Can I run toilet and septic w/12 volts

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Small Cabin Forum / Off-Grid Living / Can I run toilet and septic w/12 volts


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ketchgould Member	# Posted: 16 Apr 2021 09:53am Reply Connecting to the grid costs $47 each month for electricity at our cabin site. I would like to design the cabin to use just 12 or 24 volts, use a generator for occasional use. I would prefer to not have an outhouse. I have built and designed 12 volt systems on the sailboat we spend our summers on. Does a toilet and a standard septic system need 120 volts? I am building on a slope and have a 275 gallon water tank with rain collection and a sand point well (pump would require 120 volts via generator I assume if rain collection isn't adequate). I believe I can keep the water tank full. I did some math and the tank half full still provides 16.4 psi, also the tank is 20 feet above the cabin site, where you get 1 psi for each 2.3 feet of elevation, adding an extra 8psi giving me 24 psi at the cabin on gravity alone. Is there a minimum psi necessary to run a toilet or a septic? The L5 water heater needs 20 psi, is that psi a target to keep the cabin systems running? Thanks

paulz Member	# Posted: 16 Apr 2021 10:02am Reply I have a standard home toilet, my water tank is 20' above the cabin. Toilet refills from gravity, pump off, no problem.

Irrigation Guy Member	# Posted: 16 Apr 2021 10:04am Reply Traditional septic only needs gravity to function properly and you only need enough pressure to fill your toilet tank gravity does the rest

SE Ohio Member	# Posted: 16 Apr 2021 10:25am - Edited by: SE Ohio Reply There are 12 volt pumps. Depending on head height, you might be able to fill tank that way without generator. Also a 12 volt DC to 120 VAC inverter properly sized might do the job for AC motor. Gas generators require a bit of upkeep and are burglar-desired items. No fun to lug a generator to/from weekend cabin SE Ohio

ICC Member	# Posted: 16 Apr 2021 10:34am - Edited by: ICC Reply Quoting: ketchgould I did some math and the tank half full still provides 16.4 psi, also the tank is 20 feet above the cabin site, where you get 1 psi for each 2.3 feet of elevation, adding an extra 8psi giving me 24 psi at the cabin on gravity alone. As others have stated the toilet will refill from just about any incoming water pressure. The standard tank fill valve falls wide open as the water level drops and the float drops with the water level. The rising water lifts the float and that shuts off the mechanical fill valve. But your water pressure figures appear to be wonky. Your figure of 1 psi for each 2.3 feet of elevation (or 0.433 PSI per 1 foot of elevation) is correct. But where is that figure of 16.4 PSI coming from?

ketchgould Member	# Posted: 16 Apr 2021 10:45am Reply The 16.4 is the psi from a half full 275 gallon IBC tank. If the 275 gallon IBC tank is full it should produce 33psi from my math. Next question, so what appliance or convenience makes the $45 a month and costs of 120volts worth it?

gcrank1 Member	# Posted: 16 Apr 2021 10:50am - Edited by: gcrank1 Reply Atmospheric pressure at sea level is 14.7psi. depending upon ones location above or below that changes it up some. You basically start with that much and add on any head from moving uphill/higher.

Nate R Member	# Posted: 16 Apr 2021 11:24am - Edited by: Nate R Reply Quoting: ketchgould so what appliance or convenience makes the $45 a month and costs of 120volts worth it? Depends on your use patterns for this place. Laundry? Dishwasher? Starlink internet using 80+W ALL The time? Need for a deep well pump w/ 240V? Not needing to replace batteries or maintain them? Sounds like you don't need any of that for your part time cabin.....so in your case, it's probably NOT worth it. Is the cost of a septic system worth it just for toilet use? Or is it required for your area? We're finding for our part time/occasional use, our ventilated privy is just fine, and even in winter, my wife is finding it's not bad at all!

Brettny Member	# Posted: 16 Apr 2021 11:43am Reply As nate said look into what's needed for a septic as that's going to far exceed the $47 a month for electric. If a septic is to much I believe you can make (call local authorities) a pit privy. Basically a holding tank with a toilet on top. You will need to get it pumped every so often.

