Solar panels

[matty40s]

39 minutes ago, WotEver said:

But he has a controller in between. 

Indeed, I referred to the controller as well.

[WotEver]

1 hour ago, matty40s said:

Indeed, I referred to the controller as well.

The controller sets its voltage from the batteries, not the panels. Hence my comment about 120V from the panels. Panel voltage is irrelevant. 

[Tony Brooks]

2 hours ago, WotEver said:

The controller sets its voltage from the batteries, not the panels. Hence my comment about 120V from the panels. Panel voltage is irrelevant. 

But if the batteries are open circuited are we sure the full panel voltage wont be applied to the controller output?

[WotEver]

53 minutes ago, Tony Brooks said:

But if the batteries are open circuited are we sure the full panel voltage wont be applied to the controller output?

Yes. It’ll either be around 14V or around 28V. 

[Richard10002]

9 hours ago, WotEver said:

Yep, that makes sense. So it’s like 1b from my list

 

If the controller ‘knows’ that the bank is 12V then it’s not going to try charging it as a 24V bank. I wonder how it knows and under what circumstances that persists?

I could guess that I set it as such when i installed it

 

With hindsight, it is 1) from your list, never mind the "b" 

 

 Having said that, I could guess that a lot of people with a Tracer, or some other brand, may not know that they can set it as a fixed 12V or 24V, controller, rather than leaving it to sense for itself.

[Tony Brooks]

12 hours ago, WotEver said:

Yes. It’ll either be around 14V or around 28V. 

Don't understand that. With no load (batteries disconnected) the panel voltage could be anything up to its maximum voltage because there is no load as such to pull it down. Especially with the domestic panels we are seeing at good prices or panels connected in series.,

 

It seems to me that one way or another the controllers pulse the voltage with MPPT doing it in a more sophisticated way. the question is does the pulsing allow full panel voltage to reach the controller output terminals. If yes then the controller might see that  is telling it that it is on a 24 volts system. If no then why do many instructions stress connecting the batteries first.

[Detling]

If the full panel voltage was presented on the output terminals when open circuit, then not only would you be at risk of electrocution, you battery isolater would be arcing and sparking (most are rated at 48volts) the output regulator on the controller would be fried and your whole system annihilated.  The controllers are designed to accept the high voltage on the input and not pass it through the ouput terminals.  The only common connection may be the 0 volt connection although even that is not absolutely required.

[Chewbacka]

4 hours ago, Tony Brooks said:

Don't understand that. With no load (batteries disconnected) the panel voltage could be anything up to its maximum voltage because there is no load as such to pull it down. Especially with the domestic panels we are seeing at good prices or panels connected in series.,

 

It seems to me that one way or another the controllers pulse the voltage with MPPT doing it in a more sophisticated way. the question is does the pulsing allow full panel voltage to reach the controller output terminals. If yes then the controller might see that  is telling it that it is on a 24 volts system. If no then why do many instructions stress connecting the batteries first.

I think the pwm controllers will send little pulses into it’s output capacitor to achieve the target voltage which is connected to the battery to be charged.  These usually have a fairly low max input voltage.  The better mppt controllers pulse into a big inductor and can transform the output voltage for battery charging, so can take much higher input panel voltages without any risk of very high output voltages.

 

The controller therefore needs to know the target voltage so as to control the output voltage, it can do this either by sensing the connected battery or through software.

Edited July 23, 2019 by Chewbacka

[WotEver]

9 hours ago, Tony Brooks said:

Don't understand that. With no load (batteries disconnected) the panel voltage could be anything up to its maximum voltage because there is no load as such to pull it down. Especially with the domestic panels we are seeing at good prices or panels connected in series.,

 

It seems to me that one way or another the controllers pulse the voltage with MPPT doing it in a more sophisticated way. the question is does the pulsing allow full panel voltage to reach the controller output terminals. If yes then the controller might see that  is telling it that it is on a 24 volts system. If no then why do many instructions stress connecting the batteries first.

Just think of it as an auto-ranging mains battery charger. That doesn’t give you 230V on an oc output, it gives 14.x or 28.x or, with the better chargers, nothing at all until a battery is connected. 

[ditchcrawler]

4 minutes ago, WotEver said:

Just think of it as an auto-ranging mains battery charger. That doesn’t give you 230V on an oc output, it gives 14.x or 28.x or, with the better chargers, nothing at all until a battery is connected. 

But if the battery is not connected and it decides your system is 24 volts, will it change its mind when you connect it to 12 volts. For some reason most instructions tell you to connect to the batteries before the panels 

[WotEver]

44 minutes ago, ditchcrawler said:

But if the battery is not connected and it decides your system is 24 volts, will it change its mind when you connect it to 12 volts. For some reason most instructions tell you to connect to the batteries before the panels 

No it won’t. It has to wake up with the battery connected in order to know. 

[Chewbacka]

20 hours ago, ditchcrawler said:

But if the battery is not connected and it decides your system is 24 volts, will it change its mind when you connect it to 12 volts. For some reason most instructions tell you to connect to the batteries before the panels 

It will probably just think it’s a very discharged 24v battery.......