RV News RVBusiness 2021 Top 10 RVs of the Year, plus 56 additional debuts and must-see units → ×
 


Reply
 
Thread Tools Display Modes
 
Old 10-15-2011, 07:32 PM   #1
Senior Member
 
coyotearms's Avatar
 
Join Date: Jan 2010
Location: Seattle, WA
Posts: 188
Off the Grid Camping with a 110v AC Water Heater

With space a primary concern at the time of the build of the van last year, I toyed with the idea of doing a small 2.5 gal 110v AC Insinkerator W152 water heater installed under the sink after SMB suggested that the great thing about it was you can heat water "for free" while driving because we have an inverter to supply the AC power and the engine alternator supplies the inverter. The fact that the E350 came with a factory heavy duty 200 AMP alternator tipped the scales to do it. The other factor that lured me to that decision was that we have a 540 W solar system (4 Kyrocera panels on the roof) and thought that could make the water heater useful at other times too, i.e. off the grid camping in sunny weather. Here is why. To heat up the 2.5 gal tank, say from 50 to 120 or 70 degrees F takes 35 amp-hr (calculations below). And that takes less than 20 minutes. With 300 amp-hr of house batteries that load is 10% of the total capacity, or 20% of the 150 amp-hr (50%) one should not go beyond to keep the batteries happy. Heating water that way around dinner and breakfast time and considering other electrical loads is quite doable with enough sun to recharge the batteries after breakfast. With an outdoor shower, but only a 17 gal fresh water tank, our hot water needs are not too excessive. And, hey, if that is not possible, just heat water like a Neanderthal and use the propane stove---redundancy is good. . .

But there was one problem. The 1500W water heater pulls 1500W/12V = 125A from the batteries, and even though our TrippLite inverter is rated at 2000W continuous, that is quite a heavy load even when running it "for free" while driving, at which time the poor alternator is trying to charge three house batteries, two engine batteries, run lights audio and diesel fuel injectors among other things. In addition, the solar battery monitor indicates the actual current draw is about 140A, which is not surprising given other losses such as the efficiency of the inverter itself. While camping using our 700W microwave oven at the same time puts you into no-no inverter territory (> 2000W). So I decided that I would consider a rheostat capable of handling 1500W attached to the water heater, the kind you use to dim lights. Unfortunately, these usually require a pure sine wave coming from the inverter, and the TrippLite I have is not that type. TrippLite tech support even said it would probably not work. So go out and replace the Tripplite?---too costly---the mistake was getting the TrippLite in the first place. I decided to gamble the $60 it cost for a Lutron rheostat and tried it. I also have one of those Watt meters you can buy to see how much AC energy various appliances use. I played with it at home (sine wave power) using a half-gallon electric tea pot experimenting with turning down the Wattage to half or about 750W. By measuring the time it takes to heat the water a certain amount I verified these rheostats are fairly efficient, even though the heat sink on them is quite large! By fairly efficient I mean around 95%. The only problem I found was that the tea pot, which automatically turns off when the water boils, did not work at 750W even though the water was clearly boiling. That would seem to indicate in the van the water heater might blow up if its thermostat did a similar thing. However, in the van on battery power, it worked flawlessly. I am guessing the inverter puts out a good enough approximation to a sine wave. I dialed down the power until the solar display of battery current read about 70A and by watching that panel could see the water heater cycling on and off. So it was a go! For now the rheostat is in a single gang electrical box bolted to another single gang electrical box that has an outlet in it. I made a three-conductor 14 AWG power cord plugged into the wall outlet that the water heater was plugged into and plugged the water heater into the outlet connected to the rheostat. I have not decided where to permanently mount it---I worry about water if mounted outside the sink cabinet. So for now it just sits inside the kitchen cabinet where it can be set to 750W by watching the battery monitor current gauge that is part of the solar system. The rheostat stays at that 50% setting unless we are at a campground that has shore power and want hot water more rapidly.

.

In summary, if you have sufficient solar or drive every day, a good amount of house battery capacity and an inverter, an electric hot water heater wired to control the wattage it consumes can work for off-the-grid camping! Note in the boating world of larger hot water heaters and larger inverters, dual voltage standard size dual voltage 110V AC/12V DC heating elements of are available. The small Insinkerator water heater we have has a non-standard length heating element, so that was not an option. If that were the case, spare solar energy after the batteries are topped off could be sent to the hot water heater, which would be even better. There is such an auxilary output on the BlueSky solar controller I have.

