DC breakers in parallel

stephendv
stephendv Solar Expert Posts: 1,571 ✭✭
in Off Grid Solar & Battery Systems #1
I'm building a small system for a friend on a tight budget who needs a DC fuse/breaker for the battery bank rated at about 150A (that's the max peak inverter draw).
Looking at the outback DC breakers, a single 175A breaker is more than 5 times the cost of an 80A breaker. So would it be possible/advisable to use 2 of the 80A breakers in parallel?

The inverter is a Victron 1600/24V, with peak power of 3000W and nominal 1600W, data sheet here: http://www.victronenergy.com/upload/documents/Datasheet-Phoenix-Inverter-1200VA-5000VA-EN.pdf
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #2
    Re: DC breakers in parallel
    stephendv wrote: »
    Looking at the outback DC breakers, a single 175A breaker is more than 5 times the cost of an 80A breaker.

    At the NAWS store, midnite 80 amp breakers are $40 each and the midnite 175 amp breaker is $81.

    If you do use 80 amp breakers, will they take a heavy enough cable on their lugs?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #3
    Re: DC breakers in parallel

    My supplier only has the outback breakers. With the two breakers right next to each other I could divide the strands of the thick cable in two and get it into both breakers. Not pretty, but it should work. Are there no issues with using 2 in parallel?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: DC breakers in parallel
    stephendv wrote: »
    My supplier only has the outback breakers. With the two breakers right next to each other I could divide the strands of the thick cable in two and get it into both breakers. Not pretty, but it should work. Are there no issues with using 2 in parallel?

    Not a good idea.
    The two breakers would need to be ganged to trip simultaneously. Even then there is no guarantee the current will flow evenly between them.
    Especially if you just try to hack one cable in half and put an end in each one. You need to terminate the heavy cable at a splice point and then run two separate equal-size wires to each breaker (and the same on the other side).
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #5
    Re: DC breakers in parallel
    stephendv wrote: »
    Are there no issues with using 2 in parallel?

    Not sure... Usually the only fault that could trip the breaker would be current from the battery to the inverter, and a polarized breaker is installed with that polarity in mind.

    When charging the battery through the inverter the current is in the reverse direction. Normally the breaker is sized larger than the charger can supply, so it will not trip during charging. With smaller breakers, if they are polarized, I could see a situation where if one is turned off the other could be tripped by a large charging current that has the wrong polarity for the breaker. Perhaps if they are ganged together it would be safer.

    --vtMaps

    EDIT: I didn't see Cariboocoot's post before I replied. His point about uneven current sharing is well taken... even if you do use two identical cables from a splice point, I could see a lot of nuisance trips.
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #6
    Re: DC breakers in parallel

    Thanks guys, I guess it's gonna be one of those mechanical automotive battery cut-off switches and a fuse then, to be on the safe side.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,891 ✭✭✭✭✭✭
    #7
    Re: DC breakers in parallel
    stephendv wrote: »
    Thanks guys, I guess it's gonna be one of those mechanical automotive battery cut-off switches and a fuse then, to be on the safe side.

    It should be a class T fuse if you are trying to protect against a worst case battery failure. I just had an insurance inspection on a burned house that someone in the next county installed.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    Re: DC breakers in parallel
    stephendv wrote: »
    I guess it's gonna be one of those mechanical automotive battery cut-off switches and a fuse then, to be on the safe side.
    Dave Angelini wrote: »
    It should be a class T fuse if you are trying to protect against a worst case battery failure. I just had an insurance inspection on a burned house that someone in the next county installed.

    If you're worried about insurance inspections, those automotive cut-off switches are not listed for residential systems.
    http://www.amplepower.com/primer/burnt_sw/index.html

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,891 ✭✭✭✭✭✭
    #9
    Re: DC breakers in parallel

    I tried to find if Dave Smead is still alive in your link. I had heard he died??? He was one of the pioneers of RE that took it out of the realm of old hippies with jumper cables and into real electronic instrumentation. His Marine 3 step battery chargers are still working from the 80's.
    vtmaps wrote: »
    If you're worried about insurance inspections, those automotive cut-off switches are not listed for residential systems.
    http://www.amplepower.com/primer/burnt_sw/index.html

    --vtMaps
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • TucsonAZ
    TucsonAZ Solar Expert Posts: 139 ✭✭
    #10
    Re: DC breakers in parallel

    http://www.solar-electric.com/pamodccibr.html

    Will that in 100a not work?
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #11
    Re: DC breakers in parallel

    Some of midnites breakers are exactlythat, pairs of breakers in parallel. However they are ganged, and they have a bus type connector on each terminal.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #12
    Re: DC breakers in parallel
    zoneblue wrote: »
    Some of midnites breakers are exactly that, pairs of breakers in parallel. However they are ganged, and they have a bus type connector on each terminal.

