Battery Bank Fuse

SurfpathSurfpath Posts: 334Solar Expert ✭✭
After a little research I would like to go with one of those nifty Blue Sea battery terminal fuses.

Aside: except the one I have picked out here seems to be a slightly different model than the ones I have seen posted before.
Attachment not found.
After a little more research on fuse sizing I'm back to the forum with a question.

Here goes:

From a previous thread [BB I believe]:
Battery Fusing:
Typically, the maximum expected current * 1.25 (or 1/0.80) for rated fuse/wiring/breakers. For example a 1,200 watt inverter running on a 12 volt battery bank (100 amps "nominal" becomes):
•1,200 watts * 1/0.85 inverter eff * 1/10.5 volts minimum battery voltage * 1.25 NEC factor = 168 amp fusing/breakers/wiring
And round up to next standard fuse/wire (175-200 amp in this example).

OK, Before I start, my Flexpower 1-6 (48v, 230VAC panel) comes with a "175ADC breaker" and a "80 amp charge controller breaker" (dont know if that helps) and a "VFX3048E" inverter.

What will be my maximum expected current. No idea really (pretty economical fridge, freezer, lights, blender)...lets go with 3000 watts (I think around the inverter max).

3000w*1/.85*1/42V (battery cutoff for a 48v bank)*1.25= 105 amps minimum circuit.
I'd then go for a 150 amp fuse.

I just need one battery fuse, right? My bank is one string of eight 6volters. This fuse should be screwed on to the battery + terminal that leads to the inverter....?

Am I on the right track my friends, or just still con-fuzed?:cool:
Surfpath
Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, no genny, 100% off grid.
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Comments

  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse

    That looks like a piece of hardware for mounting an external fuse, not the same as the nifty Blue Sea holders.

    If it were me, I'd size the inverter wiring for the maximum current (111 according to my calculations) which would be 2 AWG and size the fuse for the more likely expected 60 to 70 Amps. So that would be 100 Amps. The best source of info for this would be the inverter manual itself; hard to beat factory recommendations!

    And yes you only need one fuse on one battery string, and standard practice is to put it on the (+) side.
  • SurfpathSurfpath Posts: 334Solar Expert ✭✭
    Re: Battery Bank Fuse

    On the Amazon link I supplied the model number correlates to the Blue Seas' "Terminal fuse block 1 terminal stud"
    The Amazon photo looks similar but perhaps more...basic?
    Hmmmmm..
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, no genny, 100% off grid.
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse

    I guess they look odd with the fuse removed.

    I'm used to seeing them like this:
  • vtmapsvtmaps Posts: 3,471Solar Expert ✭✭✭✭
    Re: Battery Bank Fuse
    If it were me, I'd size the inverter wiring for the maximum current (111 according to my calculations) which would be 2 AWG and size the fuse for the more likely expected 60 to 70 Amps. So that would be 100 Amps. The best source of info for this would be the inverter manual itself; hard to beat factory recommendations!

    Cariboocoot, if the DC breaker for the inverter is 175 amps, shouldn't the fuse be at least that large? I presume that the cable from battery to inverter must be sized with an ampacity greater than 175 amps, and I don't think 2 AWG is adequate.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • SurfpathSurfpath Posts: 334Solar Expert ✭✭
    Re: Battery Bank Fuse

    From the Flexpower 1 manual:

    Battery Positive (+) Minimum conductor size= 2/0 AWG, Breaker size 175 Adc
    PV Positive (+) Minimum conductor size= #4 AWG, Breaker size 80 Adc

    Dont know if that helps
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, no genny, 100% off grid.
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse
    vtmaps wrote: »
    Cariboocoot, if the DC breaker for the inverter is 175 amps, shouldn't the fuse be at least that large? I presume that the cable from battery to inverter must be sized with an ampacity greater than 175 amps, and I don't think 2 AWG is adequate.

    --vtMaps

    You can undersize supply lines provided you know they are undersized and you keep the relation between wiring and circuit protection so that the CP always gives out first.

