24v bank supplying 12v power to inverter

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  • taxer
    replied
    Pwm input should read <34v

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  • taxer
    replied
    What I want to do is use my 50amp pwms and one of my 12v inverters- probably the 1000w for now.

    Remember this is a bunkie.
    fans, lights , electronics, pellet stove ( max 350 watts to start it - igniter, then 100w)
    Occasional 600w heater

    The pwms are generic kw2450 50amp 12v/24v
    max panel input 650w/1200w
    mav v input says 50v on label
    but poor manual translation, it says &lt;34v
    Equalization for flood batteries is 14.6v
    Double for 24v 29.2v

    Panels are OSM off grid 235w pmax
    and as mentioned 3.65 vmp
    7.69 imp I have many

    2 panels per inverter is a waste at 12v
    But 5 at 24v is more efficient.

    Lots of 6v golf batteries
    but want to do 2 x 24v banks

    Again,

    Looking to charge batteries at 24v and discharge at 12v....

    And not looking to blow it up.

    I'm testing in theory only at this point.

    Any electrical engineers here that want to educate me on the theory behind what works and doesn't, I'm all ears. Or anyone that may have tried this before.

    I have Different scenarios I have sketched out, with switches, etc., but looking for some brain storming here.

    Previous posts discourage not taking 12v from the 24v array and discharging separately to which I fully agree.

    How can I discharge the 24v battery bank 12v at a time for my inverters?

    I questioqed discharging them by doing a parallel hook up to the inverter from the same 24v bank.
    I believe the answer was they would now become a 12v bank and fry something..
    still trying to determine the properties and principles of these arrays....

    The other possibility was to draw 12v from one bank and 12v from the other into one inverter and the remaining 12v from each bank into another inverter. The discharge connections to the inverters would be equal .

    Also, my mention of doing solar on the cheap may have been misinterpreted.
    cheap in costs is what I referred to as in mppt vs pwm. Solar does not have be expensive anymore.

    I believe proper wiring requirements is essential, but there should be many scenarios to arrive at the same solution.

    So with the equipment I mentioned anyone with an idea would be greatly appreciated.

    Switches and breakers added have given me some other solutions but they involve more manual maintenance and attention to keep the batteries at peak condition.

    Thanks

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  • checkthisout
    replied
    Originally posted by taxer
    Yes, and sounds like I have to use one of my mppt cc's too. Was hoping to set it up on the cheap for a bunkie...
    Ok. What equipment do you currently have? List it like this so it's clear

    1) X brand charge controller(s) @ amps, volts, watts
    2) Quantity and volts/watts of panels
    3) Inverter

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  • SunEagle
    replied
    Originally posted by taxer
    Yes, and sounds like I have to use one of my mppt cc's too. Was hoping to set it up on the cheap for a bunkie...


    I am sorry but the words "cheap" and "solar" should never be used in the same sentence.

    Leave a comment:


  • taxer
    replied
    Yes, and sounds like I have to use one of my mppt cc's too. Was hoping to set it up on the cheap for a bunkie...



    Leave a comment:


  • checkthisout
    replied
    Originally posted by taxer
    Ok, thanks for your input, at least the comments that are not smart ass ones.

    I'm trying to think outside the box, to power a bunkie with limited equipment without blowing up the place.

    I would have 2 banks of 24v (6vx4 x2)
    And 2 cheap inverters.
    min 5 x 230w (30v) panels
    2 × 50amp cheap pwm charge controllers allowing solar panel power streams of 650w for 12v and 1200w for 24v.

    I am attempting to use only 1 charge controller(cc)

    Again, another scenario...

    2 x 24v banks with 5 panels 5x230w = 1150w
    With cc charging 24v.

    tap into one 12v from each string to one inverter and the remaining 2 on another inverter.

    Ideally it would discharge them more evenly if they were tied to the same inverter, but I would be doing much the same as the original scenario.

    Of course I will ask if anyone has tried it.


    Idea by sdold of charging and then disconnecting might work ok with the 2 banks

    So one charging and the other discharging

    Lots of switches and constant attention to battery charge/discharge though..
    What are you trying to avoid doing? Spending money on a 24V Inverter?

    Leave a comment:


  • chrisski
    replied
    If you can't find a manual telling you the input Voltage range for your PWM, then download any and take a look.

    My PWM is 18-24 volts for a 12 volt battery, and 36 to 48 volts for a 24 volt system. Your panel fits neither 12 volt or 24 volt battery charging criteria.

    With PWM, about the only option is to add panels in parallel with those voltages, so amperage and voltage loss can become a factor in those systems. Again though, panel voltages fall outside all PWM specs I've read. I have not read all PWM specs, only about 10 or so. Maybe your PWM is different.

    If you must use those panels, appears to me you need to buy a MPPT controller. With those panels, Five can only be put in parallel, but 4 can be put 2S2P or 1S4P; Six can be put 3S2P, 2S3P, or 6P. More options with non-prime numbers of panels,.

