diy solar

diy solar

24V DC wiring in the cabin worthwhile?

H

ho1

New Member
Joined
Feb 17, 2024
Messages
9
Location
Colorado
I'm planning my electrical system for a small (450 sqft) cabin.

Here are the high level specs of my plan:
  • 6 kW of solar with Victron MPPT
  • Victron Multiplus Inverter/Charger (5 kVA)
  • 10-15 kWh of 48V LiFePo4 battery bank
My main power loads will be:
  • Induction cooktop
  • Toaster oven
  • 6 gallon electric hot water heater (plan change to 48V heating element)
  • RV-style water pump (probably 24V)
  • Various (LED) light fixtures
  • Various USB-C type chargers (phones/laptop/etc)
  • Internet router and cameras

I am wondering if it is worthwhile to run a separate 24V DC wiring in the house to power LED lights (LED strips, so no need for power adapters), and USB chargers. These would be connected to a 24V AGM bank and charged either via a separate single solar panel, or from a DC-DC charger from the 48V. My main rationale for this is that I would be able to leave the 24V system on all the time, and only turn on the 48V inverter/batteries when I'm at the cabin. Because the cabin is un-heated, the 48V batteries wouldn't take a charge colder winter months, but it would be nice to have the 24V AGM system be able to work no matter what.

So my question is, is it worthwhile the extra hassle of wiring in 24V DC for fixtures and USB outlets, or should I just keep the 48V batteries and inverter on all the time? The inverter has pretty low idle consumption (15W), but I would want to figure out a way to keep the batteries warm during the cold months to make sure they can get topped up.

Thanks!
 
ho1 said:
I'm planning my electrical system for a small (450 sqft) cabin.

Here are the high level specs of my plan:
  • 6 kW of solar with Victron MPPT
  • Victron Multiplus Inverter/Charger (5 kVA)
  • 10-15 kWh of 48V LiFePo4 battery bank
My main power loads will be:
  • Induction cooktop
  • Toaster oven
  • 6 gallon electric hot water heater (plan change to 48V heating element)
  • RV-style water pump (probably 24V)
  • Various (LED) light fixtures
  • Various USB-C type chargers (phones/laptop/etc)
  • Internet router and cameras

I am wondering if it is worthwhile to run a separate 24V DC wiring in the house to power LED lights (LED strips, so no need for power adapters), and USB chargers. These would be connected to a 24V AGM bank and charged either via a separate single solar panel, or from a DC-DC charger from the 48V. My main rationale for this is that I would be able to leave the 24V system on all the time, and only turn on the 48V inverter/batteries when I'm at the cabin. Because the cabin is un-heated, the 48V batteries wouldn't take a charge colder winter months, but it would be nice to have the 24V AGM system be able to work no matter what.

So my question is, is it worthwhile the extra hassle of wiring in 24V DC for fixtures and USB outlets, or should I just keep the 48V batteries and inverter on all the time? The inverter has pretty low idle consumption (15W), but I would want to figure out a way to keep the batteries warm during the cold months to make sure they can get topped up.

Thanks!
Click to expand...

I have such a setup.

Yes and no. If you do, make it 12 volts as there is gobs of RV stuff you can use and take advantage of very thin gauge wire along with no grounding conductor..

If your solar fails, you can always at least have some lights by plugging into your car battery.


If something happens and your bms cuts power, you'll still have working lights on the 12v side if you have an auxiliary battery.
 
I would say no it is not worth it. I also would not wire 48vDC elements into your water heater. Wiring the heater with 120vAC elements and run normal 120vAC setup in your cabin. But only you know what would work best for you.
 
I have a 625 foot off grid cabin. I 100 percent agree with the 12 V comments.

You can run a string of 12 V lights with an alligator clamp on the battery. easy lighting and there’s so much RV stuff if you want it.

I’m not using the 12 V stuff much anymore. I bought a little 12 V victron inverter and now I run most things on 120 V AC. It’s just easier, the stuff is cheaper, and the stuff is more reliable. RV stuff isn’t the best quality. Also wonder about whether it’s worth having a 24 V system at all .

