Is it possible?

[georgia088]

Is it possible to have one solar array connected to two separate solar chargers with one solar charger connected to a 12v battery and the other solar charger connected to a 24v battery bank. Here is some more infor about each.

The solar array is 4 100 watt 12v panels. They each have a short circuit voltage of 22v and 18v of output voltage. Their max current is 5.65 Amps. The panels are wired so two pairs of panels are wired in series with and the two sets of series panels are then wired in parallel.

If I am understanding correctly this should be producing somewhere between 36-42v. And slightly over 10 Amps.

The solar chargers are both renogy wanderer chargers. They auto detect the battery source of 12 or 24v will handle up to 50v of solar power and 15 Amps of current.


If they are connected to two separate battery banks (one 12v and the other to 24v) Could it possibly work? How does the energy get divided between the battery banks/solar controllers?

THANKSI!

[PNPmacnab]

I've found that in solar anything can be connected to anything and that is what people do. Electrons will always find a way. Yes, the two controllers will fight each other down to a much lower than ideal panel voltage. It won't be efficient. When one battery fully charges, the other will start charging normally. Bad idea, you decide.

Some charge controllers use a common positive instead of negative. In that case there will be lots of smoke in connecting 12 and 24V batteries. It's your stuff..

[SunEagle]

Is it possible to have one solar array connected to two separate solar chargers with one solar charger connected to a 12v battery and the other solar charger connected to a 24v battery bank. Here is some more infor about each.

The solar array is 4 100 watt 12v panels. They each have a short circuit voltage of 22v and 18v of output voltage. Their max current is 5.65 Amps. The panels are wired so two pairs of panels are wired in series with and the two sets of series panels are then wired in parallel.

If I am understanding correctly this should be producing somewhere between 36-42v. And slightly over 10 Amps.

The solar chargers are both renogy wanderer chargers. They auto detect the battery source of 12 or 24v will handle up to 50v of solar power and 15 Amps of current.


If they are connected to two separate battery banks (one 12v and the other to 24v) Could it possibly work? How does the energy get divided between the battery banks/solar controllers?

THANKSI!

As PNPmacnab stated you can wire your panels just about anyway you want but from past experience one or both chargers may cook your batteries or worse go up in smoke. Sometimes it is best to wire a separate set of panels to a charger and batteries. Anytime you have 2 chargers wired to the same set of panels one will take over the control and the other may hurt the batteries it is connected to.

But again as PNP stated it is your stuff. Just be careful and follow all safety rules concerning electric.

As I have stated before, anyone that said solar was inexpensive was using a shortcut and probably ended up replacing their equipment.

[jflorey2]

If they are connected to two separate battery banks (one 12v and the other to 24v) Could it possibly work?

Not in this case, no. There will be fireworks.

How does the energy get divided between the battery banks/solar controllers?

Here's what will happen:

You will connect your (discharged) batteries to the system. The PWM controller will see that the batteries are below their max charge voltage, and will connect them directly to the solar panel. An unlimited amount of current will then flow from the 24V battery, to the panel, to the 12V battery - and a fuse somewhere will blow. (Hopefully)

This is unique to PWM chargers since they are just switches that close to control the charge voltage.

[georgia088]

As PNPmacnab stated you can wire your panels just about anyway you want but from past experience one or both chargers may cook your batteries or worse go up in smoke. Sometimes it is best to wire a separate set of panels to a charger and batteries. Anytime you have 2 chargers wired to the same set of panels one will take over the control and the other may hurt the batteries it is connected to.

But again as PNP stated it is your stuff. Just be careful and follow all safety rules concerning electric.

As I have stated before, anyone that said solar was inexpensive was using a shortcut and probably ended up replacing their equipment.

So with 12v batteries connected or 24v batteries connected what voltage is typically the cut off voltage for the charger to stop “charging? 14.2vdc for lead acid?

If I had a relay disconnect from one set of batteries and connect to the other set once it reached a set voltage, would this work? This would completely isolate the 12v from the 24v.

Thanks

[SunEagle]

So with 12v batteries connected or 24v batteries connected what voltage is typically the cut off voltage for the charger to stop “charging? 14.2vdc for lead acid?

