Need help matching panels controller, please...

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biged
biged Registered Users Posts: 7
OK, Well I am finally taking the plunge!
First, I will tell you, I am on a sailboat. I have been wanting to add solar for a long time.
I found a fantastic deal on some discontinued panels. I purchased 3 of them, and my neighbor purchased 2.
They are as follows: Sharp, Model #ND-208U1F, 208 Watts each
If I am reading this right, they have an open-circuit voltage of 36.3V.
I have traction batteries at 12V and 1500Ah at 20 hr rate.
We are both looking for controllers. My neighbor needs for 2 panels, and myself for 3 panels.
The panels are rated at 8amps, but if that is at 36.3V, do I just need a 24amp controller? Since I am using 12V batteries, do I need a 72amp controller?
Any suggestions?
Thanks!
Ed

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Need help matching panels controller, please...

    First of all, since your panel Voltage is higher than your system Voltage you should use an MPPT type controller to down-convert the extra Voltage into charge current.

    Controllers are rated by their output current limitation. Basically, you would be looking at:

    2 * 208 Watts = 416 Watts * 80% efficiency = 332 Watts / 14.2 Volts charging = 23 Amps current.

    That would mean a controller like this: http://store.solar-electric.com/sbchco2512vm.html

    Since you're on a boat, you probably won't see peak output often due to the difficulty in maintaining proper insolation.

    That 23 Amp output isn't going to do much for a 1500 Amp/hr battery bank. It would at best keep ahead of the self-discharge rate. In charging terms it would handle 230 to 460 Amp/hrs.

    And I've left out the efficiency derating for the charge controller, line loss, and temperature. Just so you know.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Need help matching panels controller, please...

    i agree you will want an mppt controller due to the vmp not being very conducive for straight pwm, but each pv is rated at 7.25a as shown in this pdf,
    http://www.txspc.com/documents/sol_dow_208U1F.pdf
    coot did figure this at 2 pvs and that's good for your neighbor, but you have 3. assuming you both are shooting for 12v out to the batteries, your neighbor should get an mppt at least capable of 30a because in the downconversion process you will reciprocally gain some amps. same goes for you, but you need a higher current rating and that puts you in the 50-60a mppt cc rating.
    for a 24v battery configuration all pvs would need to be in series including your 3. your neighbor's current requirement of an mppt controller will be cut roughly in half allowing something like the morningstar ss mppt to be used, but only with 24v output and with no margin for expansion unless going with the tristar mppt or other high current mppt controller. the same output current halving is true for you too, but due to the higher input voltages needed for downconversion the higher current models are still warranted. which one you guys pick depends if you may want to expand later and with how much from what pvs aimed how. i won't get into all of the ifs here as that could be too involved.
    remember to always get the bts for temperature variations and calculate what wire size is needed due to voltage drop to have. also safety with fusing or circuit breakers.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Need help matching panels controller, please...

    Yep; I got confused on the 2/3 thing. :blush:
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
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    Re: Need help matching panels controller, please...

    OK I just gotta ask, do you really have a 12 volt 1500 Amp hour battery? ...that would likely be 8-900 lbs of battery.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • biged
    biged Registered Users Posts: 7
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    Re: Need help matching panels controller, please...

    Yes I do and honestly I figure the weight at 1300+ pounds.

    By the way IS there a way to charge at 24v but run the boat on 12v?
    I have 12seprtate 2v batteries wired 6 in a series in two banks to make 2 twelve bank batteries. I can't run 24v because of the nav instruments So I am stuck using 12v.

    Thanks guys
    P.S.
    They are wired using 0000 wire.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Need help matching panels controller, please...
    biged wrote: »
    Yes I do and honestly I figure the weight at 1300+ pounds.

    By the way IS there a way to charge at 24v but run the boat on 12v?
    I have 12seprtate 2v batteries wired 6 in a series in two banks to make 2 twelve bank batteries. I can't run 24v because of the nav instruments So I am stuck using 12v.

    Thanks guys
    P.S.
    They are wired using 0000 wire.

    There's a certain familiarity to your question. :D
    You can use a Voltage converter to drop 24V to 12V, but it probably wouldn't handle the Amperage load (judging by the size of your bank). You can have a separate 12V battery bank and re-charge it from the 24V via MPPT, but there's not much point in that either, is there? You'd just be back where you started, so to speak.

    What are you using to charge it now? On-board generator?
  • biged
    biged Registered Users Posts: 7
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    Re: Need help matching panels controller, please...

