question on inverter/charging setup

NilaNila New UserPosts: 106Solar Expert ✭✭✭
HI Everyone,

Its nice to be a member of this forum where a lot of experts seem to give advices to people like us.

I live in India , southern part, lots of sun!!.

I have 8x 250W all 24 volt solar panels.. I am in the process of mounting them at my roof.

I have a Charge controller which is 48V / 50 AMPS rating and which I believe is suitable for the 2KV system.


My home already has a domestic Inverter from Su-kam . It is 3.5KV and needs 48V battery. ( I have 4, 12V batteries connected in series, 200 AH each : so 200 AH at 48v )

As soon as I setup the panels I believe the setup is straight forward.. connect the panels to charge controller and the output from charge controller goes to battery.

My problem however lies with my Inverter's Charging facility..


My inverter will charge batteries automatically at 12AMPS or 16AMPS and I cannot turn that feature off .

So when i connect my panels to battery , I believe it will overcharge them .. 12AMPS from inverter + output from the panels ( approx 30AMPS+ ? )


My batteries are Lead acid and not sealed. I m worried it may reduce life of batter or even kill them/cause an accident.


My idea to prevent this for now is to switch off the Mains (utility) during all the morning like 8am - 6pm to be safe. Inverter wont charge batteries for sure ONLY when the utility is cut off.

Instead of this manual function is there anyway to do it better .. like using a circuit or device? .. so when the charge controller has an output > 10 Amps , the mains are auto disconnected?


Expecting the opinions from experts.

Please do ask if you have any questions to make this clear. Forgive me if i am not very clear in explaining this.

Mods please move this post to appropriate topic if i posted it at wrong one.
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Comments

  • CariboocootCariboocoot Gone Fishing... Posts: 17,615Banned
    Re: question on inverter/charging setup

    Welcome to the forum.

    I would not be worried about over-charging the batteries. The inverter has a built-in charger, but it should be a regulated charger. When does it activate? At a minimum Voltage and/or whenever AC IN is present? Usually such is the case, and the Voltage level can be set.

    You've got a good estimate on the panel output. With an MPPT controller that array would probably manage 32 Amps maximum. If the inverter's charger can't be shut off the maximum total current would be 54 Amps which is 27% of the battery capacity (if truly 200 Amp hours). This would only occur during Bulk charging, and only if the array has full sun at that time. Usually it would start out charging in the morning and the batteries would reach Absorb before the panels are capable of their maximum output.

    I'm putting a lot of caveats in this post because I don't know the exact specs of any of the equipment.

    I will say that if this is like other hybrid GT inverters that battery bank at 200 Amp hours total is very small for a 3.5 kW inverter. Doubling the size of the battery bank would solve all the problems at once.
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    Welcome to the forum.

    I would not be worried about over-charging the batteries. The inverter has a built-in charger, but it should be a regulated charger. When does it activate? At a minimum Voltage and/or whenever AC IN is present? Usually such is the case, and the Voltage level can be set.

    You've got a good estimate on the panel output. With an MPPT controller that array would probably manage 32 Amps maximum. If the inverter's charger can't be shut off the maximum total current would be 54 Amps which is 27% of the battery capacity (if truly 200 Amp hours). This would only occur during Bulk charging, and only if the array has full sun at that time. Usually it would start out charging in the morning and the batteries would reach Absorb before the panels are capable of their maximum output.

    I'm putting a lot of caveats in this post because I don't know the exact specs of any of the equipment.

    I will say that if this is like other hybrid GT inverters that battery bank at 200 Amp hours total is very small for a 3.5 kW inverter. Doubling the size of the battery bank would solve all the problems at once.

    Thanks for your reply.

    To answer your question, it is a regulated charger , it activates depending on the battery level automaticaly.

    Inverter has a small LCD where it shows me some status on battery level as well as if its charging / charged state.

