240AC Electric Hot Water in Campervan

[Darcar]

One day, I’m sure Electric will power not only the habitation area but also the the vehicle. But I don’t think we are there yet!

I must admit that I admire wildebus in his commitment to electric, and I’m very interested to see how it goes.
As he says it’s not really for the average joe motorhome builder.
Darcar

 

[wildebus]

So there is an idea that you need an massive battery bank in order to run an Electric Heater. But you do not!

I thought I would do another section to this Thread - "Solar Hot Water Heating".
Now you can do genuine Solar Hot Water heating, but it really means having the water heated directly by the heat of the sun, which is not really practical in a vehicle for any significant extent in the UK. What is usually meant by "Heated by Solar" or "Run by Solar" is run off batteries which are recharged by Solar Panels. It this possible in the UK though?

A few charts to show why the answer is yes I think ....
Here is a typical chart showing solar harvesting in the summer. I selected a couple of days to show the pattern
Solar Yield - Power Wave by David, on Flickr
You can see the energy yield ramping up as the sun rises; and then dropping off in the late afternoon.
But something odd is happening in the middle? What is happening to the yield?

Well, when we look at the battery state we see it is pretty full
Solar Yield - SOC Match by David, on Flickr

And superimposing the Battery SOC chart on the Solar Yield chart, it is clear what is happening
Solar Yield & SOC by David, on Flickr
Quite simply, the batteries are full by around 9:00-10:00 AM and there is no place for harvested energy to go. The peaks in solar between the red lines will be when power is called for and the solar contoller responds to provide extra power. but apart from those times, we basically have many hours of available energy wasted.

To take advantage of this, I have set the Victron BMV-712 to turn on its internal relay when the SOC hits 99% and then turn off when the SOC hits 94%
Victron BMV Relay Setting by David, on Flickr

I put the heater switch to position I - this is the 'activated by Relay' mode (position II bypasses the relay for direct control)
Control Bank by David, on Flickr


How does this work in a typical summers day? This chart will illustrate showing the Battery SOC overlaid on the Power used by the heater
Sequential MeterControl - Battery Use and SOC by David, on Flickr
As said, when the Battery hits 99% SOC, the relay turns on, which in turn starts the On-Off timer (described in an earlier post) and turns the heater on and off on a 60 second on/120 second off cycle. When the SOC has dropped down to 94% (as the heater uses more power than the solar can provide), the relay turns off, removing power from the On-Off timer and so turning the heater off. Omce the heater is off, the Battery SOC will start to rise again as the Solar Panels provide charge until the SOC again hits 99% and the process starts again.
The chart above shows this pattern between the hours of 10AM to 2PM and would continue throughout the day until the time the SOC does not rise back to 99% to kick off the next cycle.

This is what the Charger States are doing during this process
Sequential MeterControl - Charging State by David, on Flickr
( the batteries were fully charged when I put the switch onto position 1 to start the process to capture the data, hence why the initial status is 'storage')
The charging pattern show is for my AGM Battery install. Different batteries and battery bank sizes will result in a different timeline but the basic pattern will be as shown unless you have Lithium, where where is no Absorption or Float phase, just a Charge phase.


How well is the water heated? The results will vary depending on various factors (the bigger the battery bank and the bigger the solar bank, the longer it will be on as the SOC will take longer to drop to 94%; the bigger the Hot Water tank, the longer it will take to raise each degree in temperture), but these are the results for my 10L Water Tank for the cycle shown in the charts above in my test mode (I am using an AC charger to act as the Solar Charger which is why I selected 10AM to 2PM as my test times as that represents Peak Solar in the day).

Starting Temp

Interim

Last Temp

Each run added around 15C to the Water Temp. In the summertime, the water temp would start significantly warmer than 5 Celcius of course, so not many heating cycles will be needed to get very hot water.

I think the above shows how heating water can be a very effective use of Solar energy that would be otherwise wasted (see the very first chart again as a reminder of what usually happens to the solar power when you have a full battery)

For those interested, this is the block diagram for the Electric Hot Water System as installed in my Camper

Clarence - Hot Water System by David, on Flickr


I think this will probably be the last update

 

[makaveli7]

Hi @wildebus.



I hope you don't mind moving my question to your original post, as it is inline with the subject I think it would benefit other members.


So almost 2 years now since you last posted about this subject, what is your overall verdict on the 10l Ariston heater and the overall of the setup.


I read all 3 parts carefully and I was eager to know more about the heat data. I found it in part 3 but I will appreciate it if you can elaborate more.


- When the heater reaches the desired temperature how long can it hold the water hot before turning on again?

- Did you record in real heat loss data?

- Why didn't you go down the calorifier route? they come in as low as 500w element on both 12v and 240v, I appreciate the cost might be slightly higher but again I have no idea about their heat loss proof either.



