solar panel out put conversion to amps

rake1
rake1 Solar Expert Posts: 173 ✭✭
in General Solar Power Topics #1

  • I have 420 watt total 12 volt solar panels and I want to make sure my c35 pwm controller will handle them. If I take the 420 and divide it my my 12 volt system I get 35 amps which is the max my c35 will handle. But when I add up the maximum output (imp) of all three panels i get 23.51 amps, which is correct to use.



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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #2
    With a pwm controller, output current potential is the sum of Imp (~23.5).
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #3
    thank you what if I change to a MPPT what happens then
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #4
    With mppt, it bucks higher voltage from panels to charging voltage. For example, you could wire the panels in series for Vmp of ~18x3=54v and Imp of ~7.8a. In theory, the mppt bucks the 54v down to ~15v to charge with current of 420w/15v=28a. Real world numbers would likely be lower, but that's the general idea.

    The main advantage to mppt is being able to use smaller wire to the array, and/or longer runs. It can also produce a bit more with cold panels.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #5
    Ok I guess I will just stick with my pwm thanks
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #6
    I am going to buy 6 awg I will need a combiner box any suggestions what type I need. I will have three solar panels into the box  the panels do have MC4Y connectors on them now so I could just run an extension from each one to the box 3 cables. But since I have never even seen solar a combiner box what do I need to handle this?
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    edited February 2018 #7
    They are available from a number of mfg. like Outback and Midnite Solar and fairly inexpensive. They are fairly easy to build too if you are so inclined although homemade wouldn't be UL rated.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    edited February 2018 #8
    @rake1

    This is the combiner box:

    https://www.solar-electric.com/mnpv3.html

    This is the DC breaker, you will need three of them at 15 amp:

    https://www.solar-electric.com/mnepv.html

    If there is a probability of future expansion, the MNPV6 would be a better choice. 

    Rick

    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #9
    thank you very much, do I have to use a box designed for solar or could I use a regular electrical box bought at wholesaler
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #10
    You can use anything you want as long as DC breakers can be mounted and all connections properly made. However, as Estragon pointed out, it will not be UL approved. Needed if inspected. The MN combiner just makes it more convenient. 

    Rick
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #11
    thanks again
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    edited March 2018 #12
    The combiner I built for our place in Mexico has touch safe solar dc fuses a lightning arrester and MC-4 inputs for each string of panels. The combiner box pics are very similar to what I built. The MC-4 connectors make connections a snap. I have capped the extra MC-4's to keep the contacts from oxidizing. It is mounted on the roof with the panels. You can see it above the rear of the Jeep

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #13
    One BIG WARNING about using touch safe fuse holders--They are not designed to "turn off" the electrical current.

    If "you" just pop the fuse in the middle of the day, without removing it, it can cause an arc and eventually destroy the fuse hardware.

    Only pop working touch safe fuses at night, or by turning off the loads (charge controller/etc.) first.

    https://www.youtube.com/watch?v=ghBBW9aytzk

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    edited March 2018 #14
    BB. said:
    One BIG WARNING about using touch safe fuse holders--They are not designed to "turn off" the electrical current.

    If "you" just pop the fuse in the middle of the day, without removing it, it can cause an arc and eventually destroy the fuse hardware.

    Only pop working touch safe fuses at night, or by turning off the loads (charge controller/etc.) first.

    https://www.youtube.com/watch?v=ghBBW9aytzk

    -Bill


    I totally agree. There is a load center with switch rated dc breakers next to the charge controller. There needs to be some form of over current protection in the combiner box though,  either fuses or dc rated breakers.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #15
    That's why i prefer the DC Switch rated breakers midnight sells.  no worries.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #16
    I know I am jumping all over the place here, but after listening to you guys and a solar guy here It appears the simplest thing for me to do is change my panels to series and buy a  MPPT charge controller no changing wires an no combiner box and use the installed wire I have now. It is either 12 or 10 AWG, I am going to the camp now and will let you know the size. I am told my 420 watts of Array will work fine with a 40 amp MPPT. He sell the outback FM60 little more than I need but that's Ok. Should I have an inline fuse on the input side of the FM60 if so how big.Again thanks for the input.
     PS anything else I should be aware of?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #17
    Lighting in area?

    Vmp and Imp of panels? How many? Distance from array to battery bank? Battery bank voltage? Temperature range of location?

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #18
    All panels are close to the same VMP 22.38, 21.9,  22.4  IMP 7.03, 7.54, 9.02   125w 135w and 160w MONO Distance from array to battery bank about 40 ft. Battery bank voltage is 12 volt Temperature range of location winter -15 max summer maybe 90F the od day, but average maybe 80F.
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #19
    At camp now my array wire is 10AWG
    All panels are close to the same VMP 22.38, 21.9,  22.4  IMP 7.03, 7.54, 9.02   125w 135w and 160w MONO Distance from array to battery bank about 40 ft. Battery bank voltage is 12 volt Temperature range of location winter -15 max summer maybe 90F the od day, but average maybe 80F.
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #20
    > With a pwm controller, output current potential is the sum of Imp (~23.5).

    Actually, the sum of Isc - which will be higher.

    I am available for custom hardware/firmware development

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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #21
    Yea thats is why I am going to a MPPT in series. Should I have an inline fuse on the input side of the FM60 if so how big.Again thanks for the input.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    edited March 2018 #22
    rake1 said:
    Yea thats is why I am going to a MPPT in series. Should I have an inline fuse on the input side of the FM60 if so how big.Again thanks for the input.
    It's "nice" to have a circuit breaker you can also use as a switch, for troubleshooting. 

    Rating should be at least what the sticker on the panels calls for as Series Fuse, if you have several strings of panels, add the several series fuse specs together,  you don't want normal power to trip the breaker off.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    edited March 2018 #23
    @rake1

    Recommend a15 amp breaker like this one.

    https://www.solar-electric.com/mnepv.html

    And this box to install it.

    https://www.solar-electric.com/baby-box.html

    Rick


    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #24
    I have a 30 amp inline fuse on the positive side. now but changing to series. I am told that my 420w panels could actually put out as much as 35 amps (420W divided by 12 = 35 amps) with my new MPPT is that correct? IMP of all three is about 24 amps.
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #25
    In series IMP should be a little over 7 amps, VMP about 65 volts, charging at 33 to 37 amps.

    rick
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #26
    so how big of a in line fuse do i need
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #27
    A line fuse is not needed with the breaker.
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • rake1
    rake1 Solar Expert Posts: 173 ✭✭
    #28
    I realize that but I have the in line fuse now so i may just replace it with the appropriate size if someone tells me what I need
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #29
    If in parallel, then 12 to 15 amps for each panel.
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #30
    A breaker is preferable to a fuse, if only because if you need to power down the controller, you want to disconnect pv first, and reconnect last. A breaker makes it much easier to do so. In series, a 12-15a DC rated breaker should do the job.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
    · Share on Twitter
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #31
    You need to understand the difference between the Input and the output.
     the input of a bunch of series panels will be  7 amps at some high voltage (90v?)  The magic happens inside the MPPT and converts the high voltage to amps @ 12V
    You have x Watts input, and x-2% Watts output, the MPPT downconverts the high voltage, low amps to High amps, low voltage

    So a 10A breaker on input and a 40A breaker on output  would be my guess at at start
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

    · Share on Twitter

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