AC coupling with Sunny Island or XW6048

RK_Solar_Hopeful
RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
in Grid Tie and Grid Interactive Systems #1
There has been a lot of discussion regarding AC coupling with grid tied islanding inverters and regular GT inverters. The islanding inverters require a large battery pack because it passes the PV current through to the batteries and does not act as a charge controller. But the GT system owners want to add an inexpensive battery backup to make the PV panels work during the day even with no grid power.

What would happen if you installed a high current diode like: http://www.vishay.com/diodes/list/product-93490/ to block the current from charging the battery?
Since the diode would block the current flow, what would happen to the islanding inverter?
What would happen to the regular GT inverter?
Another battery charger would be needed to charge the battery as the islanding inverter could not.

I'd like to think nothing detrimental would happen, but are the inverters designed for this situation?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: AC coupling with Sunny Island or XW6048

    If the power from the GT inverter(s) doesn't have batteries to go to, where is it going to go?
    That which is produced but not consumed by loads has to go somewhere. Left to its own it will push the Voltage high until its out of spec and shut down, whereupon it will come back in to spec and start up again. A lot of unstable AC and much cycling of the system, I'd think. This is the whole problem with trying to get power out of GT inverters when there's no grid; there's not enough electrical inertia in a generator or small off-grid system to keep the GT's regulated. I'm not sure how the Xantrex units work, but I believe the Sunny Island will purposefully shift frequency to knock the GT's off when not needed. When used with their own units the regulation is seamless.

    But I'm not a GT guy, so lets here from those who really do know this stuff! :D
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: AC coupling with Sunny Island or XW6048

    While we're tossing crazy ideas around ...
    A charge controller or even a VCS could be used to detect when the batteries are full and switch the GT inverters off. Load demands would draw the batteries down below switch-on point, allowing the GT's to feed loads and recharge batteries until the "full battery" condition was met again.
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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #4
    Re: AC coupling with Sunny Island or XW6048

    That's what I was thinking. The difference with having the blocking diode would be that the batteries would not be subjected to the full PV array current, only what the extra charger output to them.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #5
    Re: AC coupling with Sunny Island or XW6048
    RK_Solar_Hopeful wrote: »
    That's what I was thinking. The difference with having the blocking diode would be that the batteries would not be subjected to the full PV array current, only what the extra charger output to them.

    Would not work. The batteries are acting as the voltage reference and reservoir capacitor for the AC inverter.

    The PV charge controller puts out a constant D.C. current (dependent on PV illumination level). A single phase AC inverter will suck up sine squared shaped current pulses at 120 Hz rate from battery/controller connection. The constant DC from the charge controller to batteries will be pushing current into the batteries during the valley of AC cycle and batteries must make up the shortfall during peak of AC cycle.

    A capacitor across the batteries is theoretically possible to reduce the ripple current on batteries (allowing a smaller battery AH), but practically impossible as it would take a capacitor of several farads to keep the ripple current low on the batteries.

    XW6048 allows GT AC inverter output to push backwards through XW to grid, or to batteries when there is no grid. There is no battery current regulation so the push to batteries will be whatever the output of PV system (minus any AC loads) is. When batteries reach full charge the XW moves its frequency slightly to cause GT inverter to shutdown. The weakness of the XW AC coupling is it is all or nothing with regard to GT inverter power.

    The Sunny Island / Sunny Boy GT inverter has a secondary control mechanism. Sunny Boy GT will reduce its output in correspondance with the slight movement of the AC frequency from the Sunny Island inverter. In this way it can regulate the output of the GT inverter to avoid too much current being pushed to batteries and regulate battery charging as they reach full charge voltage.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: AC coupling with Sunny Island or XW6048

    I was suggesting to leave the diode out, let the GT charge the batteries, monitor them and use their Voltage level to trigger a disconnect for the GT coupling. This assumes you're not using an XW or Sunny Island as the off-grid inverter and that you don't have so much GT as to overwhelm whatever size battery bank is used (so that the charge current doesn't cook the batteries).

