upgrade to new mppt controllers

mrleemus1
mrleemus1 Registered Users Posts: 28 ✭✭
My solar system consists of forty two 100 watt panels. (4,200 WATT SYSTEM) They are series - paralled to give 8 strings of 34 Volts at @ 12 amps and 2 strings of 34 volts 18 amps. They are fed to 3 combiner boxes then 3 xantrex 60 amp charge controllers which control a bank of sixteen L-16 batteries configured to give 24 volts. I am using 2 Xantrex 4,000 watt inverters to provide 240 volts for my pump. Too often the battery bank doesnt get a full charge depending on cloud cover and usage during the day.
1. COULD I GET A SIGNIFICANT IMPROVEMENT BY UPGRADING TO THE NEW MPPT CHARGE CONTROLLERS.
2. Would it require rewireing the panels (series them to max allowed by the controller?)

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: upgrade to new mppt controllers

    Welcome to the forum.

    Let's do a quick analysis of what you've got now:
    640 Amp hours 24 Volt battery bank (sixteen L16's; four in series for 24 Volts * two strings). That would want 64 Amps @ 29.6 Volts meaning 1894 Watts, less derating would be 2460 Watt array.
    4200 Watts of panel.
    Something is wrong.
    You shouldn't need three 60 Amp controllers.
    Can you provide full panel specs? Make, model, Vmp, Voc, Imp, and Isc? And how they are wired to each controller?

    There appears to be a configuration problem here. That needs to be looked at first. You probably will not see any benefit from switching to an MPPT controller.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: upgrade to new mppt controllers

    You might get a ~10% increase in power generation with MPPT.

    Generally, the best reason for MPPT is to allow you to cost effectively mount the solar array some 20-100+ feet from the charge controllers/battery shed. The ability to run Vmp-array at ~100 VDC maximum (for a 150 VDC max input rated MPPT controller) can reduce your copper usage to 1/4 or even 1/8th or more.

    What is the wiring run (gauge, distance) from the Solar array to the charge controllers?

    Also, what is the voltage drop (wire gauge/distance) from charge controller to battery bank...

    Too much voltage drop in either place (array or charger wiring) with a PWM controller can reduce your charging efficiency a lot...

    Rewiring and installing a MPPT controller(s) may help because of wiring issues--But without the details it is impossible to tell.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mrleemus1
    mrleemus1 Registered Users Posts: 28 ✭✭
    Re: upgrade to new mppt controllers

    Thanks for the welcome and your quick response. The panels are Photowatt Brand

    ☀ PW6 - 100W ☀
    ☀ Electrical Characteristics:
    ☀ Typical power: 100W
    ☀ Minimum power: 95.1W
    ☀ Voltage at typical power: 16.7V
    ☀ Current at typical power: 6A
    ☀ Short circuit current: 6.5A
    ☀ Open circuit voltage: 21.5V
    ☀ Maximum system voltage: 1000V DC
    ☀ 12V Configuration

    The panels are roof mounted and and the installation was done by a liscensed solar contractor -- distance from panels to controllers @ 20 -- 30 ft is my guess.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: upgrade to new mppt controllers

    be sure that all of your pvs are in good working order before you make any moves.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: upgrade to new mppt controllers

    Do you know the wiring gauge (diameter) from the panels to the controllers?

    The other way to look at this--can you tell us your average peak current (sunny day, near noon, batteries needing charging)?

    Do you have a Battery Monitor of some sort?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: upgrade to new mppt controllers

    Well looks like we have a winner: Vmp 16.7 Volts. Put two in series you get 33.4. That's slightly under what you'd want for charging a 24 Volt system. My guess is that coupled with the usual V-drop over wires your charging Voltage is not up to the 29.6 those big Trojans want.

    In this case rewiring to more (at least four, possibly six) in series feeding MPPT controllers will be beneficial. One problem is you don't have a neatly divisible number of panels for two controllers (to handle what could be over 100 Amps). Fortunately you shouldn't need all those panels for 640 Amps hours @ 24 Volts.

    Initially I'd suggest six strings of six panels in series. Three strings per 60 Amp MPPT controller.
    But I think we'll have to triple-check the numbers and leave the possibility for some reconfiguration if the Voc is too high or the Wattage too low.

    What do you think, Bill?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: upgrade to new mppt controllers

    Probably would help... I believe the poster is in the foothills near Sacramento Ca... Some pretty warm summers will push those Vmp voltages down too.

