Overload Issue at the cabin this weekend...

GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
Hi all,

Had an issue at the cabin this past weekend.  Here's my setup:

  • 12V 210AH battery bank (2 golf cart batteries)
  • Blue Sea Systems Terminal Fuse Blocks w/ 60A fuses on both positive and negative terminals
  • Xantrex ProWatt 600W Inverter
  • PowerMax Automatic Transfer Switch
  • Champion 2000W Inverter Generator

I have this setup in such that when the Generator is running the AutoTransfer switch transfers to Generator and the entire cabin is run off of that.  When the Generator is shut off, the transfer switch auto switches back to the ProWatt Inverter.  Works so fast, that the TV and XBox doesn't even blip :-)

Now, what happened...  Unknown to me, my wife tried to run her blow dryer while the generator was running (she thought it would be OK, since she heard it running).  Unfortunately, the generator was also running the freezer/TV/XBox/Lights/Shurflo Pump, etc. at the same time....

The Generator went into Overload and the Inverter shut off all at once.  Took me about 20 minutes to figure out that the 60A fuse on the negative terminal blew (at first, I thought I lost my Inverter).  So apparently, when the Generator went into overload, the transfer switch auto switched to the Inverter and instead of sending the Inverter into Overload, it blew the fuse on the battery!?!?

According to the manual, the ProWatt has an internal (non user serviceable) 80A fuse and a Max DC Input Current of 60A.  Hence, why I went with 60A fuses at the battery.

So...  My questions: 
  1. Why didn't the Inverter go into Overload before blowing the battery fuse?  (It's gone into overload once before when my buddy tried to start the coffee maker)
  2. Why did the fuse on the negative blow instead of the positive?
  3. Could it just have just been time for the fuse to go?

Just want to understand if this is avoidable in the future?  (Already planning on putting labels on all the receptacles "Check if OK to run Hair Dryer"  :p

Thanks all,

Jeff



Comments

  • mike95490mike95490 Solar Expert Posts: 8,755 ✭✭✭✭✭
    be glad it was just the fuse and not the transfer switch.
     if you have 2, 60A fuses, one will always blow at a lower setting than the other, they are not that precise.
    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 ,

  • mcgivormcgivor Solar Expert Posts: 3,401 ✭✭✭✭✭
    ..  My questions:  
    1. Why didn't the Inverter go into Overload before blowing the battery fuse?  (It's gone into overload once before when my buddy tried to start the coffee maker)
    2. Why did the fuse on the negative blow instead of the positive?
    3. Could it just have just been time for the fuse to go?
    1. The fuse failed before the inverter could react
    2. Tollerance variations between the fuses, it could have been the positive, then the question would be why not the negative
    3. Generally a single fuse is all that's needed, basically the same answer as 2
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    Thanks for the feedback guys!

    Yes, I realize that is the purpose of the fuse  :)  (To save everything else)

    So, now I understand either fuse could have went.

    Maybe that fuse was weakened from the previous coffee maker incident...

    At any rate, I guess I just have to be prepared for that and have spare fuses on hand.  (Although those Blue Sea fuses are not especially cheap  :#)
  • littleharbor2littleharbor2 Solar Expert Posts: 1,515 ✭✭✭✭
    I use a electric Mr. Coffee,coffee maker most times. My system easily handles it in combination with other high current items. When my battery bank got tired recently I decided to break out the old Pyrex percolator. They make good coffee and wont tax the inverter/battery at all. 

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    Just did some calculations based on info from the ProWatt manual...

