building 1st 24v system to run attic fans

flyedfflyedf Registered Users Posts: 10 ✭✭
hello everyone, hoping this will run my two 120watt 120v masterflow eg5 attic fans.

EcoSolargy 230 W Watt 24V UL Polycrystalline PV Solar Panels x2 less then $200 ebay
MicroSolar 12V 600W (Peak 1200W) Pure Sine Wave Inverter - with Remote Wire Controller $90 amazon 
Duracell Golf Cart - Group Size GC2  x2 in series for 12volts $180 sam's club

I'm in southern CA, so and get fair amount of sun. 
how's this mppt 2400W smart solar controller, regulator, MPPT, DC12V/24V, 3.5" LCD monitor, 100A from ebay $70 

Comments

  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited May 2017 #2
    The Power Jack is most likely not an MPPT but a PWM, the price is simply too low, as far as being 100 amps the terminals look way to small, personally I've no experience with Power Jack, they do have a reputation of not being what they claim and not being very reliable

    If budget allows it might be better to spend a little more and go with name brand equipment rather than seeking out the lowest prices, but it's your budget and my opinion, for what it's worth. 

    Alternatively to keep costs down you could go PWM with an excellent CC but at 12V you would need 12V nominal panels, so if you haven't bought anything yet, you are in a good position to make alternate choices, you've come to the right place to get advice, there are some very smart and helpful people here, welcome aboard.



    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • littleharbor2littleharbor2 Solar Expert Posts: 1,626 ✭✭✭✭
    edited May 2017 #3
    Ditto  mcgivor.

     Power Jack markets poor quality electronics. I wouldn't trust a single word of their advertising. The next 100 amp MPPT controller is over $1000.00. Plus there is no reason you would need a 100 amp controller for your two 230 watt panels.

    BTW from your list of materials you are building a 12 volt system.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 540 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • mvasmvas Registered Users Posts: 384 ✭✭✭
    Below is the description of the product.
    They claim, "it is not usual MPPT"  !!!
    So it is is "unusual" MPPT ?  :)
    I am having a hard time translating this into "English"  ...

    "...

    MPPT + PWM + on line grid technology (95 ~97% efficiency)
    This is MPPT technology also, this is not usual MPPT for other supplier, we use grid tie inverter technology to catch best voltage & amp, other supplier mentioned when voltage up to 17V~18V, the amp will start to come, that's not correct, because the solar panel’s voltage can not always keep at 18V, if so, once the voltage can not match, amp will stop income until the voltage to be 18V.  So the best voltage is to be 14V~15V, and the amp will be come-in stable, it is better for long time use. As we are the on grid inverter supplier over 5years, that's why we can offer same technology for the solar controller.

    Other supplier’s MPPT controller, they put a choke & re-sort out the power, then charge the battery, our engineer team have testing this way, we found no need to re sort out, during the operation, it will lose 3~4% power, no need to waste green power even more power income.

    For example:

    if use 1000w solar panel input, 3% different for 1 hour, 1000w x3%=30watt

    1 day might lost 360w at least (30W * 12 hours/day time = 360W

    One month will lost 10,800W

    One year will lost 129,600W

    So please use our solar controller to save more power!

    ..."
  • jonrjonr Solar Expert Posts: 1,386 ✭✭✭✭
    My guess is that's it's fast PWM with inductance/capacitance such that it holds the panel voltage at Vmpp.   MPPT and the use of a DC-DC converter are actually independent things.

    I am available for custom hardware/firmware development

  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    "we found no need to re sort out" ..."it will waste 3~4%". I suspect that means no sweeps or step-down, so their "not the usual mppt" is actually just the usual pwm.

    How much of the day will the fans be running? If they're meant to run most of the daylight hours, you should get more panel. Once warmed up, two panels wouldn't supply enough to run the fans so they would mostly discharge and rarely charge the batteries.

    Also, I suggest getting a controller and inverter that provide for load control.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • flyedfflyedf Registered Users Posts: 10 ✭✭
    mcgivor said:


    If budget allows it might be better to spend a little more and go with name brand equipment rather than seeking out the lowest prices, but it's your budget and my opinion, for what it's worth. 





    so what's the least expensive mppt that I can get that can still give me some headroom if I add 2 more 6v batteries for full 24v system and a 24 inverter?  how many amps should I be looking at w my 2x solar panels?  what about this one
  • flyedfflyedf Registered Users Posts: 10 ✭✭
    Estragon said:


    Also, I suggest getting a controller and inverter that provide for load control.

    what would be a good value?
    Estragon said:
    Once warmed up, two panels wouldn't supply enough to run the fans so they would mostly discharge and rarely charge the batteries.

    these solar panels are supposed to supply up to 8amps each.  my fans only pull an amp each. 
    I was hoping the deep cycle batteries would only discharge at end of the day when the sun goes down.  fans sometimes run for about an hour after sundown (on hottest days)  

    also, the system would start charging the batteries few hours before the fans come on which is about noon. 

  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    8a at what voltage? A 230w panel supplying charging voltage at say 14.5v with an mppt controller *could* produce 230/14.5=~15a. Two could produce ~30a. Keep in mind though that's amps at 14.5v, not amps at 120v. At 120v (before inverter losses) that's 260/120=~2Aac, about what the fans pull.

    Real production will be lower because:
    1. Output depends on temperature. Ratings are typically for 25C. Actual panel temp in full sun in southern CA is likely higher.
    2. Ratings assume 1000w/sq.meter, which may not be the case for panels at less than optimal angle to the sun (eg morning/evening and seasonal changes).
    3. Other impediments (bird bombs, atmosphereric conditions like smog, marine haze, light cloud, etc.)
    4. Losses involved in wiring and charge controller.

