Heating water with 12V battery or generator?

[willib]

It seems there is a need to heat water with a battery or

 directly from your generator.

This can be acomplished by using resistance wire

http://www.wiretron.com/nicrdat.html

My proposal is to fill a cavity with resistance wire and

push water through it , thus heating the water .

I've worked out some of the details :

6.3 Feet of #20 gage NiCr Resistance wire   = 4 ohms

this will draw 3 A from a 12V battery..

Now if this wire were to almost fill the cavity and

 you restricted the flow of water it should heat the water

 to any desired temp.

Of course the length can be doubled and put in parallel to increase the heating area while keeping the same current draw..

if you want to heat the water faster , use more current ,ie alter the resistance to fit your need.

[Ungrounded Lightning Rod]

There are inexpensive electric heating elements available for heating water, suitable for being powered from 120, 240, or 12 volts and already designed to be installed in a water tank.  For higher voltages you can combine them in series.  You can also run them (or a combination of them) at a lower voltage then that for which they were designed to achieve a lower power consumption and heating rate.

These have been carefully designed to avoid contaminating the water with toxic metals.

I suggest you look into these before you try to build your own.

Having energized metal in direct contact with water causes the metal to oxidize and/or go into solution very rapidly at the segments currently at a positive voltage relative to the water, and may cause plating or gas generation at the segments currently negative ditto.  Moving water will encourage gas generation and metal solution as the water carries the metal ions away, leaving nothing to plate out at the negative plate but hydrogen ions.  The effect is especially pronounced with DC, since the metal always goes away at the positive regions, which never experience a negative half-cycle to plate some of it back.

So you need to put your resistance wire inside an electrical insulator that nevertheless carries the heat to a suitable moisture barrier, in a design that won't leak, won't fail in a number of ways from thermal cycling, provides reliable electrical connections, and so on.  That's what these elements are.  The commercial ones are mass produced and have received extreme scrutiny for safety and low toxicity, with the costs of the engineering and testing spread over many units.

A failure in such a heating element can start a fire.  So the commercial ones have also been tested (and a number sacrificed quite violently) by the Underwriters' Laboratories - an institution set up by the insurance companies for this purpose.

Doing home-brew wiring that isn't to code and doesn't use UL-approved parts will void your homeowners insurance if you have a fire that starts from a mishap with it.  A home-brew water heating element is MUCH more likely to start a fire than any of the other stuff we discuss here - and other electrical heating devices come in second.  Electrical heating devices are not a good idea for home brew - especially if you have family to protect.

[willib]

You have some good points . the obvious one is to use some sort of over-heat protection.

And i certainly wouldnt attempt this if you dont know what you are doing.

but i know someone who wants to heat a Hot tub with his geny and connecting this device directly to the geny output , with the load wired in star should cut down on electrolysis .??

And i was just thinking of using it to heat shower water, not drinking water by any means..

[ghurd]

I have to believe it's going to be cheaper, easier and more reliable to use a factory made, UL listed device. Don't reinvent the wheel idea.

Direct connection, without batteries or electronics, adds it's own problems.

[willib]

I've googled and googled and cant find a 12v dc device as you say exists??

[ghurd]

Google '12vdc element water-heater'.

An example, without suggesting the supplier...

http://www.almostfreeenergy.com/hotwater.html

G-

[Laylow]

This is the cheapest 12v element that I could find anywhere.  $40 for 600W.  http://hydrogenappliances.com/hotwater.html  

[willib]

Laylow & ghurd , these units are very nice ! and to top it off you can (they say) insert one of these on the bottom of a two element waterheater and thusly saving energy by not using your electric as much.. i Guess what i had in mind was sort of an on demand water heating element ie , when you need hot water you turn on the valve , the valve starts the heating element and automatically adjusts the flow to a specific required temp..But not for drinking, no no !! and it wouldnt be UL listed, yet..

[dinges]

Hi,

Apart from the problem of manufacturing your own heater, ask yourself some questions and do a quick calculation:

P=U*I=12*3=36W (electrical energy input)

Compare this with your 'average' water heater (mine is 2500W...). This should make you suspicious.

Or calculate how long it would take to heat x amount of water:

Q=m*C*(Thi-Tlo)

Suppose we want to heat 50 liters of water (m=50kg), from Tlo=10deg.C to Thi=50deg.C (hot water of 50 degrees I wouldn't call hot). Thermal capacity of water: C=4.2kJ/kgK.

Plug into formula:

Q=50*4200*(50-10)=8.4MJ

(1kWhr=3.6MJ)

(1J=1Ws)

Q=8.4*10^6Ws; you have a heater of 36W; then it would take 8.4*10^6/36 = 233.000 seconds to heat the water; this is almost 65 hours... for only 50liter of water to only 50 degrees C....

My guess: even with the best insulated watervessel, you would lose more heat than you put into it. I.e., your water wouldn't even reach 50 deg.C because of heatleaks greater than 36W. And even if it wouldn't leak; 65 hours is a long time.

In the mean time, your batteries get drained for 65hours at 3A--> 195Ahr. You would need some big batteries, plus a source of energy to do the charging of them.

Another case where 5 minutes of highschool-physics & math give you a reality check.

Back to the drawing board...

Peter,

The Netherlands.

[willib]

Peter

Why heat water just to let it sit there and loose heat.??

i previously wrote

" I Guess what i had in mind was sort of an on demand water heating element ie , when you need hot water you turn on the valve , the valve starts the heating element and automatically adjusts the flow to a specific required temp"

On demand means just that, on demand .