    Which ones? I am aware that their higher voltage breakers are a ganged pair in series. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #13
    Re: DC breakers in parallel
    TucsonAZ wrote: »
    http://www.solar-electric.com/pamodccibr.html
    Will that in 100a not work?

    Bit too small. Inverter has peak power rating of 3000W and the inverter itself has a 150A mega-fuse inside. So wouldn't like to artificially limit the power with a breaker.

    vtmaps, no issues with insurance around here as there are no specific standards or laws around off-grid systems.
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  • TucsonAZ
    TucsonAZ Solar Expert Posts: 139 ✭✭
    #14
    Re: DC breakers in parallel
    stephendv wrote: »
    Bit too small. Inverter has peak power rating of 3000W and the inverter itself has a 150A mega-fuse inside. So wouldn't like to artificially limit the power with a breaker.

    vtmaps, no issues with insurance around here as there are no specific standards or laws around off-grid systems.

    My inverter has the same specs and calls for a... ahhhh, sorry, my fault, I have a 24v inverter. Have you checked out the Stinger marine style breakers?
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #15
    Re: DC breakers in parallel

    Yeah the Stinger looks good, but can only find them for US $100 for a 150A breaker, which is more than the 175A outback breaker.
    The cheapest I can find look like this: http://www.amazon.co.uk/Marine-Stereo-Inline-Circuit-Breaker/dp/B00KRP5H38/ref=sr_1_16?ie=UTF8&qid=1403419191&sr=8-16&keywords=marine+circuit+breaker ...but it looks cheap too, not sure I trust it.

    My current choice is a separate disconnect switch: http://www.ebay.es/itm/Desconectador-de-Bateria-150A-pico-400A-con-Llave-y-Tapa-Terminales-Coche-4x4-/321390605416?pt=LH_DefaultDomain_186&hash=item4ad45f7468&_uhb=1
    And a 150A mega-fuse.

    The inverter is also 24v, but with 3000W surge, that's 125A. ...and as cariboocoot mentioned in the other thread, it could even be more with batteries discharged.
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  • TucsonAZ
    TucsonAZ Solar Expert Posts: 139 ✭✭
    #16
    Re: DC breakers in parallel
    stephendv wrote: »
    The inverter is also 24v, but with 3000W surge, that's 125A. ...and as cariboocoot mentioned in the other thread, it could even be more with batteries discharged.

    Did you read up on what the inverter manufacturer calls for? I'm curious only because they call for a 100amp on mine and I'm wondering if yours is calling for more? If yours at 1,500 watts continuous? 100amp covers you to well over 2,000 watts continuous even at 90% efficiency on the inverter so I would think 1,500 would be fine on a 100amp breaker but just ask my ex-wife and she would tell you I don't really know anything.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #17
    Re: DC breakers in parallel
    TucsonAZ wrote: »
    Did you read up on what the inverter manufacturer calls for? I'm curious only because they call for a 100amp on mine and I'm wondering if yours is calling for more? If yours at 1,500 watts continuous? 100amp covers you to well over 2,000 watts continuous even at 90% efficiency on the inverter so I would think 1,500 would be fine on a 100amp breaker but just ask my ex-wife and shit tell you I don't really know anything.

    The inverter itself has a 150A fuse inside. But the purpose of the main battery fuse is not to protect the inverter, it's to protect the cabling and the battery from short circuit. And it should at least be able to handle the largest possible instantaneous draw, which is the surge rating not the continuous rating. Yes mine is 1600W continuous. But if you're ever going to use the surge and if the inverter can actually delivery it, then you need a fuse/breaker that can handle it and not nuisance trip everytime the fridge comes on.
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  • unicornio
    unicornio Solar Expert Posts: 217 ✭✭
    #18
    Re: DC breakers in parallel

    hi, Stephen!...
    long time not to see you! ...
    hope you are well in the nogal!...;-)

    I can get the outback 125A breaker for battery for 30 €, but the 175A and 250A cost me 60€ ... I think for that inverter with 125A are going well at 24v ...
    these inverters are giving many drawbacks, and often they can not work with a 5Kg washer full of wet clothes, you've tried? ... I've repaired two of these in a little time ...

    a gfx1424 costs 800€, a fx2024 costs 1,100€ , a VFX3024 1200€, how many are this victron? ... ;-)

    best regards!...
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #19
    Re: DC breakers in parallel

    Hola hombre!

