Water Heater - Pure Sine Wave VS Modified Sine Wave Inverters

CamperJack

CamperJack

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I'd like to be able to run this little water heater for occasional use. I've done the sums and reckon my batteries can handle it. It's rated at 1.5kw and takes about 15 minutes to heat up. Would I need a pure sine wave inverter or would a modified sine wave be sufficient? I don't plan on charging my laptop via the inverter (I've got a 12v charger for that) so don't need pure sine for that reason.

Can you recommend a specific inverter for this purpose? ⚡?

<Broken link removed>
 
A modified sine wave will be fine as long as the heater has no complex electronics. Although I agree with Stealaway - it's never wise to run anything off batteries that can operate on gas. 15 minutes use will take more than 25Ah from your battery needing at least 28Ah to replace it.
 
Thanks for the replies, both.

Stealaway said:
How big are your batteries? 1500w will pull 150amps from them while ever it's connected. Not an option in MHO
Click to expand...

The batteries are 220 ah.

The figure you give would be true if it was being run for an hour. As it is running for 15 minutes its 31.25ah.

1500w / 12v = 125ah. 125ah / 4 = 31.25 ah.
Plus inverter losses of say, 20%, is 37.25 ah.

If I used it in the morning I'd then have all day for the 300W solar panels or battery to battery charger to top the batteries back up.


tonyidle said:
A modified sine wave will be fine as long as the heater has no complex electronics. Although I agree with Stealaway - it's never wise to run anything off batteries that can operate on gas. 15 minutes use will take more than 25Ah from your battery needing at least 28Ah to replace it.
Click to expand...

I'd prefer not to have gas in the van. I only plan on having one gas item, the hob. How do you know what constitutes complex electronics and what has it?

Is there a particular brand of inverter to look out for? There seems a lot of impossibly cheap ones out there on eBay which can't be any good.
 
The problem is the peak draw not the energy total. Lead batteries have a peukert effect. They are 220ah at 20h rate, when you draw 125a, that’s 1,7h rate, the capacity will be more like 170-180ah. The voltage will collapse so much that inverter could shut down.
Also the efficiency at best is 75-80%, that is due to voltage sag and inverter conversion efficiency. The inverter will eat something like 1150w to deliver 1000w. This can work with Li batts. Or, chose a lower power heater. I know propex do a 10l electric only boiler that runs on a 750w element. I got this element in the propex Malaga that is a dual fuel electric/ gas. I run it of a 400ah Li bank and on a victron inverter without solar contribution, it’s stil border line. I get voltage sag, and it draws something like 820-850w for a 750w supply. In combination with solar, (590w) is not that bad.

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CamperJack said:
Thanks for the replies, both.



The batteries are 220 ah.

The figure you give would be true if it was being run for an hour. As it is running for 15 minutes its 31.25ah.

1500w / 12v = 125ah. 125ah / 4 = 31.25 ah.
Plus inverter losses of say, 20%, is 37.25 ah.

If I used it in the morning I'd then have all day for the 300W solar panels or battery to battery charger to top the batteries back up.




I'd prefer not to have gas in the van. I only plan on having one gas item, the hob. How do you know what constitutes complex electronics and what has it?

Is there a particular brand of inverter to look out for? There seems a lot of impossibly cheap ones out there on eBay which can't be any good.
Click to expand...
Complex electronics: in the case of a water heater maybe programmable or with an electronic timer - unlikely from your description of yours. As far as a 'good' inverter goes ask on here (like you just did) - someone will be running what you're after. 300W panels would only ever output anything like 300W at the Equator on a cloudless sky at lunchtime. In this country, mounted flat, you might see 150W on a good day. A cloudy sky will see that down to 50W. You already have gas for the hob: what do you intend to use for heating & the fridge? A gas supply is effectively limitless and cheap - what's not to like? I have 330W solar but it may as well not be there on a grey, wet, autumn, or spring day - just the time when heat & a cuppa is needed :smiley: .
 
You mentioned in another post about having a 12v fridge, is that's coming of the same batteries?