The calculation promised: The energy it take to heat up the water is E = M Cp DT, where M is the mass of 2.5 gal of water = 9 kg, Cp is the specific heat of water = 4180 Joules/Kg K and DT is the change in temperature. If water is heated from 50 to 120 or 70 degrees F or 40 C, then E = 1,500,000 Joules. Sounds like a lot, doesn't it? The equivalent electrical energy to do that is E = P Dt where P is Watts of power and Dt is heating time. At 1500W it takes Dt = E/P = 1,500,000/1500 = 1000 sec = 0.28 hr. At 12v the current associated with 1500W is 1500/12 = 125 amps. The amp-hr is therefore 0.28 x 125 = 35 amp-hr.

Caveat: If it wasn't for the ability to have the hot water tank on while driving, using the microwave to heat just the amount of water needed at any one time in the microwave could be an even greener method but not as convenient.

Edit of 10/22/2011: Realizing the water heater has a thermostat that the manual says can be adjusted from 110 to 170 degrees F, but only accessible after removing the front plate that SMB made difficult to remove, I did one more thing. I removed the coverplate and drilled a hole in it from the backside at a location that that exposed the adjustment screw on the thermostat and finished the hole with a rubber grommet, which can be seen centered on the front slightly below center.



It is highly unlikely that a screwdriver in that hole can touch anything live given the plastic plate over the thermostat and the grommet I installed, but anyone with any sense can just turn off the heater with the rocker switch that can be seen on the top of the front panel. With the thermostat turned down pretty much all the way and with the ambient temperature about 55 degrees F, I measured the water temperature coming out of the tap after a completed heating cycle which took about 20 to 25 min. using battery power only, and it was 108 degrees F, which is hot enough for most of our purposes, such as washing dishes and such. Our solar system battery monitor indicated that it took 30 AmpHr of energy to heat the 2.5 gal of water and run the inverter, which made sense based on the equations above.
__________________

__________________
2008 E-350 6.0L diesel: Bought new in 2010, 4x2, 4.10 LSD, HD spring-lift all 'round,
Cruiser II Top, 6'7" inside, full-time upper bed w/ kind'a EB50 layout, cozy 4-season rig
Solar: 540 W of Kyrocera w/ Blue Sky 3024iL, 3x100 AmpHr AGM's
Electrical: 4 cf fridge, nuker, water heater, compressor
Propane: stove top, furnace Travel: https://www.lugnutlife.wordpress.com
coyotearms is offline   Reply With Quote
Old 10-17-2011, 03:59 PM   #2
Senior Member
 
carringb's Avatar
 
Join Date: Jan 2009
Location: Corvallis, OR
Posts: 4,850
Re: Off the Grid Camping with a 110v AC Water Heater

Have you though about a coolant heat exchanger? You can tap into your rear heat lines easily (if you have them) and pre-heat your water using truly free engine heat, and therefore need less electricity.

http://www.suremarineservice.com/W001-225K.aspx
__________________

__________________
2000 E450 dually V10 wagon
carringb is offline   Reply With Quote
Old 10-17-2011, 08:38 PM   #3
Senior Member
 
coyotearms's Avatar
 
Join Date: Jan 2010
Location: Seattle, WA
Posts: 188
Re: Off the Grid Camping with a 110v AC Water Heater

Quote:
Originally Posted by carringb
Have you though about a coolant heat exchanger?
Isn't the Sure Marine device pretty much the same thing as the flat plate heater SMB installs that requires water pipes and engine coolant lines running under the vehicle? Seems less fragile though.

I went the electric route, in part, because I did not want any of that. Not only is all that plumbing vulnerable to damage, but it is another thing to worry about with freezing temperatures. And you have to worry about antifreeze in your drinking water if the coolant side leaks into the water side. I also did not like the space the propane heater takes up nor the gaping hole needed in the side of the van. I love the Espar and Webasto combo diesel units that heat water and air, but they are very spendy, need regular maintenance, are not green and reduce your driving range as they compete for "food" with the engine.

So I am happy doing my experiment with electric, using the propane stove top when electric is not possible or the microwave if I don't want 2.5 gal of hot water. Of course, "free" electric water heating while driving is a misnomer, because as the alternator puts out more current it needs more torque from the engine, but at least all those panels on the roof are making it free some of the time!

Addition 10/17/2011: BTW the coolant heat exchanger on the Sure Marine website is advertised as 20,000 BTU. A rating of 20,000 BTU actually means 20,000 BTU/hr. That's 5860 Joules/sec, i.e. 5860W, or almost four times the heating power of my little 1500W water heater that I only dare use at 750W! I am guessing that is also far more than the flat plate heater SMB installs, but maybe that is not so surprising given it is 2 ft long.
__________________
2008 E-350 6.0L diesel: Bought new in 2010, 4x2, 4.10 LSD, HD spring-lift all 'round,
Cruiser II Top, 6'7" inside, full-time upper bed w/ kind'a EB50 layout, cozy 4-season rig
Solar: 540 W of Kyrocera w/ Blue Sky 3024iL, 3x100 AmpHr AGM's
Electrical: 4 cf fridge, nuker, water heater, compressor
Propane: stove top, furnace Travel: https://www.lugnutlife.wordpress.com
coyotearms is offline   Reply With Quote
Old 05-06-2012, 02:44 PM   #4
Junior Member
 
