Another panel question

System
System Posts: 2,511 admin
in Solar Beginners Corner #1
Hi folks, new member here. I have a question that I thought might be answered in this thread but I don't see it.

Using 2 HQRP 20 watt 12v nominal panels wired in series to charge 2 12 volt deep cycle batteries also wired in series (24v). I bought a HQRP charge controller that says
"12/24volt auto sensing" but I think this is just for input from the solar cells. It says
in the specs, regulation point 14.4volt

This controller is not going to work is it?
http://hqrp.com/hqrp-solar-10a-charge-controller-12v-24v-with-battery-charge-monitor.html

Assuming that's correct, would you have a recommendation for a low end 10 amp charge controller that will accept 24v input and give 24 volt output?

Any help appreciated, thanks!
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  • rss2q
    rss2q Solar Expert Posts: 75 ✭✭✭✭
    #2
    Re: How Many 12v Solar Panels Needed To Charge 24v Battery?
    frankd wrote: »
    Hi folks, new member here. I have a question that I thought might be answered in this thread but I don't see it.

    Using 2 HQRP 20 watt 12v nominal panels wired in series to charge 2 12 volt deep cycle batteries also wired in series (24v). I bought a HQRP charge controller that says
    "12/24volt auto sensing" but I think this is just for input from the solar cells. It says
    in the specs, regulation point 14.4volt

    This controller is not going to work is it?
    http://hqrp.com/hqrp-solar-10a-charge-controller-12v-24v-with-battery-charge-monitor.html

    Assuming that's correct, would you have a recommendation for a low end 10 amp charge controller that will accept 24v input and give 24 volt output?

    Any help appreciated, thanks!

    I went with this charge controller (Morningstar Prostar 15) for this project, as I already have the Prostar 30 that has the meter on it and it's been working fine for over a year now. So I definitely know I can trust this brand. I was at the time going to go with an off brand controller like the one you linked to, however, I need something that's reliable and didn't want to take a chance with my batteries and other circuitry.

    I'm sure someone else here can shed more light on what that regulation term means in regards to charge controllers as I'm not 100% sure, but I'm assuming that charge controller should work just fine for your application but I may be wrong.
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  • Urbandialect
    Urbandialect Solar Expert Posts: 107 ✭✭✭✭
    #3
    Re: Another panel question

    20 watt panels at 12 volts wired in series, so i'm guess the panels are rated at 18volts witch would put you at 36 volts at 20watts, which is nothing... you need more watts from the panel to charge the batteries... i'm sure you're pulling out more than you're putting in.. you're putting in less than 1 amp.. you need 120 watts just to put in 6 amps... what's your load like on the battery? what are you trying to run?

    Also the charge control should be fine, you just not collecting enough power with a 20 watt panel
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Another panel question

    Welcome to the forum.
    We're going to give you your own thread here 'cause we're generous like that. :p

    From the looks of it, that controller should be a basic PWM type which will put out 24 Volts if you put in 24 Volts. However it seems to have fixed "12 Volt" charging set points, which doesn't make any sense. Then again, neither does this line:

    "4 Stages: equalization, PWM, Boost and Float, temperature compensated charging"

    The 4 charging stages being Bulk, Absorb, Float, and Equalization; "PWM" isn't a stage, it's a process.

    So the short and insulting assessment of this controller is that it is a cheap piece of junk and a total waste of money. You probably figured that out already. :roll:

    Now the ugly reality is that 40 Watts of panel will deliver about 1 Amp to a 24 Volt system, and that's not going to charge anything. It's not even going to stay ahead of the self-discharge rate of a typical FLA battery.

    Have you got the batteries' Amp hour specs? It's not too difficult to figure out what you'd need to recharge based on that. It's probably going to be hundreds of Watts, by the way.

    Morningstar makes some reasonable low-cost controllers http://www.solar-electric.com/mochco.html - but you're going to need a lot more panel.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #5
    Re: Another panel question

    Cannot tell--looks like a cut and paste from their 12 volt only and their 12/24 volt (battery I assume) model. It may very well be a 12/24 auto select model--You will have to call them or order and return if they give you the incorrect model.

    You certainly can get a Xantrex or MorningStar PWM controller for at different current levels:

    Morning Star
    Xantrex Solar Charge Controllers
    Steca Charge Controllers for Solar Electric Systems

    And others...

    How large is your battery bank? The largest battery bank I would (humbly) suggest for a 40 watt Vmp=35 volt array at 5% minimum rate of charge:
    • 40 watts * 1/29 volts charging * 0.77 panel+charger derating * 1/0.05 rate of charge = 21 Amp*Hour @ 12 volt battery bank.
    If this is for a "float charger" (keep batteries charged when not in use), then you could look for 1% rate of charge which would support ~105 AH 24 volt battery bank.

    Maximum size charger needed would be around:
    • 40 watts / 35 volt Vmp = 1.1 amps or so
    So, a 2 amp 24 volt charge controller would be more than enough with these panels (unless I misunderstood your solar array size/setup).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #6
    Re: Another panel question
    Cariboocoot wrote: »
    Welcome to the forum.
    We're going to give you your own thread here 'cause we're generous like that. :p

    <snippers>

    Thank you for the help Cariboocoot, and all others as well.

    This is a weird application, an emergency signaling line that might draw 3 amps in use but it sits idle most of the time. 1 amp output at 24vdc in full sun will keep the batteries charged.

    The Morningstar and Xantrex links were most helpful, $100 or so for a decent charge controller, no problem. I'm a big Google fan but the right keywords just escaped me, you guys pointed me in the right direction.

    Thanks so much!

    Frank D
    Colorado
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