Inverter low voltage at 12.6 Volts?

stmoloudstmoloud Registered Users Posts: 100 ✭✭
I have a new 600 PSW inverter which I was hoping would be sufficient to run a small fridge.  The plan is (was) to use this inverter dedicated solely to running the fridge.
When I disconnect the AC and then connect to the inverter, the inverter does indeed start the fridge.  According to the inverter panel, the fridge draws 8.1 amp. 
However every subsequent time, approx every 30 minutes, the fridge will attempt to cycle but cannot. I can hear the motor begin but then it will fail and the inverter will throw an E3 fault which according to the manual is low voltage. But the voltage is reading 12.6 which I have always thought is OK.
Am I missing something?
  
760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 

Comments

  • Raj174Raj174 Solar Expert Posts: 660 ✭✭✭✭
    edited October 2018 #2
    Hi stmoloud,
    I believe the low voltage referred to, is the 120 volt output and is sagging due to the load requiring more power than the inverter can handle. I understand that it started the fridge, but it may be that the size of the inverter is borderline when it comes to handling subsequent surges.

    Rick
    3600W PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 195AH LiFePO4 no BMS, 4500W genset.
  • stmoloudstmoloud Registered Users Posts: 100 ✭✭
    Raj174 said:
    Hi stmoloud,
    I believe the low voltage referred to, is the 120 volt output and is sagging due to the load requiring more power than the inverter can handle. I understand that it started the fridge, but it may be that the size of the inverter is borderline when it comes to handling subsequent surges.

    Rick
    Thanks. So even if the voltage on the panel reports 12.6 DC, the E3 fault is referring not to the DC but to the AC output. Would it help if I were to increase the size of the AC cables? Also, as the inverter is borderline would it help if I were to introduce some additional cooling?
    760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 
  • BB.BB. Super Moderators, Administrators Posts: 28,858 admin
    What could help... Heavy/short DC battery to inverter cables (low voltage drop). As much voltage and current to the inverter input as possible.

    And, actually try a 50 or 100 foot "cheap" (14 AWG or 16 AWG extension cord) from the inverter to the refrigerator (reduce surge current on the AC circuit). That will help "unload" the inverter+battery bank a bit.

    What is the AH rating of your battery bank? What is the battery (flooded cell car battery, deep cycle flooded cell lead acid, AGM, etc.)?

    In general, for standard refrigerators (US, standard AC compressor, bar fridge or full size fridge), in general, a 1,200 to 1,500 Watt inverter will be more reliable.

    Assuming you are getting 8.1 amps on the 120 VAC circuit (~960 VA/sort of Watts)--That is sort of in the range of a typical starting current for the standard fridge (a bit high sounding).

    And, it is possible that your (FLA?) battery is near 13 volts for the initial starting bus voltage, but when the voltage drops to 12.5 or so, the inverter simply cannot support the surge current requirements.

    Adding the extension cord to the fridge, reduces starting surge current (while still allowing enough to start the fridge). There are hard start compressor kits you can try. Or even look at the motor start capacitor and get a couple smaller sizes (mFd) and try one of those to reduce starting surge.

    One of the issues with an "undersized" power system... Even if you get it working now--A few days or months from now, it may again not start-And you end up with spoiled food...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stmoloudstmoloud Registered Users Posts: 100 ✭✭
    Thanks Bill. Battery is FLA 85 A/Hrs. It reads 13.1 volts initial starting. The fridge is 240 VAC. I will try your fixes. But it looks like a bigger inverter is needed. 
    760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 
  • BB.BB. Super Moderators, Administrators Posts: 28,858 admin
    85 AH @ 12 volt FLA battery... That is probably not near large enough to provide a useful amount of energy for even a small fridge...
    • 110 Watts * 24 hours per day * 1/3 cycle time = 880 WH per day (pure guess)
    • 880 WH per day * 1/12 volt battery bank * 1/0.85 AC inverter eff = ~86 AH per day @ 12 volts
    So--Even if everything goes "right", in 24 hours, your battery will be dead (and ruined).

    You need to estimate your power needs (hot weather, fridge uses more energy) and size the system to supply the needed energy... For example, a nominal setup for the battery bank would be (assuming 1,000 WH per day for standard fridge and our "rules of thumbs" for a reliable off grid power system):
    • 1,000 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 maximum discharge (longer battery life) * 1/12 volt bus = 392 AH @ 12 volts
    That would be 2x 6 volt @ 200 AH "golf cart" batteries in series * 2x parallel strings = 12 volts @ ~400 AH

    A 400 AH battery bank will support a 1,000 Watt AC inverter (with 2x surge current)... It is close, but a 1,200-1,500 Watt AC inverter would probably be OK to (keep DC cables short and heavy). There are many >200 AH 6 volt batteries, or if you use AGM (much better at surge current support)--Some options.

    Problem is that a refrigerator pretty much requires a mid-size solar power system... That is one of the largest energy users for most people.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 28,858 admin
    8.1 amp draw at 240 VAC???? That is a lot of current... Is that 8.1 amps @ 12 volts (an "inverter refrigerator")?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stmoloudstmoloud Registered Users Posts: 100 ✭✭
    Yes I thought twice about this. Previously I measured just under 4 amp with a kill-a-watt but the inverter panel says different. Thanks for the numbers Bill, appreciated.
    760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 
  • PhotowhitPhotowhit Solar Expert Posts: 4,862 ✭✭✭✭
    stmoloud said:
     I measured just under 4 amp with a kill-a-watt but the inverter panel says different. 
    There may be additional loads you aren't aware of unless it is directly wired and nothing else connected. I didn't know there was a 240 volt version of a Kill-A-Watt meter. Even at 120 volts, a 4 amp load is huge for a small fridge, That's 480 watts. My 20 year old full size fridge uses about 2 kWhs a day during the summer. and <300 watts running.