You didn’t ask, but the first thing I would do is lose all that electric powered heating. Propane is pretty easy by comparison. I’ve really enjoyed the little $25 butane stove. I got off Amazon. Take care of the vast majority of my cooking needs. refill canisters are about five bucks apiece.
 
You like that butane stove buy a Coleman 500 gasoline stove or 4M...
Profane is expensive....
Gasoline is cheap.


A completely unmodified 4M will burn Kerosene and diesel with preheat ( latter will cause serious carbon fouling and require a lot more gas gen cleaning )
 
Either using a lower voltage DC or not has its case. To me with cold being a factor for you and needing some, but not all power when too cold to charge lithium makes me thing its a good idea to build it. A worthwhile luxury.
ho1 said:
  • Various (LED) light fixtures
Click to expand...
IME 12 volt options are much more available thanks to automotive and RV. 24 volt is there, but less choices. 48 volts less so.
ho1 said:
  • Various USB-C type chargers (phones/laptop/etc)
Click to expand...
IME looking for USB 48 VDC chargers, they all convert it to 5 volts 2 amps. Many manufactures make 24 volt USB-C chargers. Those with the correct device will use the 24 volts for a faster charge. For my apply phone and iPad with lightning connection, appears 24 volt is not available, but the 24 volt USB QC3.0/USB-C charger coverts to and uses a 12 volt protocol that is faster than that 5 volt 2 amp.
ho1 said:
The inverter has pretty low idle consumption (15W), but I would want to figure out a way to keep the batteries warm during the cold months to make sure they can get topped up.
Click to expand...
Is that idle draw in ECO mode, or is that the full draw? I have a 1000 watt inverter that is about 15 watts in eco mode, but closer to 30 watts in regular mode.

I’m finding low idle consumption like this comes in an “ECO” mode that turns out not to help me at all. Mostly because of two cases:

1) The “ECO” mode comes with a “minimum” wake p draw, and sometimes low amperage draws like your LEDs won’t wake it up.

2) Might not work with inductive loads that turn on and off quickly. I have a rock tumbler I tried to run in ECO mode on a 300 watt inverter and a 1000 watt inverter, and because the load is only 23 watts and goes on and off 44 times a second, this trips the inverter when in ECO mode. Normal mode works fine.
=======
Does ECO mode work for anyone on a whole house system?
 
Last edited:
Honestly, if you're going to have a 48V battery system and an inverter already then it really doesn't use as much as people say it does to just run everything on 120AC.

Spend that money on regular capacity on your 48 volt bank and solar panels rather than the extra money on an entirely separate bank of 24V batteries and runs of wires for a 24V setup.
 
With my first system I went 12v and went with a 12v water pump, lighting and fridge. I have mixed feelings on if I'd do it again. The lighting is fine and we likely saved quite a bit on wiring. It does mean I'm stuck running a 12v system that is expensive and difficult to grow. Originally I thought we would only run the inverter when watching tv and such but it ended up running 24/7 anyway. I'm currently building a new, much bigger 48v system that will run along side and provide the 120v power, taking that load off the 12v system.

That system will be similar in size to your system. I don't see a problem with all the electric cooking appliances during the summer. When the sun is out you will have lots of power to burn.

The downside is of 12v or 24v lighting is that you are a bit limited in what fixtures you can find. That said you can find 12v and 24v led lamps with standard bases and then use a wide array of 120v fixtures. They are more expensive than 120v lamps and the lifespan is often a bigger wildcard than the mainstream lamps. LED strips are ok for work lights but don't always give the best atmosphere. I've also struggled to find LED strips that actually last a long time. I've had many LED strips fail within months of being installed.

Running the water heater directly on 48v might not be that great of an idea. The safety cutoff and thermostats are designed to switch AC and may fail under DC power then your only a failed pressure blow off away from a steam explosion. I'm planning on sticking with a 120v water heater and putting a switch in the kitchen. It will switch between on, auto and off. On auto it will turn on when the batteries are fully charged and there is more than 1500watts of solar coming. On permits turning on at night if needed and Off will permit high draw appliances to run without over taxing the inverter. I think I'm going to implement this using an arduino(or teensy oresp32) that will poll the inverter over a serial port for the battery state and solar charging rate then turn on the water heater using an SSR when the conditions are met. Now that I'm thinking about it, I could also have the controller shed the water heater if the load is too high but I'm not sure it would be fast enough to prevent an overload.
 
