24V DC Load in Controller

[BigIronOnMyHip]

Hi all. My friend is building a new system and has a bit of clarification with the DC Load in the controller.

I have 12V system and I connect a few 12V DC devices such as LEDs and fans on the DC Load in the controller. So if he builds a 24V system, would the terminals for the DC Load in the controller be 24V as well or would it automatically convert it to 12V?

From what I've read, they would need a step down device to convert it from 24V to 12V, them connect the device. I'm not referring to the Load for the Inverter.

 

[snoobler]

SCC load terminals are battery voltage at all times.

Would need 24-12V DC-DC converter. Lots of cheap ones on Amazon.

 

[45North]

Many SCC's can handle either 12 or 24v and it's set automatically. That's why it's important to connect the batteries before the panels because the SCC senses the battery voltage, determines whether it's a 12 or 24v system, and then uses the power from the PV cells to charge the batteries to the appropriate level.
In other words; the same SCC could be used in either a 12v or 24v system but you must take care to connect the batterie(s) before the panels.
And, as snoobler says, the load will get whatever the battery voltage is.

Edit: You could still use a 24v system to power 12v devices if you put them in series.

 

[snoobler]

Edit: You could still use a 24v system to power 12v devices if you put them in series.

Huh?

 

[MrNatural22]

Edit: You could still use a 24v system to power 12v devices if you put them in series.

“Wut choo talkin bout Willis?” ?

 

[45North]

Mebbe I misunderstood the OP's original question.
I thought he was looking for a way to power some of his 12v devices from his friend's 24v system.
So, I was suggesting if he just wanted to power a couple of 12v lights, for example, he could safely power them from a 24v battery if he wired them in series.
No? If you have 2 x 12v lights can you not connect them in series and power them with a 24v battery?

This may not be a workable solution for the whole system, agreed. But if it's just a matter of a few 12v devices that can be conveniently combined in pairs and wired in series, this could work.

 

[snoobler]

Mebbe I misunderstood the OP's original question.
I thought he was looking for a way to power some of his 12v devices from his friend's 24v system.
So, I was suggesting if he just wanted to power a couple of 12v lights, for example, he could safely power them from a 24v battery if he wired them in series.
No? If you have 2 x 12v lights can you not connect them in series and power them with a 24v battery?

This may not be a workable solution for the whole system, agreed. But if it's just a matter of a few 12v devices that can be conveniently combined in pairs and wired in series, this could work.

The items would need to have nearly identical operating resistances. In your examples, 2X 12V light bulbs in series would be fine, but other 12V loads would experience a voltage inversely proportional to their portion of the series circuit resistance. One device might get 18V and the other get 6V... likely not good for either.

$30 24V-12V converter is easy-mode.

 

[Rider]

Keep in mind also, that the voltage on the load terminals is typically not regulated, ie battery voltage. That could range from 10VDC or less (dead battery) to 15VDC or higher during peak charging.

Same thing if you configure for 24V.

 

[carbon60]

Keep in mind also, that the voltage on the load terminals is typically not regulated, ie battery voltage. That could range from 10VDC or less (dead battery) to 15VDC or higher during peak charging.

Same thing if you configure for 24V.

Very good point and I'm glad you brought that up. In fact, one of my systems has Trojan T105 Plus GC2 batteries (FLA), which are specified to require 2.7V/cell for equalization, which is 16.2V or 32.4V. And that's at standard temperatures! In my trailer, neither the Proper/Whale Propane furnace nor the Maxxfan can tolerate more than 15V and 14V, respectively. So regulators are required. This doesn't seem to be a commonly brought up issue with solar charge controllers programmed to match manufacturer's specifications.

The less than 14.6V/29.2V max of an LFP is much less of an issue.

 

[BigIronOnMyHip]

SCC load terminals are battery voltage at all times.

Would need 24-12V DC-DC converter. Lots of cheap ones on Amazon.

Many SCC's can handle either 12 or 24v and it's set automatically. That's why it's important to connect the batteries before the panels because the SCC senses the battery voltage, determines whether it's a 12 or 24v system, and then uses the power from the PV cells to charge the batteries to the appropriate level.
In other words; the same SCC could be used in either a 12v or 24v system but you must take care to connect the batterie(s) before the panels.
And, as snoobler says, the load will get whatever the battery voltage is.

Edit: You could still use a 24v system to power 12v devices if you put them in series.

Thank you for all of your input, he may just get a step down device for the appliances.

Also a quick question, he's also considering getting a 12V system but has a concern about the BMS and the amount of cells.

The Four 280AH Cells are pretty expensive here being around $600 with the tax. However, Four 100AH Cells is around $175 so he gets two sets for $350.

From what I've researched, you can combine and parallel the cells so it's 2 a block and it totals 200AH. All the cells are the same so there's no risk complications.

Our only clarification would be, is if he can attach each of the 12V 4S wire to two cells (paralleled) and would there be no issues with this setup?

Or would he need to place the 12V 4S to each of the four cells, then once they both have BMS he can parallel it?