Instant hot water heater with 48V DC

[Diysolar123]

as others have pointed out instant hot water heaters take a HUGE amount of power...
Each technology is like a tool for a specific problem, solar/batteries are not always the right answer depending on the situation.
If you want instant hot water propane is much easier and cheaper.

 

[davelondon]

Thanks for your input but in this application I would like to use 48v DC. I’m using diesel for most of my heating needs, but when I have solar power going spare I would like to use it to heat the water.

 

[Zwy]

Exactly.

 

[keepsake]

Instant heaters switch 240 volts within the 1/60 of a second waveform. No way to do this with DC.

 

[Abodyofscience]

It's easier to convert furlongs per fortnight into miles per microsecond.

Using 6kw, you can have 120F hot water at the rate of 0.6 GPM.
Our bathtub gives us 6 GPM.

 

[NMNeil]

It's easier to convert furlongs per fortnight into miles per microsecond.

Using 6kw, you can have 120F hot water at the rate of 0.6 GPM.
Our bathtub gives us 6 GPM.

But Americans measure everything in football fields.
And I honestly don't know how big a football field is, and if it's a real football field(pitch) or one of the strange American versions?

 

[Rednecktek]

Also, I'm not considering multiple fuels, so no gas... diesel only.

I don't have the bandwidth on the ship to search YouTube, but I know there is such a beast as an exhaust gas heat exchanger for the chinese diesel heaters that seemed to work pretty well. I think it was a knock-off of the Webasto units. 1 fuel, heat, AND hot water, you'd just need a storage tank.

EDIT: Found the videos I was looking for, looks like he just got a new model in.

Just a thought.

 

[keepsake]

I think of batteries as storage. And diesel stored in a tank is stored energy too. So is hot water in a tank. To expect to 'instantly' put energy into water is a concept not compatible with inverters and conversion from battery energy to water, in real time. Thus I strongly recommend a large tank and use water storage logic the same as in batteries or fuel tanks.

 

[Don B. Cilly]

I have a 3VDC instant water heater. Two batteries for the spark, a can of butane for the flame.
-

 

[schmism]

Problem is with an inverter I'm spending ~$2,000 and 30kg in order to provide AC to a $100 device which is basically a resistor in a tube. No reason at all that it can't be 48V DC!

Yes there are reasons why you cant.

And considering the inverter as single use for JUST the water heater is intentionally disingenuous in terms of the function it adds to the camper build for the other 99% of the time your using the camper.

And like most of these hypothetical discussions of "it should be easy to....." Yep im sure you think that it is, however if it was, the product would exist and it doesnt soooo no there is nothing going to be simple or cheep about the solution.

 

[Hedges]

There are 48V (and 12V) water heater elements. Just not instant hot water.

Input and recommendations on Voltage regulators

Ive been looking online trying to find specs to these elements but there are none, to the public anyway. Ill get with the manufacture tomorrow and get all the details i can and instructions. Hopefully tomorrow ill have more info. then be able to make a best decision on a step down.

diysolarforum.com

Whether DC or AC, resistance heater in storage tank is a good use of surplus PV that would otherwise go unused.
Heat-pump might perform better for some applications, if 20x to 100x the price makes sense.

 

[Rednecktek]

There are also things like the Lavaner diesel powered water heater system. Just as an option.

 

[SolarGarden]

I am thinking about making a heat battery with pipes running through a concrete block that is well insulated. Something like this https://sunamp.com/

But I also have a 120L water tank for extra solar storage...

Edit: Heated with resistance wire run though it, or even better, a few PTC elements. https://www.amazon.co.uk/gp/product/B09QQRJRWV/ref=ox_sc_act_title_1?smid=A2BHI72PCORNE7&psc=1

 

[timselectric]

I believe that a well insulated water tank, is a more efficient way to store heat energy. But if we don't try new things, we don't learn new things.

 

[Abodyofscience]

"it should be easy to....."

The
https://en.wikipedia.org/wiki/Is–ought_problem
strikes again!

Re: insulation - I hooked a clock thru a voltage dropping resistor to the 4500w heating element in my water heater.

With factory insulation the heater came on 5 minutes each 5 hours. With insulation it was 5 minutes each 7 hours.
I think it works out to a 75w continuous loss.

 

[SolarGarden]

I believe that a well insulated water tank, is a more efficient way to store heat energy. But if we don't try new things, we don't learn new things.

That sounds like a challenge.. I will see if I can put a small 1kW one together in the summer (don't have the time at the moment). I acquired some old economy 7 bricks last year that might be useful for it.

 

[ianganderton]

Why not use solar to heat the water? Aren’t the numbers something like

PV = 20% efficient
Solar water heating = 80% efficient

Plenty of simple roof rack mounted pipe water heaters kicking around that prove how something really simple can work

Maybe you could use a rack mounted solar pipe to pre heat the water before your Truma

 

[Hedges]

Why not use solar to heat the water? Aren’t the numbers something like

PV = 20% efficient
Solar water heating = 80% efficient

Plenty of simple roof rack mounted pipe water heaters kicking around that prove how something really simple can work

Maybe you could use a rack mounted solar pipe to pre heat the water before your Truma

PV = $50/m^2
Solar Thermal = $200/m^2 (at least once all plumbing, freeze protection, etc. included)

Or something like that.

Even if the cost ratio isn't so compelling, PV can be used for other things when you don't need another hot shower. Or more accurately, resistance water heating can be used as a dump load when you don't need electricity for anything else.

Perhaps a batch thermal pre-heater make sense. Water tank in a glazed box.
I was tempted by evacuated tube heaters but haven't bought any.


Now that we can buy PV panels for around $0.25/W vs. $5.00/W of yesteryear, things aren't the same anymore.

 

[timselectric]

PV panels are so cheap now. It's more cost effective.

 

[efficientPV]

"I think it works out to a 75w continuous loss." That is very close to what I calculated for my home water tank.

I have a 50L (13 gallon) tank at my camp and that is sufficient for my camp needs even with a dishwasher. Super cheap, $150 shipped, but a lot of heat loss and I had to build it into a compartment. Another point of use tank 6 gallon tank had much less heat loss but cost a lot more. You all have enough excess PV power to heat water, you just don't know it.