I need to monitor a battery bank 250ft away

I’m building a small house on a Wisconsin farm with off-grid solar power. I’d like to have an electric heater that only runs when the house is cold and the solar battery bank is fully charged. The solar equipment is in a shed 250ft away, with clear line of sight. The charge controller can be programmed to energize a 12v, 200mA circuit at the appropriate time.

I have electrical experience and I’m fairly tech savvy, but new to the world of home automation. So I’m hoping folks here have some ideas. My first impulse was to just run direct burial Ethernet cable, and use relays to trigger a switch inside, such as on a Zooz ZEN16. It’s not a great area to bury cable, but I think this would work and cost $150 or less.

My other options..

Do it with Z-wave. I can’t find any Z-wave voltage sensors. I could probably rig a temperature sensor probe to detect 12v vs 0v. Using battery powered range extenders to relay the message seems dicey in subzero temps, but I’m open to it. But I don’t know how many I would need though. I could run wire from the shed to power a Z-wave outdoor smart plug, but it’d probably take two long sections of wire and two plugs. Or, I could use a 12v relay to energize 150ft of wire with a plug at the end. If the plug was on my mesh, it’d mean the batteries are full.

Do it with wifi. There’s no internet in the shed. I’d need some sort of extender or bridge, some Ethernet cable, and a PoE adapter. Then I still need something in the shed that will communicate the state of the batteries to Hubitat. Best I can think of is powering or not powering a wifi bulb with the 12v relay. Again, if Hubitat could communicate with it, that would indicate the batteries are full.

Do it with RF. There are remote controlled switches and relays that can operate over long distances. They have a fob with buttons to open or close the relay. If I were able to rig up a NO-C-NC relay on the charge controller so that it activated one button when energized and the other when de-energized, I could hook the RF controlled relay up to a ZEN16 in my house. I know this sounds far fetched, but these things are pretty cheap, and this is the only plan that keeps all components indoors.

RF Relay example

Any ideas welcome, thanks!

I have a shop that is about 200’ behind my house and I use wifi to connect to a another hub.

I use a tp-link cpe510. I have one at the house and one at the shop. I get about a 30mbs connection.

I reach 200'+ with a zigbee extended range router.

I'm not an arduino user, but HubDuino comes to mind for the voltage reading

Also, I found this

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Nice! Not sure if I can pull the current voltage from that or just get alerts, but definitely worth looking into, thanks!

And no guarantee there's a driver for HE,

I’ve been using the Shelly Uni to monitor 12v battery voltages. It uses Wifi, so there would need to be some signal getting to the shed…


I use a wifi Shelly Uni adco as well to monitor the voltage on my battery for an inverter to run a sump pump. It is powered by the 12 vdc from the same battery. You might be able to to connect directly to that with a directional AP antenna from the house.


I like this idea but you still need something to sense the 12v and report back to HE. A zooz would definitely do that with the help of a relay but it's not an IP device, so you're still left with your RF relay and a big long wire.

Depending on what else is going to happen in the shed, what if you ran Ethernet and put a second HE out there, along with a Zooz relay? That way the future automation possibilities are almost endless!

+1 (2 Brad votes) on this one. I put in a garden with a pergola, and when I built the pergola, I ran electric and ethernet out there and put a mesh Wi-Fi node on wired backhaul (I use Eero) in a project box. This gets me great Wi-Fi in the nether regions of my property and allowed me to add on AirPlay music streaming to speakers out there via an old AirPort express.

I do something similar to this (heat a shed based on temperature and time) but not with solar involved, although I'll start that in a few weeks in a different building (more on that below). What I do is run a Hubitat Elevation hub in the building itself, so as to not need to span such a long distance with z-wave or even wifi. I use a small oil-filled radiator heater set to the middle (I think about 900W) setting and have that connected to a Leviton z-wave plug connected to that local HE hub. I also have a Homeseer-brand z-wave sensor that reports every 0.1F change in temperature. I then set up rules to turn the heater on at a certain time and off at a certain time, and vary that based on whether it's during work hours or off hours (I use this as my office). The building does have ethernet, but if for some reason that goes out the HE doesn't care because it's operating locally.