When we did our sprinter conversion we'd looked at going no gas, using a alcohol hob and with all the solar running the 240v fridge and everything else. But then when you start looking at heating and water heating the only viable source really was gas. And in reality if you've got to have it on board for the cooking hob may as well use it for other things. How much hot water do you need, are you going to shower regularly in the van or use sites? We only have our water heater on when we are going to shower otherwise it's just the kettle on the gas hob for strip wash, washing up etc.
Of course it's all about personal preference and choice as to what is important to you, so no right or wrong. Some self builders don't see the need for having a loo but for us it was a big yes and the van design was arranged around that as was having a full size mattress ready made all the time.

We ended up with a instant gas water heating system using a normal household boiler, I think 11ltrs but still would only use it for shower as it only had about 40cm of pipe between boiler and hot tap, so no wasting water to run hot.

Shawn
 
Referencing tonyidle comment re solar.

We have 420w of solar flat on the roof. We spent last May-september in mainland Europe and even in the middle of the summer the most that was recorded was 367w of solar feed.

A lot will depend on where you plan to spend your time.

I love the idea of trying/using something that is not the norm but sometimes you just have to look at the evidence from others experinacees.

I wanted to have a wind turbine, all the research showed that it was not really a viable option on the van but I still wanted to give it a go, does it work, yes but another couple of solar panels on the roof would have given me more energy.
 
As Raul says with a heavy current use the normal Ah rules don't apply. It is possible, especially if you are going to use this in the morning that the batteries could be down to 50% afterwards, adding in the loads from the evening before and anything overnight.

Depending on what type of batteries you have they may only last a couple of hundred cycles down to 50% discharge possibly even less.

Could be expensive on batteries. ?
 
Straight away I can see one problem you've not thought of. Both the water in and out are at the top, so how do you drain it down in winter and get all the water out of the heater. The whole idea sounds like a non-starter to me. Frankly if you must avoid gas, and it seems illogical to try to do so, then it would be much easier to simply use a low wattage electric kettle. A 6 litre tank is very little, and once you draw even a litre of water off it, the rest will be that much colder, or you will be using more of your battery to keep it topped up.

Also consider that pulling nearly 20 amps out of each leisure battery will have a considerable effect on their lifespan.

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Unless you have at least a 500 a/h battery bank your batteries will be shot in no time. Batteries do not like sustained high loads for more than a very short time. For long life it is best to limit high current draw to 30-40 amps per 100a/h battery. Allowing for inverter inefficiency you will be drawing around 80 amps per battery the batteries will have a very short life.
 
thebriars said:
Straight away I can see one problem you've not thought of. Both the water in and out are at the top, so how do you drain it down in winter and get all the water out of the heater. The whole idea sounds like a non-starter to me. Frankly if you must avoid gas, and it seems illogical to try to do so, then it would be much easier to simply use a low wattage electric kettle. A 6 litre tank is very little, and once you draw even a litre of water off it, the rest will be that much colder, or you will be using more of your battery to keep it topped up.

Also consider that pulling nearly 20 amps out of each leisure battery will have a considerable effect on their lifespan.
Click to expand...
OP says they gonna have gas for cooking, not sure why you wouldn't extend it for water and heating?
 
I made a mini solar siphon a few weeks ago, worked well and got 10L of water up to 45°c in march. Being a siphon it would be difficult to incorporate it into a van, but fit a little pump and you can fit one anywhere ?

20200327_131932.jpg


It's simply a copper sheet with ⅜ copper pipes soft soldered onto it which are brazed into ⅝ copper headers. All sprayed black with polystyrene insulation behind and a perspex sheet in front. Bit of a faff to make but better that than buying severel batteries a year ??

en.m.wikipedia.org

Thermosiphon - Wikipedia

en.m.wikipedia.org en.m.wikipedia.org
 
Richard and Ann said:
I made a mini solar siphon a few weeks ago, worked well and got 10L of water up to 45°c in march. Being a siphon it would be difficult to incorporate it into a van, but fit a little pump and you can fit one anywhere ?

