Still trying to find a way to make hot water without running generator. We have Seaward electric 6-gal water heater currently which heats in about 20 minutes.
I'd install an LP heater, but they all require side venting, except for tank less and we don't want that.
So, I was thinking that I could possibly use what I already have on hand. We have a Samlex 2000-watt (continuous) inverter and four Trojan L-16 making 790 Ah of capacity.
We also have 540 watts of solar that can easily push 30+ amps back to the batteries.
I've got an extra manual transfer switch I can use to switch the power input to the water heater between pole and inverter.
Running the water heater on the inverter seems like it would be possible without pushing anything near its limits. Has anyone done this? Or, do you see problems with the plan I've missed?
What's the rationale against tankless?
I have a similar setup. I have 2-10gal electric water heaters (straight from HD). The first one is wired straight to the breaker box and the second one is wired through the inverter so we can have hot water going down the road, and have hot water in the morning when boon docking. Works well. Good Luck, TomC
How much power does the hot water tank use to get the temperature change you want?
Is that 20 minutes from cold, or warming yesterday's still warm water? Best case / worst case needs to be considered.
Is there enough power available in the time that the hot water tank is drawing it?
Simple calculation, 30 amps of solar at 12 volts is only 3 amps at 120 V.
A significant hole will be dug in the battery bank, is there enough left over for other needs / is there enough sunlight left to re-fill?
Heating water is an energy devil.
It's all in the math.
Happy coaching!
Buswarrior
Quote from: windtrader on May 26, 2019, 08:44:53 PM
What's the rationale against tankless?
From what I have read, they don't typically do well in very low-flow situations or when taking Navy showers. We often dry camp so water conservation is important. With very low flow burner may not kick on. I know some have put recirculation systems in, but there would still be other issues.
We can both wash up in the morning on the 6-gal tank. We'd only use it if we were expecting a sunny day or a travel day (we could easily recharge batts underway).
Twenty minutes is from cold water to scalding.
Thanks for the info guys.
Try it and report back.
Quote from: buswarrior on May 27, 2019, 03:54:25 AM
How much power does the hot water tank use to get the temperature change you want?
Is that 20 minutes from cold, or warming yesterday's still warm water? Best case / worst case needs to be considered.
Is there enough power available in the time that the hot water tank is drawing it?
****** Simple calculation, 30 amps of solar at 12 volts is only 3 amps at 120 V. *******
A significant hole will be dug in the battery bank, is there enough left over for other needs / is there enough sunlight left to re-fill?
What ^^^^ he ^^^^ said.
There's never enough sunshine to make solar useful. We had a 3 way switch so that we could switch the water heater to run off the inverter but we rarely used it. Even running down the road with the alternator pumping into the house bank the water heater would still eat into our SOC. The smart way to heat water on the road - IMNTBHO - is with engine coolant. You could buy a marine water heater with built in heat exchanger loop or rig up your own using a flat plate heat exchanger. Either way there's heat being shed off the engine that is free for the taking while you're moving.
Quote from: windtrader on May 26, 2019, 08:44:53 PMWhat's the rationale against tankless?
At my home, I have a moderate sized tankless (propane) water heater. Since I live in a hurricane area, i did a survey on what I needed to have a connection to run on a generator and I found that the electronic controls on the tankless heater use less than .8 of an amp at 120V. It seems to sip propane (but I'm the only person living there full time, so several people in a bus conversion would see higher/more expensive use but i've seen very low propane use).
I had already installed an Atwood 120V/propane/engine coolant loop 10 gallon heater in my bus before I had the experience with the home tankless but -- based on my results from the heater at home -- I would have no reluctance to install one in my bus if I needed to re-do my install.
I should add that I don't have the papers with me now, but my memory is that the tankless heater was about three times the price (installed) of the Atwood heater. Also, single person at home meant I never was washing dishes while I was taking a shower. I have never had a single problem with low water flow, etc.
