converting shore kwh to battery amp hrs

[Blazeaway]

I am currently on shore power and we are consuming about 100 kwhrs per week. Immersion heater fridge and freezer plus others. We will be off cruising soon and need to plan ahead for that power wise.

We will of course switch of the immersion heater.

 

So my question is how do I use current info of 100 kwh per week to work out how many amp hrs per week I will need when out on the cut.

[nicknorman]

You just divide by the system voltage. Presuming you boat is 12v, 100kwh is therefore 8.3kAh. If much of the power is consumed by devices via an inverter, you need to take inverter inefficiency into account. Also remember you have to put back perhaps 10% more AH than you take out of batteries due to charge efficiency. So overall it would be a good idea to divide by 11 or even (to be very cautious) 10. So dividing by 10 of course gives 10kAH.

 

By the way, that (over 1kAH per day) is a LOT! Of course having the immersion off and heating water via the engine will make a big difference. What size battery bank do you have and what type of batteries are they?

Edited March 15, 2016 by nicknorman

[Dave_P]

Or to put it another way, you're gonna have drastically reduce your power consumption!

[nicknorman]

Of course the other thing to bear in mind is that you are only using power from the batteries whilst you are not cruising. So if you cruise for 8 hours, you only have 16 hrs of relevant consumption. This makes a big difference to things like fridge consumption, although not to other things like lights and telly since hopefully you will be cruising in daylight with the telly off!

[Alan de Enfield]

10K Ah is 10,000 Ah per week, or 1400 Ah per 24 hour day.

 

If (say) your alternator put out an average of 35 amps you would need to run your engine for 40 hours every day ( which you are unlikely to achieve)

[Dave_P]

I'm just trying to figure out how you can use over 1000ah per day. As an example as cheap as chips and not very efficient freezer, like this http://www.currys.co.uk/gbuk/household-appliances/refrigeration/freezers/essentials-ctf34w15-mini-freezer-white-10117029-pdt.htmlwill draw about 40ah per day from your batteries. That should be your biggest draw.

 

In other words, you could have 25 freezers like that, all running and still not use that much power.

 

The only thing I can think of is the immersion is on all the time, your calorifier is not insulated at all and your hot tap is permananently running.

 

Unless I'm missing something really obvious.

[bottle]

Taking Alan's figure, which I was about to post, you would need a battery bank of at least 2,800 amp.hrs and a charger of at least 280 amps.

 

Frank (Blazeaway) how are you getting this figure of 100 Kwh's (100,000 wh's)

[Dave_P]

With a name like Blazeaway, I'm wondering if there's some hydroponic 'farming' going on, with sodium lights and all the rest. That might explain the high power consumption

[John V]

As Bottle says....that is very high consumption....are you sure?

I consider myself to be a very high consumption boat on shore power but it is less than that

and I have immersion, washing machine , tumble dryer, dishwasher, fridge freezer, electric oven, hob and kettle. (big boat, salty water and built in big generator in case you are wondering)

[Dave_P]

It seems you already knew the answer you your original question http://www.canalworld.net/forums/index.php?showtopic=72327

[Alan de Enfield]

Are you sure you are using 100KwHr per week ?

 

We have fridge, freezer etc etc and sparingly use the immersion heater when not cruising, & Central heating

We obviously have other 'small use' items like TV, phone charger, lights, pumps, computer etc etc ( I know they all add up)

 

Fridge is 50KwHs per annum = 0.137KwH per day

Freezer is 153KwHrs per annum = 0.419KwHr per day

Immersion heater ( 4 hours per day) 1,460KwHr per annum = 4.0KwHr per day

Central heating (12 hours per day) = 1.380KwHr per day.

 

Apart from the central heating we are using less than 5WwHr per day what are you using that gobbles up so much electricity ?

 

It may be a useful exercise to conduct an electrical usage audit of YOUR circumstances as they will be somewhat different to anyone else, and you will then know by how much you will have to change your lifestyle.

[Chewbacka]

Are you sure you are using 100KwHr per week ?

 

We have fridge, freezer etc etc and sparingly use the immersion heater when not cruising, & Central heating

We obviously have other 'small use' items like TV, phone charger, lights, pumps, computer etc etc ( I know they all add up)

 

Fridge is 50KwHs per annum = 0.137KwH per day

Freezer is 153KwHrs per annum = 0.419KwHr per day

Immersion heater ( 4 hours per day) 1,460KwHr per annum = 4.0KwHr per day

Central heating (12 hours per day) = 1.380KwHr per day.

 

Apart from the central heating we are using less than 5WwHr per day what are you using that gