12 volt water heating ?

Thanks for that-- seems to add up ; I had v. roughly worked out , for the wife (who has done physics , at least to o level-- astonishingly , my grammar school in the early 60`s channelled biologists into german , no french , and no physics even o level) , that a year of solar into our cylinder could approximate a day of immerser , from your earlier figures ; we never use either immerser , of course . J
 
Wow, what did I start here - from August 2006 till now and still rearing its head !!

I shall think more carefully before asking questions in the future

/forums/images/graemlins/laugh.gif
 
Yes you can!

And it's easy too.

I've got a 1980 Morgan 46, 10cu ft fridge dropped to 8cu ft with extra insulation and then installed a WONDERFUL seafrost fridge system with a freezer box. the amphr consumption on this system is tiny. We liveaboard in the caribbean with 5 people on board (3 sons) - meaning the fridge gets opened and loaded with new stuff often, and we still calculate only 50-60 amp hrs per day.

On the arch/davits on the stern I have 3 - 135w kyoceras charging the 6 - 12v trojans via 2 different charge controller (and this is important, the charge controllers have a direct supply line for loads you want to run only via solar and never to draw from the batteries. Most mornings my batteries are full by 9am, covering the fridge, fans, lights (all LED lights now), tv and laptop charging.

Once the batteries have filled from the previous nights use, we start the water maker, also run from the batteries via inverter.

After all this is done, we still have 1/2 the day with the solar panels doing nothing!

So, got a 200w 12v heater element. simply screw out the 110v element that is worthless as we're NEVER on shore power, and haven't run the generator in 2 years, then screw in the 12v element and connect the supply wiring (using the existing thermostat to the supply feed on one of the charge controllers). i also put a simple toggle switch in line so it doesn't come on until all other loads are satisfied.

This runs the water heater (yes, slowly, and never scalding hot but nice and warm for the morning shower!) while still leaving one panel via it's own charge controller keeping the batteries topped up.

Why can i make it work when others say not?

1. Efficiency! Start with your refrigeration !INSULATE! and get one of the super efficient 12v danfoss systems!

2. Efficiency! Brushless dc fans are the only ones permitted.

3. Efficiency! Every light in the boat is LED and my wife loves them! (including nav lights, spreader and arch mounted deck lights, look for the led spotlights made for sportfisher cockpits, great lights and almost no draw)

3. BIGGER is better on your battery bank, not just to last thru a cloudy week but because the lower the draw rate the better batteries perform and the longer they last as they don't cycle deeply. (most mornings we wake up to batteries saying 12.5 - 12.6v).

Yes, it took a few years to get the system as we like it now, but there is still more to go, namely:
- remove the 120amp alternator from the engine and go back to the stock 65 amp.
- remove the old shore power battery chargers
- get rid of the generator
 
DrBruce said:
And it's easy too.

I've got a 1980 Morgan 46, 10cu ft fridge dropped to 8cu ft with extra insulation and then installed a WONDERFUL seafrost fridge system with a freezer box. the amphr consumption on this system is tiny. We liveaboard in the caribbean with 5 people on board (3 sons) - meaning the fridge gets opened and loaded with new stuff often, and we still calculate only 50-60 amp hrs per day.

On the arch/davits on the stern I have 3 - 135w kyoceras charging the 6 - 12v trojans via 2 different charge controller (and this is important, the charge controllers have a direct supply line for loads you want to run only via solar and never to draw from the batteries. Most mornings my batteries are full by 9am, covering the fridge, fans, lights (all LED lights now), tv and laptop charging.

Once the batteries have filled from the previous nights use, we start the water maker, also run from the batteries via inverter.

After all this is done, we still have 1/2 the day with the solar panels doing nothing!

So, got a 200w 12v heater element. simply screw out the 110v element that is worthless as we're NEVER on shore power, and haven't run the generator in 2 years, then screw in the 12v element and connect the supply wiring (using the existing thermostat to the supply feed on one of the charge controllers). i also put a simple toggle switch in line so it doesn't come on until all other loads are satisfied.

This runs the water heater (yes, slowly, and never scalding hot but nice and warm for the morning shower!) while still leaving one panel via it's own charge controller keeping the batteries topped up.

Why can i make it work when others say not?

1. Efficiency! Start with your refrigeration !INSULATE! and get one of the super efficient 12v danfoss systems!

2. Efficiency! Brushless dc fans are the only ones permitted.

3. Efficiency! Every light in the boat is LED and my wife loves them! (including nav lights, spreader and arch mounted deck lights, look for the led spotlights made for sportfisher cockpits, great lights and almost no draw)

3. BIGGER is better on your battery bank, not just to last thru a cloudy week but because the lower the draw rate the better batteries perform and the longer they last as they don't cycle deeply. (most mornings we wake up to batteries saying 12.5 - 12.6v).

Yes, it took a few years to get the system as we like it now, but there is still more to go, namely:
- remove the 120amp alternator from the engine and go back to the stock 65 amp.
- remove the old shore power battery chargers
- get rid of the generator
Click to expand...