I am grateful I found your setup, before finding your post there was only one guy on youtube that went down the electric heater route but he didn't explain at all. again I am so grateful for your detailed posts.



What is more interesting is how you automated it all to take into account the SOC, I was planning to have a timer on the heater to turn it on only in the early morning now I am gonna follow your footsteps



I have a slightly bigger setup than yours 8x90ah batteries, 3000w inverter ( not pure sine wave) but surprisingly have been running my domestic 240v fridge just fine and can handle a 2000w hair dryer just fine too. so I think I will modify your timer to run for 2 minutes and off for 4, what do you recon?



I like playing around and automate things in the van, I have just installed a nest thermostat to control the heating in the van which is fantastic, this will also help tackle the humidity as I park it for long time, so it is handy to be able to fire the heater from anywhere, I will have 2 dehumidifier thats comes on when the humidity is high . we can talk more about this if you wish. i have just installed the victron Grafana which opens up a lot of scopes of what you can do and much much more powerful than the VRM. After I thick the heater box I will move to security, cameras amd sensors and automate the lot . I hope you don't mind chatting about these things and helping out when you can .

 

[wildebus]

Hi there.
Ok, so this is my thinking... I may be repeating some stuff, and some may be new

How long does it take to reach the desired temp?
Well, this is going to vary depending on time of year (so the temp of the source water). You are heating water to around 70C. if summer, the water starts from around 20C or so in UK. In winter maybe that is 5C or lower? that 15C or so difference will mean more time needed of course.
say the water is around 20C, I found it only took around 9 minutes of continuous heat with the Ariston to get to the thermostat cut-off, so I reckon that is pretty good.
I found if I heated the water and didn't use it, the heater would come on again around 5 hours later for just a few minutes, so again, I think that is pretty good and shows good insulation on the Ariston. I didn't record any heat info, just used VRM to see the power trend to see when the heater was on and off.

Why didn't I use a Calorifier?
Well, those tend to be mainly used for other heat sources (engine coolant typically) as far as I could see. They are also a lot more expensive than the Ariston 'instant' heater and from my brief looking at them seem to have no insulation?
The Ariston was a good price for this and if it turned out not to be very good for the purpose, not as much money wasted.

Now ideally, if I could change the 2kW AC element in the Ariston to a lower wattage (maybe 800W) and DC rather than AC, that would have been good as it removes the Inverter out the picture, or at least if AC allows a smaller one.
If you have the infrastructure already in place, then not too much of a problem, which is why I didn't search for different option for elements. But a 2kW element could limit the use when on hookup at a limited power site if you wanted to use mains.
The timer thing I like as I feel it is less intense on the batteries, but I am not sure if it is really needed TBH. It was my way to replicate a smaller element. One possible downside is how well the inverter likes to go from no load to 2kW load and back every few minutes? some may not approve!

Interestingly (to me, anyway ), as I now have a Motorhome which is fitted with a Truma Ultrastore, I repeated the same test with that heater (but as installed - no timer). The Ultrastore is a Gas Heater, but is also fitted with a 850W AC Element. I found the heat pattern very similar to the Ariston, except being lower power, took longer to heat water. There is a post on this here - https://motorhomebuilder.com/threads/not-a-self-build-but-a-tweaker.67074/page-2#post-874750.

I have not heard of Grafana? Victron Product?


In summary anyway, I think the water heater experiment has worked very well in fact. I have actually just bought an external hot&cold water point and shower to install as while I don't have an internal shower in the camper, I do have a perfectly good hot water supply to run an external shower within something like a shower tent.

 

[Sprinter 1 cup]

As you now are fully electric can I say . Thank you for the fridge and the hob information and I'm going all electric in my van build.
So, looking above posts you have 400 watts at what amps in summer? Please .
This thread is only for hot water, so my van should charge up fully by 1pm if all hab is electric fridge heating lights TV breakfast cooking.

 

[wildebus]

As you now are fully electric can I say . Thank you for the fridge and the hob information and I'm going all electric in my van build.
So, looking above posts you have 400 watts at what amps in summer? Please .
This thread is only for hot water, so my van should charge up fully by 1pm if all hab is electric fridge heating lights TV breakfast cooking.

Not sure if I have fully updated the spec of my Camper, so this is little Summary:

Batteries - 645Ah of Lead Carbon, which with those batteries means around 400Ah usable easily
Solar - now 460W of Solar Panel (4 x 100 + 2 x 30).
Electric Cooking, Electric Water.
I have used a small oil rad occasionally and remarkably I can run that off the batteries a good length of time if need be. I have used it as a way to drop the Battery SOC when doing various testing and it takes quite a long time! But Electric Heating when it is proper cold? nah!