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Old 01-19-2021, 08:19 PM   #1
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Question 240v Appliance - How to Wire?

It seems as though all of the tankless water heaters capable of providing enough power for a shower run at 240V.

Example: EcoSmart ECO11 240V 11 kw Tankless

As a newbie to residential electrical wiring, could someone give a quick explanation of how the 120V AC output from an inverter could be modified to provide 240V for this particular appliance, while providing 120V for all other appliances?
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Old 01-20-2021, 11:37 AM   #2
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If your inverter is 120vac only, you'd have to use a step up transformer to get 240vac.

But, that water heater is a huge energy hog. You'll need a pretty large dc-ac setup to power it.

I don't know where you're at in your bus build, but if powering 240vac items is on your lists of needs, you'd be better off served buying a 120/240 inverter.
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Old 01-20-2021, 03:38 PM   #3
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I wouldn’t try unless you have one giant AC setup. That’s a good place to go with a fossil fuel.
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Old 01-20-2021, 04:15 PM   #4
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11 kW is more than most RV type generators put out. It is 7.5 kW seems about average
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Old 01-20-2021, 07:38 PM   #5
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Think of it this way. 11kW is 11,000 Watts. At 240 V that's a bit over 45 amps. But you're supplying that 11,000 Watts through an inverter, which gets its input from the batteries. Let's assume that the inverter is 100% efficient at conversion...they're not, but it makes the math easier...so your inverter needs to draw 11,000 Watts from the batteries. Divide 11,000 by 12 V and you're looking at 916 amps current draw. That will require huge cables and even then an 800Ah battery bank won't run that heater for very long...it's gonna be a short shower! Brrrrr!

Like Danjo said...go with propane or diesel.
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Old 01-21-2021, 05:40 PM   #6
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Why do you need such a massive water heater?. In a bus a electric hot water tank makes sense to me. I have a small system and love it. I just took a shower using my wall hung 4.5 gallon 120 volt water heater. I was in a hurry and it is slightly cloudy so I used the Honda eu2200i inverter generator. Sunny days I can use the solar and/or alternator. I turn the water heater off a couple times to let the battery recharge for a few minutes. I only have a 200ah Battery. Ive piled my dirty laundry on top of the water heater fittings and it stays hot longer lol. imagine what you could do with a Honda eu3000i and a slightly larger water heater. It could even be wired for AGS (automatic gen start) because the eu3000i has a starter motor (on the more expensive model). Also with tanked hot water you can divert surplus solar energy to the water heater using the “dump load” feature of a charge controller. Its really a elegant solution I think. You can use fossil fuel or solar. If my engine is running I use my alternator sometimes for hot water along with solar but am careful to not overheat the alternator by idling the engine for long. Also you are adding to your total water storage by having a tanked heater (if you start with it full).
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Old 01-21-2021, 05:45 PM   #7
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I’ll add that for myself “recovery time” of the water heater is not a issue. In a house, with a family, recovery time is important. In a bus if you are going though water so fast that recovery time is important then you are likely to run out of water. If the bus is parked and connected to water and shore power then disregard my posts. I’m referring to dry camping.
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Old 01-24-2021, 11:41 AM   #8
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What about the small, under sink water heaters? They're 120V and you may be able to run a pair in series?

I'm fairly certain that they're only intended to supply "hot enough" water until heated water can reach the sink from a home's water heater. Like on a second floor, but it's always been something that I've wondered.
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Old 01-24-2021, 03:12 PM   #9
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Quote:
Originally Posted by jsweet89 View Post
It seems as though all of the tankless water heaters capable of providing enough power for a shower run at 240V.

Example: EcoSmart ECO11 240V 11 kw Tankless

As a newbie to residential electrical wiring, could someone give a quick explanation of how the 120V AC output from an inverter could be modified to provide 240V for this particular appliance, while providing 120V for all other appliances?
To get 240V in addition to 120V out of an inverter, you need a "split phase" inverter.
ima_eeb5c75_20%.jpeg

These have two hots- L1 and L2 (Red/Black), Neutral (White), and a Ground (Green) connection. When you measure voltage between L1 and N, or L2 and N, you get 120VAC. When you measure voltage between L1 and L2, you get 240VAC.

A split phase inverter setup allows you to use a normal residential load center with single and double-pole breakers. Single-pole breakers are for normal 120V AC runs, like standard 15A/20A outlets. Your 120V runs usually consist of three wires: Hot, Neutral and Ground. Double-pole breakers are for 240V AC runs, normally to heaters, dryers, air compressors, etc. These runs consist of four wires: L1, L2, Neutral and Ground. Many 240V Appliances also use one or both of the 120V lines as 120V, which is why neutral is typically run regardless of whether it is actually used or not.

I believe anyone who meets any of the following criteria should consider wiring for Split Phase, (RV 50A) service:
  • Plans a solar setup with more than 1000W charge/discharge rates
  • Needs more than a few outlets and/or outlets more than 15 feet apart
  • Wants to run any 240V appliance
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