    I can reduce the charge current of my inverter to 12A, and if i get 30A from solar panels , thats 42A, total ( may happen around noon and only if (the battery not charged and the AC IN is up))

    I dont know the type of my Inverter . This is the from their website/catalog.. they seem to lack most of the important info that you look for anyway

    http://www.su-kam.com/Upload/UploadedCatalogue/1fd75_Fusion_Series_-_brochure-Revised-1.pdf
  • nielniel Solar Shotgun Posts: 10,309Solar Expert ✭✭
    Re: question on inverter/charging setup

    with all due respect marc, i think you made a math error as 2000w of pv at 48v could possibly produce about 42a through an mppt cc.

    you are right to ask us on the concerns of overcharging as that could at the least increase the maintenance to the batteries or at the worst warp a few plates. personally, i think you need more battery capacity as a 3.5kw inverter should at a minimum have 350ah in battery capacity due to ripple voltages that could develop. if you double the battery capacity then you fix both possible problems.

    now i am going on the assumption here that all else is fine with the install. for instance what many persieve to be 24v pvs actually aren't suitable for charging 24v battery banks as the vmp needed is not 24v+, but more like 35v+. this is a problem for a controller that has a limit of 48v as the number of pvs needed for pvs that contain 60 cells to charge up a 48v battery bank would be 3 and would exceed the safe area of your controller.

    maybe to be sure you should list the specs for your cc and your pvs.
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup

    Another question :

    My batteries are like 6 month old, Is it possible to add another set of 4 batteries to this? I was told by someone to not mix old/new batteries,etc.

    Adding 4 more 200 ah batteries would cost me close to 1K$ lol at India. So I would prefer not to..

    But if i did do that, Is it possible for me to go almost off-grid? I am using close to 20-25KWH a day. with more panels sometime in future?
  • CariboocootCariboocoot Gone Fishing... Posts: 17,615Banned
    Re: question on inverter/charging setup

    Looking over the information, this would appear to be a standard UPS unit. It will cut in if AC line Voltage goes too low or too high (a good feature to have in areas where the grid is erratic in function). It does not back-feed the grid.

    The charger is regulated, and only comes on when the batteries fall below a certain (not defined in the info) set point. This should work fine, as the solar would keep the batteries up most all the time and the grid presence would keep them from being drained by supplying the load power. If the grid goes down, it isn't there to power the charger so there's no risk of over-charging.

    The only issue here I can see is possibly getting 32 Amps from the panels, which is a 16% charge rate on the 200 Amp hour batteries. That's a bit high, but they probably will take it for short periods every now and then. If the charge controller is not of the MPPT type you probably won't see even that much current, and you may have a problem with the panel Voltage (250 Watt panels are likely to be 30 Vmp, which means you need at least three in series to provide enough Voltage to charge a 48 Volt battery bank. Four in series would put the V in at 120 and the controller may not be able to handle that or handle it properly).

    I see nothing horribly wrong so far. Do you have the specifications on the panels and charge controller?
  • nielniel Solar Shotgun Posts: 10,309Solar Expert ✭✭
    Re: question on inverter/charging setup

    i don't see a problem with adding the batteries at 6 months if the present ones have not been abused and have been maintained properly.

    no you can't go off grid with that much to be required of it because it is recommended to not exceed 50% dod to preserve battery life. half of a 400ah battery bank is 200ah and at 48v is 48v x 200ah = 9600wh. with a good deal conservation you could make this work for off grid. keep the grid as back up even if you make a go of it off grid as stuff happens.

    i am still concerned of the pv and cc specs to be sure there isn't a problem here.
  • CariboocootCariboocoot Gone Fishing... Posts: 17,615Banned
    Re: question on inverter/charging setup

    Niel;

    I did the standard derating and nominal system Voltage formula: 2000 * 0.77 = 1540 / 48 = 32
    This is usually close enough to max on an MPPT under most circumstances.

    Definitely go for reducing loads as much as possible. That's a strategy that works no matter what the power source.
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    Looking over the information, this would appear to be a standard UPS unit. It will cut in if AC line Voltage goes too low or too high (a good feature to have in areas where the grid is erratic in function). It does not back-feed the grid.

    The charger is regulated, and only comes on when the batteries fall below a certain (not defined in the info) set point. This should work fine, as the solar would keep the batteries up most all the time and the grid presence would keep them from being drained by supplying the load power. If the grid goes down, it isn't there to power the charger so there's no risk of over-charging.