    480 watts will be a serious load on a 600 watt inverter and I'd be surprised if it started it once. I think some value isn't being measured correctly.

    Also when was the fridge at 12.6 volts? Was this before hooking up the fridge, but during the day when charging? If so your battery was likely less than 1/2 full!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • BB.BB. Super Moderators, Administrators Posts: 28,858 admin
    Assuming Stmoloud is somewhere Auckland New Zealand... There are 230 VAC Kill-a-Watt and other brands out there.

    Measuring surge current is always difficult... Most digital meters sample the voltage and current once a second or so... A true peak reading meter--You have to specific get a DMM with that function. It is matter of luck if you get a true peak current reading with a typical meter (surge many be only a few handfuls of cycles--1/10ths of a second.

    A surge current of 5x to nearly 10x running current for an induction motor is not usual (i.e., 120 Watt motor will probably have an easy 5x120w=~600 Watt minimum surge to as much as >1,000 Watts)...

    Technically, the surge current is probably 600-1,000+ VA (volts * amps)... Watts (power) is:
    • Watts (power) = Volts * Amps * Cosine current phase angle = V*A*Power Factor...
    A typical induction motor, the Power Factor (PF or Cosine of the angle between voltage and current) is typically around 0.6 to 0.8 ... (Watts is either equal to or less than VA). Designing wiring/transformers, you need VA. Most residential AC inverters have Watt Max = VA Max...

    AC power math is a whole 'nother post... (what Thomas Edison was not great at, but  Professor Tesla was--the Physics and Mathematics of AC energy).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stmoloudstmoloud Registered Users Posts: 100 ✭✭
    Photowhit said:
    stmoloud said:
     I measured just under 4 amp with a kill-a-watt but the inverter panel says different. 
    There may be additional loads you aren't aware of unless it is directly wired and nothing else connected. I didn't know there was a 240 volt version of a Kill-A-Watt meter. Even at 120 volts, a 4 amp load is huge for a small fridge, That's 480 watts. My 20 year old full size fridge uses about 2 kWhs a day during the summer. and <300 watts running.

    480 watts will be a serious load on a 600 watt inverter and I'd be surprised if it started it once. I think some value isn't being measured correctly.

    Also when was the fridge at 12.6 volts? Was this before hooking up the fridge, but during the day when charging? If so your battery was likely less than 1/2 full!
    Actually maybe it is possible I misread the meter and it draws 0.4 Amp. It's only a few years old. So, 240 x 0.4 would come out to 96 watts? That will make it more likely to start but not very well I guess.
    The 12.6 volts was the reading before the subsequent attempt just prior to the inverter failing. I did though use a fully charged jump starting battery (12v 19 amp/h) just for proof of concept, so no, it was not hooked up to any panels.  
    760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 
  • BB.BB. Super Moderators, Administrators Posts: 28,858 admin
    96 Watts is closer to what I would expect for a running refrigerator compressor.

    Induction motors are notorious for high starting current. More or less like starting your car (or a bit more) current from your battery.

    Another issue, if you used alligator clamp jumper cables, they generally do not make good enough connection to pull substantial amounts of current (many AC inverters will simply DC voltage fault with jumper cables).

    Anyway... The above numbers or a "minimum" battery bank of FLA "golf cart" batteries is where I would start (golf cart batteries are generally cheap and pretty rugged). About the cheapest way to get started with this type of system (in the US, roughly USD $100 each).

    Have fun,
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stmoloudstmoloud Registered Users Posts: 100 ✭✭
    edited October 2018 #13
    Thanks Bill, in my second attempt with the jump starter I had it out of the casing and was bolted directly to the terminals. Yes I agree I am going to have to spend more.
    760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 
  • petertearaipetertearai Solar Expert Posts: 390 ✭✭✭
    try an inverter fridge 

    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . victron battery monitor . 24 volts 450 ah surette batterys . off grid  holiday home 
  • PhotowhitPhotowhit Solar Expert Posts: 4,862 ✭✭✭✭
    stmoloud said:
    Thanks Bill, in my second attempt with the jump starter I had it out of the casing and was bolted directly to the terminals. Yes I agree I am going to have to spend more.
    A jump start battery of 19 amp capacity, would be less likely to start it than standard  FLA 85 A/Hrs. In my opinion, if they are both in good shape. You are drawing a higher percent of it's total capacity, so the voltage drop should be dramatic.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • mcgivormcgivor Solar Expert Posts: 2,767 ✭✭✭✭✭
    The main problem in my opinion, is the conversion ratio of a 12V to 230V ~20:1, this puts extreme stress on the battery to provide any useful amount of current on the AC side, use the refrigerator as an example, 0.4A running current with an inrush of 4A. Running would be 8A with 80A inrush on the DC side, lead acid batteries can provide enormous amounts of current however the voltage drops significantly, higher voltage is definitely an advantage to avert this phenomenon, or use a chemistry that suffers less by being able to support the demands. 
    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.
  • stmoloudstmoloud Registered Users Posts: 100 ✭✭
    edited October 2018 #17
    So maybe I should try connecting the batteries in series?  Probably not.
    Furthermore upon reading the specs they say it is good for a 1200W output power surge but I suspect for only so many micro-seconds.
    Perhaps that's the reason the subsequent start only starts the motor a quarter turn but goes no further.
    Thirty minutes from a cold start-up the logic chip in the inverter has warmed up and no longer accepts what did get by thirty minutes previous. 
    760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 
  • BB.BB. Super Moderators, Administrators Posts: 28,858 admin
    edited March 14 #18
    No, on series batteries, your bus voltage would be around 24 volts. 
    That would ruin your inverter (assuming 12 VDC input inverter).
    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.