A couple questions

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steelheadguy
steelheadguy Registered Users Posts: 19 ✭✭
in Solar Beginners Corner #1
My fans like to operate at 24v. Im setting up a 48v system. I have 10 fans, 2 per circuit in series to create 24 volts for them.

My fans dont have a ground wire, do I need to ground them?

Where can I buy a breaker box for the fans? About 12 amps full load.

I have the panels mounted and the fans hung. I am about to run the wire today. I also bought an outback flex 60 charge controller. Can I run the fans from the panels before I buy my battery bank?
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
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    steelheadguy wrote: »
    . I also bought an outback flex 60 charge controller. Can I run the fans from the panels before I buy my battery bank?
    In general Charge Controllers (CCs) need to be connected to a battery bank before being connected to panels in order to power up and initialize properly. Not sure about the Outback. But it is not designed to regulate voltage without a battery present.

    Depending on the panel specifications you may be able to connect the panels (in parallel) directly to the fans.

    SMA SB 3000, old BP panels.
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  • steelheadguy
    steelheadguy Registered Users Posts: 19 ✭✭
    #3
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    I bought the (4) 24v 285w panels at the same store I bought the fans. The fans are 75 ft from the panels. Do I really just connect the panel straight to the fan nothing in between?

    What voltage can I expect from one of these panels?
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
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    steelheadguy wrote: »
    I bought the (4) 24v 285w panels at the same store I bought the fans. The fans are 75 ft from the panels. Do I really just connect the panel straight to the fan nothing in between?

    What voltage can I expect from one of these panels?
    The 24V figure is the nominal voltage, intended to work with a PWM controller to feed a 24V Lead Acid battery bank.
    Its Vmp (maximum power voltage) is probably around 36V and Voc (open circuit measurement) will be between 40 and 44V.
    Yes, you should be able to connect those panels directly to the fans. If you connect too many fans the voltage will drop below 24V, so you should monitor the voltage as you try it out.
    Note that if the fans contain electronic circuitry rather than using brushes, the direct panel voltage may damage the fan electronics. Check with the place you bought them to see if this is an acceptable configuration. It probably is.

    SMA SB 3000, old BP panels.
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  • steelheadguy
    steelheadguy Registered Users Posts: 19 ✭✭
    #5
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    When you say intended for a PWM controller, what do you mean? I bought a MPPT controller. Is this wrong? Did I waste money?
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #6
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    steelheadguy wrote: »
    When you say intended for a PWM controller, what do you mean? I bought a MPPT controller. Is this wrong? Did I waste money?

    Yes and no. The lower voltage "battery" panels will work just fine with an MPPT controller, particularly if you wire them up in a series string instead of in parallel.
    But the fact of the market is that low voltage panels cost $1.50 per watt or more while high voltage ("grid tie") panels cost lower than $1.00 per watt if you shop around.
    The low volt panels are physically smaller and lighter, so that may be useful to some people.

    In short, you may have wasted some of your money, but not all of it. :-)
    SMA SB 3000, old BP panels.
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  • steelheadguy
    steelheadguy Registered Users Posts: 19 ✭✭
    #7
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    My panels are 24v 72 cell 285 watts, are theylow voltage or high voltage panels? I was planning on wiring the 4 of them together series parralel for 48 volts
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #8
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    They are Around Vmp=36 volts.

    One one is good for 24 vdc battery bank. Two in series is good for 48 volt bank.

    3 in series should be good for a Midnite or Outback MPPT controller, ideally charging a 48 volt battery bank (as always, read the specification)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • steelheadguy
    steelheadguy Registered Users Posts: 19 ✭✭
    #9
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    The spec sheet says it takes variable voltages ( 12, 24, 48 ) input and output. I have two series for 48 volts. This should be enough to use the outback flex 60, no?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #10
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    More or less, for charging a 24 volt battery bank, you need Vmp-array >= 35 volts. This will work well with either a PWM or MPPT controller.

    If you put two or three panels in series, then you really want a MPPT charge controller. This allows you to use smaller gauge wiring from the Array to the Charge Controller. And a Vmp~35 volt array on very hot days may have less than optimum charging current for a 24 volt battery bank (Vmp-array can drop upwards of 20% on hot days--28.8 volts Vmp-array worst case--And you want ~28-29 volts to quickly charge a lead acid battery bank).

    What a MPPT controller cannot do is have a Vmp-array ~ 36 volts and charge a 48 volt battery bank... An MPPT controller can only "down convert" voltage (Vamp-array > Vbatt-charging). They cannot (in general) "up convert" voltage (take 36 volts and step it up to 59 volts charging).

    A MPPT controller is usually the better choice for larger systems (800 watts or larger array). For smaller systems (less than 400 watt array), a PWM may be more cost effective--But do several paper designs and cost them out based on your costs/needs. These are just rough rules of thumbs so we can give quick/clear answers to "general questions".

    Does that sort of make sense?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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