how many amps can mc4 wires handle in parallel?

cupcakecupcake Solar Expert Posts: 254 ✭✭✭
Hi pals,

My system is 12volt... with two 280watt panels wired in parallel...

My question:

How many more of these 280watt panels can I connect in parallel before I exeede the amperage rating on the 2 mc4 leads terminating at the 60amp controller?

I'm using 'standard' mc4 wire (600v)

Thanks guys..

--cake
~1.5Kw PV in parallel
Morningstar MPPT-60 controllers (2) in parallel
3 Trojan tr-1275's in parallel 450ah total
Samlex 2,000 watt 12-volt inverter hardwired


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Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how many amps can mc4 wires handle in parallel?

    Couple of things.

    First, your 280 Watt panels are unlikely to be 12 Volt. Probably they have a Vmp of around 30 and an Imp of about 9.

    Second, MC4 is a connector type. The wire it is normally found on is typically 10 AWG which is good for 30 Amps continuous in most applications.

    If you are paralleling more than two panels they need to have some form of over-current protection on each panel, i.e. fuse or breaker. This usually means using a combiner box, with a down-link to the charge controller of wire sufficient to handle the combined current and prevent serious Voltage drop over the distance involved.

    Your 60 Amp rating on the charge controller is for its output, not input. If it is of the MPPT type (which it should be with the probably panel specs) it will have an input Voltage rating which is the maximum Voc of the array allowable. That is key to configuring the array to optimum advantage, although with a 12 Volt system you probably do not want to go with panels in series as upping the array Vmp more will decrease the efficiency of the controller.

    It's the details that get you. :D
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    Couple of things.

    First, your 280 Watt panels are unlikely to be 12 Volt. Probably they have a Vmp of around 30 and an Imp of about 9.

    Second, MC4 is a connector type. The wire it is normally found on is typically 10 AWG which is good for 30 Amps continuous in most applications.

    If you are paralleling more than two panels they need to have some form of over-current protection on each panel, i.e. fuse or breaker. This usually means using a combiner box, with a down-link to the charge controller of wire sufficient to handle the combined current and prevent serious Voltage drop over the distance involved.

    Your 60 Amp rating on the charge controller is for its output, not input. If it is of the MPPT type (which it should be with the probably panel specs) it will have an input Voltage rating which is the maximum Voc of the array allowable. That is key to configuring the array to optimum advantage, although with a 12 Volt system you probably do not want to go with panels in series as upping the array Vmp more will decrease the efficiency of the controller.

    It's the details that get you. :D




    OK, so the 2 final 10AWG leads are good for 30amps continuous. THANKS.

    SO - my next question is how many more 280w panels can I wire in parallel here before burning up the 30amp wires (theoretically, I will have a fuse installed to prevent actual burn up)?

    Im n00b here, so I appreciate you bearing with me through this... 30amps X 12 volts = 360 watts, does this mean the MAXIMUM I can pull from the panels using that 10AWG wire is 360 watts? Or am I missing something?

    Basically I want to add on some more panels eventually, and just make some parallel MC4 *connections on the roof which all feed into the 2 10AWG wires going to the controller...

    but if I turn on something that say runs at 500 watts AC I dont want to fry the wires - or say I add a few more batteries to the bank - that will draw more DC current from the panels to charge them right, meaning more amps through the wires...

    so anyway, bringing it back to my question: I got two 280w panels hooke up in parallel, 10AWG wire to the controller - how many more 280w panels can I connect in parallel before I reach the amperage threshold of the 10AWG wires going to the controller???


    Thanks for your help...

    --cuppy
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how many amps can mc4 wires handle in parallel?

    Panels are a current source and will have two current ratings: Imp (current at maximum power) and Isc (current into a dead short). You need those numbers to know how many of any type of panel you can feed into a given wire gauge.

    With the estimated 9 Imp the most 10 AWG should have would be three in parallel: 27 Amps. It is unlikely you would see the maximum current for long and you would not see the Isc in a normal circuit and wire can take momentary current above its continuous rating. The regulations actually base sizing on the Isc, figuring worst-case scenario of a short at the other end and wanting the wire to resist overheating before the circuit protection trips.

