workaround for inverter circuit protection

System
System Posts: 2,511 admin
in Advanced Solar Electric Technical Forum #1
i have 2 trace 4024 [stacked] House has 100 amp main w/ 15 and 20 amp breakers. I was away for a day and a short had developed in my shop - instead of tripping that individual 15 amp breaker, the entire inverter shut down. Boiler was off, freezer shut down, and my 8 panel glycol array blew the PT valve. with subzero temps i was lucky this was not a disaster.

i had run into this a few years back when i overloaded a circuit but was just bothered by the inconvenience of walking to the remote "utility room" to switch the system back on- did not dawn on me what the broader implications might be.

Is there a solution? quicker response house breakers? inverter monitor to send an email alert? seems problematic to risk all my infrastructure like this.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #2
    Re: workaround for inverter circuit protection

    They do make some self resetting type thermal curcuit breakers--but those are probably more for 12 VDC RV's and such. I don't remember ever seeing any for a 120/240 VAC home type use...

    The problem may be that the output trip on the inverter is faster than any fuse/breaker would be. You can find Magnetic Breakers for some equipment/boxes that may be faster than a thermal type trip that is pretty standard for many circuit breakers. Of course, if you have surge currents (motor starting, etc.) then you may have false trips when you try to start a skill saw or something similar.

    Even then, you can have a short that will take out a ~100 amp main breaker on a 15 amp circuit trip for a normal home (I had that happen when a 120 watt outdoor security flood turned on (motion detector) and the filament assembly somehow failed in the bulb and actually tripped the main house breaker.

    Probably the only way to be sure is either use two Inverters--one to run the critical devices, and the second to run the rest of the home/shop. And/or get in the habit of shutting off the shop circuits.

    You could create a UPS type system... A second inverter with its own transfer switch. In "normal mode" the main inverter runs everything and the second inverter only turns on if the main power faults--and powers the critical sub-panel.

    I am not sure how efficient you can make this all run (electrical AC Transfer switch, second inverter running "search mode") or the costs of running two inverters 100% of the time (shop+critical loads)....

    Running a cellular phone based alarm system (major brand or perhaps non-monitored system) to notify you of problems at home? (if you have land-line phones, you can get notification dialers pretty cheap)..

    Perhaps some folks here have other ideas.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: workaround for inverter circuit protection

    Just a couple of comments on the situation from an old guy.

    This happens a lot.
    The inverter(s) see the whole system load at once, not just the overload on a particular branch, so they are reacting to more current than any one breaker sees. They also react far faster than a standard thermal-type circuit breaker can. Since we nearly always run inverters whose capacity is pretty close to the maximum cumulative load, 'tripping' is a frequent problem.

    One possible solution (although I've never actually done this) is to use arc-fault breakers. They react almost instantaneously. They are also expensive and known to register 'false trips' under some load conditions.

    I like Bill's idea of splitting the loads up so critical devices are supplied separately from occasional use circuits which might get over-loaded.
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  • System2
    System2 Posts: 6,290 admin
    #4
    Re: workaround for inverter circuit protection

    thanks for these replies. As i keep my utility room a couple hundred feet from my house, another inverter- or splitting my 2 on hand 4024s [240v] i believe would mean digging and installing a lot of wire- and i am not sure about interaction w/ battery bank/or 8kw propane genset.

    i am contemplating a small 2kw , 12v older trace i have laying around- maybe set it up w/a couple golf cart batts and a 120v charger and dedicate it to the boiler/solar heat room....
    [i was really hoping to use that old Trace on the catamaran i am building....]

    i do like the idea of shutting down all but kitchen and boiler room circuits when i leave for 24+ hrs. still, anyone who wants the freedom to leave their off-grid home for extended periods of time would do well to look carefully at this situation.

    thanks again for replies- anyone have direct experience w/ those quick response breakers?


    -off grid, stacked Trace 4024s, Kohler 8kw propane auto start,400w AIR 403 , mishmash of PV that can put out 55amp 24v
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  • blackswan555
    blackswan555 Solar Expert Posts: 246 ✭✭
    #5
    Re: workaround for inverter circuit protection

    When you say stacked do you mean in a power save type mode, eg one is idle until needed ?
    Tim
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  • System2
    System2 Posts: 6,290 admin
    #6
    Re: workaround for inverter circuit protection

    one inverter is slave - both are stacked to produce 240v-

    one thought- would it be useful to substitute a GFI breaker [squareD] and try it on that circuit which gave me problems? I have yet to isolate the problem- everything has been unplugged from that circuit- so i could recreate the problem/situation easily enough.

    or perhaps the real question is: " anyone been able to trip a 120 circuit breaker PRIOR to their inverter switching off?"

    another query- has anyone looked into the Google 'powermeter' with T.E.D. as a way of instantly monitoring your system?

    thanks again for the replies

    -off grid, stacked Trace 4024s, Kohler 8kw propane auto start, 400w AIR 403 , mishmash of PV that can put out 55amp 24v
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #7
    Re: workaround for inverter circuit protection

    The SW inverters will react quite fast. The output load will react in about five cycles. You will not find a breaker that fast.

    First defense would be to but an extra cut off switch or two to the non-critical loads and cut them off whenever they are not needed.

    I doubt even a fast blow fuse would react in time before SW trips out but you might try it. If your loads are motors you can not use fast blow fuses.
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  • System2
    System2 Posts: 6,290 admin
    #8
    Re: workaround for inverter circuit protection

    thanks RC

    i will do the switch-off-breaker thing . Since the offending circuit is in my shop, sounds like fast fuses won't work there.
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