I am still looking for help in this thread - upgrading an immersion heater to 48V... hopefully that won't be so difficult!

 

using an inverter to convert to 240Vac single phase or 230/400 3 phase would simplify the wiring, and widen the choice of heating elements you could use ...

 

OK everyone, thanks for all you help. It seems like this will be too difficult / expensive so I'm cancelling this part of the project.

You're in a room full of nerds who tend towards pessimism. It is not that complicated. 48V heaters exist, as do 36V, 24V, 12V, and many other voltages. Here's a 1,500W 48V heater.

https://www.amazon.com/dp/B08G149YSN/ref=cm_sw_r_cp_apa_glc_fabc_MBWJKAMHNAY4YP372XC2

6 or 7 of those should do the trick, if indeed you actually need 10kW, which I'm pretty sure you don't.

Also, custom heaters are a thing. There are shops who specialize in making these kinds of heaters to your specs; one-offs, no minimum order quantity. Not cheap, but not as bad as one might think.

Why do you think 10kW is required? My home water heater has (2) 1000W elements and provides enough hot water for two showers at once plus the washing machine and dishwasher.

 

10kW is about that needed to heat a sufficient flow of water from 10 deg C to 45 degC for a shower, the 2kW mentioned above heats water overnight

 

Yes, correct... this application was for an instant water heater for a shower, so 10kW was needed. If the application was an immersion heater then a much lower wattage would have been fine. My other thread is asking about exactly that.

 

10kW at 48V is complicated. At that current, connections can blow themselves apart if there's too much resistance. Or they could just heat up and cause a fire... If you go this route, you need someone who's certified for high power applications.

 

10kW at 48V is complicated. At that current, connections can blow themselves apart if there's too much resistance. Or they could just heat up and cause a fire... If you go this route, you need someone who's certified for high power applications.

blow themselves apart is a wee bit dramatic, as long as the conductors are rated and all the joints are tight, 200A is straightforward ( we do this at work all the time ) - the trickiest bit might be the joint from the conductor to the heating element at 200ADC - as this has additional heating from the elements as well as the DC current ( 1 milli-ohm = 40 watts ) . This is why a higher voltage AC approach with lower currents ( 10kW 230Vac = 44A, 0.001 ohm = 2 watts ) is often preferred by the professionals.

 

the other issue for "instantaneous" hot water systems is that the heater must be powered down VERY QUICKLY if the flow stops or reduces drastically, as the water around the heater will boil very fast, then you will get a steam pressure rise - which will only stop when the element melts, shorts, and the local fuse blows - thus you need to have TWO over temp sensors close to the element that can shut of the power via separate control circuits if the flow stops.

 

blow themselves apart is a wee bit dramatic, as long as the conductors are rated and all the joints are tight, 200A is straightforward ( we do this at work all the time ) - the trickiest bit might be the joint from the conductor to the heating element at 200ADC - as this has additional heating from the elements as well as the DC current ( 1 milli-ohm = 40 watts ) . This is why a higher voltage AC approach with lower currents ( 10kW 230Vac = 44A, 0.001 ohm = 2 watts ) is often preferred by the professionals.

400-800A switchboards are bread and butter. Hell, 2-6kA, 480V services happen all the time in medium industry. Takes a lot of very controllable heat to run an injection molding machine or twelve. You can push thousands of amps through a single multi-barrel lug - as long as the equipment, the termination and the wire itself are all listed and sized for the same temperature rating. If either one is too small it will get hot.

I remember something about a code reference restricting the size of any given heating element to not more than something to the tune of 48-ish amps or so. Somewhere towards the front of Chapter 4 for water heating equipment. I don't deal with boilers or water heaters beyond "run a 200A, 480V branch circuit from this gear over to there" so it's not fresh in my memory. I'd look into that.

 

First hear about 48 Volt power grids but 220/380 V verison is rather popular and easy available in Europe (made by Checzhs and Slovenians). Price about 30-60 Eur according to power. If power is 1 kW it is useable exclusively for washing the cofee cups. If 10 Amp - only for hands. If 25 Amp, may begin to dream about dousche but very tiny water. From 6 kW it is brand serious, but most of homes have only 10-16-25 A input, for example, the monthly pay for fuse caliber is nil for 5A, about 100 Eur for 50 Amp - Latvenergo do everything to convince to install a weaker fuses. So, solution is to take the three phase version of device, but surprize - it contains only one heater element for 380 V. So, I have be redo it to full three phases through the diode bridge, thus the 16 A network may produce the 10.5 kW power what is clear enough for good dousche. Yet then all that temperature regulation system is wrong thus I made a triac switcher providing that function as well the leak-sensing if any (originally not installed (!!awful!!). Now it is working already about year and everyone are happy.

 

the other issue for "instantaneous" hot water systems is that the heater must be powered down VERY QUICKLY if the flow stops or reduces drastically

The Chezch system uses thermo-relay. As soon T increases over some 70 or 80 C the heating is closed by relay.

 

Or just use a photovoltaic inverter to obtain

Aaaah, from here You got the 48 Volts! Firstly, the Photovoltaic efficiency is around 20-22% (only!!). Secondly, the solar heat accumulator efficiency is about 50%. Thus. it is very trashy to use photovoltaics for heating the water. But if, then first complication is that if factory makes a wrong device and someone dies, the death is not Your fault. Whilst if You Yourself wound a heater and someone was electrized to the death, Your rest of the life will be spent in the prison. Thus You SHOULD keep on fabricated products with proper warranty, and that means 220 or 380 V versions and nothing else. Ah ya, probably America have something local for 110V. And 48->110V may re-shape any appropriate boost-up type of SMPS.