    It will surge to 1200W 5.8A AC output.  That equates to 64A DC  :o .  (Not sure how the stated 60A Max DC Input current comes into play?).  But, does that imply I should maybe bump up to a 75A fuse (that still keeps it below the internal 80A fuse)?

    littleharbor,  Agreed,  I switched to a percolater after that incident myself.  Tastes better IMO too :-)
  • mike95490mike95490 Solar Expert Posts: 8,755 ✭✭✭✭✭
     But, does that imply I should maybe bump up to a 75A fuse (that still keeps it below the internal 80A fuse)?
    I would not go to 75A. too much risk of blowing the 80A fuse.  Remember, they are NOT precise.   Is 65A avaib ? or just stock some spare 60A fuses.
    The 80A internal fuse may be a fast blow and let loose before a 65A standard can blow.
    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 ,

  • BB.BB. Super Moderators, Administrators Posts: 30,494 admin
    There are fast and slow blow fuses... And fuses are there to protect the wiring and connections, not the devices themselves. The fact that your device blew the fuse vs something internally--That is good luck.

    And, worst case, even a 600 Watt AC inverter on a 12 volt battery bus can draw a substantial amount of current:
    • 600 Watts * 1/0.85 AC inverter eff * 1/10.5 battery cutoff voltage (all typical values) = 67 Amps worst case continuous
    And add that most "higher quality inverters" will support upwards of 2x rated power for a few seconds to a few minutes, you are looking at 134 Amps for short term worst case. (example: a 1,200 to 1,800 Watt hair dryer).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    edited May 2019 #9
    Unfortunately, the Blue Sea fuses go from 60 to 75.  (Nothing in between)

    Bill,  I understand what you're saying.  But, not sure I understand what you're recommending :-)

    Sounds like any size fuse (within reason) will blow under the worst case.  However, if fuses are only for protecting the wiring and connections... shouldn't the Inverter go into Overload first?

    EDIT: 

    After re-reading... I guess the fact that the Inverter will surge up to 134A DC at worst case, would imply why the fuses will let go before the Inverter goes into OverLoad.  However, if that 134A is possible, why would Xantrex only put an 80A internal fuse (non-servicable non the less)?

    Note:  My batteries were above 90% charged (as per TriMetric) when this happened.  But, I suppose the onrush of current was/is too much for such a small battery bank as well?

  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    Personally, I'd switch to breaker(s).  Probably cheaper than fuses in the long run, and they make handy disconnects.
    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
  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    edited May 2019 #11
    Estragon,

    Would this do?  https://www.amazon.com/Blue-Sea-Systems-Circuit-Breakers/dp/B000THNMGS/ref=sr_1_4?keywords=DC%2BBreaker&qid=1559066302&s=gateway&sr=8-4&th=1

    Edit:  How many?  IE:  1 for positive and negative.  Or just 1 total (and which terminal, positive?)
  • BB.BB. Super Moderators, Administrators Posts: 30,494 admin
    At most, I would suggest a C/2.5 surge rate for your battery bank (you can go higher surge current, but the system would probably not be "reliable" over time, temperature, state of charge)...
    • 210 AH * 1/2.5 surge current = 84 Amps
    And, at that level (and higher), the battery bank (and wiring) will start dropping output voltage to 10.5 volts or lower. AC Inverters are "constant power" devices... I.e., as the DC Bus voltage falls, the inverter draws more current to keep up with the output current demands.

    And I have seen "weird" breaker trips too... I had a 125 Watt filament based outdoor flood lamp that failed and apparently the internal filament/supports fell against the input to the bulb. The 15 amp branch breaker did not open, but the 100 amp house breaker did and plunged the whole house into darkness...

    Why, I do not know (all breakers were the same brand/series in the main panel).

    I would size the over current protective device (OCPD--fuses or breakers) to be 1.25x the maximum continuous load you expect. For a 600 Watt AC inverter on a 12 VDC bus. 
    • 67 amps * 1.25 NEC fuse/wiring derating = ~83 Amp minimum fusing/breakers/wiring
    Or, you can go backwards and limit your loads to:
    • 60 amps * 1/1.25 NEC derating * 10.5 volts cutoff * 0.85 inverter eff = 428 Watts
    If you limit your loads to a rough maximum of 428 Watts, you can reliably stay with the 60 amp OCPD.