View attachment 384799

It's simply a copper sheet with ⅜ copper pipes soft soldered onto it which are brazed into ⅝ copper headers. All sprayed black with polystyrene insulation behind and a perspex sheet in front. Bit of a faff to make but better that than buying severel batteries a year ??

en.m.wikipedia.org

Thermosiphon - Wikipedia

en.m.wikipedia.org en.m.wikipedia.org
Click to expand...
Still trying to work out what to give that post a "like" a"Funny" or a "i". :LOL:
 
PV solar panels get hot ? just thinking ??

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Another hand up here for suggesting you don't run this load on batteries. You will regret it real fast. But instead of just banging on about that let's see if we can find another workaround.

I installed refillable LPG tank. Cheap as chips LPG (once the initial install is paid for). I wouldn't mind telling more if you are interested.

But for hot water. How about a Webasto Thermotop instead? It's a Diesel water heater. It still takes a little while to heat up but you can run the hot water on Diesel instead of gas or electricity. These often come up second hand on eBay and the like but be very careful not to buy a vehicle branded one as they use special wiring looms to integrate with that particular vehicle's electronics.
 
That's a lot of replies. Thanks a lot!

After reading peoples doubts I have re-watched a few videos online (where I got the idea) and have noticed that these people have bigger electrical systems than I remembered. The 220 ah batteries and 300w solar figures I gave are what will be installed initially. There is room on the roof, should I want to in the future, to install another big 300W panel. Same for batteries. I could always add more later. But I'm trying to spread the cost during the initial build. This game isn't cheap!

Perhaps the heater isn't such a good idea with the initial electrical system I will have.

As a work around I will spend some time and look into some of the other options given here.

Gas is not an option and I will not change my mind on this. Understand it or not that is a fact. I'm sorry if it seem totally illogical, and perhaps it is, but I will not be comfortable in the van with gas (with its open flame and all the risks that go with it). I want to go away in the van to relax. Not lay awake all night, waiting for a bang or suffocation. It doesn't bother me for cooking. Turn the gas bottle on, cook a meal, turn the gas bottle off and shut it away in its vented gas locker. Not leave it open all night running the heat. Logical or not I will lay awake all night if I have it in the van worrying about it. Therefore it's not going in.

vantastic said:
But for hot water. How about a Webasto Thermotop instead? It's a Diesel water heater.
Click to expand...

I like this idea a lot because I plan on heating in the van with a diesel heater, eliminating the requirement for gas. If I could tap into this extra diesel tank to run the hot water that would be fantastic! This seems like the best option to me because it's not gas, uses something I'll have anyway and doesn't require the sun.

Raul said:
Or, chose a lower power heater. I know propex do a 10l electric only boiler that runs on a 750w element.
Click to expand...

I will have a look and see if I can find something with a lower watt rating, starting with propex.
 
CamperJack said:
Logical or not I will lay awake all night if I have it in the van worrying about it.
Click to expand...
Therapy might be an option :giggle: . There are many, many, things that worry motorhomers. LPG is on the list but most definitely not at the top.

More seriously if you don't intend to use gas the alternative is Diesel rather than electricity.
 
CamperJack said:
Gas is not an option and I will not change my mind on this. Understand it or not that is a fact. I'm sorry if it seem totally illogical, and perhaps it is, but I will not be comfortable in the van with gas (with its open flame and all the risks that go with it).
Click to expand...
Totally illogical, something like 95% or more of all motorhomes on the road use gas for heating & water.
Gas heaters & water heaters are balanced flue, no exposed flames & do not use the oxygen in the van.
Modern vans have anti rupture hoses combined with gas regulators that have crash sensors so the gas system can be left on even while driving.

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best use gas for heating, cooking . lights and heating water .very cheap to buy and run.
have 6 x 80wt panels on the roof and about 500amp of batteries but if not in spain or morocco etc in winter its not really enough.
i do power a 240v fridge and use some 12v for telly computers etc
gas is available all over the place , sun isnt. specially on shorter winter days .
 
You need to buy an 800W 240V Propex 10L water heater.
£175 on ebay.
 
Digital settable easy read display so you can set and see the water temp.
 