    The only issue here I can see is possibly getting 32 Amps from the panels, which is a 16% charge rate on the 200 Amp hour batteries. That's a bit high, but they probably will take it for short periods every now and then. If the charge controller is not of the MPPT type you probably won't see even that much current, and you may have a problem with the panel Voltage (250 Watt panels are likely to be 30 Vmp, which means you need at least three in series to provide enough Voltage to charge a 48 Volt battery bank. Four in series would put the V in at 120 and the controller may not be able to handle that or handle it properly).

    I see nothing horribly wrong so far. Do you have the specifications on the panels and charge controller?

    Panels are close to this spec. except that it is 250.. values must be pretty close though.
    http://www.suranaventures.com/images/pv-modules/SVL-230.pdf

    I cant the pdf for my exact panel which is 250.


    Charge controller is from a company in China, RemotePower, I literally sat with them in their office before purchasing this at Beijing when i was touring China last month.

    Product manual only says it is 48v/50Amps and it is PWM and not MPPT.

    Is there any other parameter that you would look for ? I can ask the company in an email and My friend works there and I can get answers pretty quickly.
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    Looking over the information, this would appear to be a standard UPS unit. It will cut in if AC line Voltage goes too low or too high (a good feature to have in areas where the grid is erratic in function). It does not back-feed the grid.

    The charger is regulated, and only comes on when the batteries fall below a certain (not defined in the info) set point. This should work fine, as the solar would keep the batteries up most all the time and the grid presence would keep them from being drained by supplying the load power. If the grid goes down, it isn't there to power the charger so there's no risk of over-charging.

    The only issue here I can see is possibly getting 32 Amps from the panels, which is a 16% charge rate on the 200 Amp hour batteries. That's a bit high, but they probably will take it for short periods every now and then. If the charge controller is not of the MPPT type you probably won't see even that much current, and you may have a problem with the panel Voltage (250 Watt panels are likely to be 30 Vmp, which means you need at least three in series to provide enough Voltage to charge a 48 Volt battery bank. Four in series would put the V in at 120 and the controller may not be able to handle that or handle it properly).

    I see nothing horribly wrong so far. Do you have the specifications on the panels and charge controller?

    I was actually planning to have 2 panels in series each to create 48V set and create 4 sets and use parallel connection to add all that and bring it to charge controller..

    Im now worried it may not work?
  • nielniel Solar Shotgun Posts: 10,309Solar Expert ✭✭
    Re: question on inverter/charging setup

    ok. even so the 32a + 12-16a from inv = 44a-48a and is way too much for a 200ah battery bank that is probably undersized for the size of the inv in the first place. ok i'll conceed that requirement as it is a ups inv and they aren't meant to be run all out for short periods of time. overcharging on his batteries can still happen.:roll::p

    the concerns on the solar setup are still real as he indicated he has 8 pvs and if they are 72 cell pvs then i'll agree they are 24v pvs that having 2 in series could charge a 48v battery bank. if the pvs are of the 60 cell variety he'll need 3 in series to get the proper voltage to be high enough and that necessitates an mppt controller that can handle much higher input voltages. he speced 48v for his cc and we don't know if that is input or output. that max input v rating is important and what the cc type is is also important..
  • inetdoginetdog Fizzycist Posts: 3,112Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    niel wrote: »
    with a good deal conservation you could make this work for off grid. keep the grid as back up even if you make a go of it off grid as stuff happens.
    My interpretation of the OP's intention (FWIW) is that he has a grid-driven UPS and is either trying to extend the runtime of the UPS off the batteries during the day or is trying to reduce his power bill as long as he has the panels anyway.
    I think that he would like to keep the grid connection regardless, either for at night or for better charging, and will actually be powering his loads from the grid whenever it is present.
    But we need to see inverter/charger specs and get clarification from the OP in any case.
    SMA SB 3000, old BP panels.
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup

    To make things real clear..

    You are mostly right anyway.

    My state at india has terrible utility power.. sometimes it is off like 14 hours a day and works only for 8-10 hours

    So I am like trying to go off-grid ( as a long term- final goal) but in short term I just need to reduce the power bills..

    They are raising the power costs while providing less and less power lol..

