Classic charge controller question

ws9876
ws9876 Solar Expert Posts: 448 ✭✭✭
in Off Grid Solar & Battery Systems #1
what is the lowest voltage the classic can take and still convert it to 24v???
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Classic charge controller question
    ws9876 wrote: »
    what is the lowest voltage the classic can take and still convert it to 24v???

    The same as the recommended Vmp for use with a PWM type controller: 35 Volts.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: Classic charge controller question

    technically that isn't an exact cutoff as it will still convert will lower voltages, but between losses, efficiency factors, and temperature deratings during hot spells it is better not to try to be exacting. why do you ask?
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  • ws9876
    ws9876 Solar Expert Posts: 448 ✭✭✭
    #4
    Re: Classic charge controller question

    you mean if a turbine isnt putting out 35V it wont charge 24v?? I thought it could up convert too?? like 10v to 24V just less amps..
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #5
    Re: Classic charge controller question
    ws9876 wrote: »
    you mean if a turbine isn't putting out 35V it wont charge 24v?? I thought it could up convert too?? like 10v to 24V just less amps..
    Nope, MPPT down-converts extra voltage and turns it into extra amps, not the other way around.
    If there are no extra volts, there will be no extra amps, and if the voltage isn't high enough, there will be zero amps.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #6
    Re: Classic charge controller question
    ws9876 wrote: »
    you mean if a turbine isnt putting out 35V it wont charge 24v?? I thought it could up convert too?? like 10v to 24V just less amps..

    That was a planned feature of the classic, but I don't think it made it in to the final version. Any voltage above the battery voltage will charge it. If you wanted to do a full and proper absorb then you'd need 28.8V from the turbine + voltage loss in the classic (1V?). If you wanted to EQ the battery with the turbine then you'd need about 31V from turbine + 1V voltage drop in classic. (Assuming you have flooded lead acid batts)
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #7
    Re: Classic charge controller question
    stephendv wrote: »
    That was a planned feature of the classic, but I don't think it made it in to the final version.

    A 'final version' of the classic likely will require the catastrophic loss of boB and Robin(god bless them and keep them healthy) and maybe others... It appears to be constantly evolving. There was some discussion recently, and I did a quick search and found a thread recently with boB saying every thing is there just requires a lot of programing (from 2010 or 2011)
    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.
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  • ws9876
    ws9876 Solar Expert Posts: 448 ✭✭✭
    #8
    Re: Classic charge controller question

    can any other controller convert up???
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  • mahendra
    mahendra Solar Expert Posts: 188 ✭✭✭
    #9
    Re: Classic charge controller question

    i have seen mine give output with only 11 volts from the array for 12v system (two 29.4v vpm panels in series).But it only did this for short periods like 10mins max.Think there is a forum on midite site that dealt with this>administrators said the hardware is capable of doing that but software is not needs upgrading. Don't know if they will ever fix the software part.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: Classic charge controller question
    mahendra wrote: »
    i have seen mine give output with only 11 volts from the array for 12v system (two 29.4v vpm panels in series).But it only did this for short periods like 10mins max.Think there is a forum on midite site that dealt with this>administrators said the hardware is capable of doing that but software is not needs upgrading. Don't know if they will ever fix the software part.
    I am not sure I understand...

    Are you saying that the Midnite would only output 11 volts from a ~60 VDC Vmp array?

    That would be normal operation with a near dead battery bank (i.e., the battery bank is at ~10.5 volts "dead' and the charger is beginning to bring the bank voltage backup up... It would take a lot of charging for the bank to reach "absorb" of ~14.5 volts--and at that point, the Midnite would begin voltage regulation.

    What people are asking for here is the ability for the MPPT charge controller to talk a Vmp~18 volt panel/array and recharge a 24-48 volt battery bank ("boost" the array voltage to battery bank voltage).

    Most all MPPT controllers have a "buck" type switching power supply--Which can only "drop voltages" -- They cannot increase voltages. A Boost converter can only increase voltage, not drop.... And then we have Buck/Boost converters which can increase, maintain, or drop voltages efficiently.

    However Buck are the cheapest and most efficient form of converters (in general). Boost and Buck/Boost are more expensive (more components) and less efficient.

    For larger systems (which MPPT controllers are usually used with), setting up with a "low voltage" Vmp-array would be counter productive to most of our needs. Which is to reduce voltage drop/current/copper wire diameter by increasing array voltage.

    I can see a boost converter for a small system (not much power and what to use a single lower voltage panel for charging--But that is not something that would usually make sense for a large (>~400-800+ watt) system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Classic charge controller question

    I don't know of any controller that will up convert. The reason being there's not much point to doing it. In order for any power to be realized you need both Voltage and current, and having to double the Voltage results in halving the current so you still end up with not much power especially after the buck converter takes its share to operate.

    Typically controllers are meant to work with PV's, which have no trouble providing sufficient Voltage (Voc is achieved with almost any amount of illumination) until asked to provide current as well; the Voltage is "pulled down" until current is realized. If there's enough power you have V>B and current so charging takes place.

    With wind turbines the Voltage being too low would be a matter of design; like trying to charge a 24 Volt battery from a 12 Volt PV. Unless the power source is designed to work with the battery you're really stuck.

    Voltage converters can turn lower Voltage into higher at the expense of current (and power), but they are meant to work with a stable Voltage source which neither PV's nor turbines are. One exception to this are the "magic box" units for PV's which try to keep each panel at the same V as the others despite insolation differences, again at the expense of current (and power). I doubt such would work with a turbine.

    It is technically possible to charge 24 Volt batteries from a 12 Volt source, but off-the-shelf solutions are unlikely because it is not the best way to do it. Rewiring the charge source so that it provides the necessary minimum V is. In the case of a turbine this means different windings or a step-up transformer on the AC side.
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  • mahendra
    mahendra Solar Expert Posts: 188 ✭✭✭
    #12
    Re: Classic charge controller question

    no input voltages are about 11volts from the array.Of course this would only be seen when sky is very cloudy or on rainy days.From observation what i saw is that the midnite classic was able to step up/convert the 11volts from the array to 13.8volt required by the battery>from the display it read input it read-approx 11 volts and battery volts was approx 13.2-13.6 .output amps was about 1-1.2.I know the classic is suppose to be resting but that is what is saw on several occasions it did this too.Cant explain it other wise
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #13
    Re: Classic charge controller question

    Well here's the my recent post on the thread Air 30;

    Apparently the Classics can be setup to boost voltage, but it hasn't been implemented, I don't know to what extent, boB has said he might spend some time on it, I think, but his plate is pretty full. You might ask over at the Midnite forum..

    Here's one of the threads. Doesn't sound like boB has a great interest in working on it at that point. He does suggest that all the hardware is there, just a lot of software work. Of course that was back in 2011, I had read something more recently, but it's not of great interest to me.
    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.
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