    Far from perfect, which is why they make the Sunny Boy / Sunny Island combination which does this quite seamlessly. :roll:
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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #7
    Re: AC coupling with Sunny Island or XW6048
    RCinFLA wrote: »
    Would not work. The batteries are acting as the voltage reference and reservoir capacitor for the AC inverter.

    The high current diode would allow the batteries to be a voltage reference and reservoir capacitor for the AC inverter.
    The PV charge controller puts out a constant D.C. current (dependent on PV illumination level). A single phase AC inverter will suck up sine squared shaped current pulses at 120 Hz rate from battery/controller connection. The constant DC from the charge controller to batteries will be pushing current into the batteries during the valley of AC cycle and batteries must make up the shortfall during peak of AC cycle.

    I'm not sure I understand this part. I thought the inverter itself made the AC into DC and presented DC only (with ripple) to the battery while PV production was greater than consumption.
    A capacitor across the batteries is theoretically possible to reduce the ripple current on batteries (allowing a smaller battery AH), but practically impossible as it would take a capacitor of several farads.

    I had not considered this. Ultra capacitors are available. On the Electric Vehicle forums one guy had a car he was driving around and performing burnouts using only ultra capacitors for the stored charge. He did say he got the capacitors at a discount.
    XW6048 allows GT AC inverter output to push backwards through XW to grid, or to batteries when there is no grid. There is no battery current regulation so the push to batteries will be whatever the output of PV system (minus any AC loads) is. When batteries reach full charge the XW moves its frequency slightly to cause GT inverter to shutdown. The weakness of the XW AC coupling is it is all or nothing with regard to GT inverter power.

    This specifically was why I mentioned the high current diode, to block current flow into the batteries. The diode I found is a sample of what is available. Voltage 600vac, current 125amps. If more current flow is needed, use 2 or more in parallel.
    The Sunny Island / Sunny Boy GT inverter has a secondary control mechanism. Sunny Boy GT will reduce its output in correspondance with the slight movement of the AC frequency from the Sunny Island inverter. In this way it can regulate the output of the GT inverter to avoid too much current being pushed to batteries and regulate battery charging as they reach full charge voltage.

    It may not be an option for those GT owners looking to retrofit a battery backup to their existing system. For a new installation using the Sunny Island / Sunny Boy GT combo is almost ideal, except it takes two Sunny Islands to make 240VAC. And they are expensive.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #8
    Re: AC coupling with Sunny Island or XW6048
    Cariboocoot wrote: »
    I was suggesting to leave the diode out, let the GT charge the batteries, monitor them and use their Voltage level to trigger a disconnect for the GT coupling. This assumes you're not using an XW or Sunny Island as the off-grid inverter and that you don't have so much GT as to overwhelm whatever size battery bank is used (so that the charge current doesn't cook the batteries).

    Far from perfect, which is why they make the Sunny Boy / Sunny Island combination which does this quite seamlessly. :roll:

    This is what the XW is doing. Doing it externally would only be duplicating what is already being done.

    The only thing that would help the XW situation would be to put a variable load dump on the PV GT, to say, heat water when nothing else can consume the PV generated power. Most GT inverters take several minutes to reconnect so forcing GT inverter to shutdown cannot respond to rapidly changing loads.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #9
    Re: AC coupling with Sunny Island or XW6048
    RK_Solar_Hopeful wrote: »
    The high current diode would allow the batteries to be a voltage reference and reservoir capacitor for the AC inverter..

    I assume you mean put a high current diode in forward current direction from battery to AC inverter, then AC couple GT inverter to output of XW6048.

    First, the diode would add a signifcant battery voltage drop to normal AC inverter operation. If you have any poor power factor loads, like an electric motor, they will likely cause the XW to shut down because it cannot push partial cycle negative reactive current back to batteries.