(Another discussion we've had before ... and before.)
Having owned a thankless water heater my advice is: Just Don't. It's a great concept that just doesn't work well in the real world. Maybe some day it will but the problem is the enormous quantity of heat that has to be compressed into a very small space. (That was an electric unit however, propane may be significantly better.)
There are however a lot of good options all depending on your lifestyle. Once you know exactly what your needs are it gets a little easier to configure. But this is one place where it really is a good idea to stick with old reliable tried and true methods. Doesn't mean you can't combine them in new and different ways though.
For my money, a completely conventional dual heat RV water heater is hard to beat. You have your electric for shore power and your propane otherwise, plus you can run both for rapid heat-up. A manual switch and indicator light for the electric side is a great convenience. A second switch to go from pilot to burner on the gas would be that much better. Left on pilot they keep the water pleasantly warm. But that leaves the venting issue. You're not going to be able to mount it inside the bay very easily, certainly you aren't going to butcher your bay door for it. That does leave the option of mounting it in the cabinet under the sink however and cutting through the signboard to mount the cover. Might be a little tricky to get that to match but it can be done. Considering the small appetite of the pilot and the short delay to go to full hot as well as the extended shower time by kicking on both burners a few minutes before stepping into the shower, I don't see the extra expense of a propane tankless as being justified.
I've not been impressed with the coolant loop incorporated into those RV water heaters however. That strikes me as very much a stop-gap bailer twine and bubble gum type of solution. It's light years from a proper heat exchanger. Until they start installing it as an internal loop or coil it's not really anything but a nod in that general direction. An extermal heat exchanger though, that's a decent idea but it requires the water to be circulated through the water heater tank to really be effective, adding in more complexity. Maybe it could be done with a thermosiphon loop but those are generally dependent on having plenty of time to do their thing, so not much better than the existing external coolant loop. However if hot water with engine on is a frequent need, maybe a copper line wrapped around the exhaust pipe would serve.
But as for solar heating of water, the most effective is also the most direct. Run the water through the solar collector box. Doesn't have to be a large line, a 3/8" diameter that has a long run could collect enough heat on a sunny day to give you a comfortable shower. But saving that in a battery bank and converting it to warm water when you want it is going to take a lot of battery storage. You can calculate how much, based on the volume of water needed, the degrees of temperature rise desired, and applicable loss factors. Water happens to be a particularly good heat sink though so it'll be more than you want to see.
Jim
Why not just add another small electric water heater. With a larger heating element, it'll heat water quickly. You have a generator, use it.
Lots of ways to skin a cat. I'm happy with my tankless propane water heater now that I have a recirculating system and a thermostatically controlled on/off switch. The heater takes 2 degree C water to 42 degree C (107 F) in about a minute and keeps it there until all the water is gone. Jack
Quote from: bobofthenorth on May 27, 2019, 06:41:01 AM
The smart way to heat water on the road - IMNTBHO - is with engine coolant. You could buy a marine water heater with built in heat exchanger loop or rig up your own using a flat plate heat exchanger. Either way there's heat being shed off the engine that is free for the taking while you're moving.
Our water heater is a marine model and includes the coolant loop. I'm hesitant to cut into the bus cooling system, only to have hot water for the day we arrive in camp. Day two, three, and beyond the loop won't help.
Quote from: chessie4905 on May 27, 2019, 10:32:00 AM
Why not just add another small electric water heater. With a larger heating element, it'll heat water quickly. You have a generator, use it.
Can't stand the noise. Vibration of the generator puts my nerves on edge. We go camping for the peace and quiet. No, we can't afford a better/quieter/smoother generator.
Problem isn't how fast our water heater makes the water hot, it's the source of energy for it.
