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AStinker-'s avatar
AStinker-
Explorer
Mar 22, 2014

Portable panels wire size

Hey guys, I need some help. Would you consider giving me some advice please?

I’m putting together a portable solar panel setup. The panel’s will be the following.

Max Power: 140Wp
Open Circuit Voltage (Voc): 21.0V
Short Circuit Current (Isc): 8.40A
Maximum Power Voltage (Vmp): 17.0V
Maximum Power Current (Imp): 8.00A

Originally I was planning on paralleling 2 of them on the same wires and just jumpering directly to my batteries when I need to use them but several said don’t do it that way so I got scared and decided I will probably get a controller. It will probably be PWM Charge Controller big enough so I can use it when I do a permanent roof install.

I would like to be able to set the panels up at least 100 ft from my batteries / (PWM Controller) if necessary to find sunlight. I was planning on using a 2 conductor 10 ga stranded wire to accomplish this. But after reading all the discussion on wire size from solar panels to controller on the thread mena661 started “Panel to Solar Controller Wire Size” for his new solar build I’m wondering if I will have too much of a voltage drop at that distance. So I would appreciate your advice if you would consider it. Will 100 ft of 10 ga wire from 2 of these panels work or not?

It would not be a deal breaker if I need to add a 2nd cable or even a 3rd if I needed to as I can buy 100 ft of stranded 2 conductor 10 ga wire for $35.00. The problem is I don’t know what I need.

I’m not sure I’m using the calculator that was posted on mena661’s thread correctly but what I am entering is Wire Size: 10 AWG Voltage: 21.8 Phase: DC Number of conductors: Single set of conductors Distance: 100 Ft Load Current : 8.95 Amp. The RESULTS: Voltage drop: 1.79 Voltage drop percentage: 8.21% Voltage at the end: 20.01. Will it work but not efficiently??? I don’t know. Then when I increase Load Current for 2 panels to 17.9 Amps it doubles the losses which drops the Voltage at the end to 18.22 volts. But also I don’t know what the minimum voltage into the controller should be for it to achieve reasonable bulk & absorption charge when batteries are at 50 to 80% SOC.

My short term reason for solar is to supplement my generator when off grid where there is limited generator run time. I want to get the most out of the panels that I can with existing conditions but right now I do not need the panels for topping off or equalizing my batteries. I will have a 485 Amp battery bank, will be off grid no more than 4 days at a time & will be on back on grid afterwards long enough to top off & equalize batteries as necessary. My problem is I will be running a 5 cu ft residential freezer with an inverter. It pulls 1.4 amp AC & I anticipate it will run at a min 50% to a max 75% of the time. If 50% of the time it will take 180 of my 240 usable amps if 75% of the time it will use over my 240 usable amps. I have a 55 amp Iota converter with Q4 controller plus a portable 40 amp charger I will be running with a generator but concerned if I can only get 2 or 3 hours of gen run time. My goal is to get as much as possible but hopefully at least supplement enough amp hrs from the portable to keep from killing my batteries. I think I will need to have the controller set so it never has over a 14.9 or 15 volt temperature compensated output but I don’t know what the voltage from the solar panels need to be to accomplish this when my batteries are at say a 60% SOC. If you could advice me it would be greatly appreciated.

Thanks,
Alan
  • AStinker-'s avatar
    AStinker-
    Explorer
    Mar 23, 2014
    Thanks tuna will keep that in mind. No not full time. If all goes as planned we will be leaving form home the middle of May heading to Alaska for the summer. Will be living in it till the middle to end of October. Will see how that goes The DW thinks she want to go full time but I want to check out the water a bit more first.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Mar 23, 2014
    Hi,

    It will take between 25 and 50 cycles for the batteries to reach their full capacity with most of the improvement coming from the first 15 cycles.

    So it may be important to NOT do 50 to 90 for the first few cycles.\

    Are you full time in the rv?
  • AStinker-'s avatar
    AStinker-
    Explorer
    Mar 23, 2014
    BFL13 has it exactly right. He said… “In the OP's case, he has that freezer inverter load going all day, so his battery voltage is never going to get very high.” Exactly and is why I was originally going to connect directly to the battery without a controller. But after what if’ing it I decided why take the risk and decided to add a controller now since I expect to need one latter anyway.

    He said… “He will do better with the solar than without it, but he is still going to be a generator and charger guy.” Again exactly right. And if I’m going to spend my money on some solar I not only want to maximize my return but more importantly I think I’m going to need all the amps I can scrounge up.