    Yes I have a generator hooked to a 140 amp charger that does a great job. But as you know the batteries wont accept the full 140 for long. I was hoping to run the generator to give it the initial base charge then use the solars to top off the system.

    By the way I don't need 1500 hundred amp hrs I made it so large so that I would not have to run the generator everyday.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Need help matching panels controller, please...

    Maybe you want to get some better charge control from your gen set-up. If the existing charger has a fixed current output, you could feed it through two or three PWM controllers (like this: http://store.solar-electric.com/tr60amp12244.html) so that the charge current is better regulated.

    I'm not sure those panels will do much even for 'finish' charging, especially as you can't be sure when you'll get the sun. A little comparison: your bank is about five times the size of mine, and I use 700 Watts of panel.

    I can see you'd be concerned about putting 140 Amps to the bank all the time.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Need help matching panels controller, please...

    it may be easier and simpler to keep it at 12v, but pvs can be higher voltage if downconverted to the 12v required by the batteries on an mppt controller that can handle the voltage put to it.
  • biged
    biged Registered Users Posts: 7
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    Re: Need help matching panels controller, please...

    Ok so, which mppt controllers are worth the money? Which are best .which are worst or to be avoided? Personally I don't mind paying more for a really good unit .The 3 panels 208ea. But my nehbor is on a tighter budget. He is the guy with 2 panels @208 both 36v

    Thanks for all your help guys you have really put thing in perspective.

    ED
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Need help matching panels controller, please...

    stay away from bz.
    xantrex, morningstar, and outback all have some decent ones. you may have to weigh that one for yourself by reading up on them and deciding for yourself what appeals to you best.
    almost forgot rogue has an uncertified 30a for 12 and 24v.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Need help matching panels controller, please...

    BZ: named for the sound it makes when it quits working! :p
    No, that's not fair; some of them don't work straight out of the box.

    I was just recommending the Morningstar somewhere else around here: http://store.solar-electric.com/motr45ampmps.html

    At 45 Amps it would handle your three panels potential 36 Amp output and it's reasonably priced.
    But you have to ask yourself what future expansion there might be. If you have the potential to add even more panels then you should buy the higher-capacity Xantrex 60 Amp or Outback 80 Amp unit.

    I bought my MX60 years ago when it cost $1000. Haven't regretted it since. The system has been reconfigured about three times since then, and is getting a further 'adjustment' this year (adding panels).
  • biged
    biged Registered Users Posts: 7
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    Re: Need help matching panels controller, please...

    What have you heard about the Blue Sky 2512i?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Need help matching panels controller, please...

    blue sky stuff in general works, but you have to be careful for that cc has a max of 35v input. their controllers are older technology and limited on the input pv voltage they can take and if paying big money for a controller you may want more bang for the buck that some of the other brands offer.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Need help matching panels controller, please...
    biged wrote: »
    What have you heard about the Blue Sky 2512i?

    This is a 25 Amp controller. It'd do for your neighbor, but your 3 panels are going to put out about 50% more - possibly 35-36 Amps. Unless I've got confused again about who has how many of what. :p
  • biged
    biged Registered Users Posts: 7
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    Help, behind an 8 ball

    As you know, I am looking for controllers, one for me and one for my neighbor. Thought I had found one in the BlueSky 2512 for my neighbor. I wrote the company and they said the controller would not handle his. He wants to keep the price as low as possible. I need help because I can not figure out what will be the lowest cost for him.
    Solar panels as follows:
    Sharp, ND-208U1F, 208 Watts, he has 2 panels
    I am trying to find an answer so he can get his system up and running. I am getting very frustrated with all the numbers and need your help, and input. I am reading your responses on the other thread, but I am not seeing an obvious answer to this, sorry!
    Thanks!
    Ed
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Help, behind an 8 ball

    The Vmp=28.71 volts is a real tough point for a battery based sytem... You should be around 18 volts for a 12 volt battery bank or ~36 volts for a 24 volt battery bank to efficiently use a "cheap" PWM type controller.

    At this point, you are really left with using a MPPT type solar charge controller that can efficiently down convert from high panel voltage / low current to low battery bank voltage / high current charging.

    Depending on your battery bank voltage (12 volt or 24/48 volt)--you will limit your MPPT controller choice even more (to more expensive/larger charge controllers).

    The difference between ~$100-$200 (PWM) vs $300-$600 (MPPT).

    There might be some other choices--but we need to know the details (panels, bank voltage, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Need help matching panels controller, please...

    i merged the 2 threads as it is just a continuation of the first one.