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  1. #1
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    Dec 2003
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    Default Solar Panel battery charger

    Hello folks,

    Been a long time since I have posted and played here. . .. I am now retired. ..

    I have a situation. . .

    I have a 24 volt battery system for off the grid power. i have a lot of panels that charge the batteries,
    and I want to make a charge controller out of mosfets. . . My problem comes in reading the battery
    voltage without the panels affecting the reading. . .

    Panel Voltage varies between zero and 40 volts.

    I want to charge the batteries to 28 volts and shut off the panels.

    My problem lies in the instant the panels are connected, the voltage shown on my meter is almost
    instantly at 28 volts, because the panels are shoving 30+ volts into them at 50 amps. Yet the
    batteries are actually not fully charged.

    Anyone know of a circuit that i can use to accomplish this feat?
    iSeems like everyone else can figure it out, but me.

    Dwayne
    Ability to Fly:
    Hurling yourself towards the ground, and missing.

    Engineers that Contribute to flying:
    Both optimists and pessimists contribute to the society. The optimist invents the aeroplane, the pessimist the parachute

    Pilots that are Flying:
    Those who know their limitations, and respect the green side of the grass...

  2. #2
    Join Date
    Mar 2003
    Location
    Commerce Michigan USA
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    1,196

    Default Re: Solar Panel battery charger

    Dwayne, Normally the charging is done in 3 stages, Attached is a .PDF of the charge controller I use. I have 2 of them and run them in parallel for the 830 amp hour battery bank I have here. It is 24 volts. I hope this will help you. I haven't had any problems with it since I installed them about 8 years ago.
    Dave Purola,
    N8NTA
    EN82fn

  3. #3
    Join Date
    Dec 2003
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    Wichita KS
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    517

    Default Re: Solar Panel battery charger

    Quote Originally Posted by Dave View Post
    Dwayne, Normally the charging is done in 3 stages, Attached is a .PDF of the charge controller I use. I have 2 of them and run them in parallel for the 830 amp hour battery bank I have here. It is 24 volts. I hope this will help you. I haven't had any problems with it since I installed them about 8 years ago.
    I am finding out that the charge controllers are not able to handle my Panels. . .So I decided to try and make my own, or find a controller that can handle
    my panels properly. . .

    I have about 2500 watts of panels charging about 30 batteries. . .on a 24 volt system. . . Thus, I am looking for something that can handle that
    kind of current, and nothing seems to be around. . .I ended up purchasing 20 mosfets that can handle 30 amps each. I figure 10 I would use
    for charging and the other 10 for a dump load heater.

    I just have to figure out the "basics" of charging those batteries without overcharging them, or find a supplier of a controller that can handle
    my current.

    Dwayne
    Ability to Fly:
    Hurling yourself towards the ground, and missing.

    Engineers that Contribute to flying:
    Both optimists and pessimists contribute to the society. The optimist invents the aeroplane, the pessimist the parachute

    Pilots that are Flying:
    Those who know their limitations, and respect the green side of the grass...

  4. #4
    Join Date
    Mar 2003
    Location
    Commerce Michigan USA
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    Default Re: Solar Panel battery charger

    Dwayne, Attached is a pic of my installation that I did myself. The 2 arrays in the foreground feed 2 of the Xantrex MPPT60-150 charge controllers. Each of the dual axis array's are 1600 watts. I have 830 Amp hour's of 6 volt battery's that are configured in 2 series/parallel banks for 24 volts. There are a lot of company's that make charge controllers. What do you mean by "charge controllers are not able to handle my Panels"?
    Dave Purola,
    N8NTA
    EN82fn

  5. #5
    Join Date
    Dec 2003
    Location
    Wichita KS
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    Default Re: Solar Panel battery charger

    Thanks for the response. . ..

    I have something similar to yours. . .I have 3 arrays with anywhere between 3 and 6 panels on each array.
    About 2500 watts of power. . .
    I also, am on 24 volts.
    Using 14 of the big combine batteries, 8 of the deep cycle 6 volt batteries, 3 airplane batteries, and 8 car batteries.
    I too, have put them in series/Parallel, so that if one battery goes bad, I only have to take out two batteries at the
    most, leaving me with a loss of only 6 percent.

    I have tried many controllers, and they just can't stand the power. 100+ amps is more than most controllers can
    handle out there. Then they get really pricy. So I figured I could use a pic chip, figure a way to monitor the battery
    voltage, and use mosfets to TTL the solar panels on and off for less than 20 bucks. . .and handle 300 amps when
    I add more panels and batteries in the future. .

    I plan on adding 1500 more watts of panels, and another 24 batteries. Then I will be set. It is my retirement house,
    located at 9000 feet in Colorado. It is approx 1400 square feet. Right now, I have enough solar and batteries where
    I can live in it 24/7, but if the Sun doesn't show up for two days, I am in a little trouble. But, I also run quite a few
    things too. . .One is a rather large electrical usage. . .a 54 inch plasma TV. 250W.

    Thus, I want to build my own controller. . .
    Ability to Fly:
    Hurling yourself towards the ground, and missing.

    Engineers that Contribute to flying:
    Both optimists and pessimists contribute to the society. The optimist invents the aeroplane, the pessimist the parachute

    Pilots that are Flying:
    Those who know their limitations, and respect the green side of the grass...

