Anyone tried one of these or know if they're any good?

Have not tried one and never would.

Think about it. Electricity is the most energy inefficient way of heating water.

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cisco said..

Have not tried one and never would.

Think about it. Electricity is the most energy inefficient way of heating water.

Right on Cisco,
Havent done the sums, but really don't need to - the idea of heating 10 litres of water @ 12 V is stupid.
regards,
Allan

Yes it does seem inefficient I know but the power is free from the panels which helps and in no hurry to heat it. Apparently it takes about a minute per degree to reheat. With only an outboard, can't heat water using the engine and solar bags work ok. I must have spent at least half the cost of one of these units on black plastic bags! In summer we generally just use the deck shower and boil the kettle for dishes but thinking of something more permanent for winter?? Boat has a cold shower at the moment. Trying to avoid gas heating as most instant systems are now non compliant in marinas. Could possibly have an external gas heated tank I guess.

what other systems are being used out there On boats with outboards. I've never had a permanent hot water system before?

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Datawiz said..

cisco said..

Have not tried one and never would.

Think about it. Electricity is the most energy inefficient way of heating water.

Right on Cisco,
Havent done the sums, but really don't need to - the idea of heating 10 litres of water @ 12 V is stupid.
regards,
Allan

. I think the element draws about 4-5amps at 240V. Through an inverter when on the hook maybe? We have 240 shore power available while in the pen. Without gas or engine heating, options are limited

Have a look at the camping shower systems they sell at the likes of BCF and Road Tech Marine. Copy the idea or adapt one for your boat.

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Offthegrid said..

Datawiz said..

cisco said..

Have not tried one and never would.

Think about it. Electricity is the most energy inefficient way of heating water.

Right on Cisco,
Havent done the sums, but really don't need to - the idea of heating 10 litres of water @ 12 V is stupid.
regards,
Allan

. I think the element draws about 4-5amps at 240V. Through an inverter when on the hook maybe? We have 240 shore power available while in the pen. Without gas or engine heating, options are limited

Decided I should do the sums - here's the result.

It takes approximately 12 Watt Hours to raise the temperature of 10 litres of water by 1 deg C
Therefore at 12 V it takes 1 Amp Hour to raise 10 litres of water by 1 deg C
So for example, to heat 10 litres from 15 to 65 deg C (ie. raise the temp by 50 deg C) it takes 50 Amp Hours @ 12 Volts.
Not so bad I suppose if this energy is coming from solar, but if supplied by the battery bank and not being simultaneously replaced by solar or wind, it's too much of a drain on the battery bank for me...
regards,
Allan

Yeh it's not too bad and I'd only set it to say 45-50 deg. It's neat, permane the and is 240 as well. Will see what other systems are out there. Panels can cope easily with the draw.

Hello Ofthegrid, I've got an electric hot water similar to the one you pictured. Mine is 5 litre and takes about 40 minutes (@12A) to heat the water. This equates to about 8AH out of your battery. Not so scary. I then have a thermostatic mixing valve to mix the hot and cold water to a nice temperature. This means there is no waste of my 5 litres setting the taps to get the temp right each time I turn it on.

Now just what does 8AH mean. You could top up your batteries with your solar panels or maybe run the engine. My alternator is 120A but realistically puts in about 80 amps at 1200rpm. This means I would need to run the engine for a wooping 6 minutes to replace the power used by the hot Water System. 6 minutes of run time probably wouldn't even be long enough to warm up a heat exchanger type hot water system that runs off the engine.

My engine is raw water cooler. Yes salt water through the block and finding hot water systems that are built to take saltwater through them are pretty rare and expensive. It certainly makes buying a cheap 12Vdc hot water system worth while looking into it.

Thanks Crusoe. Yeh I didn't think the idea was all that stupid either. I've got a few hundred watts of panels to do the job. The tank is not 316 stainless but 304 wrapped in insulation inside the boat so it should last a while. I had a look down the street and they're all gas powered and not as easy to plumb into the boat nicely requiring flus etc.
For a night or two on the hook, Ill crank it up to hot as it will go while I have 240V in the pen, hopefully staying warm and drawing even less power from the batteries. Was thinking of modifying the internal plumbing to fit another 10L tank above. Must get one of those valves too. Cheers

I've ordered one to try and will report back after testing

Sometimes I feel soooo poor reading these forums

Hot water for a shower is aalways coke bottles filled with fresh water left on deck ....than we poke holes in them...hold them up and shower....hey...its not flash....but it works

Something does not add up with the numbers, and numbers are important.

according to ebay the unit draws 25 amps at 12 volts. So available heating power is 25 x 12 or 300 watts.

The specific energy for water is 4.2 kJ/kg degC.

So energy to heat 10 litres, by say 40 degrees is calculated as 4.2 x 10x 40= 1680 kJ.

So we need the heater running for 1680/0.3 = 5600seconds = 93 minutes.

Ie you will be drawing around 40 amp hours from the batteries, which is a fair bit, and this assumes that the unit is 100 % efficient.

I see you have purchased, so good luck, hope I am wrong.

Can only know by trying. Showers will be every 4 days on longer trips, baby wipes in between to save water but with 300Ahr stored and panels pumping in 10A or more I hope it works Ok. Will try it through an inverter as well. Will only heat it to 45-50 max on batteries so around a 30-35 deg rise in winter which is a bit easier on the cells.
Solar bags gotta be better for you than coke! And cheaper!

thats a bit bit rough on the baby !!!

