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Old 24-05-2011, 13:33   #1
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Inverter

Hi all,
I have some questions!
My goals are to run an inverter so that my sockets on the boat deliver power when not on shore power and also potentially run my hot water tank but not a priority!
I have 330 ah of batteries and are all new so should be good to get an inverter - my hot water tank is 1400 watts and probably won't be running anything bigger than this at any one time.
The question is if I go for a 2000 watt inverter and run my water tank for say 30 mins how many amps will this burn approx, I know there is a calc but can't seem to work it out!
Also does the inverter recognise when on shore power and switch off if connected to the shore?
Would Be good to get a diagram but have looked on the sterling and marlec website with no luck!

Thanks for any help
Cheers
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Old 24-05-2011, 13:51   #2
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Re: Inverter

Assuming you have a 12-volt system, I'd suppose you would use 60 amp hours in thirty minutes for heating water.

Volts Watts Amps Converter Tool Calculator
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Old 24-05-2011, 14:05   #3
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Re: Inverter

unless you have an inverted/charger,don't let a/c shore power flow back to the inverter,it will destroy the inverter immediatly!!!!

you need to fit a 3way switch so sockets are either a/c shore or a/c inverter,never both........
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Old 24-05-2011, 14:06   #4
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Re: Inverter

I think you would be better off to run your engine to heat water. That would take about 10 minutes. And you would charge batteries at the same time.

Whenever I run a big load on an inverter, e.g. microwave; I run the engine.
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Old 24-05-2011, 14:08   #5
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Thanks for the replies. Can some inverters have a connection for the shore power so recognise when shore power is connected and switch
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Old 24-05-2011, 14:08   #6
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Re: Inverter

Quote:
Originally Posted by Tomtom39 View Post
The question is if I go for a 2000 watt inverter and run my water tank for say 30 mins how many amps will this burn approx, I know there is a calc but can't seem to work it out!
Also does the inverter recognise when on shore power and switch off if connected to the shore?
Would Be good to get a diagram but have looked on the sterling and marlec website with no luck!

Thanks for any help
Cheers
Tomtom... I would recommend giving up on the idea of batteries to heat hot water. I don't think that's practical.

Hopefully you have a heat exchanger that can heat it, but if not you need a solar shower or a gas heater. It's too big a power drain for too long of a time.
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Old 24-05-2011, 14:09   #7
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Re: Inverter

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Thanks for the replies. Can some inverters have a connection for the shore power so recognise when shore power is connected and switch
The Xantrex Freedom automatically detects shore power. Never had that problem at all.
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Old 24-05-2011, 14:12   #8
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Re: Inverter

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unless you have an inverted/charger,don't let a/c shore power flow back to the inverter,it will destroy the inverter immediatly!!!!

you need to fit a 3way switch so sockets are either a/c shore or a/c inverter,never both........
Yep - and a great big fuse.

A switch lockout also works by preventing both being on at once.
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Old 24-05-2011, 14:16   #9
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Re: Inverter

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Originally Posted by Tomtom39 View Post
Thanks for the replies. Can some inverters have a connection for the shore power so recognise when shore power is connected and switch
Yes. The certain models of the Victron inverter do exactly that. You connect the inverter and shore power in parallel and the Victron will "sense" shore power or a generator and will kick in to boost the AC power if needed and shut down when not needed.
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Old 24-05-2011, 14:17   #10
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Re: Inverter

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Thanks for the replies. Can some inverters have a connection for the shore power so recognise when shore power is connected and switch
yes it is called "ubs" but on more expensive models.
all inverter/battery charger models have the uninterrupted supply function,but check with the supplier as one's that don't will be toast if inadvertantly connected to the mains!!!!!
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Old 24-05-2011, 14:42   #11
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Re: Inverter

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Originally Posted by Tomtom39 View Post
Hi all,
<snip>...
I have 330 ah of batteries <snip>
- my hot water tank is 1400 watts <snip>

The question is if I go for a 2000 watt inverter and run my water tank for say 30 mins how many amps will this burn approx,
<snip>
Assuming 12 Volt battery, and standard definition of amp hours (amps over 20 hours, not the 100 hour format):

330 ah is 16.5 amps /hour sustained drain for 20 hours..