    Then BFL13 said… “Sooo, as the OP has been saying, he has two things to do:
    A. get some solar- simple portable (say two 120w for ease of handling instead of one heavy huge 240) on cheap PWM on a long wire for parking in the shade. Don't fuss about exactly how much it will do, just accept whatever it does for you any given day…. Exactly right again except that is not my nature “not to fuss.” And right or wrong all of the above is on order with only some minor differences. And as for cables I’m going to do like Tom M is doing and make up different length cables because I’m guessing there will be locations that 25 or 50 feet may be all I need to find sun. And right or wrong I’m going to get another roll of the cheap 2 wire #10 AWG wire like I already have and either make up a set of cables for each panel (hey I may be too lazy to set up both panels sometimes) or combine them into one if after some more garbage in garbage out stuff with those wire loss calculators tell me to.

    B. get the biggest amp charger his generator can run (PowerMax 75,85, and 100 amper size are PF corrected so a Honda 2000 ought to be able to run one--I don't know for sure) This will probably be my next school of hard knocks. I’m going to try and get by with my 55 amp Iota and a portable. I have, right or wrong a 2K Champion and access to a 2nd one if I need it. I don’t know yet what it is capable of or what its limitations are but will start playing with it after I get my batteries all in.

    Speaking of batteries, I think I read in a thread some time back but can’t find it now, that you should break in new batteries and suggestions on how to do it. If that is correct and any one can point me to it I would be forever grateful. And if anyone wants to make suggestions I will graciously accept them. I have 2 new T-105’s. I have charged them, run a recondition cycle, run an equalize cycle with a VEC1098 & put them on a battery minder since I brought them home. Do I need to do anything else before I start using them hard?

    I have learned so much from all you guys it is unbelievable. Just know that each and every one of you are appreciated, even the guys that have not said anything because odds are I have read & learned something you have contributed in different thread.

    Thanks everyone and

    GO WSU!!!! :B
  • BFL13's avatar
    BFL13
    Explorer II
    Mar 23, 2014
    Your 15v limit will not be reached anyway IMO, so don't worry about it. Also that 15 is at the battery not at the controller.

    On solar in the afternoon with battery voltage finally above 14v, your amps are going to taper as battery nears full. But the voltage will only keep climbing if there is no equal or greater draw on the batteries at the same time. It doesn't take much of a draw to equal what the solar is putting in by the time you are over 14v.

    EDIT, I should make that draw to be higher than the solar amps. Until they are equal, the battery will still charge and the solar will run the draw as well, so the draw has to be higher than the total solar before the batts don't get anything and voltage stops rising.

    That is why I figure the highest SOC I will ever get to on any day is sometime before supper when I start using battery after not using it much in the afternoon. (Which allows the battery voltage to climb in the afternoon)

    Once I start using things like the inverter, that knocks battery voltage right down. The only restriction is that the pre-supper/late afternoon voltage not be over 15 or the inverter won't work to help make supper.

    In the OP's case, he has that freezer inverter load going all day, so his battery voltage is never going to get very high. He will do better with the solar than without it, but he is still going to be a generator and charger guy. The idea then is to have "some solar" to reduce the time the generator has to run each day, plus have a high amp charger for the generator to use.

    Four hours on four batts is a very long time for a 50-90 recharge.

    I can do a 50-90 on six batts in two and a half hours and I can do a 50-90 on four of them in two hours. However that is using 140 amps on the six and 105 on the four. ( PowerMax 100 amper and VEC1093 40amper)

    Now the limit is how many charger amps can the generator support --eg my Honda 3000 can do 130amps of non-PF corrected chargers. 131amps will make it conk out. The 100amper is PF corrected so I can actually go to 150a with the 100 plus another 50 of non-PF.

    Sooo, as the OP has been saying, he has two things to do:

    A. get some solar- simple portable (say two 120w for ease of handling instead of one heavy huge 240) on cheap PWM on a long wire for parking in the shade. Don't fuss about exactly how much it will do, just accept whatever it does for you any given day.

    B. get the biggest amp charger his generator can run (PowerMax 75,85, and 100 amper size are PF corrected so a Honda 2000 ought to be able to run one--I don't know for sure)
  • red31's avatar
    red31
    Explorer
    Mar 23, 2014
    AStinker- wrote:

    In my case it doesn't matter which calculator I use because I don't know for sure which Voltage or Load Current from the panel specs I should be using.


    That's why I used the table in a morningstar manual! :)
  • westend's avatar
    westend
    Explorer
    Mar 23, 2014
    I think the use of the AC freezer is going to be dictating at how you approach the solar use. You should definitely use a Solar calculator to add up all the devices you want to power but the freezer is going to rule all.

