How long can I keep hot water hot?

[Boldly]

I have bought a 12 volt 300 watt water heater. It has two separate elements and I intend to connect one to the solar controller to utilise excess solar, and the other connected to the leisure batteries switched on only when driving to use the alternator. I wil only heat 10 or 12 litres at a time but will be heated in afternoon sun or when driving. I will probably not use the water until next morning. Is it possible to keep it warm enough? If so what insulation do I need to use?

 

[Gina M]

How about a large thermos (flask) I use one when I heat water on top of my Multi fuel stove to wash dishes etc. any left over I put in a flask and it is still hot in the morning.

 

[Boldly]

How about a large thermos (flask) I use one when I heat water on top of my Multi fuel stove to wash dishes etc. any left over I put in a flask and it is still hot in the morning.

Biggest I can find is 5 litres. Was hoping for 10 or 12 litres to have a shower in morning.

 

[Gina M]

Biggest I can find is 5 litres. Was hoping for 10 or 12 litres to have a shower in morning.

5 litres is enough for what we used to call a strip wash

 

[Figaro]

Is it possible to keep it warm enough? If so what insulation do I need to use?

Is the water heater you fitted not already insulated ?
Be careful not to overload the alternator, I've no idea what they're capable of running at but 300 watts sounds a big load on to me.

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[chaser]

I have bought a 12 volt 300 watt water heater. It has two separate elements and I intend to connect one to the solar controller to utilise excess solar, and the other connected to the leisure batteries switched on only when driving to use the alternator. I wil only heat 10 or 12 litres at a time but will be heated in afternoon sun or when driving. I will probably not use the water until next morning. Is it possible to keep it warm enough? If so what insulation do I need to use?

Expondo shop

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[Boldly]

Is the water heater you fitted not already insulated ?
Be careful not to overload the alternator, I've no idea what they're capable of running at but 300 watts sounds a big load on to me.

Have not fitted it yet. It is like an immersion heater but has two elements so only approx 150 watts or about 12.5 amps at 12 volts to come from the split charge.

 

[Boldly]

Expondo shop

Top service ✓ Very reliable ✓ No delivery costs ✓ | Buy now your Stainless Steel Thermos Container - 12 L - with drain tap for a low price !

www.expondo.co.uk

Think the shape would make that difficult to incorporate easily but thanks for the link.

 

[Two on Tour]

I installed our 12v 300watt (2x 150watt elements on the same unit) water heater nearly two years ago now and have each of the 150watt elements being fed via the
load output terminals on each of my two Victron 20A MPPT solar controllers.
Initially the MPPT's were setup to switch on the load output to the heating elements when the hab battery reached a set voltage and cut off when the hab battery voltage dropped to a preset voltage.
This worked fine after a bit of adjusting the cut-in cut-out voltages to stop it pulsing on and off the load when it was applied which causes a spiked voltage drop.
This setup allows for manual switching on or off of either of the 150watt elements via the Vicron app or Victron VRM, powering via the hab battery reaching the set voltage by the solar charging or by the B2B charging as well as EHU.
This was all well and good, but after a while, I found it just easier to leave it setup for the full 300watts and manually switch the power on and off via the digital thermostat and a couple of relays to handle the load switching on and off.
It does not take that long for our water to reach 58C and then it takes not a lot out of the hab battery to maintain the temperature via the digital thermostat.

 

[Boldly]

I installed our 12v 300watt (2x 150watt elements on the same unit) water heater nearly two years ago now and have each of the 150watt elements being fed via the
load output terminals on each of my two Victron 20A MPPT solar controllers.
Initially the MPPT's were setup to switch on the load output to the heating elements when the hab battery reached a set voltage and cut off when the hab battery voltage dropped to a preset voltage.
This worked fine after a bit of adjusting the cut-in cut-out voltages to stop it pulsing on and off the load when it was applied which causes a spiked voltage drop.
This setup allows for manual switching on or off of either of the 150watt elements via the Vicron app or Victron VRM, powering via the hab battery reaching the set voltage by the solar charging or by the B2B charging as well as EHU.
This was all well and good, but after a while, I found it just easier to leave it setup for the full 300watts and manually switch the power on and off via the digital thermostat and a couple of relays to handle the load switching on and off.
It does not take that long for our water to reach 58C and then it takes not a lot out of the hab battery to maintain the temperature via the digital thermostat.

Do you have any idea how much it would use to maintain say 45 degrees overnight?

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[Two on Tour]

Do you have any idea how much it would use to maintain say 45 degrees overnight?

