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groingo
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# Posted: 15 Mar 2015 11:37am - Edited by: groingo
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Am looking at re locate the charge controller from inside the cabin to the panels.....to reduce power input losses over 60 feet and reduce to 3 feet, then would use 8 gauge wire to run from the controller to the batteries (60 feet) which should reduce line loss from 19.71% to 9.60%.....technically, or am I missing something?
The line loss calculator I use is here: http://www.bulkwire.com/wireresistance.asp
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MtnDon
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# Posted: 15 Mar 2015 12:03pm
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Whoa!! Is that a voltage drop of 19%??? Way too high a drop. We have a calculated drop of less than 1% at Imp and Vmp. That use #2 wire.
That is an unwieldy calculator IMO. Try this one. Just plug in the numbers.. (use "single set of wires and just the one way distance)
Long runs and I consider 60 feet a long run, usually are best with the CC near the batteries and the PV in series or maybe a series /parallel, with an MPPT CC. The series drops the amps in the long run and being close to the batteries suits the likely higher amps going into the batteries.
You can run different scenarios through the calc and come up with best wire size, etc for whatever drop you consider okay. A rule of thumb that is often used is a maximum drop of 3% but that can vary.
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groingo
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# Posted: 15 Mar 2015 12:28pm
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Honestly, these online calculators I take with a large grain of salt because if my voltage drop was as high as they say it should be the performance I should be getting would be very poor and it is just the opposite, but being me, am just looking to get a bit more.
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creeky
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# Posted: 15 Mar 2015 01:49pm
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Run your panels to the controller at higher voltage to reduce line loss.
As stated. Series connection for the panels. You have 4 panels. What does the decal on the back of your panels say for max voc?
It's real easy to hook up. To series two panels just plug the two panels together. One positive goes into one negative. Voila. Your two panels are now one panel. Double the voltage. Same amps. 1/2 the line loss.
For four panels, having series hooked up both panels. Now plug one positive into one negative. The remaining positive/negative goes to your charge controller.
That'll cut your line loss in 1/4.
Warning: you must be using an MPPT controller to turn the high voltage back into amps to charge your batteries. AND the controller must support the max voc (as seen on the back of the panel) times 4. Plus temp. compensation.
For the additional voltage cold weather creates: that's the degrees your solar panels will see below 25C times .03). Should give a fair number.
Add the VOC plus the temp number. That's the amount of voltage your charge controller must be able to handle.
If you want an example: my panels are 48v big boys at 250 watts.
The stated max voc is 57. The coldest I'm likely to see is -35. So (35 plus 25) x .03 = 18.
So I put two panels into series at 57 max voc that's 114v. I add the 18v of voltage compensation and I get 134 max voc. The highest I've ever seen from my panels is 128. So I guess it didn't get that cold this winter.
Or I'm really bad at math 
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MtnDon
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# Posted: 15 Mar 2015 02:44pm - Edited by: MtnDon
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Quoting: creeky To series two panels just plug the two panels together. One positive goes into one negative. Voila. Your two panels are now one panel. Double the voltage. Same amps. 1/2 the line loss.
Think that over and I believe you will find you end up with 1/4 the loss. Two panels in series means the comparison is to two panels in parallel. The parallel pair double the amps; or in other words, when changing to series, the amps are halved as the voltage is doubled. Both affect the calc for wire size and loss.
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creeky
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# Posted: 15 Mar 2015 06:39pm
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good one. i tried to get away with it.
by doubling the voltage ... which reduces the line loss by 1/2 ... you also 1/2 the amps. hence the 1/4.
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MtnDon
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# Posted: 15 Mar 2015 06:59pm
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It's why I believe a series parallel often makes very good sense. Even if there is slightly more charge controller loss in dropping the higher input voltage down to battery level, there are good solid advantages. MPPT only of course.
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creeky
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# Posted: 15 Mar 2015 07:29pm
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that's what i did with my second array. series parallel. i think we can get hung up a bit on that last 3% controller gain that we sometimes overlook the obvious ... like saving a tonne of money on power cable. I'm running #10 100 ft with less than 2% line loss. and the wire was $60 if I remember right.
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groingo
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# Posted: 15 Mar 2015 09:00pm
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The way I measure line loss is to hook up one panel at a time, record voltage at panel and then at the output end of the cable or am I over simplifying?
