24V Pannel with 12V system wire size???

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ouello
ouello Registered Users Posts: 21 ✭
in Off Grid Solar & Battery Systems #1
Hi everyone,

I have a cottage that has propane appliances and tank-less water heater. I use solar only for CFL/del lights, tv, 12v 4A water pump to put pressure in the pipes (shower...) So the load is never too big... And we go there every other week-ends. I wanted to size up only to give me more power in the winter months...

I have 7x 12V 50ah, 30A MPPT charge controller, 235W panel (little less than: 30V 9A) and a 12V 1000W inverter...

Items in red are new replacing my current 60W panel...

I know a lot of you have their personal preference when it comes to solar, and I know you'll give me some pros and cons and this, but I really just need a little advice to work with what I have!

My panel is a little far (50-75 feet), my battery bank is very close to everything else...
I'm not sure what wire size I have right now, but it looks like #6 or #8 all over and I better size up the battery bank before I plug in my new panel!

So what would be:

Wire size panel (24v) to controller?
controller (12v) to battery bank (12v)
Battery bank (12v) to inverter (12v)

I know this is never a simple question, but please don't over think it an give me what you would do...

Thanks for any help you can give me!!!8)

Image is my old config...
Attachment not found.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: 24V Pannel with 12V system wire size???

    Welcome to the forum.

    Shall I mention that the battery bank is a problem waiting to happen? You've done about the best you could for wiring that, although the wire size looks rather small. A 1kW inverter on 12 Volts can draw 100 Amps or so at maximum power/minimum Voltage. That would require 4 AWG minimum, and would be better with 2 AWG. But you probably don't use it at full power. There does not appear to be any circuit protection (fuse/breaker) on it either.

    On to the next wire! Your panel probably is rated around 8 Imp @ about 30 Vmp. The distance will make a big difference: 50 feet would have about 2% Voltage drop on 8 AWG wire. At 75 feet that drop goes up about 1%. Could be just over 3% then, which is around the limit you'd want. Less is better.

    The output of the controller: 30 Amps is large for 235 Watts - planning on adding a second panel? With one it's likely to be about half that. Again, distance makes a difference here as you don't want too much V-drop to the batteries. 10 AWG can handle 15 Amps @ 12 Volts for 5 feet with only 1-2% Voltage drop. If you are planning on adding a 2nd panel you might as well wire for it now. The same wire size will suffer an additional 1% drop if you double the current. This is another line that should have some form of circuit protection on it.

    Your battery bank is theoretically 7 * 50 = 350 Amp hours. That 15 Amps of current won't be too much for it. In fact it won't be enough; only 4% peak charge rate. You should probably re-evaluate your load requirements, adjust the battery bank capacity accordingly, then change the charging to suit. Three or four of those batteries will charge very nicely from that much panel, and would supply up to 900-1200 Watt hours, a fair size system.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #3
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    Re: 24V Pannel with 12V system wire size???

    since you want more power in winter I would go for the second panel.
    As well look into what the max input voltage to you MPPT charger is. If it will handle 60 volts I would run 2 panels in series to the CC to minimize line loss. will need bigger circuit breaker for the CC input disconnect.
    Consider going to 24 volt battery if your loads are to increase ( they will anyway).
    HTH

    ps where in the Great White North are you? Winter temps are a big consideration for max voltage produced
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • ouello
    ouello Registered Users Posts: 21 ✭
    #4
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    Re: 24V Pannel with 12V system wire size???

    Thanks for the info guys! I forgot to ask these questions earlier also about the fuse... I do want to put some everywhere I can... I do have a 75 amp (I think) breaker... I plan to buy those car fuse?!?! Are does good for solar purpose? And what amp rating should I get? I can't wait to know everything, but there's so many variables...
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
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    Re: 24V Pannel with 12V system wire size???

    For low power 12 Volt systems good quality automotive fuses and holders will work. But, that panel @ 30 Vmp is too high to be fused with auto-type fuses. The output from the charge controller could be, but (the buts keep butting in) if you get ones that aren't good they'll cause more problems than they're worth.

    This 75 Amp breaker; AC or DC? You can't use AC rated equipment for DC. Some (few) have ratings for both. And as always the Voltage rating figures in to it.