    What would happen when grid goes out is XW would continue to run drawing from batteries, and GT would run in parallel with output as long as AC loads are greater then PV output.

    Since the XW takes some time to slowly slew its frequency to shed GT inverter, what would likely happen when AC loads don't consume all the GT power is the XW inverter would immediately go into an overvoltage alarm and shut down.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: AC coupling with Sunny Island or XW6048
    RCinFLA wrote: »
    This is what the XW is doing. Doing it externally would only be duplicating what is already being done.

    Note that I specifically said "This assumes you're not using an XW or Sunny Island as the off-grid inverter".

    Attempting to find a way to duplicate the XW function in a non-XW inverter.

    What this exercise points out mostly is two things which we're all pretty familiar with:
    1). It is difficult to retrofit any existing system to significantly alter its function.
    2). Trying to use components for purposes other than their designated use is frustrating at best and usually quite a hopeless undertaking.

    Would it work? Yes, after a fashion. Would it be as good as a system designed to work this way in the first place? Not a chance. Is it worth mucking about with? Probably not.

    On the whole it is easier to install an XW MPPT80-600 or do a major reconfigure on the PV array to supply battery charging to a separate off-grid emergency power system. But if you have micro-inverters that becomes far more problematic.
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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #11
    Re: AC coupling with Sunny Island or XW6048
    RCinFLA wrote: »
    I assume you mean put a high current diode in forward current direction from battery to AC inverter, then AC couple GT inverter to output of XW6048.
    Yes
    First, the diode would add a signifcant battery voltage drop to normal AC inverter operation. If you have any poor power factor loads, like an electric motor, they will likely cause the XW to shut down because it cannot push partial cycle negative reactive current back to batteries.
    Threshold Voltage 0.8V, Max forward voltage drop 1.47V, I do not have battery experience, is that a significant drop?
    What would happen when grid goes out is XW would continue to run drawing from batteries, and GT would run in parallel with output as long as AC loads are greater then PV output.
    This is good, part one works.
    Since the XW takes some time to slowly slew its frequency to shed GT inverter, what would likely happen when AC loads don't consume all the GT power is the XW inverter would immediately go into an overvoltage alarm and shut down.
    This might work out ok. So the GT inverters shutdown for 5 minutes, and the Islanding inverter carries the load for 5 minutes, GT inverters come up and start carrying AC loads, now the extra battery charger is charging the batteries, so the increased AC load needs to be large enough to keep the GT inverters on. Maybe adding a small diversion load if needed?
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #12
    Re: AC coupling with Sunny Island or XW6048
    RK_Solar_Hopeful wrote: »
    For a new installation using the Sunny Island / Sunny Boy GT combo is almost ideal, except it takes two Sunny Islands to make 240VAC. And they are expensive.
    You can get 240VAC from a single Sunny Island if you use an autotransformer to generate the other leg.
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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #13
    Re: AC coupling with Sunny Island or XW6048
    ggunn wrote: »
    You can get 240VAC from a single Sunny Island if you use an autotransformer to generate the other leg.

    I haven't been able to find anything regarding surge capacity of an auto transformer like http://www.solar-electric.com/x-240.html
    Is it ok to wire to an XW6048 or do I need to make sure I don't exceed 4kVA? I looks good for an inexpensive way to add 240VAC to a Sunny Island. And the Sunny Island inverters have that nice ramp up in frequency based on battery voltage.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
    Re: AC coupling with Sunny Island or XW6048

    :confused: The XW 6048's output is 240 VAC: it doesn't need an autotransformer.
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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #15
    Re: AC coupling with Sunny Island or XW6048
    Cariboocoot wrote: »
    :confused: The XW 6048's output is 240 VAC: it doesn't need an autotransformer.

    I was thinking faster than my fingers were typing... I would prefer a 240VAC split phase Sunny Island over the XW6048 due to the smaller incremental freq/V ramp.

