Newbie needs guidance on battery charge controllers

[GoodJBoy]

Hi All,

I have some experience with solar panels and battery charging but I never really got it right. I have 60 watts of solar right now but I am about to add on 300 more watts of power and I have some questions.

Here is my situation, my 60 watt solar panels put out 19.5v. The 300 watts (100 watts each) put out 18.5v. I have buck converts that I can throw on the panels too. I want to have a simple 12V battery bank with 12v devices hooked up into it and these devices will run 24 hours a day. I am planning on getting a small freezer (Sun Danzer - the small one) and I have AA-AAA-9v-C-D battery chargers too that are 12v that I am going to use to charge batteries. These are the two main devices I am going to use. I will also be throwing on occasionally a DS Charger and a phone charger which take different voltages. I use buck converters to charge these devices and I set the buck converter to the appropriate voltage.

The problem is that I never figured out a good way to charge my batteries with the panels I currently have. Originally, I bought a $12 made in China charge controller that, when the batteries were fully charged, the controller would modulating really fast on and off. As a result of the flickering, the buck converters I had hooked up to my battery bank (for charging usb devices like cell phones and my kids DS charger) got destroyed over time. The buck converters eventually broke because the input voltage was flickering between 19.5Vs and 13.7V really fast all day long. This was due to the junky charge controller.

So, I threw out the charge controller and connected my 2 30 watt panels in series (1 is on the South East side of my home and the other is on the South West side) and then I drop the voltage down to 14V and hook that onto my batteries to charge them.

Here are some questions. Are all battery controllers modulating pieces of junk? That means it flickers on and off real fast when the batteries reach their charge voltage high point.

How can I hook up 19.5V and 18.5V panels to a battery charge controller to charge a 12v battery bank and still run devices off the battery bank. Some of the devices will be 12V and some will be run via buck converters.

Any advice would be greatly appreciated.

Thanks!

[Naptown]

The charge controller you are describing is called a PWM controller and it is doing what it is supposed to do. All charge controllers will do this including MPPT at some point in the charging cycle (generally when in float)
I tend to think that your problem is in your battery. How old is it(them)

[GoodJBoy]

My batteries are a few months old. The issue was that when I was using the charge controller, the solar panels were supplying 19.5V to the 12v battery charger. It charged by batteries well but when I hooked up my 12V powered AA-AAA-9V-C-D battery charger to the battery bank while the solar panels were hooked up to the battery charge controller, it fried my 12V powered AA-AAA-9V-C-D battery charger because. In addition, when it modulated, it eventually broke my buck converters.

My question is, how do I hook up 19.5v panels to a battery charge controller charging a 12v battery bank and still power 12v devices off of that battery bank while all this is occurring. My other battery charge controller hit my 12v battery bank with around 19.5V a fried a few of the 12v devices that I had attached to the battery bank. My battery bank is small though. It is 14 amp hours (2 x 7 amp hour batteries).

Are you suppose to hook the panels into the battery bank via the charge controller and hook your devices up to the battery bank and eventhough the panels are putting out 19.5v, the12v devices should work fine because the overall output of the battery bank plus the 19.5v of charging should not be a problem? Did I do it right to begin with but maybe the 12v device I had plugged in was sensitive to a slightly higher voltage?

[Naptown]

First off you have way too much solar for those batteries with the added panels.
The problem could have been too high an internal resistance on the batteries allowing the voltage to spike and not absorb.
At 60Watts you were feeding the batteries with about 5A or slightly over a C/3 charge rate Way too high for most batteries.
Adding the additional panels will fry your existing batteries you will need very much larger ones.

[GoodJBoy]

Awesome... thanks for teaching me that! How big should my battery bank be if I have 360watts of panels and I want to power 12v devices? Keep the total voltage of the battery bank at high sunny noon below 14V. How do I calculate how much battery bank I need to acheive that?

Thanks! You are a huge help. Like I said, I am a newbie.