    Would like to know more about the setup and maximum battery charging voltage reached during Absorb stage...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mrleemus1
    mrleemus1 Registered Users Posts: 28 ✭✭
    Re: upgrade to new mppt controllers

    the wire gauge is 6awg from the combiner box to the controllers -- the controllers have the faceplate meters and during a typical sunny day like now -- todays temp is 91f. here and at 11:30 am and the sum of the amps on all 3 meters is 72 amps and the voltage reading 24.3 volts. The volts were down to 22.2 volts at 7 am when i checked them. OHHHH YAAA also the controllers are set to EQUALIZE mode - i am trying to get the max possible from them.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: upgrade to new mppt controllers
    mrleemus1 wrote: »
    the wire gauge is 6awg from the combiner box to the controllers -- the controllers have the faceplate meters and during a typical sunny day like now -- todays temp is 91f. here and at 11:30 am and the sum of the amps on all 3 meters is 72 amps and the voltage reading 24.3 volts. The volts were down to 22.2 volts at 7 am when i checked them. OHHHH YAAA also the controllers are set to EQUALIZE mode - i am trying to get the max possible from them.

    Okay, take them out of equalize mode. That tries to maintain a set Voltage with varying current. It won't help a proper recharge at all.

    Next questions: What sort of charge controllers are they (make/model)? And what are the charge set points (Absorb Voltage, Absorb time, Float Voltage)?

    Chances are the panels just plain can't put out enough Voltage to bring the batteries up to proper charging levels. If this has been going on for any significant amount of time the batteries are probably ruined now.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: upgrade to new mppt controllers

    Getting your batteries down to ~22 volts is going to cause them to have short lives (months or year or so--guessing).

    And you should be bringing the batteries up to 29+ volts for several hours per day--a couple times a week. Charging at 24.3 volts or so is a very low voltage--indicating the batteries are seriously depleted.

    Are you getting a total of 72 amps from your 4,200 watt array? You should be getting something like:
    • 4,200 watts * 1/16.5 volts * 0.80 fudge factor = 204 amps
    • 4,200 watts * 1/33 volts * 0.80 fudge factor = 101 amps
    • [correct above to 24 volt battery bank]
    If this is a clear day, no shade on panels, panels pointing towards noon-time sun... Your array should be doing a bit better--need to look around with a meter and check--see post below

    You probably have serious problems... Whether it is wiring, solar panels, or something else.. Cannot tell from here.

    It could also be the PWM vs MPPT issue (Vmp-array=16.5 volts is pretty low--add long wire runs and too small of cable, it could account for many of the issues).

    However--It will take a fair amount of debugging to figure out what is good and were the problems are. Just dropping $600 on a new MPPT controller (or three) is a lot of cash if the solar panels are having problems too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mrleemus1
    mrleemus1 Registered Users Posts: 28 ✭✭
    Re: upgrade to new mppt controllers

    thanks again for the rapid response -- please foregive my very limited knowledge and electrical skills ----yesterday at @ 2: 00 pm (typical sunny day here no clouds) i shut the charge controllers off and pulled the fuses at the combiner box -- i then checked the Voltage across each of the 10 strings. (i assume this is called the short circuit voltage?) ---The readings were 34 volts + or - a tenth of a volt or so.
  • mrleemus1
    mrleemus1 Registered Users Posts: 28 ✭✭
    Re: upgrade to new mppt controllers

    The maximum chargeing amps (sum of all the controllers) that i have observed under ideal conditions was 81 amps. (bright sunny cool day at noonish). The panels are on a typical 4:12 pitch roof and has ideal southern exposure
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: upgrade to new mppt controllers
    mrleemus1 wrote: »
    thanks again for the rapid response -- please foregive my very limited knowledge and electrical skills ----yesterday at @ 2: 00 pm (typical sunny day here no clouds) i shut the charge controllers off and pulled the fuses at the combiner box -- i then checked the Voltage across each of the 10 strings. (i assume this is called the short circuit voltage?) ---The readings were 34 volts + or - a tenth of a volt or so.

    No, this would be the open circuit Voltage - Voc. It's not useful in this case.
    If you check the input Voltage to the charge controllers while they are under load you will get something at least close to the Vmp - Voltage at maximum power - which is what I think is falling short. Voltages at the panels are not relevant either, as we need to know "what's left by the time it travels through all that wire and finally reaches the controllers".
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: upgrade to new mppt controllers

    Do you want to take an electrical 101 / Solar Power debugging course from a web forum?

    If you want to debug your own system, I would suggest getting a "cheap" DC Clamp Type Amp Meter (this one seems to work OK for only $60). You can easily pay $300-$400+ for a good one... I would start with cheap and simple first.

    If you are not comfortable around electricity--might be a bit much.