    You've got three circuits here with three different current ratings: Panels to Controller, Controller to Batteries, Batteries to Inverter. Each has to be planned first so that you know how much current is expected and how long the wire runs will be.

    I agree with Westbranch about adding the second panel in series, or at least planning for that now, and looking carefully at the Voc issue. That panel's Voc is around 38, which means in our wonderful Canadian Winter (snowstorm outside today) it can reach perhaps 50 Volts. Two of these in series could hit 100 Volts, and that can be over the input limit on the smaller MPPT controllers.
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  • ouello
    ouello Registered Users Posts: 21 ✭
    #6
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    Re: 24V Pannel with 12V system wire size???

    So I need a fuse between the panel and charge controller even if the controller has all these protection built in? That 75A is definitely DC rated... Where should I put it? And would a second identical model work for that second one?
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #7
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    Re: 24V Pannel with 12V system wire size???
    Cariboocoot wrote: »
    Shall I mention that the battery bank is a problem waiting to happen? You've done about the best you could for wiring that, although the wire size looks rather small.
    Welcome to the forum Ouello.
    The battery wiring is definitely a problem. Not just the wire size, but the way the batteries are wired. You need positive and negative battery bus bars with equal sized wires from each battery to the bus bars.

    And then, even if you do that you will have problems because parallel batteries are unstable no matter how they are wired.
    read: http://forum.solar-electric.com/showthread.php?14674

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: 24V Pannel with 12V system wire size???

    Panel to Controller is the least critical for circuit protection. The panel can only produce its Isc rating in current, so it is highly unlikely anything can go wrong in that section if there's only one panel. More than two in parallel and this becomes a different situation. At any rate, you are looking at <10 Amps there (it will not change with two panels in series).

    If the controller is rated for 30 Amps output then the circuit from the Controller to Batteries needs to be wired and protected for that. Batteries can kick out a lot more current than the controller will, and that is the danger here; something shorts in the controller and the batteries can feed a huge amount of current through the wires and start a fire. Usually the controller will have a recommended fuse rating for its output. If not, just figure the wiring and fuse/breaker based on the peak continuous current of 30 Amps. NEC formula would put this at 50 Amps, but it could be scaled back to 40. The controller manual should also recommend a wire size, in this case probably 10 AWG minimum or more likely 8 AWG.

    The heaviest current will be from the Batteries to Inverter, because as I mentioned before it is capable of 100 Amp draw. This is the place to put your 75 Amp breaker, although that will limit your inverter to around 900 Watts (@ 12 Volts) max. More current and the breaker will trip. This is not necessarily a bad thing. But do always use wire size capable of handling more current than the fuse/breaker on the line: the basic idea is that the circuit protection is the weakest point current-wise and will give up before anything else does should something go wrong. That way the failure will be controlled and not left to some random section of wire burning up.

    (Not too sure I covered everything in this post as I suddenly was "off-line" due to the on-going snow storm and only had some of the content "auto-saved". :roll )
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  • ouello
    ouello Registered Users Posts: 21 ✭
    #9
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    Re: 24V Pannel with 12V system wire size???

    Thanks guys! Everything was so useful. I'm a big sponge right now and I'm starting to see a little clearer. Vtmaps mention a website that led me to http://www.smartgauge.co.uk/batt_con.html and I now get the bus bar logic... If you have any other resources that shows you stuff like that, feel free to send it my way. Being a machinist, I'll have no problems making bus bars...
    I guess your storm is coming my way now!!! :cry:
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: 24V Pannel with 12V system wire size???

    We have a whole section here full of information/sources: http://forum.solar-electric.com/forumdisplay.php?14-Solar-Information-links-amp-sources-event-announcements

    You might particularly want to look at the thread about battery system Voltages and equivalent power.

    It will be a while before our British Columbia snow storm reaches La Belle Provence! :D
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #11
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    Re: 24V Pannel with 12V system wire size???

    you might want to elaborate on what controller you have for some have differing limitations than others. odds are you will need another pv, but putting them in series might exceed the controller's abilities to handle higher voltages.
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  • ouello
    ouello Registered Users Posts: 21 ✭
    #12
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    Re: 24V Pannel with 12V system wire size???