Checkthisout said:
I have such a setup.

Yes and no. If you do, make it 12 volts as there is gobs of RV stuff you can use and take advantage of very thin gauge wire along with no grounding conductor..

If your solar fails, you can always at least have some lights by plugging into your car battery.


If something happens and your bms cuts power, you'll still have working lights on the 12v side if you have an auxiliary battery.
Click to expand...
Thanks, great points on 12V (as others mentioned too). My initial reason for 24V is to be able to get the amps down for larger lights and such, but probably not really an issue.

DPC said:
Run a 4 conductor wire use the Blue and red for DC wiring and the black and white for AC
Click to expand...
From my understanding one shouldn't run DC next to AC because I believe the AC induces something in the DC circuit? Not sure if it is a big deal or not. But otherwise, running it in the same wire makes a lot of sense!

Bluedog225 said:
You didn’t ask, but the first thing I would do is lose all that electric powered heating. Propane is pretty easy by comparison. I’ve really enjoyed the little $25 butane stove. I got off Amazon. Take care of the vast majority of my cooking needs. refill canisters are about five bucks apiece.
Click to expand...
Based on the calculations of my panels/storage, I should have plenty of margin to run induction/toaster over and I'll "never" run out of propane this way!

chrisski said:
Is that idle draw in ECO mode, or is that the full draw? I have a 1000 watt inverter that is about 15 watts in eco mode, but closer to 30 watts in regular mode.
Click to expand...
Thanks for your comments and ideas - good perspectives!
FYI - from the Victron Multiplus 2 spect sheet:
Zero load power 15 W
Zero load power in AES mode 10 W
Zero load power in Search mode 3 W
LordGarak said:
The downside is of 12v or 24v lighting is that you are a bit limited in what fixtures you can find. That said you can find 12v and 24v led lamps with standard bases and then use a wide array of 120v fixtures. They are more expensive than 120v lamps and the lifespan is often a bigger wildcard than the mainstream lamps. LED strips are ok for work lights but don't always give the best atmosphere. I've also struggled to find LED strips that actually last a long time. I've had many LED strips fail within months of being installed.

Running the water heater directly on 48v might not be that great of an idea. The safety cutoff and thermostats are designed to switch AC and may fail under DC power then your only a failed pressure blow off away from a steam explosion. I'm planning on sticking with a 120v water heater and putting a switch in the kitchen. It will switch between on, auto and off. On auto it will turn on when the batteries are fully charged and there is more than 1500watts of solar coming. On permits turning on at night if needed and Off will permit high draw appliances to run without over taxing the inverter. I think I'm going to implement this using an arduino(or teensy oresp32) that will poll the inverter over a serial port for the battery state and solar charging rate then turn on the water heater using an SSR when the conditions are met. Now that I'm thinking about it, I could also have the controller shed the water heater if the load is too high but I'm not sure it would be fast enough to prevent an overload.
Click to expand...
Thanks! I have professional experience with LEDs and there is quite the spread in quality with the strips, so spending a bit more and they'll last a really long time. I also hadn't considered that the thermostats in most water heaters are designed for switching AC, good point so I'll probably take the inverter efficiency hit and run 120V heating element (can stick with standard 12 AWG romex to supply it then too).


Based on all the feedback and my original plan, my current thinking is:
  • Run 48V battery/120V inverter "standard" setup for all larger loads
  • Run a smaller 12V system for lights (and well pump), using AGM batteries (nothing huge)
    • I plan to run 14AWG romex for the 12V system inside the walls, that way should I want to switch over to 110v later on, I just have to change outlets/fixtures etc.
    • The 12V system will be "always on", powering Internet router/security system and lights as needed
    • I'll run a dedicated small solar panel (100w) (mounted vertical on south facing wall, to prevent snow coverage in winter)
    • I'll add a small DC-DC charger for 48V-12V that will use the larger 48V bank to make sure the 12V bank is always topped up when I'm there and the 48V system (and its solar) is running (these seem quite affordable).