    Most of my usage is during the nights as I work at night online most of the days.. even though I have 3.5 KW inverter, I run it only for like 20-max 30% load So thats prob around 1-1.5 KW I believe.

    I would try to get the specs exactly from the manufacturers and product manuals,etc.

    Regarding the number of cells in PV, I can just count it if it helps!.
  • CariboocootCariboocoot Gone Fishing... Posts: 17,615Banned
    Re: question on inverter/charging setup

    Now you have problems.

    A 250 Watt panel will not have the same electrical specs as a 230 Watt; that 20 more Watts has to come from somewhere, either higher Vmp or higher Imp. Probably a bit of both.

    But in either case these panels with their 30 to 32 Vmp will not work to their best on any battery system because the Vmp is going to be 'wrong'. With a 48 Volt system you want the array Vmp to be around 70. Two of these panels in series would be too low, three would be too high. This is because the PWM type charge controller can not adjust the array Voltage down to a suitable level for charging; it delivers the current, and the power difference between that current at the panels' Vmp and that current at the battery Voltage level is simply lost.

    With eight panels you have only one array configuration that would use all panels and provide enough charging Voltage for a 48 Volt system: two parallel strings of four. You might as well say two parallel strings of three because all the power from those fourth panels will be lost.

    So you get this:

    One string of three panels in series: Vmp 90, Imp 7.6 (power loss approximately 90-70 * Imp or 152 Watts for the string)
    Multiply by two strings and the charging current is now only 2 * 7.6 or 15.2 Amps. A far cry from the 32 you could get with all panels on an MPPT controller.

    You can not use four strings of two in series because the Vmp of the strings would only be 60 or so. Throw in some heat and wiring losses and you no longer have enough Voltage to meet the charging needs of a 48 Volt system (usually Absorb Voltage would be 57.6 to 59.2). This means the batteries might never full charge from solar, resulting in shortened battery life.
  • nielniel Solar Shotgun Posts: 10,309Solar Expert ✭✭
    Re: question on inverter/charging setup

    maybe we should stop our speculation and just wait for him to list out all of the pv and equipment specs and how he proposed to have it all arranged. then we can be more specific on what works or what doesn't work.
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    niel wrote: »
    ok. even so the 32a + 12-16a from inv = 44a-48a and is way too much for a 200ah battery bank that is probably undersized for the size of the inv in the first place. ok i'll conceed that requirement as it is a ups inv and they aren't meant to be run all out for short periods of time. overcharging on his batteries can still happen.:roll::p

    the concerns on the solar setup are still real as he indicated he has 8 pvs and if they are 72 cell pvs then i'll agree they are 24v pvs that having 2 in series could charge a 48v battery bank. if the pvs are of the 60 cell variety he'll need 3 in series to get the proper voltage to be high enough and that necessitates an mppt controller that can handle much higher input voltages. he speced 48v for his cc and we don't know if that is input or output. that max input v rating is important and what the cc type is is also important..

    Please see if this helps !

    I counted the number of cells and they are 60 cell panel :(. Do you think i should buy 1 more panel of same rating and keep 3x3 setup?

    Panels are close to this spec. except that it is 250.. values must be pretty close though.
    http://www.suranaventures.com/images/pv-modules/SVL-230.pdf

    I cant the pdf for my exact panel which is 250.

    Charge controller Product manual only says it is 48v/50Amps and it is PWM and not MPPT.
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    Now you have problems.

    A 250 Watt panel will not have the same electrical specs as a 230 Watt; that 20 more Watts has to come from somewhere, either higher Vmp or higher Imp. Probably a bit of both.

    But in either case these panels with their 30 to 32 Vmp will not work to their best on any battery system because the Vmp is going to be 'wrong'. With a 48 Volt system you want the array Vmp to be around 70. Two of these panels in series would be too low, three would be too high. This is because the PWM type charge controller can not adjust the array Voltage down to a suitable level for charging; it delivers the current, and the power difference between that current at the panels' Vmp and that current at the battery Voltage level is simply lost.

    With eight panels you have only one array configuration that would use all panels and provide enough charging Voltage for a 48 Volt system: two parallel strings of four. You might as well say two parallel strings of three because all the power from those fourth panels will be lost.

