Instant hot water heater with 48V DC

[davelondon]

I'd like this (a 6kW instant electric hot water heater), but running on 48V DC... Can't find anything online... Do they exist?

DEM 6 Set Mini instantaneous water heaters of STIEBEL ELTRON

Mini instantaneous water heaters DEM 6 Set of STIEBEL ELTRON ► Product information from the manufacturer, technical data, operating instructions and customer service.

www.stiebel-eltron.co.uk

I can find 48V immersion heater elements, but not instant hot water systems. Perhaps I can just plug a 120V AC unit into 48V DC and it'll work? Would it just have 50% of the output?

 

[time2roll]

Closer to 20%. Consider a 48 volt inverter.

 

[davelondon]

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!

 

[davelondon]

How about I just use this 27kW unit:

DHB-E 27 LCD Set Comfort instantaneous water heaters of STIEBEL ELTRON

Comfort instantaneous water heaters DHB-E 27 LCD Set of STIEBEL ELTRON ► Product information from the manufacturer, technical data, operating instructions and customer service.

www.stiebel-eltron.co.uk

... if it runs at 20% of it's rated power it'll be giving me 5.4kW... But maybe the electronics won't like the different voltage...

 

[Hedges]

"SAFETY: Maintenance-free bare wire heating system, suitable for hard and soft water. Safety system with high pressure switch and electronic temperature monitoring."

Heating devices have safety switches to shut them off. If the switches are rated for AC, then they aren't likely to work for DC. With AC, it may draw an arc but when voltage drops to zero within half a cycle, arc is extinguished. With DC it can just keep pulling a flame and burn the device up.

This has been demonstrated with breakers at somewhat higher voltage than you're talking about, but 48V is close to where I arc weld.
One guy here bought a DC heating element with built-in thermostat. It was rated 48V maximum (so of course with a 48V battery he operated it somewhat higher.) His unit failed. He opened it up and inside was an AC rated thermostat. So AC thermostats do fail on 48V battery.

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

My suggestion is still to heat more slowly and store energy in a hot water tank. You can have the tank hotter and blend with cold water to desired temperature using a tempering valve.

 

[time2roll]

OK so 40% of the voltage gives 40% of the amps so actually 16% of the rated power. Maybe if it had two elements in series you could wire them in parallel. This would further complicate the switching as the amps increase in addition to the DC switching issue noted above.

 

[davelondon]

I wonder if it would be simple to build my own homemade instant hot water heater with four 1,500W 48V heating elements installed in a pipe, with a thermostat?

 

[dr.diesel]

I wonder if it would be simple to build my own homemade instant hot water heater with four 1,500W 48V heating elements installed in a pipe, with a thermostat?

125 amp DC thermostat?

If you find a suitable DC thermostat please link it.

 

[davelondon]

I'm no expert, but I kinda assumed that a thermostat could somehow control a heavy duty contactor?

http://www.rec-bms.com/datasheet/Technical_datasheet_Kilovac.pdf

 

[dr.diesel]

I'm no expert, but I kinda assumed that a thermostat could somehow control a heavy duty contactor?

http://www.rec-bms.com/datasheet/Technical_datasheet_Kilovac.pdf

Still might be an issue trying to release the contactor, even if it works initially the thermostat contacts might wear pretty fast.

The issue is the arc, easy on AC as the wave crosses 0v quickly which kills it, on DC the contact distance is the breaker and the arc continues to arc until enough spacing has been achieved.

I'm not saying it won't work, just keep it in-mind, perhaps others here have tried just that.

 

[Hedges]

Yes, switches rated for a number of amps AC are often rated for "pilot duty" low current DC.
Interrupting current from an inductive coil always causes a higher voltage pulse that arcs, so design in a snubber to absorb that.

Also use a plumbing temperature/pressure relief valve as independent protection.

 

[efficientPV]

Does it really need to be instant? I use an under sink 6 gallon 120V 1500W to heat water at my camp at that voltage. It does have electronic controls to do the switching. 1KWH gets it done, a pretty light daily load.

 

[davelondon]

Yes, my requirement is a 6kW instant hot water heater.

 

[TKB4]

I would also be interested in a similar instant electric water heater setup but it seems powering a standard instant electric water heater via inverter of appropriate size is currently the route I would go.

 

[Ampster]

500 Amp contactors that are controlled by 24 or 12 volts are made by Tyco under the name of kiloVac. They run about $100.

 

[Maast]

If you're handy fabbing an option would be a phase change based system: You use a standard 48v hot water heater element or lengths of resistance wire to heat up a silicon oil bath surrounding a densely packed array of copper pipes filled with 125 degree melting point wax then route a copper loop heat exchanger though it when you want to extract that heat for instantaneous hot water.

The phase change stores a incredible amount of heat in a small space and to heat it up would only take a 800-1000 watt input. A couple additional spring loaded check valves to prevent losing heat to a thermosyphon and you'd be golden.

 

[Capt Bill]

I'd like this (a 6kW instant electric hot water heater), but running on 48V DC... Can't find anything online... Do they exist?

DEM 6 Set Mini instantaneous water heaters of STIEBEL ELTRON

Mini instantaneous water heaters DEM 6 Set of STIEBEL ELTRON ► Product information from the manufacturer, technical data, operating instructions and customer service.

www.stiebel-eltron.co.uk

I can find 48V immersion heater elements, but not instant hot water systems. Perhaps I can just plug a 120V AC unit into 48V DC and it'll work? Would it just have 50% of the output?

I have 3 different models of the German made and/or designed Steibel Hot water Heater with inputs of 30A x 240vac (on basic version with no temp adjust except slow flow to get hotter) , to 2 x 50Amp 240vac ... that dial in temp out you dial in on digital. ... IMO: Great Dependable options that only use your amps watts when running water through em. I think finding 240vac input is likely the only way you could get those to work. One option if you only have easy 120vac output (maybe via good Inverter) ...is to study the Steibel smaller water heater options. My two cents :+) If you live in cold area, as the low temps reduce your input water temp, you needs more amps watts, and the other option for shower temps is to reduce the water flow. Good info a Steibel for data to dial in your needs

 

[davelondon]

Interesting... this Webasto unit is a DC water heater, but only operates at higher voltages (>100V):

Webasto Heating Solutions - High Voltage Heater

Elevate your electric vehicle experience with Webasto's High Voltage Heater (HVH). Choose from 5kW, 7kW, and 10kW options for optimal thermo management and cozy interiors. Enjoy 95%+ efficiency at up to 870V DC.

www.webasto-comfort.com

... could that be useful?

 

[Zwy]

Still might be an issue trying to release the contactor, even if it works initially the thermostat contacts might wear pretty fast.

The issue is the arc, easy on AC as the wave crosses 0v quickly which kills it, on DC the contact distance is the breaker and the arc continues to arc until enough spacing has been achieved.

I'm not saying it won't work, just keep it in-mind, perhaps others here have tried just that.

People forget that back in the old days, vehicles had breaker points in a distributor and used a condenser to enable the circuit to be broken without the arc.

 

[Supervstech]

I am curious what the plans are for a 6KW instant water heater? Do you want a simple hand washing station?
most sink instant water heaters are 9KW... barely able to handle the flow of a sink, or low flow shower.
Water takes a HUGE amount of energy to raise temp. Flowing water needs to be raised inside the tiny tubing route... from 50F to 110F usually...
so...
What are the plans for this heater?