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  • taxer
    replied
    50 amp pwm

    Max pv voltage is 50v

    Max Pv input power:
    650w 12v / 1200w 24v

    Leave a comment:


  • sdold
    replied
    I don't think your 30 Vmp panels will adequately charge a 24V battery, typically a "12V" panel Vmp is about 18V and a "24V" panel is about 36V Vmp. These sound like re-purposed 60-cell grid tie panels.

    I'm not trying to talk you into re-designing your system, but in case you're interested, the options seem to be:

    1. Use all five panels in parallel and wire the batteries as a 2s4p 12V system and use an MPPT or PWM CC. With PWM you wouldn't get anywhere near full power from the panels. The four parallel battery strings would likely shorten their life significantly. Having more than two parallel panels requires a fuse for each panel.

    2. Use all five panels in series with an MPPT charge controller. 5 x 37.46 Voc = 187V so the CC max voltage input must be 200V or more. Batteries wired same as above, or as 24V if you don’t mind buying a new inverter. No panel fuses since you only have one string.

    3. Add or subtract one panel so you can have two or three in series, and put two of those strings in parallel (2s2p or 3s2p) feeding an MPPT CC. No panel fuses needed since there are only two parallel strings. Your batteries can then be 12V in four parallel strings (bad) with the inverter you have or 24V in two parallel strings (not as bad) with a new inverter. That’s probably what I’d do.
    Last edited by sdold; 09-19-2021, 07:57 PM.

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  • taxer
    replied
    Solar panel is osm off grid max power
    30.65v vmp
    7.69 amp imp
    37.46 voc
    235w
    cc's are cheap no name 50 amp pwm.

    Leave a comment:


  • sdold
    replied
    I’m not sure what a “30V” panel is, is there a label that gives the specs for Vmp (max power voltage) and Voc (max open-circuit voltage)?

    What’s the make and model of the charge controllers?

    Leave a comment:


  • taxer
    replied
    Also anyone who can forward me to a site that has basic wiring rules in this area or experiments with various scenarios would be appreciated.

    I have mppt cc's but I'm looking to use these pwm cc's for a temporary cheap alternative for now.

    Leave a comment:


  • taxer
    replied
    Ok, thanks for your input, at least the comments that are not smart ass ones.

    I'm trying to think outside the box, to power a bunkie with limited equipment without blowing up the place.

    I would have 2 banks of 24v (6vx4 x2)
    And 2 cheap inverters.
    min 5 x 230w (30v) panels
    2 × 50amp cheap pwm charge controllers allowing solar panel power streams of 650w for 12v and 1200w for 24v.

    I am attempting to use only 1 charge controller(cc)

    Again, another scenario...

    2 x 24v banks with 5 panels 5x230w = 1150w
    With cc charging 24v.

    tap into one 12v from each string to one inverter and the remaining 2 on another inverter.

    Ideally it would discharge them more evenly if they were tied to the same inverter, but I would be doing much the same as the original scenario.

    Of course I will ask if anyone has tried it.


    Idea by sdold of charging and then disconnecting might work ok with the 2 banks

    So one charging and the other discharging

    Lots of switches and constant attention to battery charge/discharge though..

    Leave a comment:


  • checkthisout
    replied
    Originally posted by taxer
    I've read here many times that you can't have a charge controller charging a 24v battery bank and then power a 12v inverter...
    ok I get that using one 12v or 2x 6v batteries will cause uneven battery discharge and many problems going forward, but....

    Why can't I wire the 2 x 12v separately to the inverter so that the crital connections are 12v only.
    When we measure voltage on single batteries we pick the 6v, 12v 18v or 24v points in the connection. Why can't I pick the + and - of say each 12v battery and wire it as in parallel to the inverter?

    Charges at 24v and powers the inverter at 12v.. just a bit of a wiring mess..
    Yes, each 12V battery in a 2 battery 24V system will show 12 volts even when connected in series.

    If the batteries are connected in parallel and you go head and install a jumper between the pos/negative it's not hard to see what will happen.

    Please film the results and post link on here.

    Leave a comment:


  • chrisski
    replied
    You could do that, but the draw off each of the 12 volt batteries has the [potential to be vary uneven and kill one battery prematurely.

    This would work for a science experiment by connecting the batteries in series, then putting a separate set of wires off each battery as 12 volts, and running this sun parallel, but not sure how it would hold up day after day, week after week, month after month, year after year.

    Any reason you would want to try this?

    It’s a horrible idea to power your RVs 12 volt system by tapping into one of two batteries in series of a 24 volt system because of uneven charging, but I never read tapping into each battery and running these in parallel. To me, I will not be the first on the block to try this, especially with how much money a 2000 watt inverter, wiring, and four golf cart batteries cost. Not worth the science experiment to me.

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