    A the point of three panels in parallel each one would have a fuse or breaker on it before their output is combined. This is to prevent a shorted panel from being back-fed the combined Isc of the other two panels and starting a fire (the fuse will blow before the panel overheats).

    Do not worry about panel over current from loads as it isn't possible; panels can not produce greater than their Isc (except in rare high-insolation circumstances). A load such as an A/C would be powered through the inverter from the battery; the panels recharge and try to keep charged the battery. Any current they supply to loads directly (opportunity loads) will be limited to their maximum output, the difference made up by the battery. You can not damage a panel by plugging a heavy load into you inverter.

    With an eye towards expansion you should wire for that now. So if you want to have four panels in future, put in the combiner box with circuit protection for all of them and the right size wire to the controller to handle the full current. That way when you get more panel you just plug it in to the combiner and 'switch it on'.

    When using an MPPT controller it is possible to put the panels in series which increases the Voltage (and power) without increasing the current.

    A bit about panel configuration which may help: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller

    The amount of panel should be sized to recharge the batteries you have. If you add more battery capacity you need to add more panel as well.
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    Panels are a current source and will have two current ratings: Imp (current at maximum power) and Isc (current into a dead short). You need those numbers to know how many of any type of panel you can feed into a given wire gauge.

    With the estimated 9 Imp the most 10 AWG should have would be three in parallel: 27 Amps. It is unlikely you would see the maximum current for long and you would not see the Isc in a normal circuit and wire can take momentary current above its continuous rating. The regulations actually base sizing on the Isc, figuring worst-case scenario of a short at the other end and wanting the wire to resist overheating before the circuit protection trips.

    A the point of three panels in parallel each one would have a fuse or breaker on it before their output is combined. This is to prevent a shorted panel from being back-fed the combined Isc of the other two panels and starting a fire (the fuse will blow before the panel overheats).

    Do not worry about panel over current from loads as it isn't possible; panels can not produce greater than their Isc (except in rare high-insolation circumstances). A load such as an A/C would be powered through the inverter from the battery; the panels recharge and try to keep charged the battery. Any current they supply to loads directly (opportunity loads) will be limited to their maximum output, the difference made up by the battery. You can not damage a panel by plugging a heavy load into you inverter.

    With an eye towards expansion you should wire for that now. So if you want to have four panels in future, put in the combiner box with circuit protection for all of them and the right size wire to the controller to handle the full current. That way when you get more panel you just plug it in to the combiner and 'switch it on'.

    When using an MPPT controller it is possible to put the panels in series which increases the Voltage (and power) without increasing the current.

    A bit about panel configuration which may help: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller

    The amount of panel should be sized to recharge the batteries you have. If you add more battery capacity you need to add more panel as well.



    Thank for your response...
    ...I appreciate every word if wisdom...

    Quick quesion:

    How did you estimate my panels to be rated at 9 Imp??

    The spex on my panels are 36.4 watts...

    Does this mean my imp is 7.7 amps? (Ie 36.4 x 7.7=280 watts)

    So 7.7 imp x 3 panels = 23.1 amps which keeps me safe using 10awg conductors rated for 30amps?

    Do I have this correct? Or am I still speaking monkey?

    --cakey
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: how many amps can mc4 wires handle in parallel?

    you speak Monkey, please review what you have posted as 'spex'

    one of those numbers has to be volts...Volts times Amps = Watts
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
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    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
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  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how many amps can mc4 wires handle in parallel?

    cakey;

    Your first post says two 280 Watt panels.
    These days a 280 Watt panel is likely "GT" style, meaning it will have a Vmp (Voltage at maximum power) around 30. It would not be unusual for said panel to have a Voc (Voltage open circuit) near 36.
    Panel Wattage ratings are based on Vmp * Imp (current at maximum power). As such if you divide 280 Watts by a probable 30 Volts you get about 9.3 Amps for Imp.
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    cakey;

    Your first post says two 280 Watt panels.
    These days a 280 Watt panel is likely "GT" style, meaning it will have a Vmp (Voltage at maximum power) around 30. It would not be unusual for said panel to have a Voc (Voltage open circuit) near 36.
    Panel Wattage ratings are based on Vmp * Imp (current at maximum power). As such if you divide 280 Watts by a probable 30 Volts you get about 9.3 Amps for Imp.



