solar vent improvement

Discussion in 'The Projects Forum' started by smonc, Mar 23, 2014.

  1. smonc

    Thread Starter New Member

    Feb 16, 2014
    3
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    I have a commercially available solar vent used to ventilate a sailboat day and night. This unit has some history of motor failure and the manufacture does not support it. I have found a source for a motor and I believe I can fix the unit. My question is why the manufacturer used the specific circuit described in the attachment. It looks to me like the 1 ohm resistor is robbing power and there is no protection (diode) for battery discharge through the solar cell. Could you assist in helping me develop a more effective circuit?

    sorry if this is a duplicate post, I have had a little trouble with copy/paste.
     
  2. wayneh

    Expert

    Sep 9, 2010
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    How sure are you that the resistor is really a resistor? It would make sense for it to be the blocking diode.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Agreed, there is usually a schottky type diode there for blocking with a low drop voltage.

    Any "improvements" are probably overkill unless you are prepared to change the solar cell, battery, and add a bunch of controlling electronics just to power a fan you manually switch on and off.
     
  4. burger2227

    Member

    Feb 3, 2014
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    If it has a history of motor problems, it may be getting too much current. Maybe it could use a larger resistor to keep the solar current lower. How big is the solar panel?
     
  5. wayneh

    Expert

    Sep 9, 2010
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    Some panels have an integral diode, so it is possible .
     
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the motor may be getting too much current? the current draw of a motor is determined by the load on the motor (size of the blades and back pressure on the fan),.
     
  7. burger2227

    Member

    Feb 3, 2014
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    The solar voltage is almost double the 1.25 volt battery, but most motors I've found are rated up to 3 volts anyhow.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    That's open circuit voltage, which is not relevant. No point in that system ever sees more than battery voltage (ignoring any ∆V across the alleged resistor or diode).

    If the panel has a built in diode, then I believe the resistor is just a simple (cheap, inelegant, inefficient) current limiter to protect a discharged battery from a current over 1A or so. Note that it doesn't degrade efficiency of running off the battery.

    I really don't think you can improve the circuit (again assuming the diode is present) except to replace the motor with a better one. And I have no idea how to ensure the one you find is "better". I don't think they quote MTBF for these things.
     
    Last edited: Mar 24, 2014
  9. smonc

    Thread Starter New Member

    Feb 16, 2014
    3
    1
    Thanks for all of the responses, it sounds like we may have a reasonable project/question.
    Wayneh. I am pretty sure this is a small resistor. Color code is brown, black, gold a space then another gold band. My ohm meter is on the boat, but if there is any reason to doubt that this is a resistor, I will check into it further. I do not see anything built into the solar panel that looks like a diode.
    ErnieM. I am only willing to change the motor, and make say $10.00 or so in improvements in the circuit. This is a Nicro N2070 vent. This is the motor I am planning to try. http://www.goldmine-elec-products.com/prodinfo.asp?number=G18072
    Burger2227. The unit lasted for about 3 years 4' off the water. I am OK with that. I am not so OK with Nicro not supplying a replacement motor (little brushes gave out), and I am wondering if I might be able to soop this thing up a little, with your help. The solar panel is made up of 4 cells each 2"X2". They are embeded in a nice plastic holder with some kind of rubbery polymer. I do not have an easy way to determine the output, but the open voltage I measured is between 2.3 to 2.4 volts.
    Wayneh. Is there a way I can determine if there is a diode? Visually, I don't think so. If it does not have one, can you recommend one? Size source etc? I think what you are saying about the resistor is that it may be a safety feature to protect the battery. If so, I will take it out and monitor for a while.
    Thanks for the help.
     
  10. wayneh

    Expert

    Sep 9, 2010
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    It's easy to check for the diode by monitoring the voltage across that resistor. That'll show you the direction and magnitude of the current. See what happens when you switch from light to dark. If the voltage goes from positive (on the panel side) to zero, there has to be a diode somewhere. A negative voltage would indicate battery discharge through the panel, but that's not likely. No one would design it that way.

    Removing that resistor risks damaging your battery, with possibly serious consequences. It wastes very little power, and only when the sun is really bright and the battery is really dead. I wouldn't bother with it. You could determine exactly how much it is wasting by watching that ∆V across it under various conditions.
     
  11. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    With a $2.50 motor if it runs a season I'd say you got your monies worth.

    OK, no other changes, none really needed either. It's not the worst assumption to thing the guy who designed the thing knew what he was doing.

    The only reason I can see for a resistor there (and I've been called blind before) is to limit the stall current in the motor: when the motor is not turning but the sun is coming up. But with a battery there... well, I don't know what a resistor will do. A diode is usually there, which is why we keep saying diode. A diode keeps the battery from discharging thru the panel at night.

    Anyway, a 1 ohm resistor isn't going to waste much power anyway so don't worry about it. And if it really is a diode you need it there.
     
  12. smonc

    Thread Starter New Member

    Feb 16, 2014
    3
    1
    OK guys, thanks for all of the help. I think I will go ahead and get some parts, put it back together and try a few different versions. If I get something good in the next couple of months I will post it.
     
    ErnieM likes this.
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