    Even asking a licensed electrician to help may not work out well... Many electricians really do not know much power solar / DC power systems.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: upgrade to new mppt controllers
    mrleemus1 wrote: »
    The maximum chargeing amps (sum of all the controllers) that i have observed under ideal conditions was 81 amps. (bright sunny cool day at noonish). The panels are on a typical 4:12 pitch roof and has ideal southern exposure

    The combined current output of all those panels ought to be over 100 Amps. This can be difficult to actually measure as it would be a combination of the output of all controllers when the sun is shining brightly and the batteries actually need the current.

    If sufficient charge Voltage isn't available, the batteries will only come up to a "parity level" with whatever Voltage is possible and then stop charging. You can't reach 29.6 Volts if all you get out of the controllers under load is 24.3 Volts - no matter how many Watts of panel you have. And if you don't reach that Voltage and maintain it for a couple hours the batteries will not be fully recharged. They will sulphate and die.
  • mrleemus1
    mrleemus1 Registered Users Posts: 28 ✭✭
    Re: upgrade to new mppt controllers

    Thanks for the tip on equalizing, i went out and took it out of that mode !
    the controllers are Xantrex C-60 models. i took off the front cover and checked the pots -- they were set at the reccommended 28 volts BULK and 27 volts Float.
  • mrleemus1
    mrleemus1 Registered Users Posts: 28 ✭✭
    Re: upgrade to new mppt controllers

    Yes i would like to take that course --- and YES i have recently purchased a DC clamp meter
    now if i only knew what to measure and where to measure it at.
    And what all the accronems stand for.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: upgrade to new mppt controllers
    mrleemus1 wrote: »
    Thanks for the tip on equalizing, i went out and took it out of that mode !
    the controllers are Xantrex C-60 models. i took off the front cover and checked the pots -- they were set at the reccommended 28 volts BULK and 27 volts Float.

    that's a red flag as i'm sure it would be over 29v bulk for trojans.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: upgrade to new mppt controllers

    And, regarding the subject of this thread, YES, I'd think that MPPT Charge Controllers would be a large benefit. Your array would almost certainly need two MPPT CCs in order for the CC to never be the limiting factor. The Midnite Classic 150 can suppply 94 amps max with a 90 volt string voltage. If you were to run strings of five panels that would be about 83.5 Vmp, and you might get by with only one CC, altho it may pushing it too much.

    MidNite Classic Power Curves:
    http://www.midnitesolar.com/images/classicFrontPage/graphs.php

    As noted above, the MPPT CC would allow you to wire more panels in series, and efficently convert this to a lower voltage need by your batteries, but be able to set the correct (higher) Asorb and EQ voltage AND, it will you to see more or less EXACTLY what you are doing to/for your batteries. These modern CCs allow you to set voltages to within one tenth of a volt (usually), and monitor the resuslts, + log data.

    You have a significant investment in your solar power system. I have seen a number of battery banks RUINED by users using C40s and C60s. These were fine CC, and may still be, but most of the users of these are left in the dark as to what the settings really are, and what exactly the CC is doing at any time. One neighbor had two C60s in his system, and ruined two banks or more by not knowing that one of the C60s was not working.

    YMMV, whatta I know - it's not my $$, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: upgrade to new mppt controllers

    although i am of the consensus that mppt controllers are great and nearly anybody could benefit from them i would still look over the present system to be sure all is right with it. are all of the pvs working properly? are you charging your batteries to the right specs? are all connections and wires working and of proper design? you can upgrade, but when you overlook some of these things it may not pan out quite as you think in making the mppt move. don't forget the condition of the batteries too.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: upgrade to new mppt controllers

    niel, you are absolutely correct.

    And measuring Voc of each string means little regarding weather each string can supply at/near rated current etc.

    But, being able to ultimately get the charging voltages up to spec would seem impossible with the panel voltages and a PWM CC.

    You know all of this.
    Perhaps the OP has a handy, careful neighbor that can help in measuring the Imp, torque of connections, etc.

    Back to work, Have Fun, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • mrleemus1
    mrleemus1 Registered Users Posts: 28 ✭✭
    Re: upgrade to new mppt controllers

    Is it possible -- or advisable -- to series the strings (BUTT SPLICE) right there inside the combiner box. Seems that would be an expedient way yo do it.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: upgrade to new mppt controllers

    My opinion; Would probably be OK if done with appropriatly sized, and correctly crimped connections.

    However, Believe that the C60 is an PWM CC. Voltages very much in excess of what is needed to reach the maximum charging or EQ voltage must be dissipated as heat. The C60 should go into thermal current limit, protecting itself, but you would wind up with very low charge currents, and wasting a lot of solar input.

    If you were doing the butt splicing as a part of an upgrade to MPPT type CC, this splicing should be fine as long as the Max Voc does not exceed the max permitted Vin.

