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Old 23-02-2020, 05:44   #1
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Heating water in silence (via inverter)

Hello,

Before posting I found quite a few posts about running water heaters from the inverter and there are a lot of different opinions about this. So I asked electrician in the boat yard (where I am refiting my first boat) can I run my Sigmar SM40 (220V - 800W) water heater from the Victron Phoenix 12/3000w inverter and he said no and that I need to add one more Victron inverter and connect them both. Can someone explain me why 800W heater cannot be run on 3000W inverter? I will have 1050W solar and 1300Ah gel battery bank. As you may understood already I do not have background in electric stuff.

Please do not turn this discussion in "run your engines or generator - it is more efficient" - my goal is to have morning coffee in silent anchorage while waiting for shower to warm up thanks
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Old 23-02-2020, 05:57   #2
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Re: Heating water in silence (via inverter)

Never tried

But for the past 25 years I have run my electric 800w. Tea kettle from my inverter

No problem, makes a great cup of tea
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Old 23-02-2020, 05:59   #3
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Re: Heating water in silence (via inverter)

I think the mathematic formula behind this proposal looks like this:
$$$+$$$$+$$$$$=happy
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Old 23-02-2020, 06:01   #4
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Re: Heating water in silence (via inverter)

Quote:
Originally Posted by Mantas View Post
Hello,

Before posting I found quite a few posts about running water heaters from the inverter and there are a lot of different opinions about this. So I asked electrician in the boat yard (where I am refiting my first boat) can I run my Sigmar SM40 (220V - 800W) water heater from the Victron Phoenix 12/3000w inverter and he said no and that I need to add one more Victron inverter and connect them both. Can someone explain me why 800W heater cannot be run on 3000W inverter? I will have 1050W solar and 1300Ah gel battery bank. As you may understood already I do not have background in electric stuff.

Please do not turn this discussion in "run your engines or generator - it is more efficient" - my goal is to have morning coffee in silent anchorage while waiting for shower to warm up thanks
You should ask the electrician to explain why an 800W load can’t be powered from an 3,000W source.
Spoiler: of-course you can do that
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Old 23-02-2020, 06:16   #5
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Re: Heating water in silence (via inverter)

You can comfortably run your 800w element from the inverter if you control other simultaneous loads.

If you have an issue it will be with PV capacity and your ability to recharge your bank while using your entire PV production to heat water.

If you are comfortable with your ability to maintain and control state of charge while heating water then go for it.

(So nice sunny day when SOC is looking good, PV output heating water and bank remaining at good SOC).
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Old 23-02-2020, 06:18   #6
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Re: Heating water in silence (via inverter)

Our Victron 12/2000 inverter easily powers our 800W water heater. It also has no trouble with our 1500W induction hotplate. Your 12/3000 inverter is rated to deliver 2400W continuously at 25 degrees C ambient temperature.
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Old 23-02-2020, 07:31   #7
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Re: Heating water in silence (via inverter)

It will easily run the heater, every now and again I forget and leave our water heater CB on and when I turn in the inverter, several minutes later I hear it’s fan running, and then realize I was stupid and have been heating water using my battery bank.
I’m also bad about leaving the inverter on, and this year will buy a night light to leave plugged in to remind me it’s on.

It take almost exactly one hour to fully heat water in our heater with the generator, it takes exactly 11.7 amps at 120 VAC to do so.

To do that with a battery bank and inverter would take a little over 100 AH from a 12V bank to do it, if you have that much excess Solar or wind capacity, then do so.
I’ve never met anyone that did though.

They way to do it is to dump your excess Solar into the water tank, I’m not sure how it’s done but there are ways that once you reach absorption voltage apparently there is a way to pull amps form your Solar controller until it will just hold absorption voltage.
That way your not pulling it from your bank, your using what would normally be excess or wasted power and heating water with it.

I don’t know what kind of controller will do this, but I’ve read about people doing it, so it must exist.
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Old 23-02-2020, 08:02   #8
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Re: Heating water in silence (via inverter)

The Victron BMV ( and I'm sure others that I am not familiar with) have a potential free output that can be programmed to control an external relay. So at 100% soc you could start dumping excess capacity into your water heater, and then maybe 90% soc you stop.

Actual numbers would depend on your bank, PV capacity, and whatever else you choose to base it on.
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Old 23-02-2020, 08:31   #9
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Re: Heating water in silence (via inverter)

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The Victron BMV ( and I'm sure others that I am not familiar with) have a potential free output that can be programmed to control an external relay. So at 100% soc you could start dumping excess capacity into your water heater, and then maybe 90% soc you stop.

Actual numbers would depend on your bank, PV capacity, and whatever else you choose to base it on.

That’s SOC, but you can be at 80% SOC and yet your bank is clipping how much power it can take by being at absorption, so you have “excess” Solar.
I thought that there was a controller(s)? That could shunt off excess power until you were just barely making absorption voltage, thereby using 100% of all Solar power?

Most of us due to the 6 hours or so of time it takes to fully charge a bank aren’t at 100% SOC until the very end of the day, if at all. But around Noon or just after we are at absorption voltage, absorbing say 40 amps of power where we can make 70 amps, so there is 30 amps not being used.

Those are made up numbers, but illustrate the point.
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Old 23-02-2020, 08:51   #10
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Re: Heating water in silence (via inverter)

Unfortunately I think it generally works the other way around, with the load requirement taken care of 1st and then the excess going to the batteries. I don't know of any controller that will do what you refer to above, but that doesn't mean that they don't exist.

With a 1kwp the OP will very seldom have excess capacity after putting 800w into the water heater via an inverter. So in his case a SOC referenced switch my be a good solution.
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Old 23-02-2020, 09:06   #11
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Re: Heating water in silence (via inverter)

The programmable switch in the Victron battery monitor is a good solution because the OP has gel batteries. LiFePO4 would even been better, but with lead acid or AGM I would be more worried about not fully charging the batteries.

Not sure if OP has a genset but if so, could easily run that once every 2 weeks feeding a battery charger to complement the solar array so that the water gets heated and the batteries fully charged to keep them healthy.

Without genset or alternator to help... and assuming the solar array is not going to be able to make hot water and finish float charge at the same time... it means once every two weeks no hot water so the batteries get it all to finish charge
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Old 23-02-2020, 10:03   #12
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Re: Heating water in silence (via inverter)

Maybe the heater takes split phase 220v (two hot wires).
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Old 23-02-2020, 10:08   #13
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Re: Heating water in silence (via inverter)

Haha, must admit from the original post I assumed a 230v inverter ( I don't live in the USA so tend in that direction), but it would help if that was cleared up by the OP.
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Old 23-02-2020, 10:19   #14
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Re: Heating water in silence (via inverter)

Why not just use your propane stove to heat water for coffee, unless you only have an electric stove? A propane stove is pretty much silent.
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Old 23-02-2020, 10:32   #15
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Re: Heating water in silence (via inverter)

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Originally Posted by rfinklegal View Post
Why not just use your propane stove to heat water for coffee, unless you only have an electric stove? A propane stove is pretty much silent.
I have to admit that I first thought OP was talking about water heater for showers and the like, not for cooking.
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