ICC Member	# Posted: 16 Apr 2021 12:58pm Reply Quoting: gcrank1 Atmospheric pressure at sea level is 14.7psi. depending upon ones location above or below that changes it up some. You basically start with that much and add on any head from moving uphill/higher. Quoting: ketchgould The 16.4 is the psi from a half full 275 gallon IBC tank. If the 275 gallon IBC tank is full it should produce 33psi from my math. Not really to both of the above. The static water pressure coming out of a pipe or faucet connected to an elevated tank, a pail or a pond, lake or reservoir is determined solely by the height difference from the top surface of the water and the lower point (where the water is released or used). It does not matter if the container holds a few gallons or a million gallons. The shape of the container does not matter. Only the height differential of source and point of use. A change in the density of the fluid will change the pressure. If the tank in question was full of sea water the pressure would be slightly higher. If the liquid was ethanol the pressure would be lower. URL URL

ICC Member	# Posted: 16 Apr 2021 01:06pm - Edited by: ICC Reply We have all seen elevated water tanks for municipal water systems. If that tank at the top was at ground level the pressure from that same volume would supply would be much less.

ketchgould Member	# Posted: 16 Apr 2021 01:15pm Reply You gain 1 psi for each foot the water is raised. The volume of the liquid in the tank increases water pressure too.

ketchgould Member	# Posted: 16 Apr 2021 01:22pm Reply I meant 1psi for each 2.3 feet the water is raised.

Brettny Member	# Posted: 16 Apr 2021 01:46pm Reply Yes then you have to take away pressure for any height over the ground your sink, hot water heater or shower is above the ground.

ketchgould Member	# Posted: 16 Apr 2021 01:57pm Reply good point Brettny.

Nobadays Member	# Posted: 16 Apr 2021 02:40pm Reply Quoting: ICC The standard tank fill valve falls wide open as the water level drops No experience with this (we use an RV pump) but I understand a STANDARD flush valve works way better under low pressure, by this I mean the old style with the long arm and float. The newer style, black tubular affairs apparently will take ages to fill. I think it was on this forum somewhere this was discussed. If I recall correctly the standard valve can be opened up in some way to release more water.

Fanman Member	# Posted: 16 Apr 2021 04:50pm Reply Quoting: gcrank1 Atmospheric pressure at sea level is 14.7psi. depending upon ones location above or below that changes it up some. You basically start with that much and add on any head from moving uphill/higher. No, it doesn't work that way; atmospheric pressure doesn't matter. Since the same 14.7 psi pushes equally on both the supply (tank) side and the discharge side, it cancels out. Only the water height matters.

ICC Member	# Posted: 16 Apr 2021 07:35pm - Edited by: ICC Reply Quoting: Fanman Since the same 14.7 psi pushes equally on both the supply (tank) side and the discharge side, it cancels out. Yes, air is so much lighter than water that the very slight difference in air pressure (weight of the air) between this water tank on a hill and the lower point of use can be ignored. If the volume of the elevated tank made any difference to the pressure then the apparatus pictured in the picture below should work. Liquid water is not a solid. Liquids do not act the same as solids. Water has no shear strength like solids do. That makes a huge difference. Perhaps it is not intuitive but then real science is like that at times. Each of the three vessels illustrated below contain different volumes of water. If they were connected with a tube or pipe as shown the water level in each will be exactly the same. If the larger volume of water did actually produce more pressure at the outlet then that pressure should be sufficient to push the levels in the other vessels higher. That does not happen. The science linked to in my previous post states the pressure is only dependent on the height difference in the high and low points and the density of the liquid. If anyone can post a link to a credible science-based site that illustrates that the water pressure depends on the volume and not solely the height difference please do so. I will read them. I could post more links to more sites that all state the same basic science... the pressure of a liquid is directly proportional to the height or depth of the fluid and the density of the liquid.

gcrank1 Member	# Posted: 16 Apr 2021 08:19pm Reply Well, I sit corrected. I had filed that atmospheric pressure thing in the back of my head and guess I misunderstood or remembered it wrong! Thanx to the gentlemanly persuasion here I dont feel like an idiot like I would on some sites Ive visited. I can note anecdotally that Ive watched my rain barrel drain stream out the spigot 1/4 way up from bottom seem to lose pressure the nearer to the spigot the water level gets. That would apparently be due to the reduction in head from full to spigot level. Trying to think back where I got onto AP was likely when I started looking at what it would take to get water from my static level just a few feet deeper than what a shallow water pump is reputed to work at. That and how high a tower I would need to have my shower tank on to make the min 20psi for my L5 heater..... Strikes me now as funny but when it is results we want (in this cabin thing) it seems rarely is it a straight line from where we are.

