High voltage dc disconnect

oil pan 4
oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
I was planning on running up to around 570ish open current volts DC, and around 430v under load at 9 amps to a grid tie inverter.
The disconnects I was looking at are around  $400.
That's a lot of money for a part that doesn't produce any power.
But I do have a slightly used square D 30 amp 600vac local disconnect blade switch for 3 phase that I paid $5 for.
I was thinking that if I wired all 3 switches in serries that would be enough to interrupt that current flow at 450 volts DC.
Each blade gives about a 3/4 inch air gap, I would wire all 3 in serries.
Could this work?

Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

Comments

  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    edited July 2018 #2
    IMO 450V DC will easily sustain an arc across a 3/4" air gap. I believe the disconnect would be vaporized/melted. From what I've seen, 400 dollars is not a bad price for a DC disconnect.

    Rick
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    Don't even think about using an AC rated switch in a DC application, DC circuit breakers and switches are designed to deal with tha arc associated with DC current, Schneider has the Acti 9 series breaker https://www.schneider-electric.com/en/product/A9N61650/c60pv-dc---2p---10a---800-v---b-curve/?range=61095-acti-9-c60h-dc,-c60pv-dc&node=684682433-miniature-circuit-breaker which will do the job, there are other options if not for NEC applications at ~$8 US.
    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.
  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    edited July 2018 #4
    It's not a single 3/4 inch contact, it would be three switches in serries.
    If the schnider electric one is $8 then I can do that.
    I did click on the link and a price didn't come up, is that normal?

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    I'm not sure series wiring the switches entirely eliminates the problem. Maybe you just get three arcs for the price of one? :smile:
    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
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    The Schindler link was an example of what is available, probably will be more than  $8, to conform to UL listed devices, my particular application dose not need the UL certificate. Current flow in parallel would divide the current over 3 poles equally, in series the current would be the same over all terminals, not that I'm suggesting to use this configuration, just pointing out electrical theroy.
    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.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    My understanding is 3 breakers in parallel is no better than 1 as the current will take the path of least resistance. You will just have an arc at one of them...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    The current isn't the problem. This is a 30 amp disconnect and only 9 amps worth of panels. The power would be trying to jump 3 gaps plus the load and or fault. If I wired all 3 contacts in parallel the arc would just jump 1 of the 3 contacts. These switchs only open about 3/4 of an inch, I don't think a single 3/4 of an inch gap will stop 9 amps at 430v.
    The electrical coop here says they don't require an inspection before connecting solar to the power grid.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Midnite makes a Birdhouse disconnect for solar array's that runs $315 and is designed as an emergency disconnect for up to 600 volts;

    https://www.solar-electric.com/bisoshoff.html

    I would think their High voltage (HV) Disco would also work for a single string or multiple strings and is similarly priced. Also rated at 600 volts.

    https://www.solar-electric.com/mnbadico.html
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    Again electrical theroy, in parrallel the current will flow equally through each path in a parallel circuit of equaL resistance, therefore if the current is offered three paths each will carry equal current, current is divided 3 ways, for this reason it is common to use multiple fuses, of a lower rating  in parrallel to protect a higher load, if one fuse is overcome, there is a cascade effect, they all blow, because they are in parallel. Hope I didn't go to college for nothing.
    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.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    A workaround for circuit breakers is to wire (for example) 2 or 3 breakers in series (say 15 amp) and use the 2 or 3 pole option to cross connect the handles together.

    It will still trip at 15 amps, but the breakers will now have 2 to 3 times the rated voltage of a single breaker.

    Wiring 2 to 3 breakers in series will not work with a standard North American main panel with common power buses. Only works when using individually wired breakers that are ganged together.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    It appears that the Schindler breaker is not sold in the US, but Is available in Europe for around 80 euros. About 100 dollars.
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    BB. said:
    A workaround for circuit breakers is to wire (for example) 2 or 3 breakers in series (say 15 amp) and use the 2 or 3 pole option to cross connect the handles together.
    Looks like this is Midnite's version of what Bill is describing at $90;

    https://www.solar-electric.com/catalogsearch/result/?q=600rt

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • cow_rancher
    cow_rancher Solar Expert Posts: 117 ✭✭✭✭
    What OP4 is looking for is a disconnect not a circuit breaker, so throw classical college engineering out the window.  It is the gap that is important, and 3 gaps doesn't triple the disconnect protection, the question is, if it is under load and you throw the disconnect will the arc stop on any or all of the gaps, think of a welder, you strike an arc, how far can you draw it out before it extinguishes, and welders operate at low voltages and high current (DC).

