Xantrex system monitor - how accurate?

samuel
samuel Solar Expert Posts: 80 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
Below is an e-mail correspondence I had with a Xantrex representative:

Dear Xantrex,

I'm seeking information about my inverter. Specifications list the the MS3000 inverter as having a no load power draw of (load sense off) <60W. In practice I have consistently observed a minimum power draw of 215 to 220W. This low reading was also confirmed after switching the main AC breakers to OFF, isolating all potential phantom loads from the inverter. Below are the system specifications.

I would like to know if my observations are correct, my firmware is up to date, and what the no load power draw <60W means.

My ultimate goal is to find a way to watch a TV during the day or leave a ceiling fan on all night and use the least power (TV ~ 65W, fan ~90W).

Other information about the system:
search mode - 95W, 8 sec,
minimum power draw (breakers OFF) 215-220W, (breakers ON) 235W
two 13W lights on (when search mode disabled) 243W, (search mode on) 243W


current firmware ::

MS3000
Model # 809-3010
Serial # 000012B75B06
F/W Rev 2.10.00

System Panel
Model # 809-0910
Serial # 000011E14C4B
F/W Rev 1.06.00


Cheers,
Samuel


Dear Sam Wiltzius,

Thank you for contacting Xantrex...

Please note that the MS 3000 has a No Load Draw of @ 4 amps when the load sense is disabled.

Best Regards,


It would appear that my question was more or less answered, but I'm still at a loss for why the system panel is "reporting" 200+W power draw and the system is supposedly using <60 watts. In about one month I intend to install a battery monitor, specifically the Victron BMV 600 Battery Monitor VIC-BAM001003000. This monitor fits my purpose of remote mounting 70 feet from the batteries and so far as I can tell will provide a more reliable readout of power consumption (as well as depth of discharge which is the "killer app" for this off grid cabin).

My new question(s): is the Xantrex remote system panel actually telling the truth? Has anyone else noticed this with their system? Is there a fix? Any opinions on battery monitors (focus on depth of discharge accuracy).

I should also add that circumstantial evidence (voltage and specific gravity) suggest the system panel is in error - though I have never had a consistent load on the batteries for a specified time that I could use to assess this. If it would help, more details on the install can be found here and here
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: Xantrex system monitor - how accurate?

    I did not see where the shunt was installed--assume it is in the negative battery connection and all other negative wiring connections happen "after the shunt"?

    From your January 2011 post/photo--I do not see any shunt where I would have expected one to be placed.

    One quick thing to check. Many Battery Monitors can be programmed to take different shunts. Have you confirmed with a known load (or current clamp meter) that the Battery Monitor is reading the correct current (you could also compare with charging current from your solar array into the battery bank with no other loads).

    Opps, never mind, the monitor will be installed ~1 month and (I guess) you are using the inverter's panel to report Watts?

    If you don't have one yet, I would suggest getting a DC current clamp meter. Something like this one is about the cheapest functional unit I have seen ($60). You can certainly spend $300-$400+ for a nice True RMS reading unit from Fluke.

    Many times, the readings from various inverters/charge controllers/etc. can be estimated to have only ~5-10% accuracy at best (sometimes even 30% accuracy). 10% of 3,000 watts is ~300 watts. It is not what you would have expected--but it is possible that the unit is working "correctly" but displaying nonsense (at low power levels).

    Is the inverter still under warranty?

    Otherwise, for a 12 volt system, I would suggest adding the MorningStar 300 watts TSW 12 volt inverter. It is low power, and even has "search" and "remote inhibit"--Functions that you only find on larger/more expensive units.

    Connect it to your "low power" / "critical loads" / "24/x7 loads" (such as CFL lighting---I think you would be very happy with it--For running your smaller loads--it waste a heck of a lot less power.

    You can still use the larger inverter to power your tools and other large home appliances.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • samuel
    samuel Solar Expert Posts: 80 ✭✭✭✭
    #3
    Re: Xantrex system monitor - how accurate?

    Thanks for the quick assessment Bill!

    I'm content with that answer. Looks like the evidence is growing for an errant readout on the system panel (watts) for low loads. In a little while I'll find out what the battery monitor reports. Hopefully that will allow me to assess whether or not a secondary inverter is of a significant economic value.

    Being that the inverter idles at 4 amps (4 x 13.5V ~54W) and the smallest load we would run overnight is about 35-50W that would mean (54W)*8-10h ~500W to keep the inverter "ON". Let's see... we can net around 2500 or more AC watts on a sunny day, so we could get a 20% savings (or more) on our power gen.

    However, given our use patterns (for a cabin) it's hard to mount an argument for a second inverter. Unless, there is a way to automatically switch from a lower power inverter to a high power inverter (for those times when only the TV is being used and then someone flushes the toilet and the well pump kicks on). --- if there is a way to do this (auto-switching) then I'd love to know how. I've wondered whether or not two inverters could be wired together such that the following are satisfied:

    1 - when generator is turned on the batteries are charging and power is supplied to cabin
    2 - when load is <300W the small inverter runs only
    3 - when load is >300W small inverter automatically defers to larger inverter

    note: both inverters have search modes.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: Xantrex system monitor - how accurate?

    Run the small loads on the small inverter.

    Run large loads on the large inverter.

    Home pressurization pump could be converted to 12 volt pump?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #5
    Re: Xantrex system monitor - how accurate?

    215 watts for no load is ridiculously high.

    Xantrex told you 4 amps for no load. For a 3kW sinewave inverter, 50 watts is a reasonable amount for no load consumption.

    Either you have a measure error or there is something wrong with inverter.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: Xantrex system monitor - how accurate?

    I think this is the inverter displaying its power.

    Question is the display correct at several hundred watts and the inverter is consuming that energy, or is the inverter ok and the display wrong. Or is the inverter ok, and the display within specs?

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