    Thank you for noting my error...

    My panels are 36.4 volts not watts
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    cakey;

    Your first post says two 280 Watt panels.
    These days a 280 Watt panel is likely "GT" style, meaning it will have a Vmp (Voltage at maximum power) around 30. It would not be unusual for said panel to have a Voc (Voltage open circuit) near 36.
    Panel Wattage ratings are based on Vmp * Imp (current at maximum power). As such if you divide 280 Watts by a probable 30 Volts you get about 9.3 Amps for Imp.



    Thank you caribucoiti...

    Undrestood. I appreciate your help...

    ..on topic..I must ask you how one fits wire larger than 10awg within/on mc4 connectors...

    Can you explain or point me to a link...

    Thanxxx

    --Caxe
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how many amps can mc4 wires handle in parallel?
    cupcake wrote: »
    Thank you caribucoiti...

    Undrestood. I appreciate your help...

    ..on topic..I must ask you how one fits wire larger than 10awg within/on mc4 connectors...

    Can you explain or point me to a link...

    Thanxxx

    --Caxe

    Quite simply, you don't.
    If you have several panels connected in parallel at a combiner box that device will use ordinary screw terminals to connect to larger wire to make the down-link. Here is an example of a combiner box: http://www.solar-electric.com/misomnsoarco4.html
    Note the MC4 connectors for the panels are built-in, as are the fuse holders and bus bars. These can take up to 1/0 AWG wire for the down-link.
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    Quite simply, you don't.
    If you have several panels connected in parallel at a combiner box that device will use ordinary screw terminals to connect to larger wire to make the down-link. Here is an example of a combiner box: http://www.solar-electric.com/misomnsoarco4.html
    Note the MC4 connectors for the panels are built-in, as are the fuse holders and bus bars. These can take up to 1/0 AWG wire for the down-link.



    Sweet! So basically when I add more panels I need to get the 4 string combiner..hook it in parallel and I'll have two fat wires coming out of it and going to the controller....

    Super. It looks like you answered my question 100%!

    Thank you again!!!
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?

    Cariboocoot,

    The combiner box let's me parallel 4 panels.

    What if I eventually want to get to say 8 panels... then what?

    What's your practical suggestion for that? 2 combiner boxes combined together??

    Or something else??

    --cupz
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: how many amps can mc4 wires handle in parallel?

    What type of charge controller do you have?

    If you have an MPPT charge controller with an input rating over 100 V, you might be able to connect some of the PV panels in series to get a higher voltage instead of a higher current.
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    Quite simply, you don't.
    If you have several panels connected in parallel at a combiner box that device will use ordinary screw terminals to connect to larger wire to make the down-link. Here is an example of a combiner box: http://www.solar-electric.com/misomnsoarco4.html
    Note the MC4 connectors for the panels are built-in, as are the fuse holders and bus bars. These can take up to 1/0 AWG wire for the down-link.

    You can special order that item with Circuit Breakers, rather than fuses. Much better system. The circuit breakers can be used as switches. The fuses, on the other hand, can be dangerous... if you try to remove a fuse while current is flowing you will start a fire and burn yourself.

    Bonus: the circuit breakers take up less space than the fuses... that combiner can combine 6 strings with breakers, but only 4 strings with fuses.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how many amps can mc4 wires handle in parallel?
    cupcake wrote: »
    Cariboocoot,

    The combiner box let's me parallel 4 panels.

    What if I eventually want to get to say 8 panels... then what?

    What's your practical suggestion for that? 2 combiner boxes combined together??

    Or something else??

