Big Dream Little Experience

I am attempting to change the AC fan in my solar heater to a DC fan and run the DC with one 200 watt PV module.

I have the heater, I have the replacement fan, I have the PV module, now I just need to make it work, so that lead me here.

I was thinking of using a MPPT charge controller to step down the voltage of the PV mod to drop it to 12v and then use a DC temp controller for the off chance that it gets too hot inside.

Well, is this going to work? Or am I crazy?

Thanks for the help!

-Bob

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,171 admin
    Re: Big Dream Little Experience

    Probably not going to work--Unless you work real hard at it...

    And if it does work, then we have to figure out of the amount of heat you get is going to be useful (i.e., big difference between heating an egg brooder and heating your office).

    Basically, MPPT type charge controllers are designed to only work with a Battery Bank (12/24/48 volt typically). If you don't have a battery bank, they will not even turn on.

    Next, the heater--If it is designed for 120 VAC and feed it 12 VDC--you will get 1/100th the amount of heat at 12 volts vs 120 volts.

    Anyway--There is a lot of questions about what you are trying to do here. The electrical requirements of the loads vs the output of the solar array/battery bank/AC inverter/etc.

    In general, most people overestimate how much power they can get from solar and underestimate the amount of power consumed by the loads.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Big Dream Little Experience

    Hello is the OP talking about a thermal solar tin can heater ..I believe this is the case...
  • DrBombayDrBombay Registered Users Posts: 3
    Re: Big Dream Little Experience

    Bill,
    Thanks for the info. Really the PV mod will only haver to operate a fan. That's it. The Solar furnace makes the heat and the fan is only needed to move air. What do I need to step down the voltage to 12V to run this fan?

    All said and done I will have off grid heat. If it were easy I guess everyone would do it.

    So which way do I run now?

    -Bob
  • DrBombayDrBombay Registered Users Posts: 3
    Re: Big Dream Little Experience
    rich wrote: »
    Hello is the OP talking about a thermal solar tin can heater ..I believe this is the case...

    Yup, I didn't make this, it's actually purchased from cansolair.

    -Bob
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Big Dream Little Experience

    I would start looking at 'muffin fans', like those used to keep your CPU at its operating temp. Lots of them available in 12 volt.
     
    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
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Big Dream Little Experience

    I have a bit of experience in this, the muffin fans dont move near enough air to satisfy this application...I would suggest a high end stove top fan from an RV supply...can You post a link to the unit I luv looking at the different designs out there....The bonus here is You can purchase the reostat(sp) at the same place and make it have more functioning control ,easier to strike a balance..and run it at less noisy speeds....
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Big Dream Little Experience

    having some experience with an ECO-Fan you do not need to 'feel' the sir moving just experience it. the Eco-fan gently moves the air and you will not 'feel' it blowing the air, except right up close, but it DOES markedly improve the distribution of the heat in a room. So will a muffin fan or 2 or 3. It isnt like central heating, neither is a solar heater, in with the cool/cold, out with the warm.
     
    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
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Big Dream Little Experience

    Im familiar with those tried and true designs, are you getting Your cold air from an attic or other indoor type bulkhesd space? I believe the efficiency goes way up...as far as a 12 volt regulation I think You can find what You need on e-bay..if I can remember they take from 12 to 20 volts and deliver a regulated 12 v output,5 AMP check into it, also you will save money on a charge control as this will do for straight off the panel. Bonus with that is when you have your daily solar peak you will be running max power to keep the fan happy. Unless Im missing something I would say go for it, if Im wrong Im sure ill be corrected , (in a good way)..lol great Idea by the way.
  • shoalbillyshoalbilly Registered Users Posts: 3
    Re: Big Dream Little Experience
    DrBombay wrote: »
    I am attempting to change the AC fan in my solar heater to a DC fan and run the DC with one 200 watt PV module.

    I have the heater, I have the replacement fan, I have the PV module, now I just need to make it work, so that lead me here.

    I was thinking of using a MPPT charge controller to step down the voltage of the PV mod to drop it to 12v and then use a DC temp controller for the off chance that it gets too hot inside.

    Well, is this going to work? Or am I crazy?

    Thanks for the help!

    -Bob

    It looks like you have the fan from the manufacturer.
    A small battery and a charge controller rated enough amps to handle your panel's
    output amps should be all you need.
    That fan won't draw much and the panel seems large for one fan.
    A larger battery would be able to power more 12v devices in the future.
    The controller will limit the current to replace only what the battery needs.
    I think you might want to also contact the manufacturer about what they recommend.
  • BB.BB. Super Moderators, Administrators Posts: 31,171 admin
    Re: Big Dream Little Experience

    If this is solar heating... A 10 watt fan on a 10-20 watt "12 volt panel" (really around 17 volts Vmp) would work fine. If the voltage is too high, you can put several diodes in series to drop the voltage (around 0.7 to 1.0 volt per diode drop).