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MtnDon
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# Posted: 15 Mar 2015 09:20pm - Edited by: MtnDon
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If you are just measuring voltage with no load applied you will not get a true idea of the voltage drop.
For an example let's assume the voltage remains constant... If there are 2 amps flowing through 60 feet of #10 wire at 17 volts the voltage drop = 0.29 volts or 1.71%. If there are 8 amps flowing and everything else the same the voltage drop = 1.16 volts or 6.83%. If there are no loads on the end of the wire run there should be very little change in the readings taken at the panels and at the end of the wire run. That could be why you do not see any appreciable drop and have come to disbelieve the calculators.
In real life the both the voltage and the amperage from the panel will vary with sunlight and with the state of the battery charge. Using the theoretical calculations makes it much easier to compare what will happen when any of the variables are changed.
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creeky
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# Posted: 16 Mar 2015 11:22am
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for the sake of further discussion:
we have four panels. call 'em. 17v at 6 amps ea. Your standard 100 watt panel. the run is 60 ft of #10.
So take four 100 watt panels in parallel and you have 24 amps at 17v for 16.94% line drop.
Series/parallel 4 panels and it's 12 amps and 34v or 4.24% line drop.
All series, 6 amps at 68v you get 1.06% line drop.
A renogy mppt with 100v handling should have no trouble with scenario 3. Though you will lose some power by going from 68v in to 12v out to the batteries.
amazing how easy it is to capture a 15% efficiency increase. another reason mppt rules. rules I say.
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groingo
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# Posted: 21 Mar 2015 10:48am - Edited by: groingo
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Did the controller relocation and cable upgrade, result, now I have lots of spare cable because the performance difference was just not there.
What I did find is that the controller itself when adjusted properly worked good...problem was I would adjust and when it shut down for the night it would revert back to the much lower default settings so it had to be re set each morning but after a couple days now even the settings are holding.
The little PWM Controller is more than capable of doing what I need done and is charging much better in all conditions with amperage output now triple in most cases which wasn't much to start with but the batteries are never lacking so who am I to argue.....it's working.
As far as MPPT, all the information showed it was not effective on systems under 800 to 1000 watts and now I understand why.
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creeky
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# Posted: 22 Mar 2015 10:46am
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mppt gives you the ability to run higher voltages from your panels to your controller. thereby reducing line loss. the mppt controller will then take the high voltage and turn into the lower voltage for your battery pack. see my previous post.
mppt will also capture more power. esp. a.m./p.m. and low light / cloudy / partially shaded.
tho. if you're filling your batteries ... full batteries are full batteries. it would only give you more power if you wanted to run more loads.
like, say. for a dishwasher.
can i ask why your controller shuts down at night? it's powered by your batteries it should be on 24/7?
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groingo
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# Posted: 22 Mar 2015 12:19pm - Edited by: groingo
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Creek:
I manually turn it off because in the past it seems to backfeed and by morning I have lost a lot of juice, unplugging stopped that.
MPPT simply is not any more effective on my small system than my PWM and after three different attempts with MPPT and the warnings that if you have less than 800 watts MPPT is just not effective which may have to do with the cell scanning to capture more power where with my tiny system I don't have enough cells to make a difference.... but even with that said, in the end it is the battery resistance that controls the whole show.
Ever since I discovered the power input settings on my PWM controller it has been a whole new game and even on the worst days my batteries haven't fallen below 90% and now with more daylight hours I always have a surplus.
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creeky
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# Posted: 22 Mar 2015 05:28pm
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hey groingo. i hear the joy of long days and sunshine. i was fully charged by noon.
mppt will still allow you to run higher voltage. even with smaller systems. in my earlier post I show how to reduce 16% line loss to 1% simply by using series connected panels.
your initial concern was the power you were losing through the 60 ft distance between panel and controller. problem solved with mppt.
what panels are you using? I've never heard of panels that don't have a diode to stop back feed.
if i was losing a lot of power overnight I'd be looking at my inverter. some inverters are real energy pigs.
good luck.
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groingo
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# Posted: 22 Mar 2015 05:43pm - Edited by: groingo
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Creek:
The initial cable length was a possible issue according to all the information but in the end it simply didn't prove to be an issue to start with, just looking for a way to get a bit more.