    Is this an answer to the question? Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: upgrade to new mppt controllers

    Here is a little information on how to use a Digital Multi-Meter...

    http://mscginc.org/multimeter.html

    If you have a DC Current Clamp meter--the Current measurements instead will be made placing the clamp around one wire and setting to the appropriate AC/DC and maximum current expected scale (do not use the two meter leads and DMM set to current mode from above).

    To learn how to use a DC Clamp/DVM (digital volt meter)--Play around with your car. Measure the battery voltage with the car off and idling. Head lights on and off... Do the same measurements with the current meter clipped on one of the battery leads (+ or - does not matter--Which ever is easiest to clip over).

    Note--sometimes batteries have several leads--One to starter, another to the alternator (generator) and perhaps another to vehicle electrical system (ignition, radio, etc.). You can clip on all three wires and measure the total of any currents (+15 amps from alternator, -5 amps to run engine=total of +10 amps into the battery).

    Note a DC clamp meter measures the direction of the current... If you read +1- amps and flip the meter over on the wire, it will now read -10 amps. And on AC, it cannot tell the direction of current flow.

    Also, here is a good site to learn some basic electricity... Boats, cars, and solar PV systems are all very similar (charging source, batteries for storage, and various loads).

    Electricity for Boaters - BoatSafe.com

    Please feel free to ask questions--Once you are comfortable taking measurements (that make sense) on your car--we can go to your PV system.

    Sorry for the back to basics--but it will make working on your PV system a bit easier for all of us--and if you have a large battery bank and solar array--you are working with some serious currents... You will need to be very careful (remove rings and jewelry, perhaps ware glasses/safety glasses around battery bank, etc.). The Current Clamp Meter is much safer for measuring current--so you will be OK there unless you disconnect some wiring.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mrleemus1
    mrleemus1 Registered Users Posts: 28 ✭✭
    Re: upgrade to new mppt controllers
    Vic wrote: »
    My opinion; Would probably be OK if done with appropriatly sized, and correctly crimped connections.

    However, Believe that the C60 is an PWM CC. Voltages very much in excess of what is needed to reach the maximum charging or EQ voltage must be dissipated as heat. The C60 should go into thermal current limit, protecting itself, but you would wind up with very low charge currents, and wasting a lot of solar input.

    If you were doing the butt splicing as a part of an upgrade to MPPT type CC, this splicing should be fine as long as the Max Voc does not exceed the max permitted Vin.

    Is this an answer to the question? Vic

    Yes that does answer my question -- and you are correct the C60 is a PWM CC with a MAXIMUM of 55 Volts open circuit, so they are unsuitable. -- i would plan on getting a couple of new MPPT controllers capable of handling the higher voltage
  • mrleemus1
    mrleemus1 Registered Users Posts: 28 ✭✭
    Re: upgrade to new mppt controllers

    We have had similar experiences
    2 of the 3 C60 controllers have been replaced and one expensive battery bank replaced
    NOT TO MENTION the 300 -- 400 hours of backup generator fuel costs. I also fear the new battery bank wont last long at this rate of poor chargeing performance.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: upgrade to new mppt controllers

    Need to make a correction RE the PWM action of the C60. It is WRONG that voltages much in XS of that needed for charge is disappated as heat ... WRONG. But it results in under utilization of the maximum available charge currents.

    But you know this.

    Sorry to hear about the C60 failure(s) and the battery bank. For me, the mppt CCs with robust dispalys really make it very much simplet to set desired parameters, and to actually see in great detail the functioning of the CC.

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: upgrade to new mppt controllers

    With your clamp current meter--check each C60 output (i.e., set meter to 400 Amp full scale DC and clamp one wire--like +). See how much each controller is outputting to the battery bank. Also, log the voltage in the middle of a good sunny day at Vpanel and Vbattery right a the input/output of each charge controller (you have 3, correct?).

    Also, you really do have 42x100watt panels? Arranged in 3 arrays to three charge controllers? (all panels in parallel--should be).

    A 4,200 watt array is pretty large with C60 controllers (many years ago, it was the standard).

    At some point, we will want to ask about your generator and AC battery charger details too.

    Oh--by the way, I messed up... You have a 24 volt battery bank and I did the calculations for a 12 volt battery bank.

    Are you getting a total of 72 amps from your 4,200 watt array? You should be getting something like:
    • 4,200 watts * 1/33 volts * 0.80 fudge factor = 101 amps
    Vmp=33 volts is on the low side for a 24 volt battery bank--should be ~35 volts or so... Yes, placing panels in series to up Vmp-array behind a MPPT controller would help.

    Your array should be able to output more current--but I was way off on the previous calculations (sorry).

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