Join Date: Mar 2012
Posts: 16
Re: Off the Grid Camping with a 110v AC Water Heater

Except that the weight and wind drag of those solar panels also rob energy from the engine.
OldBear is offline   Reply With Quote
Old 05-07-2012, 12:06 AM   #5
Senior Member
 
coyotearms's Avatar
 
Join Date: Jan 2010
Location: Seattle, WA
Posts: 188
Re: Off the Grid Camping with a 110v AC Water Heater

Hey OldBear, ya' dug out a pretty old thread, but Ya' got me over a theoretical barrel on that one! I haven't met an anti-solar guy yet, but let's see how it goes. A about 1.5"x6' frontal area (.75 ft^2) of the panels is about 1% of the total frontal area of our van (9.5 ft high x 7 ft wide). So at a steady speed given all the other losses in engine and drive train that are in addition to aerodynamic drag, I imagine that is a really tiny part of a mpg effect, don't you? Some folks have used flexible panels on the roof, leading to even less aerodynamic drag, but mounting them off the roof they actually provide shade!

Probably it is a similar situation with weight. Let's see, four panels at 40 lbs each + say no more than 20 lbs for wiring and electronics is 180 lbs or 180/10,000 = 2%, of the weight of the car. Now that is mass, so that should only enter into the game when changing speed. So I venture to say the effect of the the mass of the solar system would certainly not be anywere close to something measureable in mpg, don't you?
__________________
2008 E-350 6.0L diesel: Bought new in 2010, 4x2, 4.10 LSD, HD spring-lift all 'round,
Cruiser II Top, 6'7" inside, full-time upper bed w/ kind'a EB50 layout, cozy 4-season rig
Solar: 540 W of Kyrocera w/ Blue Sky 3024iL, 3x100 AmpHr AGM's
Electrical: 4 cf fridge, nuker, water heater, compressor
Propane: stove top, furnace Travel: https://www.lugnutlife.wordpress.com
coyotearms is offline   Reply With Quote
Old 08-11-2012, 02:01 PM   #6
Senior Member
 
coyotearms's Avatar
 
Join Date: Jan 2010
Location: Seattle, WA
Posts: 188
Re: Off the Grid Camping with a 110v AC Water Heater

Clearly, an electric hot water tank is not a very popular topic, but I thought I would add a somewhat related issue with ours. We are still on the SMB warranty, so this might be helpful to those who have had or will have the same problem. The pressure/temp relief valve on the top of the tank started leaking whenever the water heater was on, even when set at a relatively low 110 F. SMB used galvanized pipe for the dump path for any water that comes out. It is supposed to be o.k. to screw galvanized into bronze, the relief valve material, but not into copper. But that valve is screwed into a copper fitting and that fitting attached to the bronze water tank! In any event there was corrosion at the galvanized/bronze interface, which was very near the valve seal. I replaced the Zurn valve with a Watts (my plumbing store says Watts is better) and replaced the galvanized pipe with PEX tubing and plastic fittings that Evergreen RV in Seattle swears by (good for hot and cold water) as shown below.



While the water heater was out of the van I also noted that the stock insulation was hard styrofoam type material on the sides and top, but nothing was on the bottom. Given condensation and corrosion questions, I decided to just use aluminized bubble wrap (so popular for insulating windows) under the tank. It was cut to the exact profile of the water heater case and simply rests between the tank and a bracket that supports the tank. I also drilled some holes in the bottom plate including holes at the bottom of the dimples that form the "feet" as it appeared without holes water from draining the tank and/or condensation would collect there (the water heater itself rests in a tray that drains through the floor).



Lastly, It appeared the water heater is prevented from moving forward or toward the passenger side by the shelf above it, but (especially with the plastic overflow tubes) I screwed in a block under the shelf to prevent movement toward the rear. I still need to put a foam block behind it for the driver side direction. The shelf had to be removed anyway to get the water heater out to work on it. When replacing the shelf I also put some non-slide shelving mesh between the heater and the shelf, which contact each other quite firmly without any mods (see black material showing in second photo below). It may not need the foam block behind as it appears to be quite stationary when shoving it by hand. But it does weigh a bit when filled.