ICC Member	# Posted: 16 Apr 2021 09:54pm - Edited by: ICC Reply The one place I can think of where atmospheric pressure does come into the calculations is for use of a shallow well hand pump. They have a maximum depth limit of about 25 feet. That is 25 feet from the valve in the head of the shallow well pump to the static water level in the well hole. Pumping creates a suction in the pipe below the valve. Atmospheric pressure pushed down on the well water and up into the pipe to fill the vacuum. That maximum depth is reduced as the ground elevation increases and the atmospheric pressure lessens.

gcrank1 Member	# Posted: 16 Apr 2021 10:49pm Reply That's it! Sadly, my static level seems to be about 26'. I havent got to messing with it, the rain barrel works fine. Back to running a 'closet fixture', when our rural power went out at home I put a five gallon bucket of water in the shower next to it with an ice cream bucket as a scoop. After 'sharing uses' we would dump into the bowl enough to overcome the goose-neck inside and make it flow. I got a good sense of how the thing functioned that way. Anybody could do the test at home for anticipating what to do at the cabin. All bets are off, though, if you have a mound system, or anything depending on pumps and grid power.

scott100 Member	# Posted: 20 Apr 2021 01:37pm Reply Concerning the septic...if you don't already have one, and local laws permit it, you could also look into a composting head and skip the septic system. We have one on one of our boats, and just bought a second one for our cabin so I don't have to lug the one back and forth. Works great. Ours are made by C-head. It really simplifies things at the cabin.

gcrank1 Member	# Posted: 20 Apr 2021 01:59pm Reply What are you doing for grey-water, Scott?

scott100 Member	# Posted: 20 Apr 2021 10:36pm - Edited by: scott100 Reply In our case, we're just sending the grey water to a drain tile in a shallow trench where it percolates out. We're out in the woods in a remote area. Cabin is used seasonally.

gcrank1 Member	# Posted: 20 Apr 2021 11:19pm Reply Similar for us, we sure dont generate near the 'greywater' at the cabin as we do at home where we have a septic system. And even at home we dont gen near the 'average' per person that Ive read about online. Its not like we try to see how little we can get by with either, we just dont let water run except when we have to. Lot of times at the cabin we just do a pers wash up and wait to shower when we get home.

scott100 Member	# Posted: 21 Apr 2021 09:39am Reply Same for us. We pay for a water delivery to fill our ibc totes and conserve water at the cabin. Just a kitchen sink and shower and bathroom sink there. Shower gets turned off for soaping up and they're quick showers. I may get a little fancier with the setup this season and dig the trench deeper and fill with wood shavings for a filter, but had no issues last season with any standing water or damp areas. I was told by our local inspector at the time we were planning the cabin, that if I put in a well I would need to put in a septic system. I didn't put in a well. We had no discussion concerning grey water, just the fact that we were going to put in a composting head, so no septic.

redwolfguild Member	# Posted: 29 Apr 2021 06:21pm Reply Not sure my experience matters here, but this is what I have. I have surface spring that is 65 vertical feet above my cabin. I have a 3/4 water line coming from the spring down to my cabin that is 170 yards long. That provides enough pressure to run my standard toilet, take great showers, and run my kitchen sink. I have a wood-burning tank hot water heater so I never had to worry about pressure. As for power - I run everything on 420 watts of solar at 48 volts into an MPPT and then into a 220 AMP 12 volt AGM Battery. I then convert it all to 120 volt with and 800 watt inverter. It runs fridge, and lights. Have never run out of power.