DC-to-DC Converter Instead of MPPT?

System
System Posts: 2,511 admin
in Solar Beginners Corner #1
Let me begin by saying that there must be something less than ideal about what I am about to propose because otherwise I would have seen at least one other post somewhere on the internet! So what's wrong with my solution for a battery charging setup that's the same price but better than PWM but cheaper than MPPT?

I have two 185W/24V solar panels. I want to charge one 12V battery (to start with). I can use a 24V/12V 25A PWM charge controller but I understand that I would lose half of my watts in the conversion. For more money I could go the MPPT route and get back most of that power. But what about if I hook the panels up to a 24V to 12V DC-to-DC converter that's rated at 25A then connect the output of that to the input of a 12V 25A PWM charge controller?

And why don't 24V to 12V charge controllers already do what the converter does to keep the current high? Or am I reading the specs on the DC-to-DC converter wrong?

Thanks!
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Comments

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #2
    Re: DC-to-DC Converter Instead of MPPT?

    Wouldn't an simple mppt controller work better, with less headache, and probably not much more money?

    http://store.solar-electric.com/mosumpsochco.html

    Tony
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: DC-to-DC Converter Instead of MPPT?

    I figure I can get the converter for about $60 and a charge controller for $40. I'm happy to use cheap components at this point just to get it working. And that certainly beats $230 for the Morningstar MPPT charge controller, cheapest I could find.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: DC-to-DC Converter Instead of MPPT?

    it won't work. the converter most likely won't have the input voltage range that an mppt controller will, but even overcoming that obstacle the converter will output a voltage like 13.5v or maybe 12v as it depends on the converter and this will not charge a battery fully let alone be able to drive a pwm controller which needs about 15v or more and even that is going with agm style batteries to charge as standard leadacid batteries require more voltage to reach a full charge. if you do it, don't say i didn't tell you it won't work.
    if you find a converter that can vary an output voltage high enough you could then use just the converter to charge the batteries similarly as to how the standard sunsaver pwm controllers work with a fixed output charge voltage. you won't get a float option with this and remember that it must have certain input voltages to function properly. here's an example of the input voltage of a samlex 24v-12v converter: Input 20-30 Volts DC, output 12 volts DC @ 15 Amps. that means both the vmp and oc voltages should fall within that range.
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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #5
    Re: DC-to-DC Converter Instead of MPPT?
    Bunky wrote: »
    I figure I can get the converter for about $60 and a charge controller for $40. I'm happy to use cheap components at this point just to get it working. And that certainly beats $230 for the Morningstar MPPT charge controller, cheapest I could find.

    Not sure where you will find a 30 amp charge controller for $40.

    In theory your idea will work, since that is about 2/3 of what an MPPT controller does. But it leaves out a lot, such as power point tracking.

    You will also need to find a dc-dc converter that puts out around 15 to 16 volts, not 12.
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