One last thing of note. The connections for the cold inlet and hot outlet were compression fittings, but the nuts had Teflon tape on them making them very difficult to remove. On reinstall I removed the remnants of tape and simply oiled the threads. With that mod when tightening the nuts it was very clear when contact between the brass sealing surfaces was made and just a little more tightening was sufficient to form a leak free seal as tested by hooking up to shore water (my home) that is at 80 psi. So now things are a bit better. Since I did the work, I feel much more confident to do on-road repairs of that system if needed, and SMB reimbursed for parts. For me that was the ideal situation as there is a lot to know about all a lot of systems that can ruin a trip if you don't have a clue!
__________________
2008 E-350 6.0L diesel: Bought new in 2010, 4x2, 4.10 LSD, HD spring-lift all 'round,
Cruiser II Top, 6'7" inside, full-time upper bed w/ kind'a EB50 layout, cozy 4-season rig
Solar: 540 W of Kyrocera w/ Blue Sky 3024iL, 3x100 AmpHr AGM's
Electrical: 4 cf fridge, nuker, water heater, compressor
Propane: stove top, furnace Travel: https://www.lugnutlife.wordpress.com
coyotearms is offline   Reply With Quote
Old 08-11-2012, 09:13 PM   #7
Senior Member
 
Join Date: May 2009
Posts: 1,762
Re: Off the Grid Camping with a 110v AC Water Heater

Because i am lazy :a3: ...

can anyone do the figure the cubic square inches

the electric vs the propane 2.5 gal

we have the old school propane 2.5

just courious of the actual space difference

bw
billwilson is offline   Reply With Quote
Old 08-12-2012, 01:51 PM   #8
Senior Member
 
coyotearms's Avatar
 
Join Date: Jan 2010
Location: Seattle, WA
Posts: 188
Re: Off the Grid Camping with a 110v AC Water Heater

Yep, you apparently are. This gets you part of the way to your goal. The manual for the 2.5 gal Insinkerator electric hot water heater is 13.5 x 10.4 x 10.7 (H x D x W) in. That, however, is just the housing and does not include the height the relief valve and other fittings protruding above the housing you see in one of the photos above, but also keeps you from having a huge cutout on the side of the van.
__________________
2008 E-350 6.0L diesel: Bought new in 2010, 4x2, 4.10 LSD, HD spring-lift all 'round,
Cruiser II Top, 6'7" inside, full-time upper bed w/ kind'a EB50 layout, cozy 4-season rig
Solar: 540 W of Kyrocera w/ Blue Sky 3024iL, 3x100 AmpHr AGM's
Electrical: 4 cf fridge, nuker, water heater, compressor
Propane: stove top, furnace Travel: https://www.lugnutlife.wordpress.com
coyotearms is offline   Reply With Quote
Old 08-13-2012, 08:03 AM   #9
Senior Member
 
Join Date: May 2009
Posts: 1,762
Re: Off the Grid Camping with a 110v AC Water Heater

Quote:
Originally Posted by coyotearms
Yep, you apparently are. This gets you part of the way to your goal. The manual for the 2.5 gal Insinkerator electric hot water heater is 13.5 x 10.4 x 10.7 (H x D x W) in. That, however, is just the housing and does not include the height the relief valve and other fittings protruding above the housing you see in one of the photos above, but also keeps you from having a huge cutout on the side of the van.
As i am in process of details for a new build
This thread IS important, so i thank you :)

I am weighing:
size vs hole in rig
complexity vs time tested tech
size vs size

i dont have a clear winner yet

some folks here advocate no hot water heater
my rig when purchased, had one
during the rebuild, it was easier
to build the galley around the existing heater
than to pull it and plug holes and patch the exterior

Me, Mrs. Wilson and Cooper the dog
are glad we have hot water
billwilson is offline   Reply With Quote
Old 09-05-2012, 01:29 PM   #10
Senior Member
 
Join Date: Nov 2011
Posts: 1,614
Re: Off the Grid Camping with a 110v AC Water Heater

Quote:
Originally Posted by coyotearms
Yep, you apparently are. This gets you part of the way to your goal. The manual for the 2.5 gal Insinkerator electric hot water heater is 13.5 x 10.4 x 10.7 (H x D x W) in. That, however, is just the housing and does not include the height the relief valve and other fittings protruding above the housing you see in one of the photos above, but also keeps you from having a huge cutout on the side of the van.
Coyote,

I'm about to pull the trigger on this unit with SMB.

Wanted to get your feedback on how's its working for you since install.

I was informed it's not recommended to use the inverter as this unit would be too much of a strain on the battery.

I was planning on using shore power or a Honda 2000 generator to power it.

Thanks

J
__________________

Ocsmb is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Powered by vBadvanced CMPS v3.2.3
Disclaimer:

This website is not affiliated with or endorsed by Sportsmobile SIP or any of its affiliates. This is an independent, unofficial site.


All times are GMT -6. The time now is 04:12 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
×