    --cupz

    Plan ahead: get the combiner box that will handle the full number of panels you intend to have and wire it for that maximum now. MidNite makes boxes that will take up to 16 panels or strings of panels.
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    What type of charge controller do you have?

    If you have an MPPT charge controller with an input rating over 100 V, you might be able to connect some of the PV panels in series to get a higher voltage instead of a higher current.


    I have morningstar tristar 60 mppt controller
    And morninstar suresine inverter
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: how many amps can mc4 wires handle in parallel?

    Electrical specifications of Morningstar TriStar TS-MPPT-60
    • Maximum Battery Current 60 amps
    • Nominal Maximum Solar Input
    12 Volt: 800 Watts
    24 Volt: 1600 Watts
    48 Volt: 3200 Watts
    • Peak Efficiency 99%
    • Nominal System Voltage: 12, 24, 36 or 48 volts DC
    • Max. Solar Open Circuit Voltage: 150 volts DC
    • Battery Operating Voltage Range: 8-72 volts DC
    • Maximum Self-consumption: 2.7 Watts
    • Transient Surge Protection: 4500 Watts/port
    My system is 12volt... with two 280watt panels wired in parallel...
    With a 12 V battery array, three 280 W PV panels in parallel would push your charge controller to the maximum. Because 280 W PV panels probably have a current at maximum power point around 9 A, a short circuit current above 10 A and MC4 cables are 10 gauge copper with a maximum rating of 30 A, the wiring can handle 2 in parallel. Depending on the exact specifications, you might be able to add a 240 W PV panel in parallel with the two existing 280 W ones but the voltage drop in the wiring might become unacceptably high.

    Another possibility is to add PV panels that point in different directions so they do not output their maximum power at the same time. For example, point two 280 W PV panels with a southeast azimuth and another two with a southwest azimuth, both at 45 degree elevation and all connected in parallel. This would allow 4 PV panels with the power output staying under the 800 W nominal maximum solar input and keep the current in a 10 gauge copper wire below 30 A.

    Another possibility is to change the voltage of your battery array to 24 V which would increase the maximum PV array size to 1,600 W, but this would require you to get a 24 V inverter. You would need to connect two or 3 panels in series to create 2 series strings allowing you to add up to six 280 W PV panels.
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    Electrical specifications of Morningstar TriStar TS-MPPT-60
    • Maximum Battery Current 60 amps
    • Nominal Maximum Solar Input
    12 Volt: 800 Watts
    24 Volt: 1600 Watts
    48 Volt: 3200 Watts
    • Peak Efficiency 99%
    • Nominal System Voltage: 12, 24, 36 or 48 volts DC
    • Max. Solar Open Circuit Voltage: 150 volts DC
    • Battery Operating Voltage Range: 8-72 volts DC
    • Maximum Self-consumption: 2.7 Watts
    • Transient Surge Protection: 4500 Watts/port


    With a 12 V battery array, three 280 W PV panels in parallel would push your charge controller to the maximum. Because 280 W PV panels probably have a current at maximum power point around 9 A, a short circuit current above 10 A and MC4 cables are 10 gauge copper with a maximum rating of 30 A, the wiring can handle 2 in parallel. Depending on the exact specifications, you might be able to add a 240 W PV panel in parallel with the two existing 280 W ones but the voltage drop in the wiring might become unacceptably high.

    Another possibility is to add PV panels that point in different directions so they do not output their maximum power at the same time. For example, point two 280 W PV panels with a southeast azimuth and another two with a southwest azimuth, both at 45 degree elevation and all connected in parallel. This would allow 4 PV panels with the power output staying under the 800 W nominal maximum solar input and keep the current in a 10 gauge copper wire below 30 A.

    Another possibility is to change the voltage of your battery array to 24 V which would increase the maximum PV array size to 1,600 W, but this would require you to get a 24 V inverter. You would need to connect two or 3 panels in series to create 2 series strings allowing you to add up to six 280 W PV panels.




    Sweet. Thanxxx for your passionate response...