    Sorry for the copy/paste, here what I found on my charge controller

    System Voltage
    12V / 24V

    Nominal Power
    360W / 720W

    Max. Input Current
    30A

    Max. Solar Panel Open Circuit Voltage
    29V / 65V

    Max. Efficiency
    > 98%

    Typical idle consumption
    <20mA

    Max. load current
    30A

    End of charge voltage
    13.4V…14.2V / 26.9V…28.4V

    Boost charge voltage
    14.4V / 28.8V

    Reconnection voltage (LVR)
    12.5V / 25V

    Deep discharge protection (LVD)
    11V…11.5V / 22V…23V

    Operating ambient temperature
    -20oC…….+50oC

    Terminal (fine / single wire)
    16mm2 / 25mm2 – AWG 6 / 4

    Degree of protection
    IP32

    Electronic Protection Functions:

    · Overcharge and Deep discharge protections

    · Reverse polarity protection for solar panel, battery and load

    · Automatic electronic fuse

    · Overvoltage protection at solar panel input

    · Short circuit protection of solar panel and load

    · Open circuit protection without battery

    · Reverse current protection at night

    · Overload protection

    · Battery over voltage shutdown

    Product Advantages:

    · LCD display with charging information

    · Micro-controller digital accuracy

    · Large terminals for easy wire connections

    · 5V output power USB connection

    · Voltage series regulation

    · State of Charge (SoC) advanced technology

    · Temperature compensation

    it also has 2 load on/off timer adjustment.
    all the charge settings are also adjustable.

    Not a Xantrex, but yet again, we're at the cottage only 15-20% of the time. Most of the time, my pv and cc will be on sleep mode because I'm away and not draining the batteries...
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
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    Re: 24V Pannel with 12V system wire size???

    "Max. Solar Panel Open Circuit Voltage 29V / 65V" = maximum problem.

    If you haven't bought this controller already, don't; it will be very difficult to accommodate.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #14
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    Re: 24V Pannel with 12V system wire size???

    do you have the brand?

    looks like it is real close with the voltages for putting 2 in series... may not work
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #15
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    Re: 24V Pannel with 12V system wire size???

    Will absolutely not work with the panel that has a 30 Vmp rating. The controller's input max for a 12 Volt system is 29 Volts.

    Somehow the words "Blue Sky" just popped into my mind. :roll:
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #16
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    Re: 24V Pannel with 12V system wire size???

    you might already have a problem with a single pv depending on what the voltages actually are that you referred to for both the pv's 30v and the cc's 29v. best configuration would be the 30v on the pv to be voc and even then it's 1v higher than the cc for 12v operation. most mppt cc's below 45a tend to have a low threshold voltage that can be applied to the input of the cc and it can be easy to blow these ccs out with some of the voltages today's pvs put out. you need a better controller as well as the wire upgrading and another like pv.
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  • ouello
    ouello Registered Users Posts: 21 ✭
    #17
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    Re: 24V Pannel with 12V system wire size???

    Your right! It's even worst than I thought... the Voc is actually 36.9V,,Vmp is 29.9V... I just received the controller today but will plan to return it...
    Let's take that 2nd PV out of the equation... Could I just run the pv and cc together if I switch my batteries to 24V?
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #18
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    Re: 24V Pannel with 12V system wire size???
    ouello wrote: »
    Let's take that 2nd PV out of the equation... Could I just run the pv and cc together if I switch my batteries to 24V?

    No. Vmp of 29.9 is not high enough to charge a 24 volt battery. But switching your batteries to 24 volts will help with the parallel battery problem.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #19
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    Re: 24V Pannel with 12V system wire size???

    vtmaps is correct because in going to a higher battery voltage the required current is cut in half, but the delivered current is also cut in half so you are still on the low end of things here for your battery bank requirements. you could go with a better mppt cc and the new pv with the intent of upgraded with another pv asap down the road.
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  • ouello
    ouello Registered Users Posts: 21 ✭
    #20
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    Re: 24V Pannel with 12V system wire size???

    I was planing to attack this project way too fast...

    I'll first take good care of replacing every wire that is way undersize and add fuses between components.

    I'll replace my charge controller for?!?! Blue Sky SB1524iX (57V max (Recommend Maximum Voc at STC < or = to 45.6V) or (Morningstar) SunSaver SS-MPPT-15L has 75 VOC max! That would make sense!