    I assume the fans are controlled by a thermostat. The problem is the thermostat won't care if it's cloudy, or if the batteries aren't charged. They will turn on if the attic gets hot, and run until the batteries die. Do that a few times (especially if the batteries live in the hot attic), and you'll be in the market for new batteries.

    A bit more info would be helpful:

    - Do you have a limitation for mounting space for panels in any orientatation (east, west, or south)?

    - Are there any obstructions (trees, wires, chimney/vent pipes, etc) in any orientation?

    - How big is the area you're ventilating?

    - Any chance the space could be reconfigured for natural instead of mechanical ventilation?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    flyedf said:

    Estragon
    said:


    Also, I suggest getting a controller and inverter that provide for load control.

    what would be a good value?
    Estragon said:
    Once warmed up, two panels wouldn't supply enough to run the fans so they would mostly discharge and rarely charge the batteries.

    these solar panels are supposed to supply up to 8amps each.  my fans only pull an amp each. 
    I was hoping the deep cycle batteries would only discharge at end of the day when the sun goes down.  fans sometimes run for about an hour after sundown (on hottest days)  

    also, the system would start charging the batteries few hours before the fans come on which is about noon. 



    So the fans are 1 amp at 120V,  that equates to 10 amps at 12V, not taking into consideration inverter self consumption and efficiency. So basically when running you would be at a net loss, actually not charging the battery, perhaps discharging, it may be necessary to add some more panel to ensure there is always a surplus to cover a cloudy day, think you would be close to that fine line, it's always better to have slightly more 30%,just to be on the safe side. IMO
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • jonrjonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited May 2017 #11
    I'm curious - do you have your fans running in opposite directions (one blowing inward, one outwards)?

    An important principle is to be careful about depressurizing or pressurizing the attic (can have a bad effect on in/exfiltration and increase energy use).  And that attic floors usually have insulation - so hot air in the attic doesn't make much difference.

    I am available for custom hardware/firmware development

  • LumisolLumisol Registered Users Posts: 374 ✭✭✭
    Might want to forgo the electric fans and use vent turbines.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    edited May 2017 #13
    The principle for air flow should be ''IN'' at the "Soffits'' and "OUT" at the ''RIDGE line'' of the roof so that the cooler air passes by the heated surface where the ''hottest'' air originates ( south facing?) and following thermodynamics will rise to the ridge line and thus needs a port to escape through... to create 'natural' upward air flow.
     
    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
  • LumisolLumisol Registered Users Posts: 374 ✭✭✭
    edited May 2017 #14
    Yep. You want 50% intake and 50% exhaust and base it on the rule: 1 square foot of total ventilation for every 150 square feet of living space without a vapor retarder. { with a 2 story the 1 story without attic space is not included. } An exception of 1 in 300 if a vapor retarder is present. Vapor retarders are used in colder climates. The key to a balanced system is doing the math.
  • BB.BB. Super Moderators, Administrators Posts: 32,004 admin
    How many Watts are your fans?

    Many "solar fans" are only 10-20 watts. 120 vac fans may be 200-300 watts, or move upwards of 10x the airflow.

    With the smaller dc fans, a couple folks found that the airflow/cooling of the attic was the same if the fans where running or not.

    Just adding ventilation holes was enough. No dc fans needed.

    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • flyedfflyedf Registered Users Posts: 10 ✭✭
    edited May 2017 #16
    these are 120v ac attic fans.  house is ranch style shaped like an "L".  I have one fan at each large attic vent.  there are numerous small hole vents around the house.  I started w one and noticed how much warm air it was sucking out, so I added a 2nd one at the other end.

    1 fan will come on hours before 2nd one does.  sometimes 2nd one doesn't even come on.  passive turbines would be nice, but wonder if any will intake air.

     
  • flyedfflyedf Registered Users Posts: 10 ✭✭
    Estragon said:

    A bit more info would be helpful:

    - Do you have a limitation for mounting space for panels in any orientatation (east, west, or south)?

    - Are there any obstructions (trees, wires, chimney/vent pipes, etc) in any orientation?

    - How big is the area you're ventilating?

    - Any chance the space could be reconfigured for natural instead of mechanical ventilation?

    nice thing is I have a clear shot at the sky, and a flat roof area to lay panels.

    the attic fan is smallest 1450cfm unit, and effective in keeping the house cooler, we didn't use house ac last year.  
    also, fan was much easier to install then opening up roof for passive turbines.
  • BB.BB. Super Moderators, Administrators Posts: 32,004 admin
    Passive turbines may not really help air flow.

    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • LumisolLumisol Registered Users Posts: 374 ✭✭✭
    Passive turbines? All the turbines I have seen are dynamic, as the wind moves the outer portion, the inner portion turns fan blades that create a low pressure point to remove the heat in the attic. They do not intake any air, their job is to exhaust the heat out of the attic which is then replaced by cooler air at the soffets which moves upwards through convection to the ridgeline and out the vents.
    They are quite efficient and modern ones use sealed bearings and are fairly silent. (A lot quieter that an electric fan)
  • flyedfflyedf Registered Users Posts: 10 ✭✭
    I just call them passive b/c there's no motor, and the wind moves them
  • LumisolLumisol Registered Users Posts: 374 ✭✭✭
    I see. Passive means no moving parts.
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    When i redid my roof on my city house 8-9 years ago (also a ranch), I got the soffits better vented, and added full ridge vent. Used to be just a couple of small soffit vents and gable vents.

    It made a huge difference, and I think the shingles are lasting better with the cooler deck. I did the same at the cabin 5 years ago with the same result. Even if the roof is pretty new, I would look at adding natural draft venting before mechanical. It's pretty straightforward to install. If old, you would want to consider replacing before mounting solar anyway.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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