  6. #6
    Join Date
    Mar 2003
    Location
    Commerce Michigan USA
    Posts
    1,196

    Default Re: Solar Panel battery charger

    Dwayne, Attached is a schematic of my first system whish is still in service as I type this.
    Dave Purola,
    N8NTA
    EN82fn

  7. #7
    Join Date
    Apr 2014
    Location
    Northeast
    Posts
    308

    Default Re: Solar Panel battery charger

    "I ended up purchasing 20 mosfets that can handle 30 amps each. I figure 10 I would use
    for charging and the other 10 for a dump load heater."
    Be sure to look at the data sheet for the MOSFETs you intend to use. I learned by melting boards, THEN looking deeper into the data sheets that the amp ratings are usually only at 2 or 3 volts. By the time you get to 40 volts, your 10 amp MOSFET may only be good for less than 1 amp. Look at the watt rating too.

  8. #8
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    Mar 2003
    Location
    Commerce Michigan USA
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    Default Re: Solar Panel battery charger

    Mike, What are you talking about? You must be thinking about running them in a linear mode of operation. Fully saturated, the fet's he is talking about probably have an ON RESISTANCE of less than an OHM. Maybe not?
    Dave Purola,
    N8NTA
    EN82fn

  9. #9

    Default Re: Solar Panel battery charger

    Charging at 50 or 100 amps.... use a heavy duty relay to charge/stop charging. Charge for a while, switch off, check battery voltage then charge more or not.

  10. #10
    Join Date
    Dec 2003
    Location
    Wichita KS
    Posts
    517

    Default Re: Solar Panel battery charger

    The mosphets I purchased are good to 30 amps and 60 volts. . I figured i would operate them via a NPN transistor.. they claim they can be operated directly from
    integrated circuits. . . Be easier to replace a 2n2222 than a 675 chip. . .

    Still hunting for a circuit that I can use to monitor batteries while charging at the same time, without panels interfering.
    Ability to Fly:
    Hurling yourself towards the ground, and missing.

    Engineers that Contribute to flying:
    Both optimists and pessimists contribute to the society. The optimist invents the aeroplane, the pessimist the parachute

    Pilots that are Flying:
    Those who know their limitations, and respect the green side of the grass...

  11. #11
    Join Date
    Dec 2003
    Location
    Wichita KS
    Posts
    517

    Default Re: Solar Panel battery charger

    Quote Originally Posted by amgen View Post
    Charging at 50 or 100 amps...…. use a heavy duty relay to charge/stop charging. Charge for a while, switch off, check battery voltage then charge more or not.
    This is not a very good way how to do it. . .You will be losing a lot of charging capabilities during the daytime. During full charge cycles, you don't want to charge over 14 volts. . thus,
    you will be switching on and off many times during full charge. This is fine, but when it isn't during full charge, you lose your charging time and buildup.
    Ability to Fly:
    Hurling yourself towards the ground, and missing.

    Engineers that Contribute to flying:
    Both optimists and pessimists contribute to the society. The optimist invents the aeroplane, the pessimist the parachute

    Pilots that are Flying:
    Those who know their limitations, and respect the green side of the grass...

  12. #12
    Join Date
    Dec 2003
    Location
    Wichita KS
    Posts
    517

    Default Re: Solar Panel battery charger

    Quote Originally Posted by Dave View Post
    Mike, What are you talking about? You must be thinking about running them in a linear mode of operation. Fully saturated, the fet's he is talking about probably have an ON RESISTANCE of less than an OHM. Maybe not?
    Hello Dave

    I also noticed that you are a ham operator. . .I have been an Extra class for over 40 years. . .Operate mostly CW a little bit of AM and SSB.
    Usually run 40M beloe 7125.

    I believe what Mike is thinking, is power dissipation. . 30amps at 10 volts is 300 watts of power. Using the same Mosfet, at 30 vp;ts you
    would be good only to 10 amps.
    Our 24 volt systems have a open circuit of around 41 volts. . .Closed circuit, I think mine runs about 32 volts.

    We are going to do some experimenting with a 24 volt panel, and see if we can get some kind of correlation between the panel voltages
    and the battery voltages.. .then program a 675 to control the TTL relays of the Mosfets.


    Dwayne

    PS. . .I run boat anchors at my house in Colorado. . .
    Ability to Fly:
    Hurling yourself towards the ground, and missing.

    Engineers that Contribute to flying:
    Both optimists and pessimists contribute to the society. The optimist invents the aeroplane, the pessimist the parachute

    Pilots that are Flying:
    Those who know their limitations, and respect the green side of the grass...

  13. #13
    Join Date
    Mar 2003
    Location
    Commerce Michigan USA
    Posts
    1,196

    Default Re: Solar Panel battery charger

    Yes Dwayne, But 30 amps across a fet which has an on resistance of .1 Ohm's is only 3 volts. Thats 90 Watts. Not too bad. But the fets now days are more in the order of 10's of milliohms. So, assuming a 50 amp fet fully saturated which has an on resistance of .025 Ohms is only 1.25 volts and dissipating about 62.5 watts. And thats only 1 fet. Now if you parallel them its only better.
    Dave Purola,
    N8NTA
    EN82fn

  14. #14
    Join Date
    Mar 2003
    Location
    Commerce Michigan USA
    Posts
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    Default Re: Solar Panel battery charger

    Hey Dwayne, Try looking here. They have some good prices on solar chargers.
    https://www.banggood.com/marketing-G...uid=udrqfXygmR
    Dave Purola,
    N8NTA
    EN82fn

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