Wire sizing or Good theory

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ArmyVet
ArmyVet Banned Posts: 20 ✭
in Solar Beginners Corner #1
Here's a good Question. Most people would go out and get 10 ga Wires for 30 amps or less run. Now Lets take a crazy thought. I was looking at 15 amp , 16 Ga 50 Foot extension cords. Lets say let get 2 cords 50 foot each.. Take each strand of 16 Ga wire in each cord. Which would be 3 Wires each cord. Lets tie all 3 wires together.

Do that for both positive and Negative sides. Wouldn't that be more effective.
Than just running 10 ga wire each side. Even though the cord is rated at 15 amps.
Do they mean 15 amps each wires or all together. I was looking at this today.
I stripped the ends off a 50 Foot cord , And tied them all together and compared them to 10 ga wire size. And actually it looks a little bigger. even though each wire is a separate run. Tied together wouldn't they all share the current. Say if your running 10 amps...y theory sharing wouldn't be 3.34 amps per wire on Load.
Just a wild Theory..Any Ideas.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
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    Re: Wire sizing or Good theory

    you are confusing standardized ac wiring practices with dc. there are limits on the distances for both, but it is more pronounced at the smaller dc voltages solar uses and as such the current rating is not standardized for dc as it needs calculated. you can see that in the voltage drop calculator in the facts area of the forum.
    as to combining wires to increase the ampacity, yes, this is true. you will find in any install that needs an inspector's approval that the practice of paralleling those wires will not be allowed. it literally will confuse an inspector.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: Wire sizing or Good theory

    To elaborate a little, the reason why such parallel circuit paths is frowned on is because one (or more) of those paths may fail, leaving the other(s) to carry all the load. So a wire that should be carrying 50% of the Amps suddenly gets saddled with 100% - and fries. A single, larger wire will not suffer this fate.

    (File this under "Why 'Coot hates AIMS inverters". :p )
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  • ArmyVet
    ArmyVet Banned Posts: 20 ✭
    #4
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    Re: Wire sizing or Good theory

    Well here's the deal Guys and why I popped this question.
    I have 2 - 100 watt Panels 22.1 Voc Max 4.8 amps max each , The run of cable i need happened to be at 48 feet. So I figured 100 feet of Quality 10 ga,
    But when I went to go they wanted almost $1.50 per foot at my local hardware store. Then while out shopping I noticed 50 Foot 16 Ga Outdoor extension cords on sale for $3.99 each...And then the Idea popped in my head. $10 versus around $160 was a a no brainer. And actually the result were quite surprsing.
    Using all 3 wires as One each Positive and Negative in was a Positive outcome.
    In fact i had 13 amps running in on a Very Clear Sunny day. The wire didnt heat up
    or falter , Yes I am using a charge controller 20 amp charge controller.
    Voltage drop was only 0.30 Volts versus single 16 ga at 1.42 Volts...
    I was like hmmm This worked. For my setup. Its just there to charge batt bank of 450 Ah. I used Several LED lights the G4-5050 12 LED. Plus a 12 Volt fan.
    And a 400 Watt poweriverter for other small devices I might need to use to cut down on lighting bill. I cut out over 850 Watt incandence lights with this way. I use a total of 18 of the LED lights. And I use a Car Radio I had also for Stereo..lol..
    Its works for me, and I saved around $50 on my power this month.
    This is a not a permanent set up. It basically portable. Because of the place I live at I rent. And it does work .
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
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    Re: Wire sizing or Good theory

    it might seem like it's working, but i don't think the 200w of pv is going to charge the 450ah of batteries all that well. roughly 10a of pv divided by 450ah of batteries is a bit over a 2% charge rate, if you are in fact getting that much current from the pvs. i'm also unsure of how much power you have drawn out of the batteries as it needs replaced and a bit more for losses. this could mean the batteries are slowly draining downward and not being properly charged back up and will lead to the batteries having an untimely death.
    we generally recommend at least a 5% charge rate to the batteries. if you lack the room and/or monies then you should get another charge source just to keep the batteries from going bad. a utility charger, or if you're desperate you can charge them from a car alternator (note that is a lot of driving or idling and is a waste just to charge batteries), will help put some of the bulk current back in while the pvs could top it off. that would be without any loads on them to draw the charge rate down even farther.
    you should be able to find #10 wire cheaper than $1.50/ft. you can buy very large gauge wires for that much money. even lowes has it cheaper than you have found as they show a 500ft spool of #10 for about $90 and you don't need anywhere near that much wire. you can find cheaper than the likes of lowes or home depot i'm sure, but if there aren't any places close to you to buy out of a store then you can order something from our host.
    http://store.solar-electric.com/hardware---wire.html
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: Wire sizing or Good theory