    So you get this:

    One string of three panels in series: Vmp 90, Imp 7.6 (power loss approximately 90-70 * Imp or 152 Watts for the string)
    Multiply by two strings and the charging current is now only 2 * 7.6 or 15.2 Amps. A far cry from the 32 you could get with all panels on an MPPT controller.

    You can not use four strings of two in series because the Vmp of the strings would only be 60 or so. Throw in some heat and wiring losses and you no longer have enough Voltage to meet the charging needs of a 48 Volt system (usually Absorb Voltage would be 57.6 to 59.2). This means the batteries might never full charge from solar, resulting in shortened battery life.

    Hey,

    THank you for the suggestions,

    Bad thing is I bought this controller already, Good thing is I can still easily give my controller to my friend or use it on some other setup and buy another MPPT controller for my use.

    Panels I think i am stuck on them , I cannot easily replace them . So we need to work around this by compensating somewhere. may be add panels,etc and change controller or do something like that.

    I will get the exact VMP/IMP at morning Indian time.. it is like 3AM so I couldnt call anyone right away.


    I really appreciate the help you two mods been giving me, I would someday hope to contribute to others like this here.

    Im sorry I dont know your name :)
  • BB.BB. Just some guy Posts: 24,218Super Moderators admin
    Re: question on inverter/charging setup

    Cariboocoot has told me his name is "Marc"--I presume it is. :p

    Anyway... Back to your needs. The problem is your need >70 Volts Vmp for a typical 48 volts battery bank, particularly in hot weather (Vmp falls with increasing temperatures).

    A "standard" 12 volt panel would have Vmp around 17.5 to 18.6 volts or so--Or ~36 cells in series... For your panel that would be ~72 cells in series for a "24 volt" battery bank.

    You could use 3 panels in series for Vmp~90 volts. But efficiency wise, you would be looking at:

    ~70 volts/90 volts = 0.78 = 78% of array capacity...

    You would have to figure out if using an MPPT controller is worth recovering that lost ~23% output (or a bit more). And the fact you have 8 panels and not 9 panels.

    Issue with 4 panels in series, Vmp~120 volts can mean that Voc-cold could exceed 140 to 150 volts maximum input for the "typical" higher end MPPT charge controller.

    There are a few MPPT controllers that can do higher voltage (Midnite Solar has some)--But it may be a very costly buy for you (including shipping/taxes/customs/etc.) and 1/2 a world away for customer support.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    BB. wrote: »
    Cariboocoot has told me his name is "Marc"--I presume it is. :p

    Anyway... Back to your needs. The problem is your need >70 Volts Vmp for a typical 48 volts battery bank, particularly in hot weather (Vmp falls with increasing temperatures).

    A "standard" 12 volt panel would have Vmp around 17.5 to 18.6 volts or so--Or ~36 cells in series... For your panel that would be ~72 cells in series for a "24 volt" battery bank.

    You could use 3 panels in series for Vmp~90 volts. But efficiency wise, you would be looking at:

    ~70 volts/90 volts = 0.78 = 78% of array capacity...

    You would have to figure out if using an MPPT controller is worth recovering that lost ~23% output (or a bit more). And the fact you have 8 panels and not 9 panels.

    Issue with 4 panels in series, Vmp~120 volts can mean that Voc-cold could exceed 140 to 150 volts maximum input for the "typical" higher end MPPT charge controller.

    There are a few MPPT controllers that can do higher voltage (Midnite Solar has some)--But it may be a very costly buy for you (including shipping/taxes/customs/etc.) and 1/2 a world away for customer support.

    -Bill

    Lets assume I buy one more Panel and have 3 in series and then use parallel connection to connect them all to charge controller..

    All I would lose is the 23% efficiency? , I m assuming my panels would already under perform that much lol as they are cheap!.
  • CariboocootCariboocoot Gone Fishing... Posts: 17,615Banned
    Re: question on inverter/charging setup

    So a 60 cell panel, about 0.5 Volts per cell, is around 30 Vmp like I said. 250 Watts / 30 Volts = 8.3 Amps.

    Best situation here would be using an MPPT type controller. Two parallel strings of four in series = 120 Vmp & 16.6 Imp for the array. Voc would be very near 150 Volts, could even go over by a couple of Volts. Cold temperatures are probably not an issue in India, but it's already pretty close to the edge.