If I had a relay disconnect from one set of batteries and connect to the other set once it reached a set voltage, would this work? This would completely isolate the 12v from the 24v.

Thanks

I just would not trust a simple relay to separate the batteries. IMO you should use a "smart" controller that will use the DC relay to disconnect or switch between the battery systems. But those relays need to be rated both DC and Arc limiting or you could weld the contacts.

Again don't try to find a "cheap" way to charge the batteries. Just get another set of panels and have 2 dedicated system.

[georgia088]

I just would not trust a simple relay to separate the batteries. IMO you should use a "smart" controller that will use the DC relay to disconnect or switch between the battery systems. But those relays need to be rated both DC and Arc limiting or you could weld the contacts.

Again don't try to find a "cheap" way to charge the batteries. Just get another set of panels and have 2 dedicated system.

Is there a smart controller you would recommend?

[SunEagle]

Is there a smart controller you would recommend?

I am not even sure if an Allen Bradley PLC is available or the cost You also need to understand how to program it It may be cheaper to get a couple of 200watt panels for the 24V battery system

[georgia088]

I am not even sure if an Allen Bradley PLC is available or the cost You also need to understand how to program it It may be cheaper to get a couple of 200watt panels for the 24V battery system

Programming and electronics are hobbies of mine. However, solar power and solar chargers i’m not familiar with. I’m cheap and I know that is never the recommended route, but if you can use cheap hardware and make the best of it, some times the bottom line may be in your favor. Especially if you enjoy tinkering with it.

I can program a mcu to read voltages and fire relays if this or that happens, but what I don’t know is what the chargers are capable of and when the batteries need to be shut down. It seems fairly straight forward. If you break the line with a relay either from the panels to the charger controllers or from the charge controller to the separate battery banks when certain voltages are read (either high or low) you could take advantage of the over production days (sunny) to fill up both sets of batteries and minimize the wasted energy when one bank is charged and the panels are putting out, only to be dissipated by the controller.

I know it won’t be that simple and there is always a risk of getting it wrong, but that is the fun in experimenting.

If I had the panels as listed above 4 12v panels wired two pairs in series and then then the two pairs parallel, two cheap pwm charge controllers (yes I know inefficient) but I charged up each bank of batteries individually until a certain threshold was reached and then switched to the next, what voltages would I need to be looking for? 14.2 and 28.4? Depending on how it was controlled, relays could be wired to power off when the load was pulling the batteries down to a certain threshold… what voltage would that be?

Thanks for the help!

[littleharbor2]

I don't think the controller would be very happy getting instantly switched from one nominal voltage to another or even can be switched. I doubt the setpoints would just change themselves.
Just a bad idea. If your 12 volt loads are small like mine are then you don't need a big separate array, controller or battery. A small battery, controller and single panel.

[georgia088]

Programming and electronics are hobbies of mine. However, solar power and solar chargers i’m not familiar with. I’m cheap and I know that is never the recommended route, but if you can use cheap hardware and make the best of it, some times the bottom line may be in your favor. Especially if you enjoy tinkering with it.

I can program a mcu to read voltages and fire relays if this or that happens, but what I don’t know is what the chargers are capable of and when the batteries need to be shut down. It seems fairly straight forward. If you break the line with a relay either from the panels to the charger controllers or from the charge controller to the separate battery banks when certain voltages are read (either high or low) you could take advantage of the over production days (sunny) to fill up both sets of batteries and minimize the wasted energy when one bank is charged and the panels are putting out, only to be dissipated by the controller.

I know it won’t be that simple and there is always a risk of getting it wrong, but that is the fun in experimenting.

If I had the panels as listed above 4 12v panels wired two pairs in series and then then the two pairs parallel, two cheap pwm charge controllers (yes I know inefficient) but I charged up each bank of batteries individually until a certain threshold was reached and then switched to the next, what voltages would I need to be looking for? 14.2 and 28.4? Depending on how it was controlled, relays could be wired to power off when the load was pulling the batteries down to a certain threshold… what voltage would that be?

Thanks for the help!