    Niel's right, of course; 450 Amp hour wants more than 200 Watts of panel for charging. More like this:
    45 Amps (10%) @ 14.2 Volts (charging for 12 V system) = 639 usable Watts or about 800 Watts of panel when all is said and done. At a minimum 5% you'd be around 1/2 that - 400 Watts.

    You've only got 200. That's in the "enough-to-eventually-replace-the-Amp-hours-but-not-enough-charge-rate-to-remix-electrolyte-and-prevent-sulphation" category.

    If you're going to run parallel wires from panels, use one set at each panel and tie them together only at the charge controller.

    Better yet, get yourself two more panels and an MPPT controller and wire for series/parallel and increase the array Voltage. It will really help on that 50' run of wire.

    Won't help any on saving money, though. :cry:
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  • ArmyVet
    ArmyVet Banned Posts: 20 ✭
    #7
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    Re: Wire sizing or Good theory

    Update you all, Yes I have a MPPT Charge Controller.
    Actually today I was doing some more reading on my Controller.
    Maybe I should have stated first, After doing some crazy measurements.
    The MPPT controller is boosting the amps, Today, I had full sun again.
    and was charging the batts with 16.4 amps, and I thought What the hell.
    Controller does go into equalizing for about 1 hr then tapers off to float charge.
    And Yes I try to conserve. This is just a temperay setup.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: Wire sizing or Good theory

    With an MPPT controller you could put your panels in series and get 44.2 Volts @ 4.8 Amps - pretty easy to handle current-wise and less Voltage drop over 50' of wire. The controller will "sort it out" before feeding the batteries. :D
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  • ArmyVet
    ArmyVet Banned Posts: 20 ✭
    #9
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    Re: Wire sizing or Good theory

    I was actually considering doing that. After I had read the manual. The controller can take up to 75 Volts So, Yeah depending on what the outcome is. I can switch them tonight and test in the Morning to see if I get the same Amps. Look like we have 3 very clear sunny days in the forcast so the next 3 days will tell the story.
    Btw . after checking on the volts I got max voltage of 23.00 even today.
    So seems the Solar panels are putting out a little more than rated.
    So max voltage of 46 I say for series . That should make it more interesting.

    also I like to say, it funny how they say you can get only like 4-5 hrs of average sun light power when i get almost 9 hrs. I am using a Tv antenna rotor I had that was programmable for turning whenever you want. I have it programed to turn every 30 minutes just a little bit. and at a certain time of day have it go back to the morning view. But you still have to make minor adjustments for seasonal changes.
    Its makes for a excellent cheap tracking system.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: Wire sizing or Good theory

    The maximum input Voltage for the controller should be based on Voc, not Vmp, as that is what will be present before the controller starts charging. This could be higher than specified if you are in a cold and/or high location. Panels will produce their Voc the minute the sun hits them, even if it's not "straight on" and able to put out maximum power. Your reading of 23 Volts (these are "12 Volt" panels, yes?) would be within limits for two in series all right.

    As for hours of sun, we don't say only 4-5 hours. That is the average of "equivalent good sun", based on year-round, middle-of-the-hemisphere data. It can change quite a lot depending on the specific site. You're using a tracking system, which can add quite a bit. If I had such a thing up here with our 16 hour Summer days my daily yield would be 2-3 times what it is with the fixed mount! :D

    TV antenna rotor? Where ever did you find that? Some museum? :p I remember when they were all the rage. You could walk through the village of an evening and watch the antennas turn on the half hour as people switched channels and re-aimed for best reception! We had three channels to choose from, too! :D
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  • ArmyVet
    ArmyVet Banned Posts: 20 ✭
    #11
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    Re: Wire sizing or Good theory