    Could you get one more of these panels and make an array of three parallel strings of three in series?
    That would be 90 Vmp & 24.9 Imp with a Voc around 114. Total 2250 Watts, with a peak output current of about 36 Amps. That would work on Morningstars 45 Amp TriStar MPPT. That's about $100 cheaper than MidNite's Classic Lite 200.
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    So a 60 cell panel, about 0.5 Volts per cell, is around 30 Vmp like I said. 250 Watts / 30 Volts = 8.3 Amps.

    Best situation here would be using an MPPT type controller. Two parallel strings of four in series = 120 Vmp & 16.6 Imp for the array. Voc would be very near 150 Volts, could even go over by a couple of Volts. Cold temperatures are probably not an issue in India, but it's already pretty close to the edge.

    Could you get one more of these panels and make an array of three parallel strings of three in series?
    That would be 90 Vmp & 24.9 Imp with a Voc around 114. Total 2250 Watts, with a peak output current of about 36 Amps. That would work on Morningstars 45 Amp TriStar MPPT. That's about $100 cheaper than MidNite's Classic Lite 200.

    Getting one more panel is very easy, I will do it tomorrow and

    I guess I can replace / buy another MPPT controller bit more cheaply with the same company by telling them I need something that works with

    90 VMP/24 IMP and 114 VOC.
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    So a 60 cell panel, about 0.5 Volts per cell, is around 30 Vmp like I said. 250 Watts / 30 Volts = 8.3 Amps.

    Best situation here would be using an MPPT type controller. Two parallel strings of four in series = 120 Vmp & 16.6 Imp for the array. Voc would be very near 150 Volts, could even go over by a couple of Volts. Cold temperatures are probably not an issue in India, but it's already pretty close to the edge.

    Could you get one more of these panels and make an array of three parallel strings of three in series?
    That would be 90 Vmp & 24.9 Imp with a Voc around 114. Total 2250 Watts, with a peak output current of about 36 Amps. That would work on Morningstars 45 Amp TriStar MPPT. That's about $100 cheaper than MidNite's Classic Lite 200.

    Thank you Marc, Bill .

    I am talking with my vendors to buy one more Panel as well as thinking ifs financially making sense to add more batteries to my setup.

    One question regarding having 9 panels on 3*3 and using the same controller in-case it can take 60 VMP input? even if it means I am losing the 23% of panel power?

    I am sure the company I bought this controller from said it can take upto 60V maximum and can charge my batteries.
  • CariboocootCariboocoot Gone Fishing... Posts: 17,615Banned
    Re: question on inverter/charging setup

    The problem is that 60 Volts at the panels isn't really enough to charge a 48 Volt battery bank. There is always some Voltage drop in the wiring, and a further reduction from the panels being hot. So even if you fed two panels in series for 60 Vmp into the charge controller what comes out at the battery may be only 54 Volts, say, and not enough to bring the batteries up full.

    Once you put that third panel in series you have 90 Vmp from the array. With an MPPT type controller, there's no problem. With a PWM type, if it can take the high Voltage input the over-all power loss is approximately the difference between the array Vmp of 90 and the battery charging Voltage times the Imp of the array. So with three parallel strings of three the difference between the MPPT controller and the PWM controller is one of about 1732 Watts vs. 1494 Watts for the same nine panel array. 238 Watts, almost one whole panel's worth, disappears due to the Voltage difference. (As always: rough calculations to explain the process, not exact figures of what you will definitely experience.)
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    You can not use four strings of two in series because the Vmp of the strings would only be 60 or so. Throw in some heat and wiring losses and you no longer have enough Voltage to meet the charging needs of a 48 Volt system (usually Absorb Voltage would be 57.6 to 59.2). This means the batteries might never full charge from solar, resulting in shortened battery life.

    Sorry If i sound noob here, but wouldn't my inverter's charging component take care of the final stage charging ?
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    The problem is that 60 Volts at the panels isn't really enough to charge a 48 Volt battery bank. There is always some Voltage drop in the wiring, and a further reduction from the panels being hot. So even if you fed two panels in series for 60 Vmp into the charge controller what comes out at the battery may be only 54 Volts, say, and not enough to bring the batteries up full.