    Long term, as Estragon says, good quality breakers will probably be a good solution here where others will be using your system. And the "underrated" fuses/breakers will give you a bit more protection against overloading.

    Also, remember you have voltage drop in your cabling... 0.5 drop at 60-84 amps and a few feet of copper wire run, can be difficult to achieve without very heavy/short cable runs. Here is a simple voltage drop calculator (I use 0.5 volt drop for 12 volt systems at rated current, or 1.0 drop at maximum surge... 11.5 volts minimum battery voltage under load - 1.0 volts surge = 10.5 volt at inverter DC input):

    https://www.calculator.net/voltage-drop-calculator.html

    So, what fuse/breaker/wiring rating... What you need to support your loads.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    Bill,

    Great Info!  Sounds to me that staying at 60A is fine.  I've been running everything I want for 5 years that way.  Never intended to handle a hair dryer (let alone a hair dryer plus everything else that I did intend)  ;)

    So the next question...  Fuse or Breaker:   I liked the Blue Sea fuse setup because it attaches directly to the battery.  But, a breaker would certainly be more user friendly (for others as well as myself)  Or maybe a combination?  (75A fuse at the battery and 60A breaker)


  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    BTW:  I'm running 5' #2/0 AWG cabling between batteries and inverter
  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    That breaker looks ok to me.  The main thing is to be sure it's DC rated (that one is), and if polarized (not sure if that one is), the battery/line and load wires  go to the correct breaker terminals.

    IIRC, floating (ungrounded) systems probably should have OCP devices on both +ive and -ive, but often just the +ive is done.  If grounded, just the +ive.
    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
  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    Estragon,  I guess it is polarized...  as it has line and load terminal markings
  • BB.BB. Super Moderators, Administrators Posts: 30,494 admin
    Your system wiring sounds fine... Just to give you an idea why 12 volts and heavy current is "expensive" to wire for... Assume 84 amps @ 12 volts over 5 feet of 2/0 wire (one way wire run, some calculators need 2-way wire run):

    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.2557&voltage=12&phase=dc&noofconductor=1&distance=5&distanceunit=feet&amperes=84&x=81&y=18

    Result

    Voltage drop: 0.065
    Voltage drop percentage: 0.55%
    Voltage at the end: 11.935

    Already a bit over 0.5 volt drop...

    Result

    Voltage drop: 0.065
    Voltage drop percentage: 0.55%
    Voltage at the end: 11.935

    You could always use a larger fuse for the local wiring (2/0 is good for ~>145 Amps relatively conservatively (simplified NEC AWG to Rated current table):

    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    And a properly rated breaker for each device hanging off the battery bus (OCPD protect wiring, but they also protect the input wiring for devices too--Too high of current/large of OCPC rating could cause a fire inside the device--Even if the exterior wiring is "more than heavy" enough).

    Review the wiring diagram(s) in the manual--That is always a good place to start.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    BB. said:


    Review the wiring diagram(s) in the manual--That is always a good place to start.

    -Bill
    Bill,  Great Advice!  I went back a 3rd time to read the manual.... (more carefully this time I guess)

    The ProWatt does NOT have an internal 80A fuse.  That's the size fuse they recommend on the battery  :o

    So I guess that explains why the 60A blew before the Inverter went into Overload...

    Just not sure why that didn't happen with the Coffee Maker incident before??
  • BB.BB. Super Moderators, Administrators Posts: 30,494 admin
    Fuses blow "faster" with larger loads/overloads. And fuses can fail (thermal cycling, vibration, over-temperature, etc.).

    And a fuse at 100% current may blow in 10's of minutes to hours... A fuse at 4x overload may blow in seconds to minutes.

    In general, I would expect the generic inverter to go into overload shutdown in milliseconds (active current measurement in control circuity), and almost always will be "faster" than a fuse.