    Yep ye old Antenna rotor trick
    This is a similar one I use, Same brand. But with actual timer to move.
    http://www.solidsignal.com/pview.asp?mc=03&p=AR-500-XL&d=Centronics-AR500XL-Programmable-Antenna-Rotator-%28AR500XL%29&c=Antenna%20Rotators&sku=
    This was mine I used on my antenna until a wind storm decided otherwise.
    So I put it to better uses. lol
    i plan on doing a actual tracking device sensor build. because after awhile
    the programming because a pain in the rear end. But I will use this rotor.
    because it has no weight bearing on thanks to the pressed on Bearings my father did on my pole. It basically floats on the rotor.
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  • ArmyVet
    ArmyVet Banned Posts: 20 ✭
    #12
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    Re: Wire sizing or Good theory

    Think I just got a chub ! check out Volts/Amps around 11:30 crazy power...

    47.1 Volts coming in Charge charge power hitting Batteries was at
    this charging charging 13.7 volts and rising at a charge current of 19.4 amps..
    Ill stick at the series high voltage. Since it like to charge better.
    I ran on the 400 watt power on my 32 inch Inch TV last night.
    Wanted to pull some power to see what the charging affect would be today.
    the other was maxed 16.4 amps.. So far 19.4 amps charging makes me happy.
    But think I want a MorningStar MPPT 60 amp controller now.
    Thinking of adding 4 more panels at 100 -120 watt each..
    Make it a more powerful solution and use a 1000 pure sine wave inverter.

    Also found some 8 GA Wire its for car audio..But good stuff at 100 foot rolls $39 :)
    Ill get 2 !
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #13
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    Re: Wire sizing or Good theory

    "Free power" can be addictive (and expensive). :roll:;)

    But the alternatives of paying huge power bills/running a genset sure make it a very interesting alternative.

    By the way, have you been paying attention to your battery bank's state of charge (specific gravity, resting voltage, battery monitor, etc.)? 13.7 volts still sounds low for charging--Either the battery is fairly discharged (below ~90-80% state of charge), the charging voltage points are not correct yet, or there is a miss-calibrated voltmeter/large voltage drop in the wiring somewhere (too small/too long of wires from charge controller to battery bank bus connection).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #14
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    Re: Wire sizing or Good theory

    Yup. You'll want more panels and more battery and a bigger inverter to run more loads ... it never ends! :p

    But yes; the charging Voltage on a "12 Volt" system ought to be up around 14.2-14.4. And even at 19 Amps you are still under the 5% minimum rate for a 450 Amp hour battery bank. You should put a charger on those batteries and see if you can't get them up to full before they start to suffer the effects of long-term under-charging.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #15
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    Re: Wire sizing or Good theory

    more pvs is a very good idea. make sure you bring the battery up to full in the meantime even if you must not use the power for the number of days needed to achieve that.
    as to the hours of sun we often refer to, this would be full sun hours based on the intensity of 1000w/m^2 and not whether or not it is daylight. during the course of the day the smaller intensities seen would add up just like kilowatt/hours do for electrical power meaning 2hrs at 500w/m^2 intensity would be equivalent to 1hr at 1000w/m^2 or one full sun hour as i like to call it. the 1000w/m^2 figure was not something we came up with as the pv industry did that as the pvs are often rated at that intensity.
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  • ArmyVet
    ArmyVet Banned Posts: 20 ✭
    #16
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    Re: Wire sizing or Good theory
    BB. wrote: »
    "Free power" can be addictive (and expensive). :roll:;)

    But the alternatives of paying huge power bills/running a genset sure make it a very interesting alternative.

    By the way, have you been paying attention to your battery bank's state of charge (specific gravity, resting voltage, battery monitor, etc.)? 13.7 volts still sounds low for charging--Either the battery is fairly discharged (below ~90-80% state of charge), the charging voltage points are not correct yet, or there is a miss-calibrated voltmeter/large voltage drop in the wiring somewhere (too small/too long of wires from charge controller to battery bank bus connection).

