Xantrex XW6848+NA planned night time disconnect and mInimize the tare loss Opinions?

new2PVnew2PV Solar Expert Posts: 305 ✭✭
Hi looking for a way to shut down the inverter when the battery volts hits about 50% SOC. I do not want to charge using GRID at all and I don;t want overnight tare loss. So this is the plan to use a relay output from the Mppt-60-150 low battery volts to trigger another relay to close the RPO or remote power off on the inverter. The 12volt small relay will drop out on low batt volts, closing the contact shutting down the inverter. I assume if the inverter in shutdown mode goes to bypass mode AC1 grid? I will keep the charger disabled on the inverter at all times. When the sun comes up the next day and the volts are high enough past the clear setting in the MPPT everything should resume as normal? Or can;t you restart the inverter this way ? When I shut down the inverter I will probably lose power to the combox as it comes from the inverter , another issue to address. Or use the supplied power adapter, which would have no power if there was a grid failure..
XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Other than suggesting turning off the internal charger and setting the low voltage limit to ~46 volts--I don't know the configuration stuff, but it seems like a possible starting point...

    My question is why do you want to do this? It sounds like you want to reduce utility power costs? However, when you configure the system to shut down and fail over to the utility power, you now don't have much in the way of back up power if you lose utility power while the battery is at 50%.

    And for money saved from utility power payments, you potentially are simply putting money into battery cycling/replacement costs (if not more--Batteries are not cheap and getting more expensive).

    A better solution would seem to be Grid Tied solar (and/or operating the XW in Hybrid mode and selling excess solar production back to the utility). Of course, this would require the utility to have a Net Metering plan--Which is always a big "what if"--And some utilities have very poor (for solar customers) metering plans where high monthly billing fees and low $$/kWH payments/credits to the customer's account.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • new2PVnew2PV Solar Expert Posts: 305 ✭✭
    I don;t want to use utility power to charge the batteries unless its absolutely necessary. I can wait until the next day and the sun charges them up. I don;t plan to do any selling back as of now but I will look into whats involved. IF the array is big enough I should have enough power on hand to have the batteries nearly full at the end of the day and use all the current loads, on a good sunny day anyway. I can break out the generator if I am stuck with a grid outage. I may not go down to 50% maybe only 70% have to get this up and running. Excess power could be diverted to AC loads hot water heating, heat pumps, etc. Do you see a problem with going with a big array 6kw with a 400 ah battery bank?
    XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    6kWatt array charging a 420 AH @ 48 volt battery bank... You will have to keep an eye on the battery bank.

    It it possible for a very large array and charge controller to over current the battery bank and cause the bank to over voltage before the charge controller can cut back on the charging current (not common, but possible). Make sure you have the remote battery temperature sensor option for your battery bank (reduce the chance of thermal run away of the battery bank).
    • 6,000 Watt array * 0.77 panel+controller derating * 1/58 volts charging = 80 amps charging
    • 80 amps charging / 420 AH battery bank = 0.19 = 19% rate of charge
    If the battery bank is near 100% full and has very high charging current available (such as when the solar charge controller is "sweeping" for MPPT -- Maximum Power Point Tracking), it is possible for the battery bank voltage to exceed the AC inverter's maximum input voltage.

    I am not sure which controllers are more likely to do the over voltage (or not do the over voltage)--But it is a possibility with the large solar array (5% to 13% is typical range).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • new2PVnew2PV Solar Expert Posts: 305 ✭✭
    Wow, Bill your scaring me I can;t baby sit my batteries If I am at work, well the combox could email me. I could put 4 battery temp sensors in the system. One connected to the inverter, 1 on each charge on controller, and one on the conext battery monitor, what do you think, good or bad idea?
    XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Monitoring the battery's temperature is very important--Particularly if the rate of charge is >~13% (this is based on recommendation for forklift batteries--Above this rate of charge, they tend to use active cooling--i.e. fans).

    The maximum array wattage (vs battery bank AH/voltage) would be a good question to ask over at Midnite's forum. Since they design/build the solar charge controllers, they can talk about the possible voltage regulation issues of their MPPT charge controllers.

    The Classics are a much newer design than many of the older controllers--Perhaps they have taken this into account.

    It is this voltage regulation issue that worries me (and thermal run away of the batteries). Lead acid batteries (flooded/agm/etc.) are very energy efficient when charging below 80% state of charge--And can take >13% rate of charge very easily. It is when batteries get >80-90% state of charge that they become less efficient. And at 100% state of charge, it is easy to overheat a battery with a ~2% (or greater) rate of charge (when all charging energy is turned directly into heat and Hydrogen/Oxygen gasses--And for AGM, the recombining of Hydrogen and Oxygen at the catalyst even causes more self heating).