[jflorey2]

I can program a mcu to read voltages and fire relays if this or that happens, but what I don’t know is what the chargers are capable of and when the batteries need to be shut down.

Then you don't need a separate charger.

Use two relays. One double throw to send the array power to either the 12V or the 24V battery. This is critical to prevent fires.
The second relay will just disconnect the array completely.

Now program your mcu to alternate between the two batteries. Read the voltage of the batteries. If the voltage is at or above maximum charge voltage of that battery, open the array relay.

You can get into more details of how to charge the batteries (i.e. bulk vs absorb vs float voltages) but those are the basics. Needless to say, a minor software error could destroy your batteries, so it may be a false economy to do it that way. But if you have the time and money to do it, knock yourself out.

In general, you want to bulk charge to around 2.4 volts per cell for sealed lead acids and 2.5 volts per cell for flooded batteries. For both you can float around 2.3 volts. As always use fuses/breakers to protect your wiring.

relays could be wired to power off when the load was pulling the batteries down to a certain threshold

You can do that but that is a very different function, since that relay has to carry all your load current, which for a typical 1000ish watt inverter could be 100 amps. So it has to be a huge relay/contactor. And you should cut off below about 1.75 volts per cell. However the battery should not actually reach that voltage, since drawing a lead acid battery down that low over and over kills it quickly.

[georgia088]

Then you don't need a separate charger.

Use two relays. One double throw to send the array power to either the 12V or the 24V battery. This is critical to prevent fires.
The second relay will just disconnect the array completely.

Now program your mcu to alternate between the two batteries. Read the voltage of the batteries. If the voltage is at or above maximum charge voltage of that battery, open the array relay.

You can get into more details of how to charge the batteries (i.e. bulk vs absorb vs float voltages) but those are the basics. Needless to say, a minor software error could destroy your batteries, so it may be a false economy to do it that way. But if you have the time and money to do it, knock yourself out.

In general, you want to bulk charge to around 2.4 volts per cell for sealed lead acids and 2.5 volts per cell for flooded batteries. For both you can float around 2.3 volts. As always use fuses/breakers to protect your wiring.



You can do that but that is a very different function, since that relay has to carry all your load current, which for a typical 1000ish watt inverter could be 100 amps. So it has to be a huge relay/contactor. And you should cut off below about 1.75 volts per cell. However the battery should not actually reach that voltage, since drawing a lead acid battery down that low over and over kills it quickly.

Thanks! This is the kind of info I wanted! Can you explain what the second relay is for? Obviously the spdt switches between the two sources 12v or 24v. But, why do you need one to disconnect the array completely from both sources? In a typical setup the array is never completely disconnected from the battery. I’m obviously not understanding something.

Thanks!

[PNPmacnab]

I had a different idea. Two panels on each controller and two DPDT relays with a micro. Each controller has its own panels initially. Switch one relay based on battery charge level, priority and one controller will get all the panels. Switching is fail safe. If both relays are on the panels connect to each other and no controller gets power. People are hampered by their own beliefs, real or imaginary.

But really, 400W 0f 12V panels! Almost all forum questions are the result if initial bad decisions.

Solar is a playground for those who know electronics. I have fridge, hot water, pumps dishwasher with heated dry, clothes washer and it all works on a car battery from 3KW of panels into a 500W controller. And a couple medical devices to keep me alive at night. Basic systems work even with three days of rain. All for a little over $100 exclusive of panels. Did I mention 70% of panels are in shade at any time.

[jflorey2]

Thanks! This is the kind of info I wanted! Can you explain what the second relay is for? Obviously the spdt switches between the two sources 12v or 24v. But, why do you need one to disconnect the array completely from both sources?

Because when the battery is close to full (i.e. has reached its max charge voltage) you want to stop charging so you don't overvolt (and damage) the battery.

As others have said, you will probably not have good luck trying to do that by having an intermittent feed into a charge controller.

In a typical setup the array is never completely disconnected from the battery.

In a typical setup with a PWM charger, the charger regularly disconnects the array from the battery. That's how they work.

And again, this would be a good project and you'll probably learn a lot about solar - but the odds of non-success are high.