It is obvious that i  would need more power for an on demand heater..BUT the power wouldnt be a constant draw on the battery or generator .

[TomW]

Sir;

He gave you every spec of information you need but you need to think and apply some algebra.

50 liters is about 11 gallons and that would  be a good long shower. The heat loss can be ignored in your application. It would still take the same amount of energy to raise the temperature of 50 liters of water that amount just applied for less time since you won't probably shower with a trickle over 65 hours.

Sorry if you feel you should not have to do any thinking to arrive at an answer. Some of us feel that getting out a spoon and finding just the exact pablum that someone wants is not our job. Some users feel being argumentative and "cute" has more value than logical thought. It doesn't.

The quality of the stuff that passes through this board sure has gone from high quality to the Walmart of discussion boards over the past couple years. An ever growing pool of unappreciative information seekers feeding off a shrinking cadre of folks with the information and expecting that information in a fast food bag from the drive up window customized to their needs and of course FREE.

Just the view from here.

You are welcome. And good day.

T

[TomW]

For the record...

50 liters is more like 13 gallons not 11..

Doesn't alter the point, however.

oops.

T

[Norm]

   Of all the ways to heat water using electricity is the worse especially with a

battery...but if you really want to ...and you

want a hot water on demand with battery power you

could use a carbon arc furnace.

   I have boiled water with a battery operated

carbon arc torch for a cup of instant coffee...

time and power wise leaves a lot to be desired.

    Just some common sense ...it takes about 1100

watts to run a coffee maker and that would be about like what you have in mind....that would be

about 91.66 amps now even if you added an equal

amount of cold water ....that would increase the

flow from a slow tricle to a fast trickle.....

    Newspapers, leaves, scrap wood, branches,

a gasifier, methane gas from compost....all are

more feasible.

                     ( :>) Norm.

[dinges]

Hi Willi,

You're right, I missed the part of 'on-demand'.

But you're free to calculate for your own situation; instead of a batch-process you have a continuous process. Should throw in flow-rate, etc. Shouldn't be too hard to calculate, but I'll leave that up to you.

As TomW says, batch or continous process, it's much alike in this case. If you assume a zero thermal leak (i.e., your water wouldn't cool while in storage, or in this case, in transit from your heater to the shower head), you're already almost there, I think.

When you say 'it's obvious that I need more power for on-demand [...] but it wouldn't be continuous' you've got me puzzled...

So you're saying 12V@3A (36W) isn't enough? Okay, let's make it 360W (30A); it would of course only run 1/10th of the time (6.5 hours in my batch example). Total energy required would still be the same: 6.5hrs*30A=195Ahr... Still need the same size battery.

My figures (50kg; 50deg.C) were only for a quick calculation; I have no idea how much water an 'average' shower uses; I don't know what temperature; or how long (I shower 10 minutes; a friend of mine 2 (!!) minutes); etc.

If you really want to size your system correctly you will need to do these kind of calculations; otherwise the risk is very high that your system is too small (cold water) or too large (=too expensive).

(BTW, I realize that this is a mostly American board, but having grown up with metrics & used them through my entire educational career, if I start using feets and gallons I would make too many errors to get at useful results)

Good luck,

Peter,

The Netherlands.

[ghurd]

It may be a lot easier, cheaper, and more efficient to preheat water with a dump load. Then the 'on demand' part would need to increase the temp a lot less.

Stray thought.

[willib]

I've learned two things from this post

1)heating water takes a lot of energy, 15,821.3J to raise the temp of 1 gal water 1 degree Celsius.

Energy used = mass of a gallon water (3785g/gal) Times the  specific heat water (4.18) times the increase in temp ( 1 degree C ).

3785 * (4.18) * 1 = 15821.3 J

And 438,250.01J to raise the temp of 1 gal water from 50 to 100 degrees Fahrenheit..27.7 degrees C

  I'm not sure what you meant by using a delta T of 40 degrees.because you said that 50 degrees wasnt hot ,50 C= 122F, this tells me you were using fahrenheit but on the other hand 10 degrees fahrenheit is colder than ice..maybe you were mixing temperature scales..anyway i chose a delta T of 27.7 Celsius , 100F-50F = 37.7-10 =27.7 Celsius

My shower flows at 14 cups /min about 0.875gal / min which i've discovered is really low(not number 2)..thats about 3.31 Liters.

power := 1 watt = 1j/sec

thats 0.14583 gal/sec *438,250J/gal = 6391 J/S =6391 Watts

 yay im done !!, can i go now ?!!

2)dont bring up a topic that you dont really feel passionate about

if this was about generators it would have been soooo much more interesting to me..

[Gagster]

Honestly, I think the best way to heat water directly from your generator would be to liquid cool your exhaust manifold with it.  --  Seriously.

[bigtoe]

Hi

I have just joined your site through reading about the above topic. I am looking for a 12v immersion heater to heat water on my boat.

I have read with some worry that people on the site are talking about heating water to about 50'c for use with showers. You should be very aware that water at this temp breeds leginares desiese, when air bourne from showers etc, breathed in this can be leathal. I strongly recommend that any heat obtained should allways have a secondary heat source timed to top the heat to above 60'c to kill the bacteria.

[Rangdrol]

Greetings from the edge of the world.

What was that about muffler?

THAT sounds right from here. Any good numbers on the heat my generator dumps?

Seems like - just from casual observation - thats a more efficiant way to heat water with a generator. Now if ic could also quiet it some.....