DC Load in Parallel with Charge Controller

ffsooo3
ffsooo3 Registered Users Posts: 8 ✭
in Off Grid Solar & Battery Systems #1
Is it possible/acceptable to put a DC load in parallel with a Charge Controller? I am doing a small setup for my greenhouse to have a CFL come on for 4 hours (between 3AM and 7AM for our chickens) and would like to have a ventilation fan come on only when the sun is shining. My thinking is that when the sun is shining enough on the panel to produce power, the greenhouse will be heating up, and the fan will kick in to cool the greenhouse a bit. As the sun is setting, the panel will start to produce less and less power and the greenhouse will start to cool down and the fans will slow down and eventually stop (for the night). My question is: while the fan is going will there be enough amperage left for the controller to charge my battery? This is my 1st foray into a PV system and I know I have a TON to learn....

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PV(100w) DCFan(80W) ChargeController==>Battery(90Ah)==>Inverter(400W)==>Timer(2W)&CFL(13W)
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: DC Load in Parallel with Charge Controller

    It would work, but first you have to find out what the fan power is, and that has to be less than you are using now, for recharge. Or look for a "Solar Powered Greenhouse Fan" kit, and run it completly seperately.

    May as well give us all the other specs for your current system and we'll see how much overhead you have in it.
    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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  • ffsooo3
    ffsooo3 Registered Users Posts: 8 ✭
    #3
    Re: DC Load in Parallel with Charge Controller

    Good to hear that it may be doable....

    100W panel (short circuit current: 6.4A / optimum operating current: 5.62A)
    30A charge controller
    12V 90Ah marine deep cycle battery
    400W modified sine wave inverter

    The inverter draws .15A (24/7). I'm running an AC timer (24/7) that draws .15A and a 13W CFL (4 hours/day) that draws .85A. The inverter, timer, and CFL together draw 1.15A.

    If I'm missing some data/spec please let me know.

    So given the above, what size DC fan can I safely run directly off my panel that will allow the controller to still charge the battery? Thanks!
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #4
    Re: DC Load in Parallel with Charge Controller

    When does your charge controller indicate the batteries reach float ? That, and using the remaining "Recharge Sun Hours" in the sky, will give you how much excess capacity you have. But a solar greenhouse fan will be a safer way to do it.
    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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  • ffsooo3
    ffsooo3 Registered Users Posts: 8 ✭
    #5
    Re: DC Load in Parallel with Charge Controller

    So, if my controller indicates float by say 11AM and we assume the panel (on a good day) will produce power until 3PM, I have 4 hours of "recharge sun hours" available as "excess capacity". How do I relate this value to fan size?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #6
    Re: DC Load in Parallel with Charge Controller
    ffsooo3 wrote: »
    So, if my controller indicates float by say 11AM and we assume the panel (on a good day) will produce power until 3PM, I have 4 hours of "recharge sun hours" available as "excess capacity". How do I relate this value to fan size?

    3pm, your panel is likely down to 1/2 power. Lets use the common 10am - 2pm, 4 hr solar window.

    Say you have 2 hours of PV light left, and while in Bulk mode that morning, you see 4.7 amps going to the battery. (You will have to measure this, we can't derive it) from your array, which may not be at "optimun" angle.

    2 hr x 4.7 = 9.4 Ahours (or in 12V watts = 112.8 watt hours)
    So you could add a 50W fan for 2 hours, or a 100W fan for 1 hour.

    Since this does not run off stored power in the battery, you don't have to allow for battery losses.
    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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  • ffsooo3
    ffsooo3 Registered Users Posts: 8 ✭
    #7
    Re: DC Load in Parallel with Charge Controller

    Understood. So I will have to measure the typical amperage going to the battery AND find out when my battery typically goes to float mode. From there I can compute the typical excess watt-hours available and determine the proper fan size. Thank you!

    Now.....would I have to manually switch the fan on AFTER the controller goes to float or can I leave the fan always turned on and the controller and fan will simply share the available amperage appropriately (if I have correctly sized the fan)?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #8
    Re: DC Load in Parallel with Charge Controller

    Depends on the fan you select and the size/ratings of your panels... The panels nominally need to be Vmp~17.5-18 volts or so with a pwm controller (I would not try the fan thing with an MPPT controller).

    If the voltage is pulled too low (by fan or fan+controller) on a hot day, (below 15.5-16 volts or so), the charger will not charge you battery bank at all (battery needs around 14.5-15 volts to recharge at 77F).

    Note that with a PWM controller, when the controller "turns on", the array voltage will drop to battery charging + controller drop (which may be 15 volts or so).

    You probably need to measure the current out of the controller with and without the fan operating too ensure that everything is playing well together.

    Some people have used 24 volt computer fans--spin slower and quieter.

    A 12 volt fan may be damaged by the solar panel which is capable of ~17.5 to ~21 volt output (depending on temperature, loading, amount of sun, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • 2manytoyz
    2manytoyz Solar Expert Posts: 373 ✭✭✭
    #9
    Re: DC Load in Parallel with Charge Controller

    Here's a simple method for running the fan. I made my own gable end attic vent fan, using a $12 camping fan from Walmart, and a 15W Harbor Freight solar panel. Nothing else needed. No regulator, no timer, no switch. When the sun is up, the fan runs. Sun goes down, fan turns off. No worries of your battery bank not being fully charged as this setup is completely independent of the other.