    So again, keeping in mind that I probably wont need 2 panels... Which one of these two cc would make more sense, or other suggestion?!

    What was the winter/snow thing about... I know pv drop V with heat and they are rated at a certain degree C for there maximum output power... so I guess the output at -30 C is way up!!!

    I think I'm going to sleep on it now, my head hurts!!!
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #21
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    Re: 24V Pannel with 12V system wire size???

    yes you have the temp issue correct....the colder it gets the more power you get...

    first rule of solar: loads always GROW

    Second rule: go to rule #1

    ie plan expansion into the present system....


    FYI my sig other, one we had some (3) lights working, "when can I use the microwave?"
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #22
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    Re: 24V Pannel with 12V system wire size???

    They're both 15 Amp panels so on a 12 Volt system that one 230 Watt panel could max out either.
    The Blue Sky you may find has some weird limits on it like "if either the system Voltage or the panel Voltage is over 'X" output is limited to 'Y'".
    My choice would be the simple Morningstar 15 MPPT. It's also slightly cheaper.

    Probably the best would be the new Rogue 3024, but as far as I know it's not available yet. :cry:
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  • Rybren
    Rybren Solar Expert Posts: 351 ✭✭
    #23
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    Re: 24V Pannel with 12V system wire size???

    If you haven't bought the PV panel yet, I've got a line on some 210W panels at a great price (for Canada). The vendor is Kemptville and will deliver to Ottawa. I picked up 4 from him this weekend.

    Please let me know if you want his contact info.
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  • ouello
    ouello Registered Users Posts: 21 ✭
    #24
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    Re: 24V Pannel with 12V system wire size???

    I looked inside my cc's manual, it says 65V max Voc input and the same on the vendors website... I'm trying to clear that out right now to either have the right info or trade for (Morningstar) SunSaver SS-MPPT-15L since they do sell the Tristar bigger models, they probably can get the smaller ones... I know, the Rogue would of been sweet!

    When I first started the post, you gave me the impression that a 30A cc was too high... So if I where to go with my newly purchased 235W pv + (Morningstar) SunSaver SS-MPPT-15L and repeat the exact same purchase in 1-2 years... That would keep the cc optimal right?

    Now you guys got me hooked on learning... Thanks!

    Got to go to work... will keep you informed of the outcome!
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  • ouello
    ouello Registered Users Posts: 21 ✭
    #25
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    Re: 24V Pannel with 12V system wire size???
    Cariboocoot wrote: »
    Panel to Controller is the least critical for circuit protection. The panel can only produce its Isc rating in current, so it is highly unlikely anything can go wrong in that section if there's only one panel... At any rate, you are looking at <10 Amps there.

    Is it me or it's really hard to find a fuse holder with adequate wire size that is rated under 20A... My solar panel's Isc is 8.47A but I was also reading about fuse having a continuous maximum amp rating?! It says max inline fuse 15A on my solar panel... Would it be safe to say to go with that instead of 10A with a continuous 8.47A...
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #26
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    Re: 24V Pannel with 12V system wire size???

    Generally, fuses and breakers should be operated at 80% of maximum rated current... 15 amps * 0.80 = 12 amps maximum continuous current.

    Use the 15 amp number from the Mfg... A smaller fuse should not be "any safer"--And will reduce the chance of a false trip.

    -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 ✭✭✭
    #27
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    Re: 24V Pannel with 12V system wire size???
    ouello wrote: »
    Is it me or it's really hard to find a fuse holder with adequate wire size that is rated under 20A... My solar panel's Isc is 8.47A but I was also reading about fuse having a continuous maximum amp rating?! It says max inline fuse 15A on my solar panel... Would it be safe to say to go with that instead of 10A with a continuous 8.47A...

    Isc is not continuous. In fact it will probably never appear since it is the current the panel can supply to a short circuit. The 15 Amp rating for "in-line fuse" from the manufacturer is your best bet. It is only needed for three or more parallel connections: if one panel shorts the other two could put 2X Isc into it. With no circuit protection this can start a fire. In this instance 2X 8.47 > 15 Amps and the fuse would blow. The rating of the fuse holder should in fact be greater than the rating of the fuse. There have been instances with low-quality auto type holders causing more problems than they prevent.
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