    Once you put that third panel in series you have 90 Vmp from the array. With an MPPT type controller, there's no problem. With a PWM type, if it can take the high Voltage input the over-all power loss is approximately the difference between the array Vmp of 90 and the battery charging Voltage times the Imp of the array. So with three parallel strings of three the difference between the MPPT controller and the PWM controller is one of about 1732 Watts vs. 1494 Watts for the same nine panel array. 238 Watts, almost one whole panel's worth, disappears due to the Voltage difference. (As always: rough calculations to explain the process, not exact figures of what you will definitely experience.)

    Marc, Thanks for the explanation , thats super helpful.

    Only last question in my mind is regarding the voltage not being enough to charge the batteries is , Can my inverter's charging facility (16 A/12 A) can do the last part?

    Sorry to repeat, I think i just asked this by quoting your earlier message anyeay.
  • CariboocootCariboocoot Gone Fishing... Posts: 17,615Banned
    Re: question on inverter/charging setup
    paimpozhil wrote: »
    Sorry If i sound noob here, but wouldn't my inverter's charging component take care of the final stage charging ?

    Yes, it presumably could.
    But would you want it to? Using an unreliable and expensive grid power source to supply that last little bit of power may not be the best plan. It's a bit like the problem with using generators off grid: they are much more efficient at doing the Bulk charging which takes the most current in the least time than doing the Absorb charging which takes the least current in the most time.

    And if you do want to go off-grid completely (or just using the grid as your "back-up generator") you want to plan on the solar providing your needs. You could muddle through as-is with two panels in series and let the grid finish and then re-wire later with a new controller to get the array to do it all.

    But that begs the question of if the built-in charger will take over on a "partial charge" or if it needs the batteries to be brought down low before it will activate.
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    Yes, it presumably could.
    But would you want it to? Using an unreliable and expensive grid power source to supply that last little bit of power may not be the best plan. It's a bit like the problem with using generators off grid: they are much more efficient at doing the Bulk charging which takes the most current in the least time than doing the Absorb charging which takes the least current in the most time.

    And if you do want to go off-grid completely (or just using the grid as your "back-up generator") you want to plan on the solar providing your needs. You could muddle through as-is with two panels in series and let the grid finish and then re-wire later with a new controller to get the array to do it all.

    But that begs the question of if the built-in charger will take over on a "partial charge" or if it needs the batteries to be brought down low before it will activate.

    I can ask my provider if my charger will take over the partial charge but i am like 99% sure it will.. but since I have used different configurations of inverters of this same company before, I have seen it take over partially or almost full battery and charge them to bring it to 100%.

    I think I would probably let it charge my last 10% of battery for sometime before I get more money to like buy more panels/ MPPT charge controller

    Actually power costs in India is not really expensive compared to western countries..1 KWH is approx 13 cents! not sure how it compares., but it was like half this price sometime ago depending on the slab you are in... like you pay very less for first 100 KWH,etc

    Reason Im going to Solar is due to the Frequent power cuts like upto 16hours/ day k.


    It is my fault to buy the panels/controllers before I get the full picture , and going on to purchase with like only theoretical knowledge and yeah there was an offer on the panels so I was quick to grab it.

    Reason for doing that was because the Solar providers available here were like extremely pricey(4K$/ 1000w and some even quoted 6k$ per 1000W) and I had no choice but to do it all myself even if it means paying the price to learn.

    I have probably learnt more here in this thread about reading the solar specs/ and comparing efficiency of PWM/MPPT than in all of my last 6 months at websites,etc

    I cannot thank you enough!.
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    paimpozhil wrote: »
    I can ask my provider if my charger will take over the partial charge but i am like 99% sure it will.. but since I have used different configurations of inverters of this same company before, I have seen it take over partially or almost full battery and charge them to bring it to 100%.

    I think I would probably let it charge my last 10% of battery for sometime before I get more money to like buy more panels/ MPPT charge controller

    Actually power costs in India is not really expensive compared to western countries..1 KWH is approx 13 cents! not sure how it compares., but it was like half this price sometime ago depending on the slab you are in... like you pay very less for first 100 KWH,etc

    Reason Im going to Solar is due to the Frequent power cuts like upto 16hours/ day k.


