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  • Jay Francis
    Hi All, Just starting to learn about solar and came across this group. Looking forward to tap the experience here and hopefully be able to add to the
    Message 1 of 90 , Apr 22, 2012
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      Hi All,

      Just starting to learn about solar and came across this group. Looking forward to tap the experience here and hopefully be able to add to the knowledge base over time.

      Jay Francis
      Merrimack, NH
    • B
      Actually, upon a little more reflection, perhaps the better thing to do, is hook the speed controller to the output voltage of the panels. The speed
      Message 90 of 90 , Nov 21, 2014
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        Actually, upon a little more reflection, perhaps the better thing to do, is hook the speed controller to the output voltage of the panels.  The speed controller would then act as a crude max power controller for the panels.  The big issue is the peak current of the motor damaging the wiring in the panels. The motor is going to suck down over 10A when the speed controller has the motor connected.  The capacitor bank will likely cost more than the motor for one that can hold the panel ripple to a reasonable level.  

        What did we do before ebay?  I like how they are orange.... as is only proper....  80,000uF at 50V is 100 Joules.  Yikes!  Anyway, that's enough to power the motor for a second or so at 100W.  In the ballpark.


        On Fri, Nov 21, 2014 at 10:58 PM, B <perlan10a@...> wrote:
        I do respect that driving wildly dynamic loads of a motor is difficult with a solar panel.  The back of the envelop calculations say that my current swamp cooler AC motor is rated at 3/4HP.  That's ~750Watts of work.  However, I never run it at the "hi" setting and always at low so the power I use to run the swampie is some fraction of that.  A quick look at a swamp cooler spec, that 3/4 HP motor generates 6400cfm.  Far too much for my winter hot air heater box in the winter anyway.  

        I did find this curve.  Seems the squirrel cage efficiency peaks at ~40% of max.  If I make the assumption that 100% output is 3/4HP (750W), then at peak efficiency of the blower, I need around 25% of that.  187W

        Inline image 1

        On the other side of the envelope, there are motors available that do run off of batteries and provide gobs of torque for e-bikes.  http://www.monsterscooterparts.com/48v-500w-motor.html.  $50

        In the winter, perhaps hook up a couple used panels off of ebay (perhaps ~200Watts peak), a gigantic capacitor, and a speed controller to control the cfm connected to regulate outlet temperature of the heat box?  IDK... I can't see why it wouldn't work but I do appreciate that nothing is simple.  Anyway, the idea is as the outlet temperature rises, the speed controller speeds the fan up, up to full energy the panel is collecting. 

        Has anybody seen any curves of outlet temperatures vs CFM for a 4x8 screen absorber hot box on a bright day?   I suspect the e-bike motors are reasonably efficient over a broad band rpm band but I could be wrong there.  

        There's a lot to consider and I've just started but I'm certainly interested in seeing what is possible... affordably. 

        On Fri, Nov 21, 2014 at 8:30 PM, alfred coppa bornagain96022@... [SimplySolar] <SimplySolar@yahoogroups.com> wrote:

        We are not talking about normal things here. Everyone who knows about power companies and power supplies and 120 volt battery banks knows all that stuff. What I thought that we were talking about here was someone hooking up a few solar panel and pointing them to the sun and having them run something. As the sun moves so does the output of the panels. The motor is not a resistor or a light bulb. The motor almost draws no current when there is no load on it. But when you connect a squirrel cage blower the whole thing is regulated by the load put on it by the movement of the air. I didn't think that anyone was going to out a buy $2,000 worth of solar panels to power one blower at full output. That would be a total waste of money and time. Al

        On Friday, November 21, 2014 6:49 PM, "RV7 builder mcsophie@... [SimplySolar]" <SimplySolar@yahoogroups.com> wrote:

        On 11/21/2014 4:58 PM, alfred coppa bornagain96022@... [SimplySolar] wrote:
        I am sure that there will be a lot of debate about this but I will start it off here. I actually did this about 6 or 7 years ago. I experimented with every electric motor known to man. I bought 12 vdc motors and 24 vdc motors and 48 and 90 volt motors. I hooked them up to a swamp cooler and played with different voltages coming from a power supply. This is what I found out: The speed of the motor is determined by the voltage supplied to it. Example: A 24 VDC motor with 24 volts will run at its rated RPM and that number in most cases is 1750 RPM.  Half voltage results in half speed.
        This is the big problem: The faster it turns the more current that it draws because the more air it blows. People think that it is a linear function, but it is not. The manufactures of fan blades know what is going on, but most people don't. If you double the speed then you more than double the current. It is not a case of  doubling one and the other doubles. I found that if you run a 90 volt dc motor the voltage is what does the work and not the current. The higher the voltage the lower the current. With solar panels it is easier to come up with voltage than it is to come up with current. If I put 3 85 watt panels in series you  get almost 50 volts at 4 amps. Not that many amps, but enough voltage to run a 90 volt motor at almost half speed. This a no load speed not actual speed under a load. You can do this. I have done it. Al
        Correct about the non-linear nature. But it would be safer to just talk about power.  Just applying a particular voltage won't run a device rated at that voltage unless the power source can supply adequate current at that voltage. P (power, in watts) is V (voltage) times I (current). Another way of stating it is P=V squared divided by R (resistance). Doubling voltage at the same resistance gives 4 times the power. Conversely, if you hold resistance (motor winding) constant and halve the voltage, you have 1/4 the power.

        The above is a gross oversimplification when talking about inductive loads like motors (especially if talking about AC motors instead of DC motors), but does come a little closer to what's happening. Here's the 1st site I googled showing V-I-R-P relationships.


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