    For the most part, it is the battery bank itself that regulates the "bus voltage". The solar charge controllers are much slower at regulation and adjust voltage/current flow to charge the battery bank--Not hold 14.8 volts with microsecond type loop feedback/control.

    Older MPPT charge controllers seem to run "open loop" every 10-15 minutes for some number of seconds while doing the "sweep"... It is this sweep time that the battery bank could be over voltaged and cause an AC inverter to fault or other loads to be damaged. The sweeping does not (I think) cause any of the thermal issues--The time frame is too short.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,656 ✭✭✭✭✭
    Bill may be scaring you but it is good for you to know about these problems. First thing that keeps coming up on the xw is temp sensors. You only need one as they are shared by all devices. Since day 1 in 2007 the xw does not display temp data on all devices only the one you plug the sensor into. I do not think this has been fixed in the XW + as it sells alot of sensors for Schneider. The sweeping is a non-issue with all xw chargers. These chargers are as good as the best out there, I would say they are the best just short of the morningstar at the current state of the art spec wise. If you want to contact me I can point you in the right direction. The xw chargers can all be current limited to protect from hi inrush
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • SolaRevolutionSolaRevolution Solar Expert Posts: 407 ✭✭✭✭✭✭
    new2PV wrote: »
    I don;t want to use utility power to charge the batteries unless its absolutely necessary... I don;t plan to do any selling back... I may not go down to 50% maybe only 70% ...

    A little hair brained here , but it might get you most of what you're looking for:

    You could use the GEN AC2 in for your grid power. Use the XW AGS (2-wire start setting) to control a relay on the incoming AC line. A relay such as:

    http://www.grainger.com/product/DAYTON-Relay-1EJJ2?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/1EJJ2_AS01?$smthumb$
    (It is a 2 pole 50 amp with a 12 volt dc coil. Use the XW's 12 volt AUX relay to drive it)
    This would make it so you would only use grid power as needed by using the controls in the AGS.

    If you turn off the SELL function you may be able to use AC1 as an input for your manual-start generator. (Your generator would need to have a fairly clean output for the AC1 input to allow it to connect.)

    Voila, no unwanted grid charging. But...the inverter would always remain on so you would still have some tare loses. At first I was thinking that you could then set the Inverter Low Voltage Disconnect to shut it down once the voltage got below a certain point but that would call for the AGS...Lol! If you really need to be able to shut down the inverter you could use the RPO on a relay but I believe that requires you to manually restart the system from the control panel. I suppose you could use an automatic transfer switch on the output to the loads (switching between grid and the inverter output) and allow the inverter to go into search mode.... but then with the T-switch being part of the daily function...how glitchy can you allow your power to be?

    Good luck. And don't forget that simple is usually more reliable!

    :cool:






  • new2PVnew2PV Solar Expert Posts: 305 ✭✭
    This is getting way to involved, but some pretty slick idea'a everyone I coming up with. Are you sure the RPO require you to go to the control panel to restart that would really suck.

    XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array
  • new2PVnew2PV Solar Expert Posts: 305 ✭✭
    Bill may be scaring you but it is good for you to know about these problems. First thing that keeps coming up on the xw is temp sensors. You only need one as they are shared by all devices. Since day 1 in 2007 the xw does not display temp data on all devices only the one you plug the sensor into. I do not think this has been fixed in the XW + as it sells alot of sensors for Schneider. The sweeping is a non-issue with all xw chargers. These chargers are as good as the best out there, I would say they are the best just short of the morningstar at the current state of the art spec wise. If you want to contact me I can point you in the right direction. The xw chargers can all be current limited to protect from hi inrush

    I'm not sure but I think you can use more than one temp sensor and it will only read the one with the highest reading. Has anyone tested this theory?
    XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,656 ✭✭✭✭✭
    you can use as many as you want. It is good for the economy! You only need one but go for it!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • new2PVnew2PV Solar Expert Posts: 305 ✭✭
    you can use as many as you want. It is good for the economy! You only need one but go for it!

    They come free with the charge controller, battery monitor and the inverter, so I have 3 already, I don;t think I can plug in any more unless I buy more equipment. AS for glitches It would be ok for the freezer and fridge, but not good the TV. Would it be a bad idea to RAISE the LBCO voltage or would it make a mess of other settings? I might have to forget the idea and just scale back the on grid charging and just deal with the tare loss, as the XW+ can go down as low as 5% bank size charge rate.
    XW6848 inverter with 2 X mppt 60 150 CC , with Canadian solar 260Watt panels 2 x 3.5 kw array
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