12v from a 48v off grid system

[DWColorado]

I want to put a growatt LVM and a 48v EG4 battery in my folks cabin..pretty simple. I would also like to give them a 12v power station without using a converter from the inverter. Can I wire 48 to 12 (step-down) buck converter directly from the posts on the EG4? It looks like it really is that simple, but I'm concerned there could be something I'm missing.

The converter will be primarily used for a diesel heater.

 

[timselectric]

Yes, it's that simple. As long as you get one rated for the intended load.

 

[DWColorado]

Yes, it's that simple. As long as you get one rated for the intended load.

The heater draws 10a at start up and shutdown so a 20a converter should be fine, but I'm thinking about a 30a for future use and the fact that it's only a few dollars more.

 

[timselectric]

Always good to have room for future expansion.

 

[Rednecktek]

The heater draws 10a at start up and shutdown so a 20a converter should be fine, but I'm thinking about a 30a for future use and the fact that it's only a few dollars more.

Mine will actually spike 12a when the fan and glow plug first start up, so going larger is a good idea. Run it to a fuse block for easier expansion later.

 

[DWColorado]

Mine will actually spike 12a when the fan and glow plug first start up, so going larger is a good idea. Run it to a fuse block for easier expansion later.

Are you saying "battery to converter to fuse block to heater"? Then having the ability to come off the fuse block if I decide to add some 12v to the cabin?

 

[timselectric]

Yes

 

[Ironman]

The unit I installed for a friend's 24v system has an adjustable output voltage, so his breathing machine, although on a 24ft run of 14ga wire, can be fed a 12.75 volts at the machine. It is a couple volts higher at the converter, but the adjusment is a great thing.

 

[timselectric]

That's a great feature.

 

[Rednecktek]

Are you saying "battery to converter to fuse block to heater"? Then having the ability to come off the fuse block if I decide to add some 12v to the cabin?

Exactly. Then in the future if you want to add another 12v device like a second heater or work lights or a very small margarita machine, it's just a matter of taking another lead off the block and throwing in the right size fuse.

 

[rmaddy]

Are you saying "battery to converter to fuse block to heater"? Then having the ability to come off the fuse block if I decide to add some 12v to the cabin?

There is one small piece missing. You need a proper fuse between the battery and the buck converter.

Let's say you get a 48V->12V 30A DC-DC buck converter. This means the converter puts out 30A from the 12V end. To calculate the needed load on the 48V input end you would have 12V x 30A / 48V / 0.85 = 9A. The 0.85 is a rough efficiency factor. Then to size the fuse you have 9A x 1.25 = 11A. Round up to 15A.

 

[DWColorado]

Exactly. Then in the future if you want to add another 12v device like a second heater or work lights or a very small margarita machine, it's just a matter of taking another lead off the block and throwing in the right size fuse.

Well, the blender is powered by the burros, but they might like a Friday night off

 

[DWColorado]

There is one small piece missing. You need a proper fuse between the battery and the buck converter.

Let's say you get a 48V->12V 30A DC-DC buck converter. This means the converter puts out 30A from the 12V end. To calculate the needed load on the 48V input end you would have 12V x 30A / 48V / 0.85 = 9A. The 0.85 is a rough efficiency factor. Then to size the fuse you have 9A x 1.25 = 11A. Round up to 15A.

OK so the fuse box between the converter and the heater protects the system in case the heater fries, and the fuse between the battery and the converter protects the system upstream of the converter?

 

[rmaddy]

OK so the fuse box between the converter and the heater protects the system in case the heater fries, and the fuse between the battery and the converter protects the system upstream of the converter?

The fuse box has a fuse for each 12V device you connect. Each fuse is there to protect the wiring to each 12V device.

The fuse I'm suggesting between the battery and the buck converter is there to protect the wiring to the buck converter.