    Question is; will the auto transformer play nice with the SI surge capacity?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #16
    Re: AC coupling with Sunny Island or XW6048

    The Outback autotransformer when mounted in its box with its cooling fan http://www.solar-electric.com/psx-240.html is rated fro 6 kVA, which is just under the SMA SI's 30 minute surge capacity and slightly over its continuous duty.

    So, how close to the limit are you going to push it? And remember that in this instance the "pushing" goes both ways (i.e. try not to have more than 4 kVA of GT inverter coupled).

    Since I've not tried it, I can't guarantee it will or declare it won't work.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #17
    Re: AC coupling with Sunny Island or XW6048
    RK_Solar_Hopeful wrote: »
    I haven't been able to find anything regarding surge capacity of an auto transformer like http://www.solar-electric.com/x-240.html

    Transformers only have a tiny bit of surge capacity, when their core saturates, you get very little extra power through.

    The XW6048 produces 240VAC, needs no transformer (but I'm going to use a "load balancing" transformer in my setup eventually)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #18
    Re: AC coupling with Sunny Island or XW6048
    Cariboocoot wrote: »
    The Outback autotransformer when mounted in its box with its cooling fan http://www.solar-electric.com/psx-240.html is rated fro 6 kVA, which is just under the SMA SI's 30 minute surge capacity and slightly over its continuous duty.

    If I use the SI5048 I would wire up just under 5kW of PV panels. Before I do that I'll have to measure what the 240VAC load really is. Better to measure twice and buy once...

    I was wondering why I didn't see the psx when I searched for "autotransformer". That's because it shows up when I search for "auto transformer". Do you know if the psx-240 is a fw-x240 with an enclosure & fan?
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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #19
    Re: AC coupling with Sunny Island or XW6048
    mike90045 wrote: »
    Transformers only have a tiny bit of surge capacity, when their core saturates, you get very little extra power through.
    That is good to know. Must buy proper size upfront. Or maybe two in parallel?
    The XW6048 produces 240VAC, needs no transformer (but I'm going to use a "load balancing" transformer in my setup eventually)
    Does the inverter need to be load balanced? Is this something that enhances performance and longevity?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #20
    Re: AC coupling with Sunny Island or XW6048
    RK_Solar_Hopeful wrote: »
    ..Does the inverter need to be load balanced? Is this something that enhances performance and longevity?

    Most split phase inverters would like to be load balanced. The XW's can go up to about 60-70% unbalanced, if I recall correctly, before they fart. I don't know if they will reset automagically when the imbalance is removed, or if I'll have to walk outside to the battery shed to do it. I found a great 3KVA transformer on fleabay, with cheap shipping (80+ lbs) with copper windings.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #21
    Re: AC coupling with Sunny Island or XW6048
    mike90045 wrote: »
    Most split phase inverters would like to be load balanced...

    Keeping the inverter happy keeps everyone happy!! Since the transformer is always "on", do you know how much power it consumes? I expect it would be a low percentage, but 1% of 3000kVA is 30watts. Assuming full load.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #22
    Re: AC coupling with Sunny Island or XW6048
    RK_Solar_Hopeful wrote: »
    Keeping the inverter happy keeps everyone happy!! Since the transformer is always "on", do you know how much power it consumes? I expect it would be a low percentage, but 1% of 3000kVA is 30watts. Assuming full load.

    Yes, idle loss is a factor, which is why it's just sitting till I discover if I really need it.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #23
    Re: AC coupling with Sunny Island or XW6048
    mike90045 wrote: »
    Yes, idle loss is a factor, which is why it's just sitting till I discover if I really need it.

    The transformer wiki mentions 98% efficiency, 2% loss in other words. Is that a continuous loss or is that only when near 100% load on the auto transformer?
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #24
    Re: AC coupling with Sunny Island or XW6048

    There are two primary loss factors in a transformer. The magnetic core loss and wire resistance. There can also be eddy current losses but these can be controlled by core laminate design.