    Or, you can put a 24 volt fan on a "17.5 volt panel"--It will turn slower (and quieter), so you may need a larger fan to make up for the slower RPM.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • shoalbillyshoalbilly Registered Users Posts: 3
    Re: Big Dream Little Experience

    Dr Bombay,

    Is this the unit you have ?
    CanSolAir Inc.
    Model RA 240 SOLAR MAX
    Energy Usage (fan) Watts 31
    Heat Energy Output Watts 1200 – 2400
    Panel Weight lbs / kg 130/59.09 (crated)
    lbs / kg 85 / 38.64 (uncrated)
    Dimensions Inches
    (metric)
    44” (1.1 m) W x 88.5” (2.25m) H
    x 4” (102mm) thick at sides, 8.5” (216mm) thick at center
    Lens Curved UV stabilized Polycarbonate
    Flow Rate cu. ft/min 100 +
    Flow Rate cu litres/min 2832+
    Temperature Gain F 50 F to 100 F degrees above ambient
    Temperature Gain C 10 C to 38 C degrees above ambient
    Modularly Expandable Yes ‐ working in parallel
    Hydronic Integration Yes ‐ with heat exchangers
    Power Supply Options 115v AC wall outlet / 12v DC / 220v‐50 Hz. Intl.
    BTU's p/hour Up to 10,000 ‐

    And it sounds like you have their 12V fan already.

    Look on the label on your panel and see what the:
    Vmp is (should be 17.5 to 18v). If so, this panel should work well for 12v use
    Imp (current) for a 12v panel I'm guessing is about 11 amps (200w / 18v = 11.1 amp)
    * If not it may be a panel with 30 volts Vmp .... not so good for 12V use. those are for grid tie use

    If it is a 12v, 11 amp panel you need at least a 12 Amp 12 volt controller or more

    Xantrex makes the C-12 12v 12 Amp controller that would also control some lights.

    There are other controllers that may work for less money.

    The 31 watts for the fan would draw about 2.6 amps but you need to figure out how many hours a
    day it will run. (e.g. 10 hours * 2.6 amps = 26 amp hours or 312 watt hours a day)
    If that panel is 12 v it should give about 40 amp hours or more daily depending on location etc.

    A 100 amp hour AGM battery will probably keep it able to run on cloudy days and run some lights too.
    something like this: http://www.ecomelectronics.com/prodinfo.phtml?id=3366020

    Maybe someone who knows more than I do could help you figure out how much battery you will need
    depending on how long the fan runs and if you want some lights also.

    So figure about probably $ 300 U.S. or more for a controller and battery plus cables and fuses.

    Solar isn't cheap ! the 120 volt AC fan would only cost about 10-25 cents a day to run .

    If the power went out, with the panel and battery you would have some heat circulated and some 12 volt lighting for a day or 2.

    Hope this info helps.
    Mark
  • BB.BB. Super Moderators, Administrators Posts: 31,171 admin
    Re: Big Dream Little Experience

    Computer fans move air against very little back pressure... If you are moving air through an evaporative cooler (for example), the back pressure is much greater, and so will the power needed to run the motor (many times a squirrel cage type fan for higher back pressure vs simple axial flow type).

    And if you want air flow "outside" of ~9am to 3pm or so--Then you are looking at a battery+charge controller+larger solar array. This will add significantly to the cost of your "off grid" power system (frequently about 4x more cost vs a "daylight only" solar panel).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Big Dream Little Experience
    BB. wrote: »
    Computer fans move air against very little back pressure... If you are moving air through an evaporative cooler (for example), the back pressure is much greater, and so will the power needed to run the motor (many times a squirrel cage type fan for higher back pressure vs simple axial flow type).
    ,,,,,,,Not sure if this was directed at me..high end rv exhaust fans are turbine inline type fans, .same as high end bathroom types in the AC format.

    To the Op, seems you have all the fan U need in that unit...id love to hear the results and gains in your experience....thanx
  • BB.BB. Super Moderators, Administrators Posts: 31,171 admin
    Re: Big Dream Little Experience

    My exhaust fans in my home (bath, kitchen, drier, central heater, car A/C, etc.) are all squirrel cage type. Work much better/consistently against high/variable back pressure.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Big Dream Little Experience
    BB. wrote: »
    My exhaust fans in my home (bath, kitchen, drier, central heater, car A/C, etc.) are all squirrel cage type. Work much better/consistently against high/variable back pressure.

    -Bill
    Yup my home also has those ..no comparison to high-end turbine type....I found several at a habitat store...picked the cream and paid 70 bucks for two...designed for resistive ducting as they build up a considerable amount of pressure in a closed loop duct..enough to blow apart non taped ductwork...unfortunatly I cannot locate my psi guage..ill look and see , if I find it ill post the PSI at full power a noise factor...lowering the rpm and so on...Ill post this on my own thread.. To the Op, I will send a private message with my email, im eager to follow this project...is that ok?
  • richrich Solar Expert Posts: 62 ✭✭✭✭
    Re: Big Dream Little Experience

    Attachment not found. This is very similar..Because the turbine is inside the duct its suprisingly quiet, seems to respond well with my router table speed control...
    fan.jpg 32.1K
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