High voltage dc disconnect

oil pan 4oil pan 4 Posts: 757Solar Expert ✭✭✭✭
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

  • Raj174Raj174 Posts: 648Solar Expert ✭✭✭✭
    edited July 5 #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
    3600W PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 207AH LiFePO4 no BMS, 4500W genset.
  • mcgivormcgivor Posts: 2,302Solar Expert ✭✭✭✭✭
    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 bank 

  • oil pan 4oil pan 4 Posts: 757Solar Expert ✭✭✭✭
    edited July 5 #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.

  • EstragonEstragon Posts: 2,924Registered Users ✭✭✭✭✭
    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
  • mcgivormcgivor Posts: 2,302Solar Expert ✭✭✭✭✭
    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 bank 

  • PhotowhitPhotowhit Posts: 4,731Solar Expert ✭✭✭✭
    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, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • oil pan 4oil pan 4 Posts: 757Solar Expert ✭✭✭✭
    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.

  • PhotowhitPhotowhit Posts: 4,731Solar Expert ✭✭✭✭
    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, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • mcgivormcgivor Posts: 2,302Solar Expert ✭✭✭✭✭
    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 bank 

  • BB.BB. Posts: 28,040Super Moderators, Administrators 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
  • Raj174Raj174 Posts: 648Solar Expert ✭✭✭✭
    It appears that the Schindler breaker is not sold in the US, but Is available in Europe for around 80 euros. About 100 dollars.
    3600W PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 207AH LiFePO4 no BMS, 4500W genset.
  • PhotowhitPhotowhit Posts: 4,731Solar Expert ✭✭✭✭
    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, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • cow_ranchercow_rancher Posts: 107Solar Expert ✭✭✭
    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 
  • EstragonEstragon Posts: 2,924Registered Users ✭✭✭✭✭
    ... 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 4oil pan 4 Posts: 757Solar Expert ✭✭✭✭
    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. Posts: 28,040Super Moderators, Administrators 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):



    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cow_ranchercow_rancher Posts: 107Solar Expert ✭✭✭
    Good demo, that's what I'm talking about... arc welder time!!!

    Rancher
  • EstragonEstragon Posts: 2,924Registered Users ✭✭✭✭✭
    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
  • mcgivormcgivor Posts: 2,302Solar Expert ✭✭✭✭✭
    edited July 6 #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 bank 

  • oil pan 4oil pan 4 Posts: 757Solar Expert ✭✭✭✭
    edited July 6 #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_ranchercow_rancher Posts: 107Solar Expert ✭✭✭
    What you need is a big old OCB that the power companies use for their high voltage breakers....
  • oil pan 4oil pan 4 Posts: 757Solar Expert ✭✭✭✭
    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.

  • mcgivormcgivor Posts: 2,302Solar Expert ✭✭✭✭✭
    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 bank 

  • oil pan 4oil pan 4 Posts: 757Solar Expert ✭✭✭✭
    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.

  • mcgivormcgivor Posts: 2,302Solar Expert ✭✭✭✭✭
    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 bank 

  • oil pan 4oil pan 4 Posts: 757Solar Expert ✭✭✭✭
    edited August 15 #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.

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