Now, re the solar... You should be able to throw a relay from a decent solar system's monitoring hardware when the bank is full, and then use a z-wave contact sensor connected to that relay to trigger the HE. That could be used to set up a "Heating Possible" mode based on the solar bank's state of charge. So, in theory, problem solved. HOWEVER... I suggest you are going to struggle mightily to make electric heat work with solar. And, it sounds like you might have a 12V solar system, which might make things right at the edge of impossible. I even looked into using a mini-split for this, and unless it's truly a large solar system with few other loads, you're going to struggle at best, especially for heat (cooling somewhat easier). Please do the load calculations to figure out your needs, as you might find yourself without heat. Solar in winter is tough

I ultimately decided to go with a propane heater. To get programmability based on time and possibly even a wifi thermostat I'm going with a direct vent Rinnai but there are others. That solution will require electricity but the unit I'm installing draws a max of 45 watts with an average of about 20-25 or less, so the daily load will be about 600 watts for heat. My little oil-filled heater in the other building could eat that up in 40 minutes on the middle setting, to give you something for comparison.

Anyway, good luck and I really hope this works out for,you. I'm happy to discuss more in private messages or email if you wish. Nice to see another solar hobbyist here. I'm just getting started as well but had to make these same calculations and decisions in my planning.

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It’s a big system with 20 panels and a 48v bank with 8x12v batteries. It’s sized to run a deep well and get us through several cloudy days in a row without running the generator. On a sunny day it’s at 100% SOC by 9am, so plenty of power. Plus, the house I’m building is 400sg ft with 2x6 walls, so a little heat will go a long way. And I’ll definitely have propane heat as needed. I did the initial solar install, so I’m definitely going to avoid running it into the ground.

Are you saying a HE in the solar shed could communicate directly with another HE 250ft away in my house? I’m trying to heat the house based on the state of the battery bank, so I need to span the gap somehow. Wifi and a Shelly Uni is looking like the best option. I can monitor one of the batteries and infer the bank SOC, and like you said the charge controller can power a relay during float charge or based on voltage.

Yes with Hub mesh. Any device on the Hub in the Solar shed would be available to the Hub in your house. The two hub just need access to each other through the wifi or wired network. As I mentioned in my post above that is what I do to control the devices in my Shop. In my case I mainly need it control AC not heat. We don't get that cold here, but it gets pretty hot during the summer. So I use a Zen15 controlling a harmony hub for IR to control a small AC unit in my shop office to keep the electronics from getting too hot.

I've got an outbuilding linked at about twice this distance with a wifi bridge and then have a HE Hub in that space with repeaters external to that building.

But do you really want to do electric heating off solar when everything about Solar Water Heating (and propane) would be pretty low power consumption in comparison? @Madcodger 's advice above is pretty much on the mark.

As for hot water (or glycol mix) making it through the night; if you circulate through a good heat sink during the day it would keep things above freezing for sure. Insulating really well, using the sun to heat, and storing it in some thermal mass, might be worth looking into.

But the comment above about a propane heater is practical advice for sure. I travel through a lot of territory where the propane tank is KING (together with a good wood stove) in most of those "way out but still accessible by a propane supplier" locations. If this Solar Water heating isn't worth the effort with cloudy days and long cold nights I think I'd be opting to save your batteries the extremely demanding cycling in cold weather and look to power a propane heater.

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Yeah, I didn’t get into the context of why I’m doing this because the post was long enough and I figured y’all would have some ideas for this piece of the puzzle. And I think the Shelly Uni and a wifi repeater will be perfect.

My main reliable heat solution will be propane, but the farm PV system is super beefy and spends most daylight hours at 100%. If I know the SOC, I can peel off 2,000+ watts all day without even dipping into the batteries. Combined with good insulation and a small space, this has the potential to cover a decent chunk of my heating needs with no detriment to the PV system.

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As you saw in some of the responding posts there's many with allied interests and projects who have often gone down similar paths and are always interested in (or challenging) a different approach.

Re reaching the HE hub for communications, I suggest you bury some Cat 6 between the buildings (maybe two cables in case one goes bad). You can get decent direct burial Cat 6 on Amazon that's better than what the local big box stores carry, and then you don't need to worry about wifi, which can be squirrelly. Just a thought... I'm impressed by that solar system and hope it performs well through winter. Nice work!

Maybe the Fibaro Smart Implant (FGBS-222).

It has inputs to connect an analog sensor (nominally, 0-10 volts), but I think if you spend some time googling it, you can find how to use a few resistors to lower your input voltage into that range.