*Machzoneman* said:
https://rover.ebay.com/rover/1/710-...0001&campid=5338547443&icep_item=302946802761

10L version not the 6L version
designed for leisure vehicles & easy to fit.
Click to expand...

I've found a propex 6L version for £167. Why do you say 10L not 6L?

I do wonder how long it will take to heat up. Remember that I'm unlikely to have it set to 75°C unless I want to burn myself!

Risking everyone above hitting their heads repetitively on a wall, this being roughly half the wattage how do we think the batteries will stand up against this? Be that 200 ah or possibly adding some more batteries to minimise impact on the draw on them.

Having less joy searching for a diesel water heater.

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CamperJack said:
That's a lot of replies. Thanks a lot!

After reading peoples doubts I have re-watched a few videos online (where I got the idea) and have noticed that these people have bigger electrical systems than I remembered. The 220 ah batteries and 300w solar figures I gave are what will be installed initially. There is room on the roof, should I want to in the future, to install another big 300W panel. Same for batteries. I could always add more later. But I'm trying to spread the cost during the initial build. This game isn't cheap!

Perhaps the heater isn't such a good idea with the initial electrical system I will have.

As a work around I will spend some time and look into some of the other options given here.

Gas is not an option and I will not change my mind on this. Understand it or not that is a fact. I'm sorry if it seem totally illogical, and perhaps it is, but I will not be comfortable in the van with gas (with its open flame and all the risks that go with it). I want to go away in the van to relax. Not lay awake all night, waiting for a bang or suffocation. It doesn't bother me for cooking. Turn the gas bottle on, cook a meal, turn the gas bottle off and shut it away in its vented gas locker. Not leave it open all night running the heat. Logical or not I will lay awake all night if I have it in the van worrying about it. Therefore it's not going in.



I like this idea a lot because I plan on heating in the van with a diesel heater, eliminating the requirement for gas. If I could tap into this extra diesel tank to run the hot water that would be fantastic! This seems like the best option to me because it's not gas, uses something I'll have anyway and doesn't require the sun.



I will have a look and see if I can find something with a lower watt rating, starting with propex.
Click to expand...
It is possible to do without gas if it is a concern. Murvi do a van with a diesel hob as well as a diesel heater. The first one they did was for someone who had suffered a bad experience with a boat blowing up.

Ours just has the diesel heater, a Webasto Dualtop. They are complex beasts and not cheap but ours has been fine for the last 7 years. They do use more electricity than a gas heater. If you have plenty of solar and batteries this won't be a problem. ?
 
Turns out there's a calculator for that.

<Broken link removed>

6L water, water start temp 8°C, water target temp 70°C, heating power 0.8kw = 0.54 hours.

800w / 12v = 66.6ah
 
CamperJack said:
I will have a look and see if I can find something with a lower watt rating, starting with propex.
Click to expand...


Won't make very much difference at all, it will use the same amount of battery power, but spread over a bit longer. Still going to chew through your battery.

Yes you thoughts on gas are truly illogical, the most dangerous part of your system is the open gas flame inside the van, which you are quite happy with.

I take it you don't have gas at home for heating or cooking?
 
thebriars said:
Won't make very much difference at all, it will use the same amount of battery power, but spread over a bit longer. Still going to chew through your battery.

Yes you thoughts on gas are truly illogical, the most dangerous part of your system is the open gas flame inside the van, which you are quite happy with.

I take it you don't have gas at home for heating or cooking?
Click to expand...

Illogical or not, I'm not going to change. ;)

Battery power taken will be:
800w / 12a = 66.6ah. For half an hour / 2 = 33.3 ah. Plus 20% inefficiency 39.96 ah.

Say I add an additional battery increasing the bank from from 220 ah to 330 ah.

If I was taking them all the way down to 50% that's 165 ah usable. 165 ah - 40 ah still leaves me with 125 ah to play with.

If I was taking them only to 33% depletion that's 108.9 ah usable. 108.9 - 40 ah and I'd still have 68.9 ah to play with.

And by slowing it down and not hitting the battery with such as massive draw all at once, that will do less damage?

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