Epever Tracer series MPPT max current bypass

FabianFabian Registered Users Posts: 96 ✭✭
The Epever Tracer series MPPT comes with various max current handling. I have one that is rated for 40A. Is it possible to increase the max 40A rating without damaging the controller by implementing additional cooling?

What i would want to know is how does the controller know that it has reach the 40A max? Is it that the controller monitors the temperature so once the heatsink or mosfets reach a certain temperature then the current limiting capability kicks in so therefore the temperature/current does not pass that level so therefore if you have additional cooling on it to keep the mosfets/heatsink cool at all times you can trick the controller to produce more current output than the rated 40amp?

Or is it that the current limiting  features kicks in base upon some I.C or circuit/sensor to know when you reach 40A max so in essence there is no way to bypass that feature?

Reason for my question is due to the fact that my epever tracer is rated at 12/24v 40A 1040Watt. I have (4) 320watt panels which total is 1280watt so that surpass the max wattage by 240watt and i would like to be able to can draw close to the 1280watt which would be that i would be pulling more than max 40amp from the controller so I would like to hear your comments on this regard.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,080 admin
    The current ratings are designed/tested/configured by the manufacturer so that they will (at least) survive the warranty period in specified conditions.

    Could you do (for example) more forced air cooling and have it survive a higher current--sure. Although, you probably would need to hack the firmware to get around the configuration current limits.

    Adding fans to power supplies is common solution. Downsides are that fans can be noisy, draw dust/dirt/bugs into systems/filters, and eventually fail.

    With good quality MPPT charge controllers, it is common to "over panel by something on the order of 1/0.77=1.3 times because solar panel standard ratings will over estimate actual operating conditions for most installations (panels tested/spec'ed at 75F/25C, but run much hotter under hot sun in most climates). A "hot panel" in warm weather can have Vmp-array about 80% of specified Vmp-std conditions. Power=Voltage*Current, so reduced array voltage by 20%, you reduce power to the battery bank by 20%.

    Good quality MPPT controllers will limit their output current to rated value... And will usually reduce output current when the controllers start to run hot (hot room, poor ventilation, lots of current through controller).

    There can be other limitations and issues with power systems. Wiring needs to be fuse/breaker protected against short circuits. The actual silicon transistors/diodes/etc. are very small--A short surge current (or over voltage) can break down that small piece of silicon well before its heatsink starts to get hot.

    The key to long life for electronics. Keep below the specified limits. And keep the controllers cool (for every 10C/18F below "room temperature, the device will age 1/2 as fast... Running at 25C vs 35C (controller in warm closet), the device will have 1/2 of the design life.

    Also, another killer for electronics is temperature cycling... Reducing the operating temperature spread (controller in freezing conditions overnight, then in direct sun during the day--The solder joints can crack, and circuit packaging can crack, etc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FabianFabian Registered Users Posts: 96 ✭✭
    if i connect (3) of the 24v 320watt panels  in parallel to charge my 24v battery bank will the charge controller operate in mppt mode seeing that the input voltage is not 1.5 times or 2 times my battery voltage?
    The input voltage will be close to my battery voltage. I will have about 33-35volts coming in while my battery is going to be around 25 or 26V.
    So with this in mind will i be able to can pull close to my 960watt total in optimum conditions?
  • BB.BB. Super Moderators, Administrators Posts: 31,080 admin
    What is the exact Vmp rating of your panels?

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FabianFabian Registered Users Posts: 96 ✭✭
    Vmp rating is 33.3v. I am wondering if running all 3 in series with my input voltage reaching 100volts or maybe as high as 105v would surpassing the 100volt limit by just a few voltages cause the controller to be damage? if i surpass the 100volt limit by just a few volts and keep the controller as cool as possible with additonal fan cooling would it be damage with the increase voltage over the 100volt by just a few?
  • BB.BB. Super Moderators, Administrators Posts: 31,080 admin
    More or less, if you are charging a 24 VDC lead acid battery bank... You are in the range of 29-32 volts.

    A Vmp panel with 33.3 volts at 25C/75F on a hot day under full sun no wind conditions, you are looking at Vmp-hot of (~0.80x33.3v) 26.64 volts.

    Now, Vmp curves are not a sharp peak--A volt on either side of Vmp-operating will not dramatically reduce current--But it is not a great place to start your design.

    More or less, a 24 VDC lead acid battery bank should have a Vmp-array in the range of 35-40 Volts Vmp-std (standard test conditions).

    And for an MPPT controller do do "its magic" (operate in MPPT mode and take higher array voltage and lower current, and downconvert to lower battery voltage and higher charging current), the Vmp-array needs to be >~40 VDC. If you operate the array in the range of ~35040 volts, an MPPT or PWM controller will be doing the same thing (operating in PWM mode).

    You mentioned a 25-26 volt battery bank... Is this a LiFePO4 (lithium ion) or other battery chemistry where you are charging at ~26 volts?

    If yes, then the Vmp-array minimum (PWM or MPPT) could be as low as:
    • 26.0 volts charging * 1.3 MPPT controller fudge factor = 33.8 volts Vmp-array-std
    In solar (and most designs), details matter. We have lots of standards and rules of thumbs--But when you go outside of the "norms", we have to know the details to make everything play well together.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 31,080 admin
    When running close to the limits--You have to understand where/why these limits are set in the first place.

    For current, you have heating both from capacitance (stray gate capacitance, gets charged/discharged as they turn on and off--Just a waste of energy).