The inverter was pulling 0.250 amps so I hard wired the switch right next to my bed, so when I am done for the night I just hit the switch and everything is off, tricky little bugger that one, only worked if I used telephone wire, the really tiny stuff.
For now, batteries are at the top of the list, these are doing great but you can never have too much... will likely get another set of the same and run them in (parallel) which will bring my AH level to 470 but for now, that tweak on the controller has really changed things for the better.
Was going to take a peek at the German made Steca Tarom MPPT 6000 but $1500 was a bit hard to swallow even though it has some very impressive features.
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MtnDon
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# Posted: 22 Mar 2015 08:22pm
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Quoting: groingo I manually turn it off because in the past it seems to backfeed and by morning I have lost a lot of juice, unplugging stopped that.
There is a problem when the charge controller causes a leakage of battery power overnight. Even the cheap HF 15 watt panels have diodes that protect against discharge when the sun doesn't shine. It could be the panels, or one of them or the problem could be in the controller. No way you should have to manually disconnect a charge controller to prevent current leakage overnight.
The inverter is another matter. They will all draw power even when not being used. Inverters with sleep/standy modes are different. They only consume milliamps, less power than the normal lead acid battery self discharge.
Quoting: groingo batteries.... ... will likely get another set of the same and run them in series which will bring my AH level to 470
Series = typo??? Probably mean parallel?
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groingo
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# Posted: 22 Mar 2015 09:20pm
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Don:
Power draw from CC is from instant on and always on LCD screen, between 2 to 5 watts.
Inverter draws 0.250 amp at rest.
Battery hookup is supposed to be parallel.....I do the same with peaches and pears.
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MtnDon
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# Posted: 22 Mar 2015 10:37pm
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OK, now I understand what you mean about the CC. That is fairly normal from what I have seen; perhaps a tad high. The Kid draws less than 1 watt; I never did meter the FM60 we used to have. I never worried about any standby uses of the CC. I consider that to be an unavoidable "cost of doing business". It is insignificant when compared alongside our normal use. The coffeemaker uses that much within seconds of pressing the start button.
Solar is supposed to make our lives better, easier, more enjoyable. We should not be a slave to our systems, IMO. It is good to pay attention to the daily performance so we can get a heads up if something is going wrong. As long as we hit float everyday the sun shines normally I'm fine.
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groingo
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# Posted: 23 Mar 2015 12:24am - Edited by: groingo
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Don:
I've always enjoyed finding out what makes things work, growing up whenever I built a model first thing I did was throw out the instructions and build it my way, must be the German, Dutch and Scott in me.....I never stop looking for a better way and mistakes make the best teacher.
Overall, the system has far surpassed my expectations and will continue to improve and thanks to keeping loads of performance records I can easily see if something is amiss and catch it early.
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Truecabin
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# Posted: 23 Mar 2015 12:52am
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ive been scrounging romex wire for awhile and just keep adding strands. i bind all 3 conductors together to make it one conductor and then solder all connections
it doesnt take long to get a lot of copper cross section like that and the amps flowing is really small for that much copper
2% for 400w on 60 feet is easy and cheap if you lower your standards hen you get it all gathered up and add some overhead capacity for more panels just put it all in a large conduit and bury it
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FishHog
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# Posted: 23 Mar 2015 07:25am
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Quoting: Truecabin ive been scrounging romex wire for awhile and just keep adding strands. i bind all 3 conductors together to make it one conductor and then solder all connections
I've never thought of that approach. Interesting idea. So would combining 2 x 14 awg wire give 2x the performance of 1 14 awg wire. I assume not, but it must be better than one.
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creeky
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# Posted: 23 Mar 2015 08:44am
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wow. that steca mppt is pretty nice. i like that it comes ready for lithium batteries. although. you can program any good controller for lithium.
and 1500 isn't bad. when you consider its two (yes two) mppt controllers in one. and handles up to 200v panel arrays. so it's a good deal for somebody building a system 2kw or higher.
plus 20 freekin' years of stored data.
two wires together basically doubles the amperage carried. just be aware of heat issues. don't overcrowd your conduit and you are also creating a magnetic field between the two parallel wires. i think some people loosely weave/twist the wire together but you might want to research that.
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