inverter reading.3 higher than bank??

John XW NYJohn XW NY Solar Expert Posts: 50 ✭✭✭✭
Yes hi I am wondering why I am getting a reading of 25.0 volts on my inverter but when i check the bank with a voltmeter it say 24.7, Why would my XW be reading .3 higher than the battery bank. If anything I would think there would be a voltage drop especially with the long 10 ft inverter cables to the bank. It doesn't make sense to me can someone explain why I am having this happen?

I just did an equalization charge for a few hours to get the bank running good.


Thanks Jon

Comments

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: inverter reading.3 higher than bank??

    it's hard to say which is off and by how much. it may be easier for you to find out if your voltmeter is accurate by comparing to another meter known to be accurate or a known voltage source as your meter is far more portable than your solar setup is. they could both be off some too.
  • John XW NYJohn XW NY Solar Expert Posts: 50 ✭✭✭✭
    Re: inverter reading.3 higher than bank??

    Yeah well its funny I guess but not really. You would think it would be the other way around. I ll have to try to get to the bottom of this ir otherwise just compensate the settings on the inverter somehow. If anybody else has suggestions let me know
    Thanks Jah Bless , JD
  • RandomJoeRandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: inverter reading.3 higher than bank??

    I can read my battery voltage at three different points on my Outback system - charge controller, battery bank monitor, and inverter - and the three never agree. What annoys me the most is that the charge controller is the only one I can actually tweak to get it exact, but it is the one that's actually correct! The other two (including quite pricey battery monitor) aren't adjustable, and are off by a few tenths.

    I have learned to use the CC voltage reading for control, as it has been accurate every time I checked with a meter.

    Current readings are the same way, a couple tenths off from each other, although I'm amazed those are as accurate as they appear to be. Not sure about the CC but the battery monitor uses 500A / 50mV shunts - and provides current readings to a tenth of an amp?!? Seems to me having something that reliably measures 0.00001V increments is quite remarkable... (At least, using devices like that at work would cost a small fortune.)

    On the other hand, the current readings for the 120VAC side of the inverter are total garbage. They are never accurate, and they aren't even consistently off - the exact same load will produce a reading anywhere between 0A and 4A! Switch it between grid and inverter, and get wildly different readings depending on source. And with a 1A resolution are way too coarse for my needs anyway - 120W is several devices here. (Granted, the inverter is pretty oversized for the normal loads I run on it.) Voltage readings can be all over the place too. Running on grid, the input and output voltages rarely match - sometimes it'll show 116V in / 122V out!

    Sorry, that turned into a bit of a rant... I'm a bit of a control freak (install HVAC controls for a living) and get bent out of shape when my sensors aren't accurate and don't have good precision! :p
  • Solar GuppySolar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: inverter reading.3 higher than bank??

    The XW reports a temperature compensated voltage, not actual voltage, read your manual for more details
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: inverter reading.3 higher than bank??

    sorry sg, but i don't think that would explain the differences between the 2 meters as voltage is voltage be it temp compensated or not as both should read the same. i am not saying the xw is wrong, but i don't know it is right either. the same goes for his voltmeter.
  • BB.BB. Super Moderators, Administrators Posts: 32,740 admin
    Re: inverter reading.3 higher than bank??

    I think SG is saying that the XW takes the battery bank voltage and adds an offset based on the bank temperature so that the displayed voltage is equivalent to a 77F temperature battery bank.

    In that case, the DVM would read higher for a cold bank and colder for a hot bank vs the XW's meter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: inverter reading.3 higher than bank??

    was that what you were saying sg and why would xantrex go through the trouble to do that?
  • boBboB Solar Expert Posts: 1,008 ✭✭✭✭
    Re: inverter reading.3 higher than bank??
    The XW reports a temperature compensated voltage, not actual voltage, read your manual for more details

    Just like the old Trace SW did I think. That's one way to do it, instead of changing the Absorb or Float setpoint on temperature, but if it is labeled "Battery Voltage", it can be very confusing.

    I prefer to show actual measured battery voltage, (inverter terminal or battery terminal voltage), and then show the compensated Absorb or Float Voltage separately.

    But, was the charging state in Absorb or Float ? Or was it still in Bulk ?

    In cases where the battery voltage reading actuall *IS* off, you *should* be able to adjust the meter reading offset.

    boB
  • Solar GuppySolar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: inverter reading.3 higher than bank??

    Yes Neil and its done that way, I see it on my SCP when the BTS is installed, why, no clue, I had nothing to do with the SCP or Xanbus hardware.software.

    http://www.xantrex.com/web/id/1871/docserve.aspx for the inverters manual

    I'm not sure how the OP has their system configured, if there is a BTS installed, if they are using the Xanbus network. When Networked, there is more than one source for the battery voltage, could be the inverter or charge controller.

    The XW is a very complex system, Xantrex when I was there wanted only trained dealer/installers , and as these questions that keep popping up show they had some convincing reasons for this, its not you plug and play system, its a hybrid whole house power center.

    BTW, 3/10th's of a volt, that is meaningless to the operation of the XW's , battery's are no where near that type of tolerance as it relates to either charging or SOC values.
  • John XW NYJohn XW NY Solar Expert Posts: 50 ✭✭✭✭
    Re: inverter reading.3 higher than bank??

    Yeah well the way I look at it is that it kind of is important for the following reasons:

    1) The XW charger is not fully charging the bank because it is reading higher than it actually is, there fore the bank is not being charged completely or correctly.

    2)The XW System is discharging the batteries more than I would ideally like to because it thinks there is more juice than there is.

