MPPT vs PWM coupled with Voltage Down Controller

SLPx
SLPx Registered Users Posts: 3 ✭
edited May 2019 in Solar Beginners Corner #1
Hi All,

I'm a Newbie here. But I do have a problem to ask and appreciate very much that If any of the seniors here could shed me a light.

I have a solar network of following
- 3 panels of 340W (36V, 47Vmp)
-Two PWM chargers of 30A/60A
-One MPPT charger with 60A
-Inverter 230V, 1500W with 12V input
-Two Lead-acid (car) batteries (at the moment).
-The network is on 12V off-grid
-Used to power the house, when the inverter power is available, the house connected to the inverter. when the juice is over, automatically switches to the grid. 
-at the moment, unable to grid tie the panels and buy new batteries (including deep-cycle) 

I have connected two solar panels parallel to MPPT and One panel to PWM
-When connected my PWM controller withdraw charging the batteries and let the voltage of the solar panel to flee
-MPPT charge controller got 20A and it did not charge the Lead batteries to full. Kept the maximum level at 12.5V (although the charge voltage is 14.2)

So I disconnect my MPPT controller and connect all to PWM.
PWM charges the batteries to 13.8V and batteries lasts to the night.

Now I have the following issues to tackle.
1. Since I'm not using collosal amounts of energy out of the panels and only the PWM controller is working,
With the least cost options and almost exclusively using existing peripherals,
 ---- can I use a 5-60V DC step down converter to 18V, between solar panels and the PWM controllers, to utilize the missing voltage area of (18 to 46)

2. Having two deep-cycle batteries with the MPPT controller at 24V (purchasing two deep cycle batteries) and convert the output with step down controller, to either other two batteries to charge or, directly to the inverter and having an ac-dc charger to charge the rest of the batteries.
(use this other battery storage to night use)

3. any other feasible solution to this.

Thanks and Best regards
Sanjeewa





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Comments

  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #2
    SLPx said:
    Hi All,

    I'm a Newbie here. But I do have a problem to ask and appreciate very much that If any of the seniors here could shed me a light.



    OK first general comments,
    1) 12V is a poor voltage to choose unless your loads are minimal.  And car batteries are awful.
    2) Sounds like your MPPT controller has a problem with its configuration.  If it's a charge controller it is likely designed to get to charge voltages.
     can I use a 5-60V DC step down converter to 18V, between solar panels and the PWM controllers, to utilize the missing voltage area of (18 to 46)
    No.  A DC/DC converter will collapse the panel voltage unless you use an LVD that somewhat matches the panel's MPP voltage.

    Having two deep-cycle batteries with the MPPT controller at 24V (purchasing two deep cycle batteries) and convert the output with step down controller, to either other two batteries to charge or, directly to the inverter and having an ac-dc charger to charge the rest of the batteries.
    Not really. You'd need a 24V inverter.  You can use a DC/DC converter to drop inverter power, but it would have to be rated higher power than the inverter, and a new 24V inverter will be cheaper.  
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