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On 5/20/2012 7:20 AM, Larry Crutcher, Starlight Solar Power Systems
wrote:
<blockquote
cite="mid:41D997FD-6262-411F-8C85-E4F00A1FA6D9@starlightsolar.com"
type="cite">boB,
<div>
<div>I know I'm getting out of my league here but I'm so
intrigued. Doesn't a LCB device work on a feedback loop that
looks at the output voltage and current to a load and compares
it to input voltage? Since we have two fixed values here, 29Ω
resistance and 4.15A PV current, how can there be any excess
voltage at the circuit input?</div>
<div><br>
</div>
<div>I can see that the PV modules should produce 1kW @
500W/m2 IF the load allowed it. As Kent said, the resistance
would have to change to 58Ω. On the other hand...if I don't
understand the function of a LCB...operating the PV module at
170 Vdc would result in 5.87 amps while feeding a 29Ω load. </div>
<div><br>
</div>
<div>Counterpoint? Inquiring minds want to know!</div>
</div>
</blockquote>
<br>
<br>
I don't know exactly how they work either... There was not quite
enough depth on the web site I went to. <br>
<br>
It just seemed sorta (to me) like what I described... An MPPT
without batteries running on the input (PV) side. <br>
i.e. Higher input voltage at a lower current transforms into lower
voltage at higher current at the output side.<br>
<br>
I did find some supposed' LCB schematics online that were pretty
much was what I expected. <br>
<br>
To get max current and therefore max power across an output
resistive load, the input voltage must be<br>
at MPP voltage of the PV which (to me) means it would have to be an
MPPT type device. Without a<br>
battery, the output voltage would not matter so I think of it as a <br>
<br>
Another use for a circuit like this would be a cathodic protection
device. <br>
<br>
So, if that is the case, it could be correct as is, OR, may be with
SMOP (Simple Matter Of Programming) which isn't<br>
necessarily all that simple. Looks like the voltage that Mick is
looking for may be too high for the application<br>
he is wanting though.<br>
<br>
Please let me know if I'm wrong here as I'd love to know.<br>
<br>
boB<br>
<br>
<br>
<br>
<br>
<br>
<blockquote
cite="mid:41D997FD-6262-411F-8C85-E4F00A1FA6D9@starlightsolar.com"
type="cite">
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<div>On May 19, 2012, at 10:16 PM, <a
moz-do-not-send="true"
href="mailto:boB@midnitesolar.com">boB@midnitesolar.com</a>
wrote:</div>
<br class="Apple-interchange-newline">
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<div bgcolor="#FFFFFF" text="#000000"> On 5/19/2012 5:47 PM,
Larry Crutcher, Starlight Solar Power Systems wrote:
<blockquote
cite="mid:31EC5436-9CFD-43A8-A0F1-9A58C51B659A@starlightsolar.com"
type="cite">Good one, Mick. Here's the way I see it:
<div><br>
</div>
<div>For question one, I say yes, other than the obvious
wire and connection losses, because you are operating
the cell(s) at the peak power point.
<div>
<div><br>
</div>
<div>Since a PV solar cell is a constant current
device and your 29 ohm load did not change,
reducing your Lab Light source to 500 W/m2 can
only affect the voltage and resulting power. This
means your load forces the voltage down to 120
volts resulting in 500 watts of power dissipated.
You have forced an IV curve shift of current AND
voltage.</div>
<div><br>
</div>
<div>The LCB boosts current based on IV curve
voltage. I don't think an LCB can change anything
in this scenario since you have forced the circuit
to operate at 120 volts and 4.15 amps.</div>
</div>
</div>
</blockquote>
<br>
<br>
<br>
Realizing that these LCB things run off the PV input
because there is no battery.... If an LCB outputs<br>
maximum current into a fixed resistance, (and therefore
maximum power), kind of like an MPPT<br>
charge controller does, then it ~should~ adjust its
voltage "gear ratio" to maximize the output <br>
current and power. <br>
<br>
At least I think the idea is correct, if the LCB was large
enough and high enough voltage operation<br>
for your application. But then again, I may be missing
something here too.<br>
<br>
<br>
boB<br>
<br>
<br>
<blockquote
cite="mid:31EC5436-9CFD-43A8-A0F1-9A58C51B659A@starlightsolar.com"
type="cite">
<div>
<div>
<div><br>
</div>
<div>Keep in mind that I'm a solar dummy. My logic
may be faulty.</div>
<div>
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</blockquote>
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<div>Larry Crutcher</div>
<div>Starlight Solar Power
Systems</div>
</div>
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<div>(928) 342-9103</div>
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<br>
<div>
<div>On May 19, 2012, at 12:35 PM, Mick Abraham
wrote:</div>
<br class="Apple-interchange-newline">
<div>Hi, Wrenchies~</div>
<div> </div>
<div>Kindly educate me regarding PV behavior
when the load is a resistor. Here's a
hypothetical situation:</div>
<div> </div>
<div>* Eight 250 watt PV modules (60 cells per
module), all connected in series for "peak"
ratings of 240 volts DC & 8.3 amps </div>
<div> </div>
<div>* Lab type cell temperature
& illumination so that the eight would
truly pump 2,000 watts <strong><em>into an
ideal load</em></strong></div>
<div> </div>
<div>* A 240 volt AC heating element designed
for 2,000 watt heat dissipation at 240 volts
AC...that's about 29 ohms resistance for the
heat element</div>
<div> </div>
<div>* Connect the PV string to the heat
element, with nothing in between except a
fused disconnect.</div>
<div> </div>
<div>In the above situation, would the
resistance of the heating element be all
that's needed to force the PV array to operate
near the "peak" wattage?</div>
<div>Would the heater actually get 2,000 watts
to turn into heat?</div>
<div> </div>
<div>+++++++++++++++++++++++++++</div>
<div> </div>
<div>Now consider the same cell temperature but
half the illumination. That's similar voltage
but half the amps at peak wattage. If this is
sent into the same 29 ohm</div>
<div>resistor--again with no intervening
electronics, could we count on 1000 watts of
heat?</div>
<div> </div>
<div>If the answers come up "no", would the
power throughput be helped by a
SolarConverters style MPPT pump controller
(Linear Current Booster kinda thing), assuming
that one could be found to operate in the 240
volt range?</div>
<div> </div>
<div>Thanks & Jolliness,</div>
<div><br clear="all">
Mick Abraham, Proprietor<br>
<a moz-do-not-send="true"
href="http://www.abrahamsolar.com/"
target="_blank">www.abrahamsolar.com</a><br>
<br>
</div>
</div>
<br>
</div>
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