[inetdog]

Awesome... thanks for teaching me that! How big should my battery bank be if I have 360watts of panels and I want to power 12v devices? Keep the total voltage of the battery bank at high sunny noon below 14V. How do I calculate how much battery bank I need to acheive that?

Thanks! You are a huge help. Like I said, I am a newbie.

If you really need to keep the battery voltage below 14 volts, you will not be able to charge them properly!

If your connected loads are really that sensitive (most devices designed for use with a automotive 12 volt system can withstand at least 15 volts, more commonly 16 or 17), then you have a problem. The only way you can assure that you will not overdrive your loads while charging the battery will be to either:

1. Put a voltage regulator between the batteries and the load, making that output independent of (but always less than) the battery voltage, or
2. Put a forward biased power diode between the batteries and the load. That will reduce the voltage to your loads to always be ~.7 volts lower than the battery voltage. You may need to use two diodes in series giving a 1.4 volt drop.

If you were just concerned with a proper balance between the panels and the batteries, the rule of thumb would have the 12 volt battery AH approximately equal to the panel wattage. So in your case ~360 AH. But even that would not keep the voltage below 14 volts.

[GoodJBoy]

Do you happen to recommend a nice battery charge controller for a 360 Watt solar array? Thanks again for your help.

[Sunking]

Awesome... thanks for teaching me that! How big should my battery bank be if I have 360watts of panels and I want to power 12v devices? Keep the total voltage of the battery bank at high sunny noon below 14V. How do I calculate how much battery bank I need to acheive that?

You cannot keep the voltage below volts, as it can go as high as 15 during a normal charge.

As to the proper size panel to battery size depends on what type of controller you have. But here is the general run down. For flloded Lead Acid batteries the minimum charge rate is C/12, and max is C/8 whenre C = the battery Amp Hour rating. So for example a 100 AH battery minimum is 100/12 = 8.33 amps and max is 100/8 = 12.5 amps.

Sounds like you have a PWM controller where its input current = output current. It also sounds like you have standard 12 volt panels wired in series with a Vmp of roughly 18 volts and at 100 watts each the current from each panel is roughly 5.6 amps. So with 3 panels wired in parallel the total current is around 3 x 5.6 amps = 16.8 amps. That will support a FLA battery as large as 12 hours x 16.8 amps = 200 AH or as small as 8 hour x 16.8 amps = 134 amp hours. So the perfect size battery for you is 150 AH using a 20 amp PWM charge controller.

[PNjunction]

A $12 solar charge controller is invariably the older on-off shunt or series switching type that when reaching full charge just ping-pongs between a high and low set point, such as 13.3v low, and 14.5v high. You can see it in action. A BIG improvement would be a PWM controller, like a Morningstar, Steca, Xantrex/Schneider or the like. This operates on a somewhat different principle, but your loads would not really notice the fast pulses - you wouldn't see it for the most part with a voltmeter across the battery terminals and the voltage would be stable once it reaches the absorb set point, or falls back to a float voltage setting - you wouldn't see the wild voltage swings as you do with the simpler on-off type.

It should have gone no higher than about 14.5 volts - sounds like you got one that was already fried, and failed in a closed condition without doing any controlling, thus over-charging (and destroying) your 14ah battery bank in addition to all the little regulators hanging off that battery at the time.

Before you spend a lot of money on additional panels, batteries, and charge controller, have you checked a solar-insolation chart based on where you are located? Solar-insolation differs from mere visible daylight, and is a determining factor when deciding on what you can support with solar.

[Gary2]

I have a very similar question on a smaller scale. I have a 9v 220mah panel and I would like to hook it up to a 6v 2300mah rechargeable battery pack to charge usb devises IE(Nexus 7 and cell phones), What would I need to make this happen. I have seen the 6v 3a voltage regulator controller from china that has a usb on it, But I am not sure it will work. http://www.ebay.com/itm/320767460367...84.m1423.l2649. and advise would be appreciated.
thx
Gary