Not really, but not a lot in our case as the water tank I used is fairly well insulated and the elements are only powered for a minute or two every now and again to maintain the temperature.
I converted a cheap 240v Chinese 8ltr water heater and it's plumbed into our existing hot water plumbing via a 12v 3-way motorised valve I fitted to use either the solar hot water or the hot water from our Whale water heater.

12v element fitted in place of the 240v element.

 

[Boldly]

Not really, but not a lot in our case as the water tank I used is fairly well insulated and the elements are only powered for a minute or two every now and again to maintain the temperature.
I converted a cheap 240v Chinese 8ltr water heater and it's plumbed into our existing hot water plumbing via a 12v 3-way motorised valve I fitted to use either the solar hot water or the hot water from our Whale water heater.

View attachment 851510

View attachment 851511


12v element fitted in place of the 240v element.

View attachment 851512


View attachment 851513

Looks like polystyrene Insulation. Do you know if the water tank is double skinned and any chance of a link?

 

[Two on Tour]

Looks like polystyrene Insulation. Do you know if the water tank is double skinned and any chance of a link?

Yes, the insulation is polystyrene and works remarkably well, but you could do your own thing. The stainless steel tank is single skinned.
I bought it off of eBay a couple of years ago, so the listing will be long gone, but this is the same sort of thing.
I found converting one of these was ideal because they come fitted with an over-temperature cut off, and a pressure relief/drain down valve, and the fittings are 1/2 bsp, so easy to hook up to John Guest push fittings, and you have a ready-made casing too.

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[Gromett]

I have bought a 12 volt 300 watt water heater. It has two separate elements and I intend to connect one to the solar controller to utilise excess solar, and the other connected to the leisure batteries switched on only when driving to use the alternator. I wil only heat 10 or 12 litres at a time but will be heated in afternoon sun or when driving. I will probably not use the water until next morning. Is it possible to keep it warm enough? If so what insulation do I need to use?

Just a quick point. You do realise that the electric from the alternator is not free. the more you pull out of the alternator the more your engine has to work the more petrol/diesel you use.
It would actually be a LOT more efficient to use a calorifier similar to this one (not recommending this one in particular). But push the engine coolant lines through this to heat your water using waste heat that would just be ejected by the radiator at the front under normal operation and would not increase your fuel usage. Should be able to keep it warm for up to 24 hours if you get a good one.

ATI 45L enamel lined calorifier boat / camper water heater 390 mm dia BL4512 | eBay

The calorifier produces hot water from the mains 220v/110v or engine's cooling system, to feed into the hot water system. It can also be used with wet sourced heating systems. It can also be uséd with wet sourced heating systems.

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[Gromett]

If the calorifier is too much work. Then a direct diesel heater makes more sense in my opinion. Sorry

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[Boldly]

@ grommett Think the routing of the pipes and the cost would make that not such a good thing to retro fit. With regards a diesel heater I may come to you for advice on that. I cannot fathom where I can fit one but I know that I want one. How hot does the exhaust get? How long can that be? Can it be lagged to avoid burning etc.

 

[Two on Tour]

@ grommett Think the routing of the pipes and the cost would make that not such a good thing to retro fit. With regards a diesel heater I may come to you for advice on that. I cannot fathom where I can fit one but I know that I want one. How hot does the exhaust get? How long can that be? Can it be lagged to avoid burning etc.

I lagged my diesel heater exhaust, but I did it to dampen the noise, but it does significantly reduce the heat the exhaust gives off.

 

[tacr2man]

Surejust > Surecal Calorifiers

 

[cyberyacht]

Not really related to your custom installs but I find the water in my Truma Combi cools down surprisingly quickly.

 

[Lenny HB]

Not really related to your custom installs but I find the water in my Truma Combi cools down surprisingly quickly.

Considering they claim it to be well insulated, it's flipping useless. By comparison it looks like the cheap Chinese heater probably has much better insulation.

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[Lenny HB]

I installed our 12v 300watt (2x 150watt elements on the same unit) water heater nearly two years ago now and have each of the 150watt elements being fed via the
load output terminals on each of my two Victron 20A MPPT solar controllers.
Initially the MPPT's were setup to switch on the load output to the heating elements when the hab battery reached a set voltage and cut off when the hab battery voltage dropped to a preset voltage.
This worked fine after a bit of adjusting the cut-in cut-out voltages to stop it pulsing on and off the load when it was applied which causes a spiked voltage drop.
This setup allows for manual switching on or off of either of the 150watt elements via the Vicron app or Victron VRM, powering via the hab battery reaching the set voltage by the solar charging or by the B2B charging as well as EHU.
This was all well and good, but after a while, I found it just easier to leave it setup for the full 300watts and manually switch the power on and off via the digital thermostat and a couple of relays to handle the load switching on and off.
It does not take that long for our water to reach 58C and then it takes not a lot out of the hab battery to maintain the temperature via the digital thermostat.

