[UnionPacific]

I am going to have 8, 6 volt batteries.
They will be hooked up to make a 12 volt system.
What stops me from making a special circuit on the same 12 volt system to charge at 24 volts?

Why? because solar chargers charge at an amperage, say 80 amps, at 12, 24, or 48 volts. So my charger could handle more wattage at 24 then it can at 12.

I would leave my current 2 6volt connections, but run more wires for a second 24 volt circuit on top of the 12 volt one.

 

[copacabana]

But wouldn't you fry anything running off the batteries if you switched to 24v to charge?

 

[Don L]

Seems like just a way to make things complicated and set you up for a big problem just to save a few dollars on getting the correct controller. I would think that it only would even be worth considering if you are going to install so much in solar panels that you need extra controllers. And if that were the case the charging capacity is already going to be so large that for the most part the controlling limit is the ability of the batteries to accept the charge rate.

 

[Don L]

BTW - after you buy all the switches and extra cabling are you really saving anything

 

[HankOnthewater]

U.Pacific, I am not an electrical engineer, but I think your thought process makes things very complicated.
Let me start at the beginning. You did not say what kind of and how many panels you had and their output.
Just for argument sake let's say you have 2 panels of 100 Watts each. If each panel can produce 100 Watt at 12 Volt, then one gets approx 8.3 Amps per panel on a good sunny day and if the manufacturer or their marketing guys have not told any lies.

Now you have the choice to connect those panels in series, which will give you an output of 24 Volt and a max Amps of 8.3 Amps or....
you can connect them parallel, and then your output would be 12 Volt and 2x8.3=16.6 Amps.
In BOTH cases the wattage remains the same: 200 Watt.

From reading your post it seems you have a solar controller that can double or half the Voltage. Really, it does not really matter what kind of controller one has (for this part of the discussion) as the output can not be be bigger than the input (200 Watt). In fact there will be electrical losses etc. So the output would be around 180-190 Watt.

The only advantage I can see is that when you operate on 24 Volt (as opposed to 12 Volt) there will will a smaller voltage drop in the electrical circuit, but if your wiring is designed properly the difference would we close to nil. BTW, 'voltage drop' in a wire is loss of power ie the wire is getting hot.

Assuming your diagram is correct, I think your suggestion makes it much more complicated, and complications is something to be avoided, especially when there is no gain.

Now, looking at your diagram, you would have to add 4 or even 6 high amperage switches. They are pricey and again, will cause voltage drop.

And then there is the problem that while all 8 batteries are charged at the same rate (at 24 Volt), your appliances (on 12 Volt) that will run during the day will only be drawn from from one set of two 6 V batteries, causing an imbalance that can only be rectified by putting all 4 sets of batteries parallel: that is at 12 Volt!

If the prime reason for your suggested diagram is that your solar controller cannot handle the amps at 12 Volt, then I suggest to buy a controller with a bigger capacity. That could be cheaper than all that switchgear and the heavy duty wiring associated with that.

 

[UnionPacific]

The benefits are more then just a single controller.
Its a controller, thicker wire for 12 over 24, The ability to run 24 volt items, less voltage drop over distance.

 

[UnionPacific]

If the prime reason for your suggested diagram is that your solar controller cannot handle the amps at 12 Volt, then I suggest to buy a controller with a bigger capacity. That could be cheaper than all that switchgear and the heavy duty wiring associated with that.

We will be starting with 1000W in panels, and most likely adding 500 more
1500w @ 14v is 107 amps. the charge controller is able to output 80 amps, at any voltage. so If it outputs at 24 volts its only putting out 53.5 amps (these are the max amps on a bright sunny day, not every day of course) also as the amps are lower there should be less heat as the controller will be below its max power rating.

The batteries will all be in parallel, both in 12 volt, and 24 volt. All of them will be charged and discharged at the same time.

 

[IStream]

Stick with 12V and get yourself some of those Genasun 140W MPPT charge controllers. Your controller capacity will scale with the size of your solar system and you'll have plenty of redundancy.

 

[newhaul]

Hook panels up for 24 volt output to the controller and use a good mppt controller close to the bank for the 14.2 v output they really like to have for charging

 

[Don L]

I don't believe I've ever regretted doing a project the right way.

 

[IStream]

Hook panels up for 24 volt output to the controller and use a good mppt controller close to the bank for the 14.2 v output they really like to have for charging

I did that on my boat and would've suggested it here but I'm assuming (there I go again) based on UP's comments that he's already considered and rejected that, perhaps because the charger can't be mounted close to the batteries. Or because he's stubborn and likes to do things the hard way.

The multiple controller solution is scalable, redundant, and easy to implement but it can cost a bit more, so I suppose that'll kill it.