using 12v to generate 24v... what now

Options
System
System Posts: 2,511 admin
in Solar Beginners Corner #1
Ok im in the middle of an experiment. I'm generating 24v-28v with a solar panel, how do I split the voltage into two 12v channels. One I can use as a 12v power supply and one I can bank into a battrey. I'm a total nube to solar. Thanks Troy
· Share on Twitter

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Options
    Re: using 12v to generate 24v... what now

    Welcome to the forum.

    The answer is (you won't like this): you don't.

    With a solar panel putting out 24-28 Volts we have to first ask the question: is that Voltage open circuit or Voltage at maximum power (Voc or Vmp)? I will guess that this is either a homemade panel or one of those meant for grid-tie with the odd Vmp (often around 26).

    The second thing is that solar panels can't really run most things directly; they are meant to recharge batteries (for the most part - there are always exceptions). In this case to charge a 12 Volt battery from a panel with that high a Voltage (is Vmp - it makes a big difference) you'd either need to use one of the MPPT type charge controllers (more money) or live with some significant power loss through a PWM controller due to mismatched Voltages.

    So after you've got your charge controller in place and charging your 12 Volt battery, all you really need do is run the 12 Volt loads from there. The panel should have enough power to both recharge the battery and run the loads at the same time (while the sun shines). The battery will supply power against fluctuations and for when there's no sun on the panel. But it is important that the panel's over-all capacity (usually measured in Watts) is capable of meeting both needs.

    Does that help any?
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,446 admin
    #3
    Options
    Re: using 12v to generate 24v... what now

    We probably need more information...

    First, what is the Vmp rating of your solar array... Typically, Vmp~17.5 volts for a "12 volt panel". And Voc may be 21 volts or a bit higher (on cold days).

    Vmp=24-28 volts would require a MPPT charge controller to charge a 12 volt battery bank efficiently.

    And, if you want to charge two different battery banks, or charge a battery bank and run a separate load would be two different answers (probably).

    Also, not many people want to charge a battery bank and run a separate 12 volt load directly from the solar array... Usually, the array charges the battery bank. And the battery bank runs the 12 volt load.

    For some people with Recreational Vehicles, they have to battery systems. One for for the vehicle (start the motor, run the lights). And a second battery bank to run the "House" power (so you don't kill the vehicle battery by accident).

    Anyway, there are probably several answers we can give--depending on your exact needs.

    Good Luck!
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Options
    Re: using 12v to generate 24v... what now

    welcome,
    the short answer is you don't.

    the sun isn't consistent enough to normally split the power into 2 12v sources and loads certainly wouldn't be either in most cases. pvs in this range are meant to be used for either grid tied inverters and would have many more pvs in series to get into the proper range the inverter wants or to be used with an mppt controller to down convert that voltage to the 12v range. you could use a pwm type controller, but you will have higher losses with the input and output far apart.
    · Share on Twitter
  • System2
    System2 Posts: 6,290 admin
    #5
    Options
    Re: using 12v to generate 24v... what now

    I've been wondering how many watts this thing is. Its a harbor freight 18-24v tool charger, but no where on the box or manual does it say how many watts. I just got a cheap one to experment with. I have found a 75watt solar panel for $160.00 locally. If thats a good deal I'll return this one and pick up the 75 watt one. And grab a controller. Any recommendations would be helpful I do a lot of dc wireing but this is my first shot at power generation. Thanks Troy
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,446 admin
    #6
    Options
    Re: using 12v to generate 24v... what now

    If you are going to be working (aka playing) with DC power circuits (especially those over 10 amps), you should look at getting a DC Current Clamp Meter.

    This one is cheap (~$60 in US) and will do the basics for you. Plus it will go to 400 Amps.

    Current Clamp meters are much easier and safer to use than any other DMM based unit where you have separate the wire and put the meter in series.

    -Bill

    PS: We suggest to people that they "know their loads" first before spending too much money on the rest of the solar hardware.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Options
    Re: using 12v to generate 24v... what now
    madfabricator wrote: »
    I've been wondering how many watts this thing is. Its a harbor freight 18-24v tool charger, but no where on the box or manual does it say how many watts. I just got a cheap one to experment with. I have found a 75watt solar panel for $160.00 locally. If thats a good deal I'll return this one and pick up the 75 watt one. And grab a controller. Any recommendations would be helpful I do a lot of dc wireing but this is my first shot at power generation. Thanks Troy

    In terms of small panels, 75 Watts for $160 isn't bad: $2.13 per Watt. And it will come with specifications instead of trying to guess at Vmp & Imp. :D

    You might expect that 75 Watt panel to put out 5 Amps at most. That would be "trickle charge" ability for 100 Amp hours or "full charge" ability for 50 Amp hours.

    A very basic charge controller that would work with that: http://www.solar-electric.com/sg-4.html
    A more advanced charge controller that would work with that: http://www.solar-electric.com/ss-6l.html

    Much depends on what you want to do with it.
    · Share on Twitter

Categories