    It will produce some RF noise that can interfere with a receiver in a garage door opener, but that's the only thing it affected. The upside is it moves a LOT more air than computer muffin fans.

    The panel produces a solid 700mA in full sun. The fan draws 450mA on high. So it will run at full speed in full sunlight, without worry of burning out the motor. There's not enough amperage left over to do much, and when the panel is loaded down with the motor running, it also brings the voltage down to a reasonable 14-15V.

    chinafan1.jpg

    dscn5310.jpg

    short4.jpg

    Video of it in operation: http://www.youtube.com/watch?v=ULQmLXw4-8E
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  • ffsooo3
    ffsooo3 Registered Users Posts: 8 ✭
    #10
    Re: DC Load in Parallel with Charge Controller
    BB. wrote: »
    Depends on the fan you select and the size/ratings of your panels... The panels nominally need to be Vmp~17.5-18 volts or so with a pwm controller (I would not try the fan thing with an MPPT controller).

    If the voltage is pulled too low (by fan or fan+controller) on a hot day, (below 15.5-16 volts or so), the charger will not charge you battery bank at all (battery needs around 14.5-15 volts to recharge at 77F).

    Note that with a PWM controller, when the controller "turns on", the array voltage will drop to battery charging + controller drop (which may be 15 volts or so).

    You probably need to measure the current out of the controller with and without the fan operating too ensure that everything is playing well together.

    Some people have used 24 volt computer fans--spin slower and quieter.

    A 12 volt fan may be damaged by the solar panel which is capable of ~17.5 to ~21 volt output (depending on temperature, loading, amount of sun, etc.).

    -Bill

    Thanks. My panel's Vmp is 17.8 and my charge controller is PWM. I'll look into 24v computer fans. I had always thought they were typically 12v. But muffin fans won't move enough air for me. I will measure the amperage out of the controller with and without the fan running once I get the fan.....
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  • ffsooo3
    ffsooo3 Registered Users Posts: 8 ✭
    #11
    Re: DC Load in Parallel with Charge Controller
    2manytoyz wrote: »
    Here's a simple method for running the fan. I made my own gable end attic vent fan, using a $12 camping fan from Walmart, and a 15W Harbor Freight solar panel. Nothing else needed. No regulator, no timer, no switch. When the sun is up, the fan runs. Sun goes down, fan turns off. No worries of your battery bank not being fully charged as this setup is completely independent of the other.

    It will produce some RF noise that can interfere with a receiver in a garage door opener, but that's the only thing it affected. The upside is it moves a LOT more air than computer muffin fans.

    The panel produces a solid 700mA in full sun. The fan draws 450mA on high. So it will run at full speed in full sunlight, without worry of burning out the motor. There's not enough amperage left over to do much, and when the panel is loaded down with the motor running, it also brings the voltage down to a reasonable 14-15V.

    That's exactly what I'm attempting to do. But I'm just trying to use my existing panel. But you may be right to go stand-alone so there are no worries about charging the battery bank (of one battery). I'll look into the WalMart camping fan. I was thinking about using a radiator cooling fan - they just draw a lot more power.....
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  • 2manytoyz
    2manytoyz Solar Expert Posts: 373 ✭✭✭
    #12
    Re: DC Load in Parallel with Charge Controller
    ffsooo3 wrote: »
    SNIP

    I was thinking about using a radiator cooling fan - they just draw a lot more power.....

    I looked into those too. Way too much power consumption for any of the ones I looked at.

    I think you'll be pleased by how much air this fan moves, while drawing less than 1/2 Amp.
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  • ffsooo3
    ffsooo3 Registered Users Posts: 8 ✭
    #13
    Re: DC Load in Parallel with Charge Controller
    2manytoyz wrote: »
    I looked into those too. Way too much power consumption for any of the ones I looked at.

    I think you'll be pleased by how much air this fan moves, while drawing less than 1/2 Amp.

    I checked out your website. Great format and great pictures. BTW I checked out Wal-Mart's website but couldn't find the camping fan you mentioned. Any chance you could point me to it? Thanks!
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  • 2manytoyz
    2manytoyz Solar Expert Posts: 373 ✭✭✭
    #14
    Re: DC Load in Parallel with Charge Controller
    ffsooo3 wrote: »
    I checked out your website. Great format and great pictures. BTW I checked out Wal-Mart's website but couldn't find the camping fan you mentioned. Any chance you could point me to it? Thanks!

    Glad you found the website useful, thanks for the feedback!

    It's not on their website, but still sold in their local stores here. The actual brand is "O2 Cool", and Walmart packages them in their Ozark Trail brand packaging. Look in the camping section of your local store. Bet you will find them on the shelves. Latest price was $12.88.

    You can buy the same fan at places like Amazon, for double the cost:

    http://www.amazon.com/O2-Cool-Model-1054-Indoor-Outdoor/dp/B000I4L15Q
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