1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS
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. -
So, just to clarify... Using my old 2/0 battery and inverter cables is fine, so long as I introduce a 150 amp fuse before the breaker? This would be much better than buying a new breaker and cables. Thanks
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The 150a fuse should go as close to practical to the battery positive. It will protect the controller internal wiring. The breaker can go close to the controller - it should never trip (the fuse should open in a controller short), but can be handy as a disconnect.Off-grid.
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 -
Can I use a breaker instead of a fuse? the cheapest 150 amp fuse block with fuse is $55 https://www.solar-electric.com/mrcb-150-amp-dc-circuit-breaker.html
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. -
"solar'' breakers are usually rated to 150V ... MidNite etc. brands. If you expect to change your system in the future you will be money ahead with a 150V model. Remember if you series your panels you could be well above 50 V
KID #51B 4s 140W to 24V 900Ah C&D AGM
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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 -
The breaker/fuse is for an inverter right? The key spec to match here is that it has Class T interrupt ability.
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"we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail offgridsolar@sti.net -
Alrighty then, it looks like I will go with the 150 amp fuse block. I'd rather spend more money to do it the right way and not cut any corners. Thanks for all your help everyone.
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I have one more question for you guys... In my inverters manual it reads: "In some installations, if the combined short-circuit current of all the batteries in the bank is determined to be 2,700 amps or less, then an ANL type of fuse may be used---if in doubt, use a class-t fuse." I'll be purchasing eight Costco insterstate golf cart batteries (2 strings of 4) rated at 215 AH.
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 -
The overcurrent protection is based on the conductors maximum current carrying capacity , not the short circuit amperage of the batteries themselves, the purpose of the protection is to prevent the conductors from becoming the fuse, the fuse/ breaker would protect the conductors in the event of a short circuit.1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS
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. -
My understanding is the ANL fuse will open in a short on the order of 100s of milliseconds to a second, whereas the class T should open on the order of 10s of ms. The risk is the inverter wiring may arc/burn before the ANL opens.Off-grid.
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 -
Also, the AIC rating (Amperes Interrupting Current) means that a 2,700 AIC fuse will catch fire, arc, explode if more than 2,700 amp short circuit.
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
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Just curious - would cranking amps be a reasonable order of magnitude guess for SC amps? I know they aren't so rated, but presumably a pair of GC battery would very roughly equal a typical auto battery CA at ~800-1000CA?Off-grid.
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 -
Estragon said:Just curious - would cranking amps be a reasonable order of magnitude guess for SC amps? I know they aren't so rated, but presumably a pair of GC battery would very roughly equal a typical auto battery CA at ~800-1000CA?1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS
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. -
Can I use Blue Sea Systems MRBF terminal fuses like this? https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A --- Apparently Samlex uses these fuses in their 2000 watt inverter install kit http://www.samlexamerica.com/products/ProductDetail.aspx?pid=91... You cant get any closer to the battery than these and like you say...Estragon said:The 150a fuse should go as close to practical to the battery positive. It will protect the controller internal wiring. The breaker can go close to the controller - it should never trip (the fuse should open in a controller short), but can be handy as a disconnect.
The following types of fuses are included in the Samlex Kit:Marine Rated Battery Fuse (MRBF Series) made by Cooper Bussmann- Voltage rating of max 58 VDC- Current ratings of 100A (MRBF-100), 200A (MRBF-200) and 300A (MRBF-300)- AIC of 10000A at 14VDC, 5000A at 32 VDC and 2000A at 58 VDC- Ignition protected as per SAE J1171- Weather Proof (IP66)Hopefully these work because I found 2 fuse blocks and 4 fuses for the price of 1 Class-T fuseblock/fuse. I'd love to save the money but I'd rather be safe.
***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.
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Looking at those MRBF terminal fuses, they say they are rated for 58v. So would they not work on a 48v battery as the charging and EQ voltage would be higher?Also, if I have a Midnite Solar 250 amp breaker (24v system) on the inverter side, Do I need a fuse on the battery side? And would it be of benefit to down size the fuse to 175amps? I am using 4/0 cable. between battery and inverter.And one other issue, the MRBF terminal fuses blocks say they connect to a 3/8's battery terminal stud, but Trojan studs are 5/16. Do I need an adapter? Or can one bolt the 3/8 ring to a 5/16 stud with no issue?
REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2017 / System, Pics and Discussion -
Jerry from donrowe.com customer service answered this same question for me, so here it is from the email he sent me...
"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. -
You should generally install the size of breaker or fuse recommended by the inverter manufacturer. Too small may not handle non-fault current safely, and too large turns the inverter and/or wiring into a fuse.
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.Off-grid.
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 -
Class T fuses (NAWS sells class T, not sure if all are Little Fuse LNN"S" series or not), but here are product page and the basic data sheets:
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.pdfSpecifications
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.pdfApplications: Full range circuit protection for automotive and marine
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:- 58 volts / 2,000 Amps = 0.029 Ohms
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)
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.pdfShort-circuit currentsSo, looking at a "typical" worst case Lead Acid Storage Battery (large AH cell) with ~0.5 mOhms per cell, a 48 volt @ 1,000 AH or more? battery bank would have:
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.- 24 cells * 0.0005 Ohms per cell = 0.012 Ohms total (and could be 2-5x higher vary easily)
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
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Community Gold. Thanks so much.REC TwinPeak 2 285W 3S-3P 2.6kW-STC / 1.9kW-NMOT Array / MN Solar Classic 150 / 2017 Conext SW 4024 Inverter latest firmware / OB PSX-240 Autotransfomer for load balancing / Trojan L16H-AC 435Ah bank 4S connected to Inverter with 7' of 4/0 cable / 24 volt system / Grid-Assist or Backup Solar Generator System Powering 3200Whs Daily / System went Online Oct 2017 / System, Pics and Discussion
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I have done the tests and seen the results. I have used Class T fuses in my batteries since 1992.
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."we go where power lines don't" Sierra Nevada mountain area
htps://offgridsolar1.com/
E-mail offgridsolar@sti.net -
Great information as always Bill and friends, thanks! As an aside here is a really good article i found on
the subject of Over Current Protection Devices...
http://www.electricityfromthesun.info/low_voltage_dc_fuse_and_circuit_breaker_applications.htm -
Something that has kind of been ignored (I have been guilty of this too) over the years are polarized vs the newer non-polirized DC circuit breakers...
Polarized DC breakers, if tripped (or even just cycled off) with "reverse current flow" (such as rated to protect against a battery short circuit, but "turned off" while battery is cycling) and easily cause the fuse/power panel to catch more when using polarized DC breakers:
https://forum.solar-electric.com/discussion/comment/426128
Many (some, all?) "polarized" DC breakers use a magnet to "blow" the DC arc into the quench chamber... If you run "reverse current" through the breaker and cycle the breaker off (even using less than rated current) the magnet will pull the arc into the "guts" of the breaker and continue the arc and set the breaker on fire.
Unless you "know" the direction of DC current flow through the breaker, you otherwise need to use "non-polarized" DC breakers for safety.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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