No Spin Zone ...

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Lobo
Lobo Registered Users Posts: 18 ✭
in Solar Beginners Corner #1
Here is another $64.00 question for the Guru's from the old guy who doesn't do formulas. I understand the need for keeping your array amperage under the amp rating of the charge controller ... pretty much a no brainer, but where does the total VOC come into play with the charge controller? How is it figured for total array voltage? Is it only a concern for MPPT controllers or PWM also?

Looking forward to a simple answer from you Guru's ... thanks in advance!
Ken
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: No Spin Zone ...

    Voc is a concern because charge controllers (especially MPPT type) have a maximum input Voltage. If it is exceeded the controller (hopefully) shuts down. Worst case: it fries. This is why in cold climates you also have to factor that in: as the temp drops the Voltage from panels go up.

    So if you have a controller with 150 Volts maximum input and your array Voc exceeds this ....
    That's why MidNite developed the 'HyperVoc' function for their Classic controllers; it gives a little extra margin of safety.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #3
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    Re: No Spin Zone ...
    Lobo wrote: »
    Here is another $64.00 question for the Guru's from the old guy who doesn't do formulas. I understand the need for keeping your array amperage under the amp rating of the charge controller ... pretty much a no brainer, but where does the total VOC come into play with the charge controller? How is it figured for total array voltage? Is it only a concern for MPPT controllers or PWM also?

    Looking forward to a simple answer from you Guru's ... thanks in advance!
    Ken

    With a simple PWM controller, you can look at the Imp of the panel array and make sure that it is not too far above (check the specs of your CC) the output current rating of the CC.

    For an MPPT controller, the amps in will not be the same as the amps out. A good way to approximate it is to take the Vmp of array, divide it by the battery voltage plus about 4 volts, and multiply that correction factor times the output current of the array. That will tell you how much current the CC would have to work with as long as it is under the output limit of the CC.
    Again, some MPPT CCs specify that you can use a very much oversized array (in terms of power) and still not damage the CC. That will allow you to get full output from the CC for more hours and on poorer sun days. Other MPPT CCs specify that the power rating of the array is not allowed to be more than a specific value (often about 110% of the maximum output power of the CC.) The difference is in the way that the input of the CC is designed, so check your exact model.
    SMA SB 3000, old BP panels.
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  • Lobo
    Lobo Registered Users Posts: 18 ✭
    #4
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    Re: No Spin Zone ...

    I'm still a bit cloudy about that. So, you would add the VOC, from each panel, to figure out the VOC going into the charge controller?
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #5
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    Re: No Spin Zone ...
    Lobo wrote: »
    I'm still a bit cloudy about that. So, you would add the VOC, from each panel, to figure out the VOC going into the charge controller?
    If you put panels in series, then you add the Voc from each panel in that string to get the Voc of the string. And it is the string which is connected to the CC.

    But if you are in a cold climate, then in the winter the Voc of the panels will be greater than the Voc at standard temperature. You can either use the temperature coefficient supplied by the panel maker and combine it with the coldest possible early morning temperature to get the actual Voc, or you can play it safe and multiply the nominal Voc by 1.25.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: No Spin Zone ...
    Lobo wrote: »
    I'm still a bit cloudy about that. So, you would add the VOC, from each panel, to figure out the VOC going into the charge controller?

    Each connected in series, not parallel.
    For example:
    If you have three panels with a Voc of 44 each in series that becomes a string Voc of 132.
    If the temperature drops the Voc of that string can go as high as 172. This is over the maximum input Voltage of most MPPT controllers.
    The MidNite Classic 150 has a hyperVoc rating of 162 with a 12 Volt system, 174 with a 24 Volt system, and 198 with a 48 Volt system.
    The Classic 200 has a 'base' maximum Voltage of 200, and the 250 likewise 250 Volts. The hyperVoc allows system Voltage over this maximum.
    Other controllers do not have this function. (Note they do not operate at these levels, but they will not be damaged either.) Most MPPT controllers will shut down before their 150 Volt (or whatever) maximum and if subjected to too much Voltage may be damaged.
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  • andercd
    andercd Registered Users Posts: 3
    #7
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    Re: No Spin Zone ...

    *Hello all from a newbie*

    When I decided to buy Marc's ROGUE charge controller I spoke with him on the phone and asked a few questions. He spoke of the "VOC" limitations of his and other charge controllers and warned me not to exceed it's limits as it could damage it. When looking at charge controllers online they seem to advertise them rated on their amperage capabilities. I belive this goes back to Lobo's question about how many VOC's can charge controllers withstand and why do we not see advertisements giving buyers caution as to how many VOC'S a charge controller can handle? Keep in mind please....this may seem like elementary to many of you who have been involved with solar for years but to some of us newbies it leads to some confusion.