    Most transformer designs balance the two primary loss factors. At full load the wire resistance loss is dominating. At low loads the magnetic losses dominate.

    Minimum transformer loss will occur at less then rated power. It can be anywhere between 25% to 85% rated load depending on particular transformer design. The smaller and cheaper the transformer the more likely that eddy currents can become dominate. I have bought a Radio Shack 24vac 1 amp transformer that gets quite hot just sitting with no load on secondary. For the the core to get that warm there must be about 3 to 4 watts of loss with no load. The transformer actually runs cooler with 50% loading on secondary.
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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #25
    Re: AC coupling with Sunny Island or XW6048

    It seems that a bit of transformer testing is needed to determine if idle power consumption is enough to worry about or not. For the application I'm considering where the battery backup is really only a backup and not regularly used, it may be better to not use the transformer if there is more than minor idle power consumption.

    Does anyone know if the blocking diode's: Threshold Voltage 0.8V, Max forward voltage drop 1.47V are too big? Will they affect the XW6048 current draw too much?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #26
    Re: AC coupling with Sunny Island or XW6048
    RK_Solar_Hopeful wrote: »
    .......Does anyone know if the blocking diode's: Threshold Voltage 0.8V, Max forward voltage drop 1.47V are too big? Will they affect the XW6048 current draw too much?

    Refresh me on the blocking diode application ? Vf 1.47 is awfully high
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #27
    Re: AC coupling with Sunny Island or XW6048
    mike90045 wrote: »
    Refresh me on the blocking diode application ? Vf 1.47 is awfully high

    I searched for a high current diode and found: http://www.vishay.com/diodes/list/product-93490/

    TYPICAL APPLICATIONS
    • Welders
    • Power supplies
    • Machine tool controls
    • High power drives
    • Medium traction applications
    • Battery charges
    • Freewheeling diodes

    Or are you asking what my intended application is?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #28
    Re: AC coupling with Sunny Island or XW6048
    RK_Solar_Hopeful wrote: »
    Or are you asking what my intended application is?


    Yes, generally schottky diodes have lower Vf drop. (less loss) Can you give us a sketch?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #29
    Re: AC coupling with Sunny Island or XW6048
    mike90045 wrote: »
    Yes, generally schottky diodes have lower Vf drop. (less loss) Can you give us a sketch?

    I'll make up something visual.

    Can schottky diodes take 160amps? The diode would be put in one DC leg from the battery to the islanding inverter to block charging current back to the battery, but allow the inverter to draw current from the battery. the XW6048 has: DC Input Current (Maximum) 160 A so a high current diode or two is needed to support normal operation when grid power is down.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #30
    Re: AC coupling with Sunny Island or XW6048

    http://search.digikey.com/us/en/products/APT100S20BG/APT100S20BG-ND/1494212
    close, 120A .95Vf Going to dissipate a lot of watts if loaded. Maybe a SSR (solid state relay/contactor) is the way to do this, they have better heatsinking capacity - 120A in a TO-247 package, is too dense for me.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • RK_Solar_Hopeful
    RK_Solar_Hopeful Solar Expert Posts: 69 ✭✭✭✭
    #31
    Re: AC coupling with Sunny Island or XW6048
    mike90045 wrote: »
    http://search.digikey.com/us/en/products/APT100S20BG/APT100S20BG-ND/1494212
    close, 120A .95Vf Going to dissipate a lot of watts if loaded. Maybe a SSR (solid state relay/contactor) is the way to do this, they have better heatsinking capacity - 120A in a TO-247 package, is too dense for me.

    Good point!! I had not considered the power loss being dissipated as heat. .95VDC x 160amps = 152watts. If two diodes were used that would drop by 1/2 to 76watts each. 75watt incandescent bulbs get very hot.

    I looked at using SSRs to control DC current before and using a diode for blocking would be much easier. If the voltage drop across the diode doesn't affect operation of the attached Islanding inverter.

    May have to find a used inverter (cheap!!) for testing.
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