    Rancher 
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    ... and it seems to me that each time such an arc occurs, material in the disconnect poles can be lost. Over time, even a closed switch could arc :neutral:
    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
  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    It would be an emergency disconnect so ideally it only ever gets used once, when I test it and that's it.
    Ideally i would work on solar panels at night. Or During a normal shutdown I turn off the inverter then open the disconnect so the is no current flow.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Modern (?) disconnects are typically spring loaded so the snap on/off (quick separate contacts to limit arcing).

    Older (?) disconnects are typically switched at the speed that the operator throws the handle (no over center spring mechanism).

    Obligatory link to AC vs DC disconnect knife switch and arcing video (~220 Volts):

    https://www.youtube.com/watch?v=Zez2r1RPpWY

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cow_rancher
    cow_rancher Solar Expert Posts: 117 ✭✭✭✭
    Good demo, that's what I'm talking about... arc welder time!!!

    Rancher
  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    If you only open it once, at night, it should work fine.
    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
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited July 2018 #20
    There has to be  UL listed disconnect switches specifically designed for solar applications, such as this
     http://www.feeo.com.cn/products/fdis-dc-waterproof-isolator-switch-ID28.html
    $21 without MC4 connectors  $25 with.
    Understandably these components are not UL listed but they appear to be common outside the US, perhaps searching will reveal a source which is.
    Edit found a UL listed one https://www.amazon.com/Aims-Power-DC1600V32A2IO-Disconnect-Switch/dp/B07C8VF2J8#HLCXComparisonWidget_feature_div
    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.
  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    edited July 2018 #21
    Yeah the one I have springs open. That's exactly why I would even only consider spring loaded.
    By old I meant a used version the current or last generation of square d disconnect.
    I may just have to test it that way no solar panels or power inverters are put in danger.
    Take 240ac power step it up to 300vac with my 5kw variable AC transformer, rectify it with a bridge rectifier, a rail gun capacitor to smooth out the DC, should give me about 500v DC, use some clothes dryer heater elements as the load, 2 of them in serries should be close enough, open the switches.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • cow_rancher
    cow_rancher Solar Expert Posts: 117 ✭✭✭✭
    What you need is a big old OCB that the power companies use for their high voltage breakers....
  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    I was reading over the technical info on my little local disconnect. It says the contacts are rated for 250v DC. I overlooked this the first time.
    All 3 switches in serries should be able to break 570v dc no problem.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    oil pan 4 said:

    I was reading over the technical info on my little local disconnect. It says the contacts are rated for 250v DC. I overlooked this the first time.
    All 3 switches in serries should be able to break 570v dc no problem.
    The voltage across each of the contacts will not be lowered because they are in series, nor will the current for the matter, in parallel the current will be divided equally through each contact but voltage will remain the same, so neither will change the voltage rating of the switch, that remains a constant.
    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.
  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    This is a 30 amp disconnect.
    My array would have a short circuit of about 11 amps. Amps aren't the problem.
    I bet 3 sets of contacts, making 3 arcs, opening at 3 times normal speed at 3 times the distance can do it.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    For less than $30 I got a 32A 1000V dc solar disconnect with MC4 connectors, designed for the purpose, http://m.feeo-solar.com/dc-isolator/dc-isolator-without-mc4.html 
    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.
  • oil pan 4
    oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    edited August 2018 #27
    I found that disconnect on eBay for $40 shipped.
    That will work.
    From the pictures it appears that switch uses contacts in serries.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    Midnite makes a Birdhouse disconnect for solar array's that runs $315 and is designed as an emergency disconnect for up to 600 volts;....I would think their High voltage (HV) Disco would also work for a single string or multiple strings and is similarly priced. Also rated at 600 volts.
    Why do I always see the birdhouse unit together with a disconnect unit?  Seems to be overly redundant?  the combiner disconnect unit is enough to satisfy 2017 NEC code requirements for fast shutdown right?
  • billybob9
    billybob9 Registered Users Posts: 141 ✭✭
    You would think so but as you see Yours and my SMA 5.0 Inverter have a DC disconnect on it and also require the Rapid Shutdown box to comply.
  • billybob9
    billybob9 Registered Users Posts: 141 ✭✭
    Since this is about the end of this string and about DC shut off, I'll share the INFO on the Relays that I believe are failing on the SMA Rapid shutdown box. The relays are Panasonic AHES4191 non latching 12 volt. Operating temp -41c to 85 c. Seems in the ballpark for under the panel mounting but time may not be on there side. Mounting Relays sideways like wall mount may also increase the possibility of friction on the lower part of the relay due to gravity. So Shaded roof top is probably the best choice for me too.