    ...however isint the consensus that I can do 3 280w
    panels wired in parallel??

    Each panels imp is 9amps

    9*3=27

    3 amps clear of the 30 amp 10awg limit...


    Correct or incorrect?


    Thanxxxx

    -- delicious cake
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how many amps can mc4 wires handle in parallel?

    Yes you could use three 280 Watt panels in parallel on 10 AWG. Check the panel specs to be absolutely sure.
  • ChrisChris Solar Expert Posts: 135 ✭✭
    Re: how many amps can mc4 wires handle in parallel?

    Just a question that nobody has mentioned on this thread.......would the amount of amps acceptable on a 10 awg wire not depend on the length of it?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how many amps can mc4 wires handle in parallel?
    Chris wrote: »
    Just a question that nobody has mentioned on this thread.......would the amount of amps acceptable on a 10 awg wire not depend on the length of it?

    Nope.
    Current carrying ability is not affected by wire length.
    Voltage drop, on the other hand, most definitely is and is also affected by the amount of current.

    So any length of 10 AWG will handle 30 Amps continuous, but the longer the wire length the greater the Voltage drop at any given current.

    Keep in mind that this V-drop can be acceptable even if over the 'desired maximum 3%' we usually plan for, so long as that is taken into account. Also this is solar so the panels will not put out their maximum current for the whole time of 'good sun'.
  • SolInvictusSolInvictus Solar Expert Posts: 138
    Re: how many amps can mc4 wires handle in parallel?
    cupcake wrote: »
    ...however isint the consensus that I can do 3 280w panels wired in parallel??

    Each panels imp is 9amps

    9*3=27

    3 amps clear of the 30 amp 10awg limit...

    Correct or incorrect?
    If the short circuit current is less than 10 A, then correct.

    If the short circuit current is greater than 10 A, then incorrect.
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?

    OK - I got:

    2 X 280 watt panels (7.82A Impp, 8.43A Isc, 35.8volts)

    And I have the MorningStar Tristar TS-MPPT-60 Charge controller


    My question, it says the maximum nominal solar input of the controller is 800watts at 12 volts (my battery bank and inverter are 12v)

    Does this mean the Morningstar TS-MPPT-60 can only handle 800watts of solar panels on a 12 volt system???

    Im basically looking to add on ONE more 280w panel for a total of 3 panels without getting a new controller...

    Thanks again



    --Cupakes
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how many amps can mc4 wires handle in parallel?

    It's a 60 Amp controller. What it can handle is however much it takes to produce 60 Amps output. Any power above that will be 'clipped' (lost). A lot of power above that is a waste of money.

    Using the standard formula we get: 60 Amps * 12 Volts minimal / 0.77 typical derating = 935 Watts being the probably maximum. Three 280 Watt panels is 840 Watts and should not be any problem for it.
  • PhotowhitPhotowhit Solar Expert Posts: 5,650 ✭✭✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    cupcake wrote: »
    OK, so the 2 final 10AWG leads are good for 30amps continuous. THANKS.

    SO - my next question is how many more 280w panels can I wire in parallel here before burning up the 30amp wires (theoretically, I will have a fuse installed to prevent actual burn up)?
    Wiring (and fuses or breakers) are sized for the amperage potential. Often we will use a wire size based on the voltage drop over the length of the run, but for the most part you want to size the wiring for the amperage potential...
    cupcake wrote: »
    Im n00b here, so I appreciate you bearing with me through this... 30amps X 12 volts = 360 watts, does this mean the MAXIMUM I can pull from the panels using that 10AWG wire is 360 watts? Or am I missing something?
    Watts is a measure of power, and you basically understand the amps x volts = watts, but as 'Coot said your panels are likely higher voltage and lower amperage than your 'nominal system voltage' of 12 volts.
    What happens (we hope) is that you have 2 panels producing something like 35 volts VMP (voltage under load) and @8 amps this currently directly feeds into your charge controller. We hope this is a MPPT type (Multi Power Point Tracking) which will convert the wattage at 35 volts to the voltage your battery needs to properly charge, and creating more amps at the voltage preserving the wattage.
    cupcake wrote: »
    Basically I want to add on some more panels eventually, and just make some parallel MC4 *connections on the roof which all feed into the 2 10AWG wires going to the controller...
    When you have more than 2(sometimes 3) panels in parallel, you must use a combiner box to insure that the potential back feeding of the combined panel output won't back feed one panel and create a fire risk. This combiner box will be a junction for the panels output with fuses or breakers for each panel, to prevent this back feeding.