    It is my fault to buy the panels/controllers before I get the full picture , and going on to purchase with like only theoretical knowledge and yeah there was an offer on the panels so I was quick to grab it.

    Reason for doing that was because the Solar providers available here were like extremely pricey(4K$/ 1000w and some even quoted 6k$ per 1000W) and I had no choice but to do it all myself even if it means paying the price to learn.

    I have probably learnt more here in this thread about reading the solar specs/ and comparing efficiency of PWM/MPPT than in all of my last 6 months at websites,etc

    I cannot thank you enough!.

    Hi Marc,

    My vendor for Charge controller tells me he can provide me an 45A/ 48V out, 150 VDC charge controller for just 210 USD.

    Whats the difference between going with some known big brands like Tristar and the ones that are from China / relatively unknown?

    This vendor, I have personally met them and have even visited their factory while I was at china ., They seem to be doing tons of testing,etc before delivering the products.

    Would you go with them or would you like go with the popular ones and play safe?
  • CariboocootCariboocoot Gone Fishing... Posts: 17,615Banned
    Re: question on inverter/charging setup

    Two things I can think of: quality and function.
    We do see some "no name" controllers that say "MPPT" which in no way are. Mostly we see "bargain" equipment that either quits working very soon or doesn't work at all. (That's not necessarily limited to "unknown" brands as a certain BZ controller is an infamous turkey.)
    You need to check all the function of the controller as well. Some BlueSky controllers, for example, have odd limitations regarding input/output Voltage and their effect on current. Some may not have adjustable output settings or limited choices so you are stuck with an Absorb Voltage that is too low for the batteries or has a fixed time limit. It may not do an Equalization cycle, or may do one automatically according to its criteria rather than yours.

    There is always going to be some trade-off between price and practice. If you trust the manufacturer to make a good quality product and stand behind it that is key. Then just be sure it can do what it needs to do.

    If you look at Morningstar's whole line you'll see what I mean: they have very inexpensive PWM controllers which have limitations in their function and they have more expensive PWM controllers that can be connected to and programmed with a computer and they have about the smallest MPPT controller you can find @ 15 Amps output (input Voltage limit of 70) and the 60 Amp TriStar MPPT which has all the bells and whistles, although the meter is still optional! I'm not trying to promote Morningstar here; merely citing one company's many products as an example of what function difference you'll find in controllers, regardless of who makes it.
  • BB.BB. Just some guy Posts: 24,218Super Moderators admin
    Re: question on inverter/charging setup

    In the end--The Chinese mfg. is actually closer, more accessible (to you), and can get a product at a good price into your home. It would be difficult to tell you that spending 3x (or more) will give you a better deal for your money--Especially since none of us here know anything about the controller you are looking at.

    In the end, the health of your battery bank is what is important. Which ever controller you choose, monitor the battery voltage, charging current, and specific gravity closely. If anything does not look right, you can debug the system and figure out what needs to happen (adjust the controller, replace with a different unit, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NilaNila New User Posts: 106Solar Expert ✭✭✭
    Re: question on inverter/charging setup
    BB. wrote: »
    In the end--The Chinese mfg. is actually closer, more accessible (to you), and can get a product at a good price into your home. It would be difficult to tell you that spending 3x (or more) will give you a better deal for your money--Especially since none of us here know anything about the controller you are looking at.

    In the end, the health of your battery bank is what is important. Which ever controller you choose, monitor the battery voltage, charging current, and specific gravity closely. If anything does not look right, you can debug the system and figure out what needs to happen (adjust the controller, replace with a different unit, etc.).

    -Bill

    Bill, thank you for the advice .

    I guess I would like start with the PWM even though it is inefficient to start using this immediately after mounting panels.. then read out all the voltage/amperes,etc and see how much I lose with this controller on a 2 in series , 4 in parallel setup.

    then see if it makes sense to buy a MPPT or just add more panels to compensate .

    Also Is it possible to mix /match some lower watts panels to add up the VMP across the series so they go upto 70 or 75 instead of the 60 as of now?
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