Quote from: Jim Blackwood on May 27, 2019, 08:13:53 AM
For my money, a completely conventional dual heat RV water heater is hard to beat. You have your electric for shore power and your propane otherwise, plus you can run both for rapid heat-up. A manual switch and indicator light for the electric side is a great convenience. A second switch to go from pilot to burner on the gas would be that much better. Left on pilot they keep the water pleasantly warm. But that leaves the venting issue. You're not going to be able to mount it inside the bay very easily, certainly you aren't going to butcher your bay door for it. That does leave the option of mounting it in the cabinet under the sink however and cutting through the signboard to mount the cover.
But as for solar heating of water, the most effective is also the most direct. Run the water through the solar collector box. Doesn't have to be a large line, a 3/8" diameter that has a long run could collect enough heat on a sunny day to give you a comfortable shower. But saving that in a battery bank and converting it to warm water when you want it is going to take a lot of battery storage. You can calculate how much, based on the volume of water needed, the degrees of temperature rise desired, and applicable loss factors. Water happens to be a particularly good heat sink though so it'll be more than you want to see.
Jim
I agree that a traditional RV electric/LP water heater is the best option. But, as you mentioned cutting up my doors is not a good option, especially with the pantograph doors. Higher up (outside the cabinets) is not a sign board on the older GM buses - it's either aluminum or steel with rivets about every two inches. Not keen on cutting into that either.
Running the 1500-watt water heater will consume about 135-150 amps/hour, which is less than the max discharge rate for our Trojan L-16 batteries. Running the water heater for 20-30 minutes would deplete the battery about 70 amps. We camped this weekend in northern Wisconsin with overnight temps cold enough to still require the furnace at night. Running heat, the compressor fridge, lighting, a little TV watching, water pump, etc. still totaled less than 100 Ah consumption overnight. Even if we added 70-100 more for the water heater, the solar panels could still have easily gotten us to full recharge by mid afternoon.
On days when solar charging doesn't look promising, we would either shower cold or skip showers till we had a larger reason for running the generator. Or, if we're traveling, we can charge house batteries at 70 amps while underway.
I've got all the parts on hand to give it a test. First step will be to temporarily connect a pigtail to the water heater so I can just plug it into the inverter and test it. Then I'll be able to record real-world data.
I thought you had a Webasto Richard ?
Quote from: luvrbus on May 27, 2019, 04:09:54 PM
I thought you had a Webasto Richard ?
That was on the 4106 - the bus that got smooshed.
LP furnace and electric hot water heater on this one.
Maybe something here may be an option.
https://www.amazon.com/Water-Heaters-Gas-Powered-Parts/s?rh=n%3A3754791%2Cp_n_power_source_browse-bin%3A542716011
When we're boon docking, I typically run the generator in the morning to heat both water heaters, make coffee, and my wife to use the hair dryer. Then during the day, the water stays warm enough in the water heaters. Sometimes will run the generator at night also to build up the batteries for the evening. I do not have solar panels. Good Luck, TomC
Yep, it's all about the wattage and whether or not you can harvest and store enough of them to cover all needs. Definitely interested in hearing how you make out. It seems that residential electric water heaters range from about 1200-4500 watts depending on the model and the voltage. So with your 1500w model at the lower end and a very health solar array you just might manage it. But obviously it's not a 1:1 relationship.
Jim
I'm going to call the folks at Don Rowe today. That's where I bought the inverter. Unless they mention any potential problems, I'm going to rig it up for testing. I'll report my findings.
Seems a waste to put those loads on inverter and batteries to heat water??? Sure, it can be done, but why??? Turn on generator for half to an hour and go for a walk. You could also plumb the coil in the water heater to your generator.
Presuming ( that's Assuming, but in a prior mode) that your heater is 120 VAC, your inverter is 120 VAC and 12VDC, your batteries are 790AH wet acid, in a 12 volt bank, and all else being equal...
