Is it possible?

[georgia088]

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 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.

I still don’t understand. I’m not sure we are on the same page. I am still planning to use a pwm charge controller, Or possibly two. As you say, they will disconnect the battery regularly from the battery and lower the power going in when the battery is fully charged. So, I don’t understand why I would need a relay to disconnect the array from the charge controller completely.

It seems to me, it would work if you used two separate relays to switch between the 12v battery and the 24v battery. If the controller will recognize the source as either 12v or 24v so that the output is correct for the particular battery.

My concern with that is how quickly does the charge controller recognize the voltage difference? If you switch the relay from 24v to 12v and the controller doesn’t switch quickly enough it could be sending 24v charging power to a 12v battery…. Not good.

I guess you could have a 3rd relay between the charger and both battery banks to completely cut the charge controller output off from the batteries while you made that switch.

I’m not sure….

[georgia088]

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

.

what do you mean by this?

[Ampster]

what do you mean by this?

I will let PNPmacnab answer the question directly.
My observation from reading all the comments on this thread is that you are trying to do something that does not have a good chance of success. You made a decision to buy 12 V panels which are not optimum for what you are trying to do.
My experience tells me that mistakes are great learning opportunities as long as you can admit that sometimes we all make mistakes.

[georgia088]

I will let PNPmacnab answer the question directly.
My observation from reading all the comments on this thread is that you are trying to do something that does not have a good chance of success. You made a decision to buy 12 V panels which are not optimum for what you are trying to do.
My experience tells me that mistakes are great learning opportunities as long as you can admit that sometimes we all make mistakes.

Because they are such low voltage panels? I have them wired up in series and then parallel. So they are more like (2) 24v panels. Does that make a difference?

Thanks!

[PNPmacnab]

I looked up the CC and these are both PWM. I had assumes ith 24V going into a 12V battery it was MPPT. It wouldn't make sense with PWM unless you were tapping off two 12V panels in parallel to charge the 12V battery. They state this controller is common negative. I don't necessarily believe what people, companies, or instruments tell me. Humor me and check resistance from solar panel minus and battery minus. Then do the same for the positive terminals.

[jflorey2]

I still don’t understand. I’m not sure we are on the same page. I am still planning to use a pwm charge controller, Or possibly two. As you say, they will disconnect the battery regularly from the battery and lower the power going in when the battery is fully charged. So, I don’t understand why I would need a relay to disconnect the array from the charge controller completely.

That way you don't need the charge controllers, which may have problems with this mode of operation.

It seems to me, it would work if you used two separate relays to switch between the 12v battery and the 24v battery. If the controller will recognize the source as either 12v or 24v so that the output is correct for the particular battery.

I think that's unlikely. But again, if you have the time and money, try it.

My concern with that is how quickly does the charge controller recognize the voltage difference?

My guess is that it checks at power-on and then retains that information for the rest of its operating time.