Paul, if you have a decent Lithium set up and plenty of solar is there much point in using the load outputs on the controllers?

 

[Two on Tour]

Paul, if you have a decent Lithium set up and plenty of solar is there much point in using the load outputs on the controllers?

It's all working okay and means that I have options if I want Lenny, but more than that I can't be bothered to empty the cupboard, remove the panelling at the back of the cupboard to reconfigure the wiring as it's doing the same as if it was wire direct to the hab battery but it's just routing via the MPPT's.

 

[Dazzola]

Have you looked at bobil vans water heater?
I have the dual element electric cylinder so use 12v while driving or good enough weather for a good supply of solar and 240v when plugged in.

Bobil Electric - Water Heater | Bobil Vans

CHEAP AND EASY HOT WATER IN A CAMPERVAN The Bobil Electric heats allows you to heat water electrically (12V, 230V or both), perfect for use in a campervan or marine hot water system. The 800W AC version can be connected to your electric hookup socket (or inverter). The 200W DC version can be...

www.bobilvans.co.uk

 

[TheBig1]

The Alde heating in my van has a heat exchanger loop to the engine coolant. This is very effective to heat the radiators while driving. I am sure with the use of bypass valves and a copper coil in a water tank would create copious amounts of hot water when driving. Basically a DiY Calorifier. The engine produces large amounts of heat that it works hard to dispose of. Very wasteful if you think about it.

Still not convinced that 300w 12v elements could heat much water. Maybe enough to wash up or wash hands with

 

[Boldly]

Have you looked at bobil vans water heater?
I have the dual element electric cylinder so use 12v while driving or good enough weather for a good supply of solar and 240v when plugged in.

Bobil Electric - Water Heater | Bobil Vans

CHEAP AND EASY HOT WATER IN A CAMPERVAN The Bobil Electric heats allows you to heat water electrically (12V, 230V or both), perfect for use in a campervan or marine hot water system. The 800W AC version can be connected to your electric hookup socket (or inverter). The 200W DC version can be...

www.bobilvans.co.uk

Hadn't seen these will look into them

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[Two on Tour]

Still not convinced that 300w 12v elements could heat much water. Maybe enough to wash up or wash hands with

You may not be convinced, but I am as we for the most part have hot water on tap via our 300w 12v elements, enough to do washing up and shower, and during the time that Yvette is drying off after her shower the water is heated and I have my shower.

Your not heating the water from cold all the time as we do not use 8ltrs to do the washing up or to have a shower, so you are only heating the incoming cold water that's replacing what has been used.

 

[Boldly]

The Alde heating in my van has a heat exchanger loop to the engine coolant. This is very effective to heat the radiators while driving. I am sure with the use of bypass valves and a copper coil in a water tank would create copious amounts of hot water when driving. Basically a DiY Calorifier. The engine produces large amounts of heat that it works hard to dispose of. Very wasteful if you think about it.

Still not convinced that 300w 12v elements could heat much water. Maybe enough to wash up or wash hands with

I have a spare battery on charge as we speak. When fully charged possibly tomorrow but probably Thursday or Friday, I intend to hook up heater and test it in the comparative warmth of the house. Before installing in van if successful . I shall report back with my findings.

 

[TheBig1]

If 12v low wattage elements were that effective, why do Truma fit 2 or more 1000w 240v elements?

 

[Two on Tour]

If 12v low wattage elements were that effective, why do Truma fit 2 or more 1000w 240v elements?

Don't really care what Truma fit to be honest.

The Bobilvans water heater is 10ltrs and only uses 200watt at 12v and that appears to be viable by all accounts

Bobil Electric - Water Heater | Bobil Vans

CHEAP AND EASY HOT WATER IN A CAMPERVAN The Bobil Electric heats allows you to heat water electrically (12V, 230V or both), perfect for use in a campervan or marine hot water system. The 800W AC version can be connected to your electric hookup socket (or inverter). The 200W DC version can be...

www.bobilvans.co.uk

We have been using the 12v 300watt water heater that I installed for a couple of years now and it works okay for us, so do I care if you doubt what I saying, not a lot.

 

[Dazzola]

Since fitting lithium I'm fairly confident that the bobil heater will serve us well, it comes with a controller to set voltages when it turns on and off, so heats up while driving or good output from solar, then uses the battery to keep it up to temperature, and lithium will cope fine with that.
The controller is fiddly to set up, and comes with a relay etc but works as it should.

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