You'll draw 1500W X 1.15 = 1,725 watts from the batteries for 20 minutes, or 1/3 hour, to heat your water. 1,725 @ 12.5 volts is 138 amps for 1/3 hour is 46 AH. Your recovery rate from solar is 30 A/H, so you will recover in around 1.5 hours (not really, I think there is an efficiency thing I am missing, but you will recover if it's sunny out). Maximum draw rate from the battery bank is going to be around 18% of the AH rating of the bank, so a somewhat aggressive load (in terms of a maximum load rate). Average draw per cycle is around 6% of the capacity of the battery bank. You could look up the load rate charts for your batteries to see where this load falls on their capacity, but those Trojans are a high spec battery.
In other words, maximum draw rate is very well accomodated by the battery bank (if fully charged), recovery from solar is well accomodated (if it's sunny), all loads and draw rates are well within range of the equipment noted, if all you do is run the water heater for 20 minutes a day. If you look at a 5:1 ratio of run time VS recovery time, you can keep going indefinitely (as long as it's sunny), and realistically you can run the hot water heater several times a day in a single cycle mode (like for washing dishes in the evening, shower in the morning.
For me this is exactly why you have an inverter, a battery bank and some solar. It's an application very well matched to a solution. I'd do it. I vote thumbs up!
Brian
Finally, some mathematics.
Thank you.
Happy coaching!
Buswarrior
Yep, glad you ran the numbers on that.
Jim
Don't forget water pump, reefer, lights, vent fans, tv,etc.
And a lot of days aren't sunny. Or sunny enough, like parked in the shade, or like up North anytime except May, June, July. Solar only isn't enough. I have solar panels on the roof of my bus and I like them. They are a nice complement to the whole system. But I could not get by without a generator.
JC
Quote from: lostagain on May 28, 2019, 04:54:54 PM
And a lot of days aren't sunny. Or sunny enough, like parked in the shade, or like up North anytime except May, June, July. Solar only isn't enough. I have solar panels on the roof of my bus and I like them. They are a nice complement to the whole system. But I could not get by without a generator.
JC
I've got a generator, I just don't like using it. The way I look at it, if this works it gives me another option for making hot water. Solar can recharge, and so can driving to the next destination since we can charge at up to 70 amps while underway.
If need be, we have the generator.
How about a 50 foot piece of black garden hose with a mini circulator. Lay that out in the sun and it'll get really hot.
You could also lay a loop or coil of tubing around your solar collectors. But that has the same issue of not being available at the hours when you might want to use it.
Jim
Got it connected today. Wasn't too difficult since the transfer switch went into a kitchen cabinet which is directly above the water heater in the bay below.
When running in inverter, the inverter panel shows about 12.4 amps being pulled by the water heater. Victron battery monitor shows about 150 amps being pulled from the batteries.
The only problem might come from the temporary drop in voltage as things get evened out - battery monitor showed a drop to about 11.6 and then it crept back up towards 12 after a minute or so. The battery protect auto shutdown right now is set to shut things when voltage drops below a set point for more than 10 seconds. I'll have to keep an eye on that to see how things go.
My thought right now is that this will be a handy backup for making hot water if either we're on the road running the battery-to-battery charger (puts out up to 70 amps) or if we have solar actively running (up to about 30 amps output). Don't think I'd want to use this as our main method to heat water, at least until we get the additional solar installed that we plan to do at some point.
All that said, it cost nothing but 8 feet of wire and a switch that was sitting in my box taking up space. I'll give the new setup a trial run from cold tank to hot the next day we have the solar running to see how things go. I'm calling this project potentially successful.
I dunno. It wouldn't work for me. I'm with Tom C on this one (and most of the time).
Geoff
If you have propane, you could use one of the tiny water heaters to assist heating the electric model. It doesn't have much output, but could run a few hours to keep the temp up. They have an automatic shut off on some models. Home Depot, Lowes, and Camping World sell versions.
Quote from: Geoff on May 29, 2019, 06:13:10 PM
I dunno. It wouldn't work for me. I'm with Tom C on this one (and most of the time).
Geoff
We've sure got a bunch of naysayers on here nowadays...