    -Bill

    After Further testing it was in Bulk charge mode, After it stayed at 19.4 amps till it got to 14.4 and stayed charging for 2 hrs at 18.5 amps then dropped into float mode. The MPPT charge controller I got is a Wellsee.. It wasnt th best in the world. But seems to work. Till I save up for the Big Morningstar 60 MPPT charger I want for expanding. When it dropped to float mode it has a float charge of 2.5 amps feeding the battery bank. As for a 450 Ah being to much for this set-up.
    In my Opinion I think its BS. My batts test out fine for secific Gravity and all cells are in rang of Voltages. When it seems to being equalizing fine. And bring the batts to full capacity. Considering that there is 6 each 12 Volt 75 Ah batts.
    I dont think its to much overkill. The over kill comes when I add the other batteries I have to the bigger set-up soon. Which I keep maintained and charged.
    because I have 45 - 35 Ahr CBS Sealed lead acid batts awaiting. Yes that right 1575 Ah awaits for me.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #17
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    Re: Wire sizing or Good theory

    "I have 2 - 100 watt Panels 22.1 Voc Max 4.8 amps max each"
    "After it stayed at 19.4 amps till it got to 14.4 and stayed charging for 2 hrs at 18.5 amps then dropped into float mode."

    what am i missing here as you are claiming around a 100% jump in current? no mppt controller will ever do that with the stated pvs. if you are getting 19.4a somehow then i can see it to be possible to charge the batteries even if the charge percentage is still considered on the low side, but i don't see 2 100w pvs doing this for with your stated readings it would be 19.4a x 14.4v = 279.36w. that's pretty darn good for 200w in pv. are you using mirrors or smoke and mirrors?:confused:

    bs? i don't know about that for we go by what you have stated as equipment. you can believe what you want and do as you want, but based on what you've posted the bs seems to be from you.
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  • ArmyVet
    ArmyVet Banned Posts: 20 ✭
    #18
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    Re: Wire sizing or Good theory
    niel wrote: »
    "I have 2 - 100 watt Panels 22.1 Voc Max 4.8 amps max each"
    "After it stayed at 19.4 amps till it got to 14.4 and stayed charging for 2 hrs at 18.5 amps then dropped into float mode."

    what am i missing here as you are claiming around a 100% jump in current? no mppt controller will ever do that with the stated pvs. if you are getting 19.4a somehow then i can see it to be possible to charge the batteries even if the charge percentage is still considered on the low side, but i don't see 2 100w pvs doing this for with your stated readings it would be 19.4a x 14.4v = 279.36w. that's pretty darn good for 200w in pv. are you using mirrors or smoke and mirrors?:confused:

    bs? i don't know about that for we go by what you have stated as equipment. you can believe what you want and do as you want, but based on what you've posted the bs seems to be from you.

    This could be an anomaly from the solar panels. stated watts are 100 . But when I tested yesterday short circuited I got 22.8 Volts 6.91 amps. So maybe they were underrated panels. So who knows. But the average amps has dropped down to 17 amps charging at 14.4 volts. either way I'm happy with the results.
    And Sorry you think its BS. But Amp meters don't lie much. at most it might be off by .1 amp. But even so. Its still good results on the cheap side.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #19
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    Re: Wire sizing or Good theory
    ArmyVet wrote: »
    This could be an anomaly from the solar panels. stated watts are 100 . But when I tested yesterday short circuited I got 22.8 Volts 6.91 amps. So maybe they were underrated panels. So who knows. But the average amps has dropped down to 17 amps charging at 14.4 volts. either way I'm happy with the results.
    And Sorry you think its BS. But Amp meters don't lie much. at most it might be off by .1 amp. But even so. Its still good results on the cheap side.

    Amp meters don't lie much, but sometimes displays on charge controllers do! :p
    Bought some surplus panels, did you? They often sell "derated" units that are "defective" and can't be guaranteed to produce full Watts. Sounds like you got lucky with yours.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #20
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    Re: Wire sizing or Good theory

    Yes, unfortunately, charge controllers tend to over estimate current/power by 5-10%, and in some cases/conditions by 30%.

    It is a choice--less expensive and less accurate meters on solar charge controllers--or more expensive and accurate meters.

    In the end, for many people, they would probably be better off getting a Battery Monitor... This should be 2% or better accuracy--plus they keep track of how much current is going into/out of the battery over time.

    For Thin Film panels--they tend to over rate them by ~25% or so to account for the fact they degrade over the first 6 months by 20% in sunlight to their "true ratings".

    So add up the metering errors and thin film panels--and people can get a real surprise when looking at their system's output current/power. The reality is that most systems, on long term average, produce about 77% of their panel's rated power.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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