    Thank you to any and all who feel compelled to share your knowledge.
    Cary
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: No Spin Zone ...

    Welcome to the forum, Cary.

    Most all charge controllers do have a spec for maximum input Voltage. However this is not the major concern in selecting a controller; the output Amps is. As such most controllers don't mention it in their 'first info'. Two exceptions are the MidNite Classic line (150, 200, 250) and the Xantrex XW 600 MPPT 80 (600 Volt maximum, 80 Amp output, big price).

    Most of the smaller capacity MPPT controllers such as the Rogue have greater Voc limitations. The Morningstar MPPT 15, for example, has a maximum input Voltage of 72. Some of the Blue Sky units have very limited input Voltage indeed. As I understand it, the new version of Marc's Rogue 3024 (yet to be released) will have higher Voc ability than the previous model.
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  • Lobo
    Lobo Registered Users Posts: 18 ✭
    #9
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    Re: No Spin Zone ...

    Hey Cary Buddy, thanks for chiming in.

    Cariboocoot, with both Cary's and my arrays everything going to the combiner box is 17.6 volts and nothing hooked up in series. So, keeping this in mind, is our VOC to the charge controller considered 17.6 volts total or do we need to add up the voltage from all the panels? Thanks.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: No Spin Zone ...
    Lobo wrote: »
    Hey Cary Buddy, thanks for chiming in.

    Cariboocoot, with both Cary's and my arrays everything going to the combiner box is 17.6 volts and nothing hooked up in series. So, keeping this in mind, is our VOC to the charge controller considered 17.6 volts total or do we need to add up the voltage from all the panels? Thanks.

    The Voc (Voltage open circuit) on a panel with a Vmp (Voltage maximum power) of 17.6 is about 22. Voltage only adds if connections are made in series; not in parallel.

    An explanation of panels in different configurations on an MPPT controller: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller
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  • Lobo
    Lobo Registered Users Posts: 18 ✭
    #11
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    Re: No Spin Zone ...
    Cariboocoot wrote: »
    The Voc (Voltage open circuit) on a panel with a Vmp (Voltage maximum power) of 17.6 is about 22. Voltage only adds if connections are made in series; not in parallel.

    An explanation of panels in different configurations on an MPPT controller: http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller

    Thank you very much, I now have the answer to my question!
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #12
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    Re: No Spin Zone ...
    Cariboocoot wrote: »
    Voltage only adds if connections are made in series; not in parallel.
    [/url]

    And Amps add at the combiner box since the lines are parallel, so 2 PVs join at the combiner box A = 7.5 the output from the CB is now 12 volts (nominal) and 15 amps, 3 panels would be 22.5A...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • andercd
    andercd Registered Users Posts: 3
    #13
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    Re: No Spin Zone ...
    Cariboocoot wrote: »
    Welcome to the forum, Cary.

    Most all charge controllers do have a spec for maximum input Voltage. However this is not the major concern in selecting a controller; the output Amps is. As such most controllers don't mention it in their 'first info'. Two exceptions are the MidNite Classic line (150, 200, 250) and the Xantrex XW 600 MPPT 80 (600 Volt maximum, 80 Amp output, big price).

    Most of the smaller capacity MPPT controllers such as the Rogue have greater Voc limitations. The Morningstar MPPT 15, for example, has a maximum input Voltage of 72. Some of the Blue Sky units have very limited input Voltage indeed. As I understand it, the new version of Marc's Rogue 3024 (yet to be released) will have higher Voc ability than the previous model.


    Thank you! It's beginning to sink in. :-)
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  • andercd
    andercd Registered Users Posts: 3
    #14
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    Re: No Spin Zone ...

    Hello Ken. My pleasure my friend. I have much to learn and am not shy to ask questions. These folks here are very helpful!
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  • DavidOH
    DavidOH Solar Expert Posts: 112 ✭✭✭
    #15
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    Re: No Spin Zone ...

    No Spin Zone? I thought you were having trouble with a non-working wind-generator.....
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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #16
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    Re: No Spin Zone ...
    DavidOH wrote: »
    No Spin Zone? I thought you were having trouble with a non-working wind-generator.....
    I thought it was the Bill O.riley show!!
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  • Lobo
    Lobo Registered Users Posts: 18 ✭
    #17
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    Re: No Spin Zone ...

    Sorry guys, lots of the responses I have seen involve formulas or long drawn out mathematical computations and it is just confusing. Just needed a simple answer w/o spin ;-)

    It would have helped had I mentioned panels in parallel to begin with.
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