Thanks for the reply. Even though its a bit late :)

Just to make sure I get this right -the solar panel goes to the controller and then to the 12v immersion -yes?

Do you use the battery terminals on the controller or the load output terminals?

So you could do this with the wind generator as well (via the controller)
 
Clarification

the solar charge controllers joins the panels to the batteries, doing their usual job of limiting voltage and preventing night drainage back to the panels, but also have a direct power take off which you can use to supply 12v DC loads which you want to run ONLY when the panels are working.

I have friends with smaller RO watermakers which they hook directly to the charge controllers like this and they leave the 1-2 gph watermaker running all day.

I toyed with the idea of running my larger watermaker like this but the start up draw was too great for the pump, so run it from the batteries. I am still planning a timer system so it comes on each day for 2 hours without me needing to remember to flip the switch.

Originally I had planned to build a solar water heater receiver mounted on the arch along with the PV panels, and then use a small 12v pump to recirculate the fluid to our water heater tank by bypassing the engine/hot water exchanger system, and for that the direct draw from the charge controller would have been perfect too. If I didn't have such excess electric production, I still would have gone this route to get hot water, because for the last 2 years, running the engine to make hot water was the only reason we ran the motor other than for propulsion.

One caveat to my other posting, we live in the caribbean, so the water in the hull tanks average 75F to start with, and we've set the thermostat on the heater to shut off at only 100F, so we really didn't need much heating effect, certainly as compared to some of you chilly weather boaters!

If we end up cruising into colder climes, I'll go back to my idea of a solar receiver.
 
wizard said:
Thanks for the theory VicS that will make the calculations easier.

I was thinking of getting a 12v element from somewhere (yet to be found) and plumb it into the existing calorifier which is already insulated.

There used to be a heater element for cars years ago to put into the bottom hose leading to the radiator to both stop the water freezing and to warm up the water to make the engine start in the depths of winter. Some worked off the battery and some with mains transformers - but with modern cars all this sort of thing has become redundant.

Still I shall keep looking...
Click to expand...

Just e bay it-plenty available-in a renewable home system often forgotten that a very good spare energy store is the hot water cylinder-so when you are producing spare energy and batteries are full you dump it into the calorifyer via the 12v immersion-my calorifier has a standard size immersion heater plug blank.
 
Not a single post in favour of the concept. However, if you size your PV large enough for all normal needs when sailing, (fridge, freezer, lights, radios, autopilot etc) and are then sat at anchor, there may well be a large surplus that needs to be used. For example, I am considering 500w of panels. Using an additional inverter specifically to heat the water in the calorifier may well be a useful means of absorbing additional power.
 
Talbot said:
Not a single post in favour of the concept. However, if you size your PV large enough for all normal needs when sailing, (fridge, freezer, lights, radios, autopilot etc) and are then sat at anchor, there may well be a large surplus that needs to be used. For example, I am considering 500w of panels. Using an additional inverter specifically to heat the water in the calorifier may well be a useful means of absorbing additional power.
Click to expand...



Actually, this the conclusion I came to as well. I often boost the hot water (via inverter) when the atteries are full to save the engine being run- only enough for 15/20 mins, but it does make a diffetence.
 
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Andrew_Fanner said:
Water has a specific heat of 4.2kJ/kg/K. To get 100cc of water to boil for 20deg is
4200 x 80 x 0.1 = 33.6kJ. In 1 second this would require 33.6kW (!), in 10 seconds 3.36kW (big domestic kettle) and in ten minutes 33600/600 = 56W. At 12V this would be 4.67A.
Click to expand...

A normal mug is 250 ml so taking Andrews maths as correct, which I'm sure it is, the 5 amp output of your solar panels would take 25 mins to boil the water for a cup of tea.

A typical calorifier is 25 litres and the normal temp you would run one up to is 60 C which would require 5 1/2 hours at your 5 amps or so. So yes it is feasible - in theory
 
solar herating / ohms

5 amp actual solar panel output at solar panel voltage of 18 volts according to Ohms is


5 amps at 18 volts = 90 watts (for heating)

10 amps at 18 volts = 180 watts



It might take a while!

Also consider running an inverter to power a 1000 watt heater in a tank requires from a 12.4 volt battery bank a battery killing
80.6 AMPS



2 car headlamps ( 100 watts ) for example require at 12.4 volts 8.06 AMPS

and we know how long the battery will last with the engine off and the headlamps on!


So it might be back to a 200 watt heater running at 12.4 volts using around 16 amps and using the heater only when enough amps are

available.

But

500 Watts from huge solar panels at 18 volts would give 27.7 amps so this would heat a custom immersion heater !!!


Now reverting to the 200 watt 12 volt immersion heater....


With the 200 Watt 12 volt heater running at 12.4 volts using 16 amps now
now converting to Joules

shows that with a 20 L tank
raising the temperature from 10 C to 25 C

requires 1 200 000 joules

so dividing by 200 watts means that it takes 6000 seconds

which is 100 minutes to heat the tank
 
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