The power calculation P=VI results in 198 Watts sustained use over 20 hours. (16.5*12 = P)

Accelerating the current drain results in a non linear power curve:




In simple words, the above sentence means that you can not have 198*2 watts over 10 hours, or 198*20 watts in 1 hour. You will have less. Much less. (depends on battery type, prior working life of battery... etc). There is a very small chance that you could power a 2000W heater for 1/2 hour.

By this time the water (if it was cold to begin with) shall be tepid, and your battery shall be run flat.

A good source of information on battery, amp hours etc is Understanding Amp Hours, yet I am sure there are many others.

The prior posts do give a better solution: use a heat exchanger to heat the hot water using your engine, while you recharge your batteries.

Good luck..
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Old 24-05-2011, 14:48   #12
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Re: Inverter

Heating water with an inverter is in fact such a ghastly bad idea that my Victron charger inverter has a special circuit to which the water heater is connected to ensure that there is no chance that it can ever be run off the inverter!
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Old 24-05-2011, 14:58   #13
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I have also been a total novice at this lot, but did extensive research before equipping our vessel. We went with two Victron charger inverters 3000 w each which means we can use up to 6000w appliances. The chargers on each inverter deliver 120ah x 2 = 240 ah ability (theoretically). They work really well and sense shore power failure automatically an totally seamlessly switch over to inverter mode and back again as the situation determines. We also installed the blue power panel which shows a layout of the electrical system all on one display so you can literally see battery bank capacity and level of charge - AC charge coming in and and charge Amps being delivered to the battery bank - AC circuit current being drawn thru inverter as well as dc current etc etc. You can also (when on shore power) limit the shore power current and if an appliance demands more than what the shore power can deliver, it automatically goes into load sharing mode and 'steals' the balance of power from your battery banks, meaning you get some power from shore and some from the battery bank. When not at shore then obviously the genset runs the chargers whilst we use it for the washer dryer etc.
We have 970ah battery banks. If the engines are on, we have 2 Balmars charging 150amps each X 2 = 300 amps if both engines run and are wired through centerfielder and smart regulator.
Additional power is solar viz. 5 panels at 135w each = 675 watts wired through a bluesky MPPT controller.
Despite all this power we find it is definitely not practical running the hotwater viz our battery banks - it sucks energy rapidly and no matter how big the battery bank one always has to be able to put back what you take out.
For hot water we either run the engine and make use if the balmar alternator at the same time to recharge the batteries or we run the genset which powers both Victron chargers at the same time. If it's a morning shower and we have good sun, then we can run the geyser viz batteries and let the solar do the work topping them up for the rest of the day.
I hope this helps because it took me a long time to understand how to get a 'perfect' balance fir what we want to do.
All my lighting is led by the way - a huge saving and the best thing I did in converting my old halogens in for the LEDs.
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Old 24-05-2011, 15:18   #14
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Great post by impi
Thanks for sharing.
I believe that I have been talked out of the water heater element and can manage by running engine or the generator,
Just need to pick the right inverter.
Thanks again everyone
Cheers
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Old 24-05-2011, 15:22   #15
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Re: Inverter

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The Xantrex Freedom automatically detects shore power. Never had that problem at all.
The downside of this is that if the inverter is shot you get no ac in the boat. After six months cruising I finally tied up to a dock in the boatyard. Unfortunately my inverter was fried in Nassau so I could not use shore power. Couldn't even run my trusty Honda as the ac has to go through the fried inverter. At least I didn't need hot water it was 96 degrees yesterday in Fernandina Beach. Too hot to do boat work.
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