    Depending on your charge controller and suitability of your panel additions, you may be able to place the panels in series with the 2 you currently have up. Panels in series add voltage, not amperage, so adding 2 panels with very similar characteristics/Spec's to the ones you currently have may be possible without adding a combiner box, since the 2 'string' would not have greater amperage than the panels you currently have up, but would double the voltage. A MPPT type charge controller will do the reducing to properly charge your battery. MPPT type charge controllers are most efficient at roughly 2x the system voltage. While designed to handle the higher voltage, it is likely that higher voltage conversion rate will also shorten the life of you charge controller.
    cupcake wrote: »
    ...but if I turn on something that say runs at 500 watts AC I dont want to fry the wires - or say I add a few more batteries to the bank - that will draw more DC current from the panels to charge them right, meaning more amps through the wires...
    Mostly wrong... Your solar panels will deliver what current they can, if needed, regardless of loads, If you have more batteries, your charge controller will handle the charging based on what it 'sees' in system voltage.

    It is not good to mix battery types or ages, If your batteries are more than a year old I would not add new batteries to them in most situations.
    cupcake wrote: »
    so anyway, bringing it back to my question: I got two 280w panels hooke up in parallel, 10AWG wire to the controller - how many more 280w panels can I connect in parallel before I reach the amperage threshold of the 10AWG wires going to the controller???
    Pretty much as many as you want, you will need a combiner box so the wires can't be back fed from the other panels, and you may want to use larger gauge wires from you combiner box to your charge controller since from the combiner box the amperage of your panels or strings of panels(panels connected in series) will be added. It's not uncommon to use several different wire gauges in this run, in my case I have 5 strings of 2 panels which are have @9 amps each on 12 gauge wires, I have them running into 10gauge connectors to the combiner box and I use 4 gauge for the 40 foot run to the charge controller, a little over kill, but I had the wire on hand, 6 would have been fine and 8 gauge marginal(as my faulty memory recalls)

    SORRY, I see I got popped back to the beginning of the thread somehow and missed that I was responding to an earlier question...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    It's a 60 Amp controller. What it can handle is however much it takes to produce 60 Amps output. Any power above that will be 'clipped' (lost). A lot of power above that is a waste of money.

    Using the standard formula we get: 60 Amps * 12 Volts minimal / 0.77 typical derating = 935 Watts being the probably maximum. Three 280 Watt panels is 840 Watts and should not be any problem for it.


    Thank you for this info -- however -- for the sake of the conversation, why does the MPPT-60 controller say the maximum solar input it can handle is 800w @ 12 volts, rather than the 935w you are saying??

    Thanks..

    --cake
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how many amps can mc4 wires handle in parallel?
    cupcake wrote: »
    Thank you for this info -- however -- for the sake of the conversation, why does the MPPT-60 controller say the maximum solar input it can handle is 800w @ 12 volts, rather than the 935w you are saying??

    Thanks..

    --cake

    They use different Voltage specs and/or skip the derating of panels. A 12 Volt system may go as low as 10.5 Volts and as high as 15 Volts so if you multiply by 60 Amps you get 630 to 900 Watts. If you divide 800 Watts by 60 Amps you get 13.3 Volts.

    Step right up, folks! Pick your own numbers! :p
  • cupcakecupcake Solar Expert Posts: 254 ✭✭✭
    Re: how many amps can mc4 wires handle in parallel?
    They use different Voltage specs and/or skip the derating of panels. A 12 Volt system may go as low as 10.5 Volts and as high as 15 Volts so if you multiply by 60 Amps you get 630 to 900 Watts. If you divide 800 Watts by 60 Amps you get 13.3 Volts.