    Yes, I can get the outback breakers for the same price. You and TucsonAZ now have me considering the 125A breaker... I don't want to install it and then have it trip with washing machine/fridge. First time I'm working with the Victron, not tried it with fridge/washer yet as they haven't bought them yet. The Victron is about 300 euro's cheaper than the 1424 outback, but it's inverter ONLY no charger (they didn't want one).
    Checking the victron pricelist, the inverter/charger version of same size is almost same price as the outback. If they had wanted an inverter/charger I would have gone with outback.
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  • unicornio
    unicornio Solar Expert Posts: 217 ✭✭
    #20
    Re: DC breakers in parallel
    stephendv wrote: »
    Hola hombre!

    hehehehe!...vamos tirandillo!...;-)
    stephendv wrote: »
    Yes, I can get the outback breakers for the same price. You and TucsonAZ now have me considering the 125A breaker... I don't want to install it and then have it trip with washing machine/fridge. First time I'm working with the Victron, not tried it with fridge/washer yet as they haven't bought them yet. The Victron is about 300 euro's cheaper than the 1424 outback, but it's inverter ONLY no charger (they didn't want one).

    perhaps i think that these victron will not know what to do with more than 125A!...

    and fridge maybe, but washing as much as possible is not. I've tried a multi 1600w with a 750w washer and it "pooped"! ... (se hizo caca!)
    it began to wash, but once it stop (washing program) and then tried to restart, kaputt! ... nothing was broken, but the victron is protected, give an error, and no AC output...

    however, with gfx1424E, work well pumps, washing machines and fridges without problems ...
    stephendv wrote: »
    Checking the victron pricelist, the inverter/charger version of same size is almost same price as the outback. If they had wanted an inverter/charger I would have gone with outback.

    i think that a isolated solar energy plant, without the possibility of charge with genset eventually, is usually a scourge ...

    glad to see you!...;-)
    regards!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #21
    Re: DC breakers in parallel
    stephendv wrote: »
    The inverter is also 24v, but with 3000W surge, that's 125A. ...and as cariboocoot mentioned in the other thread, it could even be more with batteries discharged.

    Yep. Many 24 Volt inverters will go down to 21 Volts before shutting off, and 3kW @ 21 Volts is 143 Amps. Hence why they would spec a 150 Amp fuse.
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  • Thom
    Thom Solar Expert Posts: 196 ✭✭✭
    #22
    Re: DC breakers in parallel

    How about a car audio fuse or breaker from a auto radio shop ?


    Thom
    Off grid since 1984. 430w of panel, 300w suresine , 4 gc batteries 12v system, Rogue mpt3024 charge controller , air breeze windmill, Mikita 2400w generator . Added 2@ 100w panel with a midnight brat 
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #23
    Re: DC breakers in parallel

    For auto/stereo fuses/breakers--You have to read the specifications/certifications for those devices. Some are very nice, some are "not".

    Also, for 24 and especially 48 volt systems, those devices are not usually rated for that high of voltages (need 30/60 minimum rated working voltages).

    -Bil
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #24
    Re: DC breakers in parallel
    stephendv wrote: »
    My supplier only has the outback breakers. With the two breakers right next to each other I could divide the strands of the thick cable in two and get it into both breakers. Not pretty, but it should work. Are there no issues with using 2 in parallel?
    The main issues with two breakers in parallel are:
    1. The current may not divide precisely equally, so the trip point may be lower than the sum of the two breaker amperage values. (But not by a whole lot.)
    2. You may get into a situation where you do not close one of the breakers at the same time as the other. In that case it would be helpful if one breaker will pass twice the current long enough for you to flip the other breaker switch.
    3. It would be best to have a common trip mechanism for the two (or more) breakers, but if that is not available, try to at least use a handle tie so that manual operation will move both handles.
    SMA SB 3000, old BP panels.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #25
    Re: DC breakers in parallel

    I've been using a double (ganged lever/handle) 40 Amp Square D, QO breaker one each on the output of my 60 amp controllers with excellent results. Early on I used 80 amp Maxi fuses, but in time they built up resistance with their plug in terminals and half burned half melted. NOT a good scene. Lucky they were in a metal box!
    After that i used 100 amp Blue Sky bolt on fuses with the proper holders. Worked OK but ran too hot to hold your finger on when handling 60 amps for any length of time. Didn't like that. Finally switched to Square D QO and the results have been excellent! They run cool and double as a switch. VERY happy with them. But of course my system is 12 volts.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #26
    Re: DC breakers in parallel

    Found a reasonably priced breaker on this side of the pond: http://www.fraron.de/en/wechselrichterzubehoer/150a-sicherungs-automat-mit-resetschalter-einbaumontage/a-33631037/
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