Battery interconnections

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  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Battery interconnections
    NG - have a query regarding your "shunt" and current measuring setup - just thought about it today as a matter of fact. The bottom shunt in your picture measures inverter "in" current, but would the XW6048 not provide this information, or is this a double check on the system? Second is the top shunt that measure solar charge current, should this not be provided by your XW 60 CCs with the same caveat as per the first query?

    I wanted it for 4 reasons:

    - more accurate measurement
    - ability to log the results
    - ability to count AH to determine SoC
    - abiliy to act on the results

    As I found later, Xantrex data are actually available from XanBus, so I could get away withou shunts, but Xantrex measurements are not very accurate.

    I needed three measurements - solar, inverter, and batteries. Apparenty they sum up to zero, so I needed only two shunts. I decided that solar and inverter will work the best because I can look at the waveforms at the shunts if I need to.
  • PanamretireePanamretiree Solar Expert Posts: 278 ✭✭✭✭✭✭
    Re: Battery interconnections
    NorthGuy wrote: »
    I wanted it for 4 reasons:

    - more accurate measurement
    - ability to log the results
    - ability to count AH to determine SoC
    - abiliy to act on the results

    As I found later, Xantrex data are actually available from XanBus, so I could get away withou shunts, but Xantrex measurements are not very accurate.

    I needed three measurements - solar, inverter, and batteries. Apparenty they sum up to zero, so I needed only two shunts. I decided that solar and inverter will work the best because I can look at the waveforms at the shunts if I need to.

    NG - Thanks for the info. Another reason I queried is because I have been looking at the XW CCs to determine if there is an advantage using these CCs over the Classic 150. I have found out of late that there is no duty on equipment imported from the US because of Panama's free trade agreement, and that Panama has changed its legislation and has started to relax the duty requirements on RE equipment. I have to get more info on this. The no duty issue is huge because the Classic is made in the US compared to the XW lineup, and both do a similar job, just one is connected to the XANbus and the other would not be.

    Cheers

    Ernest
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Battery interconnections
    NG - Thanks for the info. Another reason I queried is because I have been looking at the XW CCs to determine if there is an advantage using these CCs over the Classic 150. I have found out of late that there is no duty on equipment imported from the US because of Panama's free trade agreement, and that Panama has changed its legislation and has started to relax the duty requirements on RE equipment. I have to get more info on this. The no duty issue is huge because the Classic is made in the US compared to the XW lineup, and both do a similar job, just one is connected to the XANbus and the other would not be.

    There are two benefits of XW CCs connected to XanBus:

    - they share battery temperature sensor with the inverter
    - they can calculate overall amps going to the batteries (by subtracting Inverter amps from SCCs) and they can use that for absorption termination.

    The biggest benefit of Classics is that they are much more flexible. If you want to do something unusual, it is more chances you can do that with Classics than with XW CCs.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Battery interconnections
    NorthGuy wrote: »
    I wanted it for 4 reasons:

    - more accurate measurement
    - ability to log the results
    - ability to count AH to determine SoC
    - abiliy to act on the results

    As I found later, Xantrex data are actually available from XanBus, so I could get away withou shunts, but Xantrex measurements are not very accurate.

    I needed three measurements - solar, inverter, and batteries. Apparenty they sum up to zero, so I needed only two shunts. I decided that solar and inverter will work the best because I can look at the waveforms at the shunts if I need to.

    I agree. Xantrex measurements not very accurate, particularly on amps. Volts*Amps is less than watts. Would a poor power factor make Volts*Amps more than watts?
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Battery interconnections

    Power = Volts * Amps * Power Factor

    Power Factor can be equal to Cosine phase angle between voltage and current... Or between 0.0 to 1.0 (0 is no power transfer, and 1.0 is perfectly in phase and 100% power transfer).

    So VA >= Watts

    The other problem is with digital meters, the generally have two basic ways of measuring voltage and current amplitudes.

    One is to "peak measure" the voltage and know that to calculate Root Mean Square (how power is calculated--P=V2/R=I2R) for a sine wave is that:

    V (or I) RMS = V * 1/sqrt(2)

    Very easy to make a circuit that does that.

    The problem is this only works with sine waves. Different wave forms have different conversion factors. And for wave forms like current pulses (lots of electronic power supplies draw no current, then a very heavy/short current spike at the peak of the sine wave). To do that accuratly, a Digital to Analog converter needs to measure ~50,000 samples per second and "do the math" to figure out the area under the curve for RMS.

    For example, measuring the DC input current (across a shunt/precision power resistor) to an AC inverter is a "sine squared" wave form (or something else for a MSW type inverter). So--I would guess that the typical Battery Monitor is not going to be an RMS calculation but some sort of sqrt(2) type fudge factor.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Battery interconnections
    NorthGuy wrote: »
    There are two benefits of XW CCs connected to XanBus:

    - they share battery temperature sensor with the inverter
    - they can calculate overall amps going to the batteries (by subtracting Inverter amps from SCCs) and they can use that for absorption termination.

    The biggest benefit of Classics is that they are much more flexible. If you want to do something unusual, it is more chances you can do that with Classics than with XW CCs.

    I have a bunch of unusual settings, the the Midnite Classics are likely far better for geeky tweakers. XW CCs are letting me use lower bulk than absorption voltage. 58.6 Bulk, 59.8 Absorb. The inverter doesn't start selling until bulk is finished, so bulk goes up to 58.6V. When the inverter starts selling, it runs 1V under the charge controller set point, so absorption runs at 57.6V. This voltage is kept for 1 hour with no termination. After 1 hour, the set point goes up to 59.8V and the actual voltage goes up to 58.8V (1 volt under because the inverter is selling to the grid while the batteries are absorbing). I also lied to the charge controllers and told them the battery bank was only 300Ah. This makes the absorption exit point 6A. Doing the same thing on the inverter, but 58.8 bulk and 60.0 absorb. This is to get an extra good charge to the batteries when the generator is exercised every two weeks while not rushing in large quantities of current at such high voltages. I have AC2 set preferred, so when the generator turns on, the inverter switches to it and starts charging the batteries (discharged from some load shaving). After the generator finishes its one-hour exercise, it turns off the the inverter resumes charging off the grid. I have ReCharge volts on the inverter set to 56V but this is ignored when on AC2 and when AC1 is first reconnected (I think this behavior comes from the California power crisis also). Another non-standard setting is that I have ATS transfer time set to 150 seconds to allow extra time for the generator to warm up as I keep eco-throttle turned on and it needs the extra warmup because it runs only 1500RPM on idle and it will get bricked hard to 5.0-5.5KW when the inverter connects and powers the house and charges batteries simultaneously. I also have the inverter limiting charge current at 45A to better get along with the generator's eco-throttle.
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Battery interconnections
    Doing the same thing on the inverter, but 58.8 bulk and 60.0 absorb. This is to get an extra good charge to the batteries when the generator is exercised every two weeks while not rushing in large quantities of current at such high voltages.

    That is interesting. I tried to set Bulk voltage less than Absorb, but it didn't work. It kept using one of these (I forgot which one) all the time. It only worked when Bulk voltage was higher than Absorb.

    I only tried Inverter, but not SCCs.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Battery interconnections
    NorthGuy wrote: »
    That is interesting. I tried to set Bulk voltage less than Absorb, but it didn't work. It kept using one of these (I forgot which one) all the time. It only worked when Bulk voltage was higher than Absorb.

    I only tried Inverter, but not SCCs.

    I haven't observed the inverter with these settings yet. Only the SCCs. Next thursday night is next generator exercise. Thats when I'll observe the inverter.
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