Not sure what the problem is with having multiple methods to make hot water. Generally speaking, I have much more battery capacity than we need for the time we're dry camping, and if doing this once in a while allows a hot shower without the noise and vibration from the generator it's all good. Like I said, I wouldn't count on this as a full-time solution, but there are so many days with either solar or traveling that this would allow for quiet showers I'm not sure what the down side is.
Quote from: chessie4905 on May 29, 2019, 07:03:01 PM
If you have propane, you could use one of the tiny water heaters to assist heating the electric model. It doesn't have much output, but could run a few hours to keep the temp up. They have an automatic shut off on some models. Home Depot, Lowes, and Camping World sell versions.
Even the tiny ones require venting somewhere, and that's where I run into a problem. Not keen on cutting more holes in my bus for venting, especially through the doors since they are pantograph.
Side benefit of this experiment, you get a demonstration of the losses of your inverter at that level of work.
150 amps at 12 volt in, 12.4 amps at 120 volt out.
For a given output wanted, you need 21 percent more battery than the simple calculation of shifting the decimal point.
That's really important info to know for a given system.
In this case, a hidden consumer of 1/5 more power than simple calculations...
This is exactly how those without battery monitors kill their batteries... discharging significantly more than their "calculations"...
Experiments with good measurements are the path to enlightenment?
Happy coaching!
Buswarrior
Quote from: buswarrior on May 29, 2019, 08:03:42 PM
150 amps at 12 volt in, 12.4 amps at 120 volt out
About 83% efficient which fits nicely with the 15% loss that we often see referenced. And I wholeheartedly endorse the notion that battery monitors are essential.
Maybe you can make use of the battery ventilation system already installed. Since they don't need typical venting or the bathroom venting.
So I have a question. Considering that gas furnaces have many decades ago reached into the upper 90% efficiency bracket to the point that about 30 years back they started using a small pcv pipe for an exhaust vent (as well as a pcv inlet vent), why are RV water heaters still back in the stone age?
Jim
Same reason anything "RV" is back in the stone age?
The better comparison would be the current performance of gas water heaters, residential and recreational?
Not sure the same compromises that gave us efficient air heaters will work when trying to get water warmed up with a certain time line involved?
Don't try warming your house from stone cold with an "efficient" furnace... going to take a loooong time...
Happy coaching!
Buswarrior
So I'm following this discussion with great interest.
I converted my bus over 30 years ago before inverters, monitors etc were the norm. Put in a Paloma on demand hot water heater. Takes up little room and cut a 4" hole in the door with a corresinding grill on outside. Hard to even tell it is there. Also had a noisy generator. Recently we decided to go solar and discarded the generator. Changed all the lighting to led and put in a catalytic heater for chilly mornings and evenings. No power needed. We also have a suburban forced air furnace that is a real power hog. We have 300 watts of solar and 2 x12 v batteries. Works fine as long as we have sun but it's easily expandable with more batteries and solar if needed. Also added a 1500 w inverter for tv, toaster, etc. System is dead simple. Either plug into the pole or the inverter. Only problem is there is no remote switch for inverter but that is doable quite easily.
It took me a while to figure out the hot water heater. It works on water pressure so things like water saving shower heads confuse it. But like someone said you can have hot water until you run out of water.
Simple, effective and cost effective.
I think it's a great way to avoid running the generator at 6:30 in the morning when people are still sleeping yet you want to take your shower... I put a 15% efficiency factor in my initial calculation that ended up with around 140 amps out of the battery. Amps out of the battery is always a fudge factor in any calculation because it depends on the variability of the load, and the voltage drop under load. Perfectly healthy batteries will dip below 12 volts under a decent load - my old F250 would drop to 11 volts for 30 seconds or more while the glow plugs were doing their thing. Any resistive heating element (like the ones in a water heater) will draw more power when cold than when hot, their resistance gets greater (less power) after they heat up. I put an RV propane/electric 10 gallon water heater in, cut a great bloody hole in the side of the bus, I would do it differently now.