    3) The inverter should be reading lower than the bank because of the length of the cables from my inverter to bank is 12 feet 4/0 cable.


    I find it to be a pain in the butt to have to consider all these things and I think the technology should be more accurate and user friendly especially what everything costs to put it together.

    It has been quite a learning experience for me which is not altogether bad but is time consuming.

    Oh yeah the voltmeter is a cheap Sperry Home Depot voltmeter but i think should be reasonably accurate nonetheless.8)
  • Solar GuppySolar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: inverter reading.3 higher than bank??
    John XW NY wrote: »
    Yeah well the way I look at it is that it kind of is important for the following reasons:

    1) The XW charger is not fully charging the bank because it is reading higher than it actually is, there fore the bank is not being charged completely or correctly.

    Depends on the charging source is, if the Mppt/Solar is reporting higher than the battery bank, then that makes sense as you probably have some losses in those wires
    John XW NY wrote: »
    2)The XW System is discharging the batteries more than I would ideally like to because it thinks there is more juice than there is.

    The XW inverter discharges based on what the load draws, nothing else. The 3/10th of a volt will make no difference in how much energy is put to the loads, and if its Gridtie, that is above the full-charge value ( by a volt or more ), again no effect on the battery bank
    John XW NY wrote: »
    3) The inverter should be reading lower than the bank because of the length of the cables from my inverter to bank is 12 feet 4/0 cable.

    Depends if the XW inveter is powering a load or Gridtie, or if the XW inverter is charging the batterys, if the latter, it will be higher at the inverter
    John XW NY wrote: »
    I find it to be a pain in the butt to have to consider all these things and I think the technology should be more accurate and user friendly especially what everything costs to put it together.

    It has been quite a learning experience for me which is not altogether bad but is time consuming.

    Oh yeah the voltmeter is a cheap Sperry Home Depot voltmeter but i think should be reasonably accurate nonetheless.8)

    There are always variations, its ohms law, now some chargers like the MorningStar Mppt have a secondary voltage sense so the battery voltage is measured from a none current bearing path. If you making measurement during heavy operation, the current ripple ( AC ) will be VERY difficult to make accurate measurements as its a DC voltage with a large AC current ripple, except power analyzers that cost more than ALL of your hardware.

    The point I feel you are over looking is, all these potential variations will have zero effect on the performance of you battery's, any voltage over full charge, will charge a battery, its just a function of how long and 3/10th of one volt will have no effect.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,184 ✭✭✭✭✭
    Re: inverter reading.3 higher than bank??

    Would one simply measure the specific gravity and know the state of charge. If you had good batteries you might even be lazy and just measure one cell.

    Do you have the temp sensor that goes on the battery terminal or is it a case stick-on? The battery terminal type can easily be damaged if you are not careful.
    "we go where power lines don't" Sierra Nevada mountain area
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • John XW NYJohn XW NY Solar Expert Posts: 50 ✭✭✭✭
    Re: inverter reading.3 higher than bank??

    OK First off I have a battery terminal temperature measurement on my bank.

    What I am really getting at is that this technology should be more accurate and should already know how to do all this stuff for me. Especially since the XW system is complex. I am still very new to this and have learned a lot. The battery technology really seems to be the biggest problem of all. Im sure there has to be a better way to store energy, we just don't know it or it isn't publicly available yet.

    My real issue/point is that A) the banbk isn't really charging completely properly thus fully utlizing the power from the panels to be harvested and B) That the bank is being discharged more than I would like it to as well.

    I guess the only thing to do is to adjust the system settings to compensate for what ever difference there is and to raise the settings .3 higher on the controller so that the bank is getting proper current, really a no brainer i guess.

    I will call Xantrex and ask them im pretty sure they will tell me the same thing but maybe they have other suggestions as well.
    Im also going to use my XW config tool to make sure everything is set right.

    Thanks 4 your ideas as well Naws forums guys Jah Guide JD:cool:
  • toppertopper Solar Expert Posts: 113 ✭✭
    Re: inverter reading.3 higher than bank??

    SG , correct me if I'm blowing smoke here.
    If I am reading the manual right, If you have an SCP installed, you should be able to back calculate your actual battery voltage using the temp compensation # and the battery temperature.
    ie. battery temp difference from 77* X whatever it may be -125 mV/*. Should give you an actual.
  • vtmapsvtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: inverter reading.3 higher than bank??
    The XW reports a temperature compensated voltage, not actual voltage, read your manual for more details

    FWIW, my outback system does much the same thing. The actual voltage = the display voltage only at standard temperature. If I recall correctly, there is somewhere in the menu system that I can display the actual voltage after temp compensation.
    niel wrote:
    was that what you were saying sg and why would xantrex go through the trouble to do that?
    I can only guess why. Perhaps its to avoid confusion.:confused: For example: I set my absorb voltage to 29.6. When I look at the display I see 29.4 so I know that I am almost to absorb. If the battery is cold, the actual voltage might be 30.0 and actual absorb voltage is 30.2.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: inverter reading.3 higher than bank??
    John XW NY wrote: »
    Oh yeah the voltmeter is a cheap Sperry Home Depot voltmeter but i think should be reasonably accurate nonetheless.8)

    An old time trick for checking voltmeter calibration (at least on one range) is that a common ordinary carbon-zinc flashlight battery (if you can find one) when new has a very precise open circuit voltage of 1.54 volts. If you want an accurate reference for your 15 volt range, just put a bunch of them in series.
    SMA SB 3000, old BP panels.
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