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groingo
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# Posted: 2 Oct 2014 12:36pm
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Was trying to see how much line loss so checked voltage from panels 20.5 volts, then plugged wire into panels and checked how much power coming out other end...same thing 20.5 volts over 50 feet with 10 awg wire....I has expecting to see a voltage drop so also added the normal 15 watt load and no change....what am I missing because all the information told me I would be getting at least an 8.39 percent drop.
Either way the panels are performing very well, just completed a winter time test deducting 4 hours daylight and cloudy day and passed with no concerns, unless something wonky happens the generators are in for a long winter sleep or more.
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cman47c
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# Posted: 2 Oct 2014 01:02pm
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Voltage drop at 15 Watts is about 0.9%. I assumed this to be a 12 VDC system. You won't get much drop at no load(no current)unless your meter is loading the circuit...
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MtnDon
Member
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# Posted: 2 Oct 2014 01:25pm
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Need more complete info to make a sensible reply.... How many amps are the panels Imp rated for? How many panels and how are they connected?
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MtnDon
Member
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# Posted: 2 Oct 2014 02:14pm
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The panels are probably not putting out any appreciable amount of current if they are reading 20.5 volts just before the CC. A 15 watt load @ 12 VDC is insignificant more or less.
IF the batteries had a low enough charge and the sun was very bright and full on the panels, with maximum or near maximum current flowing, then you would see a voltage drop. But when there is a small current because the batteries are full or the sun is weak you won't see the calculated maximum voltage drop.
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groingo
Member
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# Posted: 2 Oct 2014 04:14pm
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4 100 watt panels rated optimum at 18.9 volts at 5.29 amps connected
in paralell.
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MtnDon
Member
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# Posted: 2 Oct 2014 05:01pm
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Thnx. IF the panels were putting out their std rating; 18.9 volts and 21 amps total, with 50 ft of #10 my calc indicates a loss of 13.44% or 2.54 volts at the far end. At the same volts but with only 8 amps flow the drop calcs to just over 5% drop.
So thinking about this some more.... If you unplug the MC4's and measure panel voltage at the panel output you should be getting a voltage close to the Voc. That's an open circuit so if the sun is bright and the panels not any warmer than STC (77F) the voltage should be close to Voc. As the panels heat up the voltage will fall, as you are aware. It could even go higher with new panels. As soon as you connect the MC4's and power reaches the CC and batteries that value will fall.
Try this; reconnect the MC4 plugs to the panels. Disconnect the PV input wires right at the CC and measure the voltage across the wires from the PV at that point. I don't think you will see any voltage drop as there is no current flow. The voltage should only drop when there is sufficient amps being pushed through those 50 foot lines. The resistance to pushing those amps is what drops the voltage. A simple voltage measurement should not cause any real flow of amps.
Sort of like putting a water pressure gauge on the end on a hose. No flow but the gauge measures the pressure fine. When water flows the pressure will drop.
If your CC indicates amps coming into the CC you could measure the voltage at the CC when the current flow is 20 amps. Measuring voltage at both ends at or near the same time while the current flows may be a tad difficult. Two people with matching meters would be nice. I'm not sure if all that will prove anything though.
I have never bothered trying to measure drop over our 325 feet. The wires are large enough that the drop should not exceed 1% at Vmp and Imp. Readings at the CC are often at or higher than the rated Vmp. Mostly the panels are cool which helps. The current often exceeds the Imp and that can be explained in part to the altitude. Less air and clean mtn air to boot = more sunshine hitting the panels.
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groingo
Member
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# Posted: 2 Oct 2014 05:43pm
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Don,
Just looking to establish a baseline for future comparisons....I am a record keeping fanatic and it helps me understand things better.
What I know fore sure is the batteries are happy as hell and have not dipped below 12.66 and typically run like this morning 12.71 and fluid levels are spot on in nearly two weeks now....dam~ it's nice not to have to spend a day a week babysitting the geny!
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Truecabin
Member
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# Posted: 3 Oct 2014 02:47pm
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you might do your record keeping with a larger load than 15watts thats a small load, find a bigger test load like 4 amps (4 x 12.66 = 50watts)
you sure its 8.39% drop that sounds like a lot for 1.+ amps but i didn't look at the tables
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toyota_mdt_tech
Member
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# Posted: 3 Oct 2014 09:42pm
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I'm not savvy on this solar stuff, never looked into it, but with multiple panels, could one series them together. set them up to produce a much higher voltage, so wire size to controller can be much smaller (or the same with much lower loss) and then regulated or bumped down lower at the controller and battery bank?
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razmichael
Member
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# Posted: 4 Oct 2014 08:38am
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Quoting: groingo Just looking to establish a baseline for future comparisons....I am a record keeping fanatic and it helps me understand things better.
Not sure why you would want to try to measure voltage drop as it provides no ongoing useful information IMO. When you use a calculator (or calculate the hard way), what you are figuring out is the impact of the wire resistance on the voltage (how much of the total voltage drop across the whole circuit is a result of the two wire portions on either side of the main load - assuming a single load). With V=IR, the resistance in the wire is the same (ignoring temperature changes) but the Voltage drop goes up as the current goes up. This is why the calculators include the current value and you plug in the maximum current you expect to see in the circuit then design wire size to keep the max voltage drop to an acceptable level. If you really want to measure something measure the resistance in the wire (or the complete circuit) and then later see if this changes which might indicate a bad connection but other than that, monitoring voltage drop is time better spent drinking beer, fishing, sitting on the deck etc.
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ILFE
Member
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# Posted: 4 Oct 2014 09:02am - Edited by: ILFE
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groingo,
Is there a specific reason you are running the four panels in parallel, rather than in series, or series-parallel? PWM controller?
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groingo
Member
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# Posted: 4 Oct 2014 10:42am - Edited by: groingo
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ILFE
This was a package deal and I am just running them the way they suggested which keeps my voltage constant but maximizes my amperage for charging which is working out sweet, even the little PWM charge contoller has been impressive.
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ILFE
Member
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# Posted: 4 Oct 2014 11:33am
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Cool. I am under the impression the controller is a 30 ampere controller? If so, you could probably get one more 100 watts panel, due to overall losses, and connect it in parallel with the others.
Just a thought. I did that with my MorningStar ProStar 30m controller.
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ILFE
Member
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# Posted: 4 Oct 2014 11:34am - Edited by: ILFE
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duplicated post.
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groingo
Member
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# Posted: 4 Oct 2014 11:53am
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ILFE
Yes it is a 30 amp controller so there is room to grow into it but as it is now my daily power requirements are very low at under 1/4 kwh a day so I regularly have a power surplus and the colder the panels and feed wire get the higher my output over the cooler months, it is actually working far better than expected at this pont.
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