How many drain/charge cycles do the batteries have?
https://www.campingworld.com/eccotemp-l5-portable-tankless--water-heater-37786.html?gclid=EAIaIQobChMIlaet5PPD4gIVAaeGCh0T3AMPEAQYAyABEgIT8PD_BwE
This maybe a feasible idea to plumb into existing water heater. IF you have propane.
Quote from: chessie4905 on May 30, 2019, 11:40:18 AM
How many drain/charge cycles do the batteries have?
https://www.campingworld.com/eccotemp-l5-portable-tankless--water-heater-37786.html?gclid=EAIaIQobChMIlaet5PPD4gIVAaeGCh0T3AMPEAQYAyABEgIT8PD_BwE
This maybe a feasible idea to plumb into existing water heater. IF you have propane.
I looked into using something like that. Read through the manual and you'll see that it requires a flow rate of 2L/min to activate the burner. When we use the water at a very slow flow odds are it won't ignite. We try to make our 80 gallons of fresh water last a week (for two of us) so we sip water very slowly for dishes and such. Even the low flow shower head may not move enough water for this thing.
Also, it is intended for use outdoors. Not sure what kind of safety hazard I'd be creating by installing it in a bay, and I have no desire to set up an outdoor water heater and run plumbing to/fro each time.
That was an example. The flow issue can be dealt with a small pump or one that doesnt need the flow you have. It may be too complicated for you to make it work. Best to just stick with your battery idea. Don't want to burn the coach to the ground or die from carbon monoxide.
All sorts of things can be solved with bypass circuits back to the fresh water tank, built-in and/or manually activated as required.
Bigger flow, without consuming lots of water, instant heat without running the water down the drain, freeze protection of fresh water tank.
With a little trickery, a busnut could have a "better" water system in the coach, than they have in their dirt house.
Happy coaching!
Buswarrior
Well, Richard did not design his bus. If he had, he might have a generator that is quiet enough to run without bothering him. I do.
As far as water heaters go, I have an Attwood that has five ways to heat 11 gallons of water:
(1) propane
(2) electric
(3) loop from engine coolant
(4) loop from Webasto
(5) Radiant heat from engine compartment
After driving for a couple of hours, the fresh water stays hot all night parked for two people to take showers in the morning. Otherwise, I can heat it up using one or two of the other methods. Fastest heating is running electric with propane at the same time.
Quote from: Geoff on May 30, 2019, 06:35:37 PMWell, Richard did not design his bus. If he had, he might have a generator that is quiet enough to run without bothering him. I do.
As far as water heaters go, I have an Attwood that has five ways to heat 11 gallons of water:
(1) propane
(2) electric
(3) loop from engine coolant
(4) loop from Webasto
(5) Radiant heat from engine compartment
After driving for a couple of hours, the fresh water stays hot all night parked for two people to take showers in the morning. Otherwise, I can heat it up using one or two of the other methods. Fastest heating is running electric with propane at the same time.
Very similar to my setup. Someone earlier said something like "the loops don't work because they're too small". Not in my experience. Within a short period of running down the road, I have 10 gallons that's at about 180º. A great feature is that there is a "tempering valve" in these Attwood heaters -- the water out of the valve is always at 106º or 110º (whatever it's set for); if the water in the tank is very hot, you get many gallons of "mixed" hot water, if the water has cooled some but is still reasonably hot, that water will be drawn out at service temp with less cooler water mixed in. But even hours later - the next morning in Geoff's example -it's still "hot water" in the dish sink or shower.
Certainly, no one would want to be stuck with that being the only source of hot water -- it would be terribly inconvenient, and highly expensive, to have to fire up the engine and run on the road (just idling wouldn't do it), but it's a feature - FREE hot water - for the days you're actually traveling, and for many hours afterwards.