    One poster talked about transistors as being "expensive" fuses (power transistors are much more susceptible to over current vs fuses).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    As pointed out above, the two incidents may not be directly comparable depending on battery SOC.  Voltage will sag under load.  A more discharged battery will be at a lower voltage initially, and could sag lower that a full one.  As voltage drops, more current is needed to supply a given wattage output.  The current is what blows the fuse, not the wattage.

    Also, a hair dryer may be a somewhat different load than a coffee maker.  The coffee maker is likely mostly a simple resistive load for a single power element.  A hair dryer likely has multiple setting in which power is pulsed through the element at various rates, depending on heat/air settings.  This pulsing could do some "interesting" things (ripple, AC waveform wierdness, etc).
    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
  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    Thanks Everyone!
  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    Been thinking about this some more....

    I see Home Depot carries Siemens DIN Rail mounted 1-5A fast trip AC breakers.

    Can I install a small AC Breaker inline between the Inverter and the circuit? (I'm thinking a 4A or 5A breaker should trip before the Inverter goes into Overload or blows a fuse)
  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    Not sure "fast" would be fast enough (you may be able to look up the trip curve chart online), but IMHO it's worth a shot.
    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
  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    You may be correct...  I found some pretty thorough documentation on Siemens website.  (Most of which is greek to me).  But, the one chart that makes any sense to me showed time in 10s of seconds (less than a minute).  That's still probably longer than what the DC fuse will blow...
  • BB.BB. Super Moderators, Administrators Posts: 30,494 admin
    In general, fuses and breakers are not going to be fast enough to "protect" the Inverter from overload. The inverter is almost always much faster than a typical OCPD (overcurrent protective device).

    Your choices are keep everything the same, put an 60 or 80 amp breaker in the DC input to the inverter--Or your 5 amp fuse on the AC output. I am not sure I see any big win with any of these things (other than breakers reset for free vs the cost of a sometimes expensive high current DC fuse).

    The only "fix" I can think of--Wire up separate outlet(s) to the bathroom (or where ever high power devices are located) directly the the genset. You could install some sort of transfer switch at the genset to "pick" well pump+everything else or the hair drier outlet...

    Another option would be to install a remote reading current/power meter inside the cabin--Then say, if >XX amp AC load, do not plug in hair drier/run toaster/coffee maker/etc.

    https://www.amazon.com/s?k=ac+power+meter

    Bunch of low cost options for remote power meters... (there are DC versions too if you want to monitor your DC bus too).

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GoneSquatchinGoneSquatchin Registered Users Posts: 29 ✭✭
    BB,  Thanks for the suggestions.  As it is, I already have the receptacle covers color coded in an effort to alert people to be aware (or at least ask) of what they are plugging in...  Next, is to put labels on them...

    I think I'll just leave things as they are, as you said...  I'll just stock up on spare fuses.  (I found them much cheaper on EBay).

    I can also probably just make sure the Inverter is turned off whenever the Genny is running (at least during the daytime).  Nightime, I like it on so if the Genny runs out of gas, the Transfer switch auto switches to the Inverter and we don't go into pitch black :-)

    Note:  After letting some time go by :-)  I asked my wife if the hair dryer ran at all or if it just clicked and blew things immediately.  She said it did run for several minutes.  So the genny was handling it.  I'm guessing the freezer compressor then kicked on and that's when everything overloaded...  If I had the Inverter turned off, nothing would have blown...




  • KenMorganKenMorgan Registered Users Posts: 33 ✭✭
    Simple answer...Take away the wives hair dryer privileges for a month.  >:)
    18 JA solar 200 watt panels, morningstar controller(s) and a magnum 4448 inverter with all the usual junk that goes with it. and a 600 a/h 48 volt battery bank
  • BB.BB. Super Moderators, Administrators Posts: 30,494 admin
    Ken--Now who wants to start an argument with their wife? Life is too short (and could be made shorter).

    -Bill  :#
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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