    Another current issue is that resistive heating equation is Power=Current^2 * R ... So, you can see that if you put 2x more current through a wire (transistor, etc.), then you get 4x more heating (^2 or "square" of the current).

    And for max voltage... When you are looking at the physical size of a transistor... You are looking at uM (micro meters)... Where 1uM = 0.00003937 inches.  Put 100 VDC across 100 uM transistor (power transistors are physically larger than logic transistors in a CPU chip). Just guessing at 100 uM (I am not a microchip guy):
    • 100 VDC / 100*0.00003937 inch =  254,000 volts per inch
    So these devices are already under a huge voltage across their active regions (small voltage across an even smaller physical transistor).

    If you raise the voltage by very much, you are running the risk of punching through the insulation and gates of these devices.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FabianFabian Registered Users Posts: 96 ✭✭
    edited October 17 #8
    If I raise the voltage by 5volts so.the input has 105volts max and include additional cooling would the controller operate perfectly without any issues?

    Suppose I use (2) 24v 320 watt in series along with (2) 24v 200 watt in series then parallel the 2 set of strings giving me a total of 1040watt which is the max wattage rating of the controller would I be able to can pull the max 40amp in mppt mode giving the fact that the 320watt vmp is slightly just a few volts different from the 200 watt vmp?
  • BB.BB. Super Moderators, Administrators Posts: 31,080 admin
    Some of the controllers will shut down if max voltage is exceeded... And some will log a "warranty violation" if voltage is exceeded.

    On the electronics side, we never designed circuits/systems to operate voltage above the IC/Transistor specifications. You could "play" with the current side by using larger heatsinks/fans/etc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FabianFabian Registered Users Posts: 96 ✭✭
    Suppose I use (2) 24v 320 watt in series along with (2) 24v 200 watt in series then parallel the 2 set of strings giving me a total of 1040watt which is the max wattage rating of the controller would I be able to can pull the max 40amp in mppt mode giving the fact that the 320watt vmp is slightly just a few volts different from the 200 watt vmp?
  • BB.BB. Super Moderators, Administrators Posts: 31,080 admin
    edited October 17 #11
    As long as the Vmp-array-string is "close"--Then yes you can parallel the two (or more) parallel strings... "Close" is 5-10% difference... Like Vmp 30/33 volts, or Vmp 60/66 volts (for 2x series strings).

    More or less, it is not perfect, but close enough you would not notice the difference between "matched" and "almost matched" strings.

    If you mix a 60 Amps (2x panels) with an 80 Volt string--That is a bigger spread... And you don't know where the MPPT controller will "lock on to the peak Pmp=Vmp*Imp" operating condition. And no matter which one is "chosen", you will lose some output as there is no "optimum" condition that will give you maximum (name plate) Wattage... The peaks are "local  optimums" for the conditions present.

    As far as max input Array Wattage for an MPPT controller... A good quality controller does not "care" about input wattage--It just does its work finding Vmp-array-optimum (by sliding the Array Current up/down and finding Pmax=Vmp*Imp). And limits the output current to spec's and present heatsink temperature (lots of different controllers out there--Just a generic description of how things work).

    The typical (fudge factor) used to "cost effectively" over panel an MPPT controller is a factor of 77% (Vmp-hot and controller internal losses... Vmp-hot ~81% * Controller eff ~95%). For a 40 amp controller on a 24 volt bus:
    • 40 amps * 1/0.77 panel+controller deratings * 29.0 volts charging = 1,506.5 Watt array "typical cost effective maximum"
    The above number is really just "magical math"--It is only a stake in the ground... If you wanted 1,800 Watt array or 1,200 Watt array--Those are perfectly OK answers too.

    One reason to "over panel"--Is during less than ideal weather (some clouds/overcast/haze)--The larger array will still harvest more energy than a smaller array. If the cost of the "extra panels" is not a big deal--Then overpanel away.

    Some controllers may list a maximum input array current--you have to check the manual closely.

    Of course, we also suggest that the MPPT solar charge controller be properly ventilated in a cool location. Placing in a closet (no ventilation) or in a hot room with full sun on the window, or full sun on the controller (vs at least some sort of overhang/sun shade)--The runs the controller hotter, and can cause the controller to reduce output current due to excess internal temperatures. And Hot electronics simply do not last as long as electronics kept cool.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FabianFabian Registered Users Posts: 96 ✭✭
    Well said. Thanks for the support. Greatly appreciate it.
  • mcgivormcgivor Solar Expert Posts: 3,558 ✭✭✭✭✭✭
    edited October 17 #13
    Running a controller at its maximum limitations, both current or voltage is, in my opinion,  not a wise choice. Being more realistic by capping maximums to around 80%, affords more comfort zone which will be easier on electronic equipment.

    Spreading the window of opportunity over a longer period of time by orienting the two strings in a SW/SE direction, for northern hemisphere, for example, will probably result in an equal or better daily  harvest, without punishing the electronics . Doing this will probably decrease the depth of discharge of the battery because the time off charge will be reduced, especially if most loads are used overnight. Additionally it may benifit the batteries by not subjecting them to rates charge close to or exceeding maximum recommend values, all speculation as I've no idea the Ah capacity of said system.

    Understandably this is not always an option but worth considering if the opportunity exists. 

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • littleharbor2littleharbor2 Solar Expert Posts: 1,559 ✭✭✭✭
    Here is a page from the mfg. This might help.


    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, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • mountainmanmountainman Registered Users Posts: 431 ✭✭
    From my epever manual?
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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