For efficiency, it's hard to beat hot water systems that use waste heat from your engine's cooling system, like these systems:

www.volvopenta.com/brand/en-en/home.html

Assumes of course that you run your engines some of the time

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Offthegrid said..
Thanks Crusoe. Yeh I didn't think the idea was all that stupid either. I've got a few hundred watts of panels to do the job. The tank is not 316 stainless but 304 wrapped in insulation inside the boat so it should last a while. I had a look down the street and they're all gas powered and not as easy to plumb into the boat nicely requiring flus etc.
For a night or two on the hook, Ill crank it up to hot as it will go while I have 240V in the pen, hopefully staying warm and drawing even less power from the batteries. Was thinking of modifying the internal plumbing to fit another 10L tank above. Must get one of those valves too. Cheers

Hello Offthegrid,
Please understand that I certainly did not mean that your idea was stupid.
What I meant was that the claims on the uses for this device was stupid.
Maybe I should have said "misleading" instead of stupid.
Reading the blurb, I was imagining somebody believing it, spending good money and then consistently ending up with flat batteries.

I get very p****d off with manufacturers and marketers who make outrageous claims about rubbishy products.

For example, the universal solar charger I bought which had a black plastic enclosure that buckled and split apart because I left it in the sun for 2 hours. Damn! I should have known not to leave a solar charger in the sun....

Or the countdown timer I bought that blanked the display after 30 secs to "conserve the batteries". This 'feature' was in the instructions which I hadn't read. Stupid me had thought I'd be able to watch the display count down!

Regards,
Allan

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LMY said..
Something does not add up with the numbers, and numbers are important.

according to ebay the unit draws 25 amps at 12 volts. So available heating power is 25 x 12 or 300 watts.

The specific energy for water is 4.2 kJ/kg degC.

So energy to heat 10 litres, by say 40 degrees is calculated as 4.2 x 10x 40= 1680 kJ.

So we need the heater running for 1680/0.3 = 5600seconds = 93 minutes.

Ie you will be drawing around 40 amp hours from the batteries, which is a fair bit, and this assumes that the unit is 100 % efficient.

I see you have purchased, so good luck, hope I am wrong.

Your numbers certainly aren't wrong LMY - it takes 1AH for each 1 deg C temperature rise.
I also wonder about running cabling at 25A for, say, 1.5 - 2 hours or more. You would want to be sure it was correctly rated for this sort of current.
Also, I wonder how the 240V mode is implemented - dual heating elements, switched mode supply, etc,?
regards,
allan

I installed one of these in Trek and its great.

The only problem is it is very power hungry on 12V. I put a 30 minute timer on it and switched its current through a relay (car headlight relay) to avoid a log run of heavy cable.

So when the missus wants to have a shower she presses the hot water button, waits 30 minutes, then bingo hot water! After 30 minutes the power switches off. I installed this after wrecking a set of good batteries :-)

For washing up the kettle on the stove is quicker.

No worries Allan, each circuit has its own element And a relay to switch between the two. I wonder if if would be better to use the 240V circuit through an inverter. According to the wiring diagram, the 12v element only draws 12A (around 150w heater) and the 240v element draws1.25A (300w heater). So 240 Heats twice as fast drawing not much current.
so would using an inverather be better???

Offthegrid...using the invertor, in any application, think twice.
Invertor to work needs energy too, has to be added to calculation.
sure heat up twice as fast / 300 Watts element / with guarantee 25 Amps plus until
temperature probe enables cut off relay.

I personally using invertor as matter of convenience, charging small device / iPad, phone, laptop / ,
also many died on me, mostly overheating. My current one is from Dickee S shop, smallish wattage
simply, has got build in fan.

yeh, I've got a good inverter with fans etc and they do take power themselves but a 300 w elament at 240v doesn't draw much current? Maybe a couple of amps as per digram. i guess I need to look at inverter efficiency of course but thought the current draw would still be way less than the 25 or even the 12 A on the 12 v circuit? Will try it and see how it goes!

Offthegrid,

there seems to be conflicting information about the current draw, 12 amps on the circuit diagram, but 25 amps is mentioned in the text.

The current draw will not make any difference to the amp hours drawn to heat a given volume of water to a given temperature. The amps drawn will only affect the time. Half the current draw will double the time. If draw is 12 amps, then you have 144 watts, or a bit more heating power than a large, old style light bulb. I cannot see that heating 10 litres of water much.

I would have thought that the heater would not work, but my wife has a " no hot shower, no saiiling holidays " rule, so maybe I am looking for something different.

Good luck, hope the heater does what you need.

I hope so too! Re the current draw, I'm not worried how long it takes but thought the batteries would handle it better through an inverter? I'm thinking the 240v circuit might be better but don't know. in an email they told me a deg a minute which might be optimistic. If the units no good it's not the end of the world. I just spent 1500 bucks on my car and it's still not bloody right. I'll get a gas fired instant system and I'm not telling anyone, just turn off when not needed...having a cold shower before work at 5 am takes the fun out if it!

Offthegrid, the inverter will draw 25A (+ maybe another 20% depending on how efficient the inverter is). The 240Vac will heat your water quicker being a 300w element than the 12V element but with the slower 12V element, there are no inverter losses. As far as heating efficiency goes the 12V element will be more efficient. My 5L version takes about 40min to get hot so maybe your 10L version wll take 80min (using 12V) and about 16AH.

My only problem is I forget to turn it off sometimes an have thought about a timers like Trek did.

The thermostatic mixing vale I installed ensures I get the most out of my heated water.

Ok thanks Everyone for the comments. I will report back Sometime In January.