Thanks again - many good perspectives and I'm hoping to have it all wired up later this spring!
 
ho1 said:
Thanks, great points on 12V (as others mentioned too). My initial reason for 24V is to be able to get the amps down for larger lights and such, but probably not really an issue.


From my understanding one shouldn't run DC next to AC because I believe the AC induces something in the DC circuit? Not sure if it is a big deal or not. But otherwise, running it in the same wire makes a lot of sense!


Based on the calculations of my panels/storage, I should have plenty of margin to run induction/toaster over and I'll "never" run out of propane this way!


Thanks for your comments and ideas - good perspectives!
FYI - from the Victron Multiplus 2 spect sheet:
Zero load power 15 W
Zero load power in AES mode 10 W
Zero load power in Search mode 3 W

Thanks! I have professional experience with LEDs and there is quite the spread in quality with the strips, so spending a bit more and they'll last a really long time. I also hadn't considered that the thermostats in most water heaters are designed for switching AC, good point so I'll probably take the inverter efficiency hit and run 120V heating element (can stick with standard 12 AWG romex to supply it then too).


Based on all the feedback and my original plan, my current thinking is:
  • Run 48V battery/120V inverter "standard" setup for all larger loads
  • Run a smaller 12V system for lights (and well pump), using AGM batteries (nothing huge)
    • I plan to run 14AWG romex for the 12V system inside the walls, that way should I want to switch over to 110v later on, I just have to change outlets/fixtures etc.
    • The 12V system will be "always on", powering Internet router/security system and lights as needed
    • I'll run a dedicated small solar panel (100w) (mounted vertical on south facing wall, to prevent snow coverage in winter)
    • I'll add a small DC-DC charger for 48V-12V that will use the larger 48V bank to make sure the 12V bank is always topped up when I'm there and the 48V system (and its solar) is running (these seem quite affordable).

Thanks again - many good perspectives and I'm hoping to have it all wired up later this spring!
Click to expand...

At the end of the day, I stated the benefits of having 2 voltages.

However, doing things over, I would just do 120V everything.

It's just easier.
 
I have three off-grid sheds (office, sauna, exercise room) connected to a single Victron Multiplus 24V 3000 KVA inverter. 300 AH of batteries, 1260 watts of panels and a Victron SCC. All monitored with a Victron Smartshunt. I also thought about running DC lighting, but just went with 120V AC LEDs, and I'm glad I did. I hardly notice the current draw from the lights, and if you're going to have the inverter on anyway, it's just much easier to run AC using plain, old Romex.
 
Madcodger said:
I have three off-grid sheds (office, sauna, exercise room) connected to a single Victron Multiplus 24V 3000 KVA inverter. 300 AH of batteries, 1260 watts of panels and a Victron SCC. All monitored with a Victron Smartshunt. I also thought about running DC lighting, but just went with 120V AC LEDs, and I'm glad I did. I hardly notice the current draw from the lights, and if you're going to have the inverter on anyway, it's just much easier to run AC using plain, old Romex.
Click to expand...
Checkthisout said:
At the end of the day, I stated the benefits of having 2 voltages.

However, doing things over, I would just do 120V everything.

It's just easier.
Click to expand...

Can't argue with keeping it simple and run 120V AC for everything, the main stumbling block is: how do I keep the batteries warm during winter months, so that they can get their daily top up?

When I'm not there, I probably have 10-20 W of loads (Internet and security system) along with 15W of inverter base load. So call it 840 Wh/day. So assuming 10 kWh of battery storage, it would draw that down in 10-12 days and I can definitely have periods of 12 days where the cabin would not get over freezing. Heating pads and insulate battery box would be one option, but then I'm adding complexity and I'm not super confident in the quality of those heating pads (including fire risk?).
 
You must log in or register to reply here.

Similar threads

Moosefinder
24 volt solar fridge questions
Replies
7
Views
192
seneysolar
seneysolar
S
Soft start for the whole cabin?
Replies
2
Views
189
seneysolar
seneysolar
D
Looking for 48v dc light switch
2 3
Replies
48
Views
2K
AntronX
AntronX
T
DC Lighting plan
Replies
16
Views
465
tmbiv56
T
Rednecktek
Is the EG4 worth the extra money for my needs?
Replies
3
Views
431
sunshine_eggo
sunshine_eggo
Back
Top