    If the freezer averages a 1.3 A draw and say, a duty cycle of 1/3, your total draw would be around 100 AH/day at 12V. Two 24V modules and a good MPPT controller would probably be a good fit. If you have batteries that need the 15V, the better controllers have a PC interface where it can be set, easily.

    The downside of the bigger modules is that they are bulky to cart around. I wouldn't want to use one or more as portables because I'm old and lazy. You may feel different.

    Oh, BTW, if you can, put some foam sheet insulation around the box. It really helped the duty cycle on my fridge.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Mar 23, 2014
    Hi,

    You have two choices for getting batteries truly full. One is to use shore power and the other is to use solar. No one in their right mind tries to get to 100% state of charge running a generator.

    You ave over thinking this whole issue. Calculate how much solar you need, go buy a quality charge controller and the necessary number of watts of panel. Use pwm or mppt. If the system is sized properly to the type of controller chosen it will be a successful installation.

    If the inverter shuts down at 15 then 14.9 should be the max charge voltage under all circumstances.

    Trojan wants batteries to be exposed to 15.8 volts. It would behoove you to have dual banks so that one can be charged while the other is in use, with easily adjusted charge maximums and appropriate disconnect switches.
  • AStinker-'s avatar
    AStinker-
    Explorer
    Mar 23, 2014
    Almot wrote:
    AStinker- wrote:
    But isn't the input voltage still important somehow? If not why are we worried about voltage drop from the panels to the controller?

    With MPPT the drop is important because this converts into lost amps and amp-hours.

    With PWM - people more familiar with these low-tech devices ;) will correct me if I'm wrong - the voltage drop is not important as long as it is not lower than the highest Absorption voltage that you might need, i.e. Absorption on a cold day. As noted, and I agree, that it should also not be higher than 15V on a cold day.

    So 15V is your lower limit of input after voltage drop at 77F. If it's lower, the controller with temp-comp won't be able to raise it as needed on a cold day. Controller with temp-comp will be able to lower it down from 15 on a hot day.

    OTH, your controller should have means to limit maximum output to 15V - maybe it already has it as factory-preset. My controller has adjustable upper voltage.


    Are all you PWM guys going to let him get away with that?? :E

    Yes sir, it will have to have a means to limit maximum output to 14.8 or 15V because over 15 volts will shut the Inverter down. And because I'm going to be a power hog with the freezer it appears to me I will want the absorption voltage as close to 15 volts as possible also. Right?? So is 15 volts the the magic number?? The controller has to limit output to 15 volts or slightly less therefore the "voltage at the end" of the cable from the solar panels into the controller need to be or "should be" 15 volts or above?? Yes?? No?? I'm going to sleep on it now and wait for all you guys to make my day or burst mt bubble. :B Why do I feel like I'm missing something??
  • AStinker-'s avatar
    AStinker-
    Explorer
    Mar 23, 2014
    Almot wrote:
    westend wrote:
    Most of those wire size calculators should be used with two conductors since you have both a (+) and (-) phase. Don't know if the one you used calculates like that or not.

    He didn't tell which one he used. Assuming it's Southwire - most people use it - you enter "single conductor" because it's obviously not a 3-phase, but you enter a total (+) and (-) run of your wire. Very often (though more often in roof installs than in portables) the + and - leads are different length, but it is the total + and - that counts.



    In my case it doesn't matter which calculator I use because I don't know for sure which Voltage or Load Current from the panel specs I should be using. You know that old saying "garbage in garbage out." But the inputs pianotuna said he would use makes the most sense to me after doing a bunch more reading, studying & playing with them for awhile. I'm about ready to say to hell with solar & buy a big enough Charger to keep from killing the batteries even if I only get 2 of 3 hours of generator run time a day!!!
  • Almot's avatar
    Almot
    Explorer III
    Mar 23, 2014
    AStinker- wrote:
    But isn't the input voltage still important somehow? If not why are we worried about voltage drop from the panels to the controller?

    With MPPT the drop is important because this converts into lost amps and amp-hours.

    With PWM - people more familiar with these low-tech devices ;) will correct me if I'm wrong - the voltage drop is not important as long as it is not lower than the highest Absorption voltage that you might need, i.e. Absorption on a cold day. As noted, and I agree, that it should also not be higher than 15V on a cold day.

    So 15V is your lower limit of input after voltage drop at 77F. If it's lower, the controller with temp-comp won't be able to raise it as needed on a cold day. Controller with temp-comp will be able to lower it down from 15 on a hot day.

    OTH, your controller should have means to limit maximum output to 15V - maybe it already has it as factory-preset. My controller has adjustable upper voltage.

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