    Step right up, folks! Pick your own numbers! :p



    Alright - so let me ask you this: If I go ahead and set up another 280w watt panel on a 12v system, thats 840w total. *Assuming that 840w goes 'over' the 800w solar input limit on the charge controller does it just 'not take' the extra 40w, OR does stuff start overheating, burning, making smoke?

    In otherwords if I 'go over' the input wattage, does the controller simply say 'no thank you', or does it start making bacon?

    Thanks again,

    -Cuppy
    ~1.5Kw PV in parallel
    Morningstar MPPT-60 controllers (2) in parallel
    3 Trojan tr-1275's in parallel 450ah total
    Samlex 2,000 watt 12-volt inverter hardwired


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: how many amps can mc4 wires handle in parallel?
    cupcake wrote: »
    Alright - so let me ask you this: If I go ahead and set up another 280w watt panel on a 12v system, thats 840w total. *Assuming that 840w goes 'over' the 800w solar input limit on the charge controller does it just 'not take' the extra 40w, OR does stuff start overheating, burning, making smoke?

    In otherwords if I 'go over' the input wattage, does the controller simply say 'no thank you', or does it start making bacon?

    Thanks again,

    -Cuppy

    Not a problem. This type of controller is current limiting; it will only pass 60 Amps maximum no matter the amount of panel on the input or the load on the output (save a dead short).
    Even Morningstar's little 15 Amp MPPT controller can be "over-paneled".

    You may have noticed panels don't come in precise Wattages of infinite variety; you always have some leeway to work with.

    The old Outback MX60 is a 60 Amp controller but can actually be cranked up to 70 Amps, for example.
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Re: how many amps can mc4 wires handle in parallel?

    For good quality MPPT type charge controllers (Morningstar, Outback, Midnite, Schneider, and others that I don't know anything about) are designed to limit their output current to the designed (or programmed) limit--Safely and reliably.

    These are switching/buck mode down converters (mostly) in the MPPT charge controller. Output current controller is part of the "nature" of these types of down converters. So, in general, nothing bad will happen (as always, running controllers near their maximum output current/power--They can run hot. They all need good ventilation/air circulation to keep cool--Do not put them in a closet or under a book shelf which blocks airflow).

    What basically happens is that if there is more Vmp*Imp from the solar array than the charge controller can process--Then the controller simply transfers less power to the battery terminals (typically limits to the output current ratings--Some will also dial back current flow based on heat sink temperature--As they run hot, they pull back on the current too).

    A good rule of thumb for "cost effective" combination of solar array and charge controller works out to be:
    • 60 amp charge controller * 14.5 volt battery charging * 1/0.77 panel+controller deratings = 1,091 Watt "cost effective maximum" array

    Basically on some cool/sunny days, your charge controller may "limit" the output current to 60 amps on occasion... If you are in a cool/higher elevations, you may get more days per year (and hour or few per day) of "clipping". If you are in a Caribbean island at sea level (hot, humid), you will get less clipping.

    The clipping is usually not much (a few amps for a couple hours a day, a few days per year).

    1,091 watt is not a hard limit... If most of your charging is at lower battery voltages (you deep cycle a lot, and or you have loads you run when the system is floating the battery bank) and want to use an average battery voltage of 13.3 volts and you are a few thousand feet up in cool/clear mountains (Marc gets ~82% of rated array output):
    • 60 amp charge controller * 13.3 volt battery charging * 1/0.82 panel+controller deratings = 973 Watt "cost effective maximum" array

    More or less, anything within ~10% is pretty much "the same" for solar power systems. It is difficult to get more accurate predictions/readings without lab grade equipment and calibrated pryometers. Just call it "rounding error".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,358 ✭✭✭✭✭
    Re: how many amps can mc4 wires handle in parallel?

    The magic is - If you convert your battery and inverter to 24V, you can install 1800W of panels, and charge batteries with that!
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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