    Those were minimal power requirements I was quoting. If you go with maximum output at minimum input for sustain operation you get quite different numbers indeed!

    The Flexpower numbers are its maximums, which are not necessarily what are needed for a particular install. For instance 175 Amps continuous on nominal 48 Volts is 8.4 kW - nearly 3X the inverter's rated capacity. The 80 Amp rating on the controller side fits with an 80 Amp controller.

    This is why it's always best to go with the specs supplied by the manufacturer of the device supplying or using the power, and make sure everything in the connections is up to that rating.

    Clear as mud? That's normal for wiring/fuse sizing questions. :p
  • SurfpathSurfpath Posts: 334Solar Expert ✭✭
    Re: Battery Bank Fuse

    More detail from the page in the manual
    Attachment not found.
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, no genny, 100% off grid.
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse

    Which inverter are you using? Outback FX3048T?
    Refer to install manual: http://lib.store.yahoo.net/lib/wind-sun/FX-VFX-install.pdf
    Page 38: DC Input Current - Rated Power: 75 Amps
    Not 175 Amps.
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse

    Also look at Page 51: Recommended Wire Sizes By Length.
    For full power at lengths up to 10 feet one way Outback indicates 1/0 only on the 3048. That actually has an Ampacity rating of 150, and they recommend it to keep the V-drop low under maximum power circumstances. A 3kW 48 Volt inverter just does not draw that much current. OB's figure for "typical" is in fact only 60 Amps. Does that number look familiar? :D
  • vtmapsvtmaps Posts: 3,471Solar Expert ✭✭✭✭
    Re: Battery Bank Fuse
    Which inverter are you using? Outback FX3048T?
    Refer to install manual: http://lib.store.yahoo.net/lib/wind-sun/FX-VFX-install.pdf
    Page 38: DC Input Current - Rated Power: 75 Amps
    Not 175 Amps.

    In his OP he wrote that he has the vfx3048E (50 hz 230 volt). I couldn't find on Outback's site any specs for DC input current. I did find that its AC overload capacity is surge to 5750 VA and 4800 VA for 5 seconds. The Flexpower system which his inverter is part of does include a 175 (not 75) amp DC breaker. I have no idea if a 75 amp breaker would trip on those overloads.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse

    Guess what? 3kW AC out is 3kW AC out, whether at 120 VAC 60 Hz or 230 VAC 50 Hz. When drawn off 48 VDC the current is the same.

    The Flexpower has the capacity to handle a lot more inverter than that. 175 Amps will never trip from normal use and is way over-sized for that inverter.

    A 2812 will draw about 240 Amps at max, so the 175 Amp breaker is under-sized for that. A 3524 will draw about 145, so 175 Amps is just about right for it.
    Why they put a breaker that big on that 3048 inverter I don't know. You could run two of them off that. For some reason this seems to be the smallest breaker offered with the FP units.

    Which begs the question that if you buy a pre-wired unit like this, why are we trying to calculate breaker sizes at all?
    And also brings up the issue that if you are running with a 175 Amp breaker do not under-size the wire at all. You must use 1/0 minimum or preferably 2/0 wire. Otherwise the wire can fry before that breaker will trip.

    Of course that inverter can go up in flames before that breaker will trip too. Seems dumb to me. I didn't design it, though. And I do always say you can't beat the maker's recommendations.

    In this case I could be wrong about that. :roll:
  • mtdocmtdoc Posts: 600Solar Expert
    Re: Battery Bank Fuse

    FWIW my Midnite prewired ePanel with an Outback 3648 inverter also has a 175 amp breaker- which seemed too large to me. I did use 2/0 cables though for that reason.
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse

    MidNite, run by the guys who invented most of Outback's equipment in the first place, sensibly offers an E-panel with 125 Amp breaker for 48 Volt inverter.
  • mtdocmtdoc Posts: 600Solar Expert
    Re: Battery Bank Fuse
    MidNite, run by the guys who invented most of Outback's equipment in the first place, sensibly offers an E-panel with 125 Amp breaker for 48 Volt inverter.

    Right, some of the bare ePanels they sell have 125 amp breakers but all of their ePanels that are prewired with 48V inverters have 175 amp breakers. As you point out, that seems too high. The question is why do they do it this way?
  • SurfpathSurfpath Posts: 334Solar Expert ✭✭
    Re: Battery Bank Fuse
    175 Amps will never trip from normal use and is way over-sized for that inverter....
    Which begs the question that if you buy a pre-wired unit like this, why are we trying to calculate breaker sizes at all?

    SO, to summarize: the Flexpower 1-6's DC breaker is (too) large for the inverter that comes with it? Also, additional fusing (a la blue seas battery terminal fuse) should not be necessary as one already pays for a DC fuse with the Flexpower package. However...

    ....given the 175amp fuse currently on the panel, this now means it is important to now install a DC battery fuse that has a smaller amp rating? That way if there is a potentially dangerous DC surge the terminal fuse pops first and stops the current.
    And also brings up the issue that if you are running with a 175 Amp breaker do not under-size the wire at all. You must use 1/0 minimum or preferably 2/0 wire. Otherwise the wire can fry before that breaker will trip
    .

    What my dealer ordered for me was "6 feet of #2/0 GAUGE Multi Strand 105 Primary Cable (BLACK)" and in RED.
    -SP
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, no genny, 100% off grid.
  • SurfpathSurfpath Posts: 334Solar Expert ✭✭
    Re: Battery Bank Fuse
    vtmaps wrote: »
    I couldn't find on Outback's site any specs for DC input current. I did find that its AC overload capacity is surge to 5750 VA and 4800 VA for 5 seconds. The Flexpower system which his inverter is part of does include a 175 (not 75) amp DC breaker. I have no idea if a 75 amp breaker would trip on those overloads.
    --vtMaps

    From the Outback web site.
    Specs attached (see last column)
    Attachment not found.
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, no genny, 100% off grid.
  • vtmapsvtmaps Posts: 3,471Solar Expert ✭✭✭✭
    Re: Battery Bank Fuse
    Surfpath wrote: »
    ....given the 175amp fuse currently on the panel, this now means it is important to now install a DC battery fuse that has a smaller amp rating? That way if there is a potentially dangerous DC surge the terminal fuse pops first and stops the current.

    No. The fuse should be sized to protect the wiring, not the inverter. You want the fuse to melt before the wire melts. It should be at least as large as your breaker.... if one of the overcurrent devices is triggered, its a lot easier (and cheaper) to reset a breaker than a fuse.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • vtmapsvtmaps Posts: 3,471Solar Expert ✭✭✭✭
    Re: Battery Bank Fuse
    Surfpath wrote: »
    Specs attached (see last column)

    Surfpath, I found that chart you posted. It does NOT give specs for the DC input current. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse

    Well I did point to the specs for the 3048 inverter: 75 Amps. By the time current draw reaches 175+ and trips that breaker the inverter could be ablaze if the problem is a short inside it. No idea why this is so far out of spec. It's completely weird that the install manual for the inverter spec's one size breaker and the Flexpower panel comes with something so much larger. :confused:

    Circuit protection always has to be the "weak link in the chain".
  • vtmapsvtmaps Posts: 3,471Solar Expert ✭✭✭✭
    Re: Battery Bank Fuse
    Well I did point to the specs for the 3048 inverter: 75 Amps.

    I couldn't find that specification at Outback's site, or at least I could not find it for the vfx3048E. The link you gave is for the FX3048T.
    The heavy cables that Outback recommends are heavy to lower their resistance, not because the ampacity is needed. Since the breakers are to protect the wiring (not the inverter), 175 amps is reasonable to protect 00 AWG cable.
    By the time current draw reaches 175+ and trips that breaker the inverter could be ablaze if the problem is a short inside it.

    I certainly agree with you on this point. Of course, an arc fault inside the inverter could cause a blaze without tripping a 75 amp breaker.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse
    vtmaps wrote: »
    I couldn't find that specification at Outback's site, or at least I could not find it for the vfx3048E. The link you gave is for the FX3048T.
    The heavy cables that Outback recommends are heavy to lower their resistance, not because the ampacity is needed. Since the breakers are to protect the wiring (not the inverter), 175 amps is reasonable to protect 00 AWG cable.

    Curiously, 3kW from 48 Volts is the same amount of current regardless if the inverter is vented or not. The spec came from Outback's install manual.


    I certainly agree with you on this point. Of course, an arc fault inside the inverter could cause a blaze without tripping a 75 amp breaker.

    --vtMaps

    This is like the old discussion about North American and European power standards: How do you want the house fire to start? From over-current (N.A.) or arcing (E)? :p
  • SurfpathSurfpath Posts: 334Solar Expert ✭✭
    Re: Battery Bank Fuse
    vtmaps wrote: »
    I couldn't find that specification at Outback's site, or at least I could not find it for the vfx3048E. The heavy cables that Outback recommends are heavy to lower their resistance, not because the ampacity is needed. Since the breakers are to protect the wiring (not the inverter), 175 amps is reasonable to protect 00 AWG cable.
    --vtMaps

    Found it. Attached is the DC input current from the Outback Manual (specifically for the VFX3048E): 75 amps (I am sure no surprise, but I just wanted to confirm)
    Attachment not found.

    Again, I am not 100% sure how to proceed (sorry guys). No additional battery fuse protection, or yes, additional battery fuse protection should be made (at what amperage), or just rely upon the existing 175 amp breaker to protect the wiring (and a trusty fire extinguisher to douse that pesky arcing inverter);)

    I agree Coot, "175 Amps will never trip from normal use and is way over-sized for that inverter"
    -SP
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, no genny, 100% off grid.
  • SurfpathSurfpath Posts: 334Solar Expert ✭✭
    Re: Battery Bank Fuse

    Addendum:
    Do these additional numbers from the Outback VFX3048 manual help to confirm:
    Attachment not found.Attachment not found.Attachment not found.

    I am no electrician, but it seems clear that Outback recommends a 125 amp breaker for the VFX3048E, but the Flexpower 1-6 which has a VFX3048E comes with a 175 amp breaker. Hmmmm
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, no genny, 100% off grid.
  • mtdocmtdoc Posts: 600Solar Expert
    Re: Battery Bank Fuse

    The possible AC surge from the GVFX 3048E is 5750 VA which would correspond to about 120 DC amps for a 48V system.

    Here is the table from their installation manual that specifies DC breaker size:

    Attachment not found.

    Why their FP1 prewired with this inverter uses a 175 amp (instead of 125 amp) breaker, I have no idea.

    Here is the corresponding table for my GVFX3648:

    Attachment not found.



    What I don't understand why the amapcity and DC breaker size for the the VFX 3648 is different from the GVFX 3648. They both have the same AC surge capability of 6000 VA

    Also I still don't know why Midnite's pre-wired ePanels for the 48V inverters all use 175 Amp breakers.:confused::confused:
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse

    As a rule current capacity of conductors/breakers/fuses is based on continuous current, not surge current. Surge does not fall under the description of "continuous" as per NEC and so should not be used as a sizing basis. In fact the Outback installation manual also mentions the maximum DC input current on Page 45 and says of it:

    "NOTE: This is the maximum DC current the FX will draw from the battery when starting very large AC loads. It is not used for sizing the DC disconnect or selecting DC cable gauge. It is used to select the minimum reasonable battery capacity."

    That number for 48 Volt FX series inverters is 150 Amps. If you were to size the breaker by this number in accordance with NEC regs you'd get an even more outrageous 250 Amp requirement.

    Surges don't last that long to come in to play. All conductors and circuit protectors are capable of handling more than their rated continuous current for some time. How much and how long will vary with the particular install.
  • mtdocmtdoc Posts: 600Solar Expert
    Re: Battery Bank Fuse
    As a rule current capacity of conductors/breakers/fuses is based on continuous current, not surge current. Surge does not fall under the description of "continuous" as per NEC and so should not be used as a sizing basis. In fact the Outback installation manual also mentions the maximum DC input current on Page 45 and says of it:

    "NOTE: This is the maximum DC current the FX will draw from the battery when starting very large AC loads. It is not used for sizing the DC disconnect or selecting DC cable gauge. It is used to select the minimum reasonable battery capacity."

    Absolutely! I understand this but then why the recomended breaker sizes? and why the oversized breakers on Outback prewired Flexpower units and Midnites prewired ePanels? ( I just posed this question on the Midnite forum)

    That number for 48 Volt FX series inverters is 150 Amps. If you were to size the breaker by this number in accordance with NEC regs you'd get an even more outrageous 250 Amp requirement.

    Not sure I understand this. What number (where did you get 150) ? and where does the 250 amp requirement come from?
  • SurfpathSurfpath Posts: 334Solar Expert ✭✭
    Re: Battery Bank Fuse
    mtdoc wrote: »
    ...why the oversized breakers on Outback prewired Flexpower units & Midnites..? ( I just posed this question on the Midnite forum)
    I also sent the same question to the Outback forum. -SP
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, no genny, 100% off grid.
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse
    mtdoc wrote: »
    Absolutely! I understand this but then why the recomended breaker sizes? and why the oversized breakers on Outback prewired Flexpower units and Midnites prewired ePanels? ( I just posed this question on the Midnite forum)

    I don't know. It's a mystery! :p
    Not sure I understand this. What number (where did you get 150) ? and where does the 250 amp requirement come from?

    That number comes from Outback's installation manual for 48 Volt inverters. The 250 Amp breaker sizing is based on the NEC "* 1.25 * 1.25 and round up" formula.

    I'm looking forward to either Outback or MidNite explaining this. It has me puzzled for sure. :confused:
  • vtmapsvtmaps Posts: 3,471Solar Expert ✭✭✭✭
    Re: Battery Bank Fuse
    I'm looking forward to either Outback or MidNite explaining this. It has me puzzled for sure. :confused:

    Ryan has given his answer over at the Midnite forum:
    halfcrazy wrote:
    The 125 amp breaker has small 1/4 studs and is sorta light duty for 2/0 cable. As you noted Outback uses the 175 as well and that is just how we have done it since we designed and built the Outback inverter. You will notice at Midnight we do offer a lot of 125 amp Epanel options but like I say it is tough wiring and in reality will never make the system safer or any more likely to prevent any damage. When the Outback blows up internally it WILL trip a 175 with ease I have witnessed this

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Posts: 17,615Banned
    Re: Battery Bank Fuse

    Well there we go!
    You can't beat the information from the guys that actually designed the unit.
    This is why I continually recommended getting the wire and fuse sizing out of the manuals. However in this case the manuals disagree. :roll: If you were to wire a 3048 without the panel you'd be using a 100 Amp fuse. It is unfortunate to note that breakers do not trip immediately upon over-current, so I still think there's the possibility of unpleasant damage from running that large a breaker. You're supposed to be able to recover a circuit that uses a breaker.

    So to my way of thinking this runs a bit backwards: you're stuck with a 175 Amp breaker, so make sure you use the big wire even though smaller would handle the inverter's demands. As I said before, the circuit protection has to be the weakest link in the chain. Although it still appears that the inverter would be.

    Maybe what we need here are better inverter breakers.

    There's a lot of "catching up" to do in the industry. The charge controllers used, for instance, are adapted to the batteries available. Only recently has there been enough demand for RE that battery manufacturers are starting to adjust products to be more suited for the application. When that happens the controllers will need to be adjusted as well. There's quite a thread on using LiFePo batteries here and the need for individual cell management. Believe it or not, lead-acid batteries would benefit from that as well (imagine being able to EQ the one cell that was out of spec and not subject the whole bank to the higher Voltage heating).

    MidNite is definitely in the forefront of innovative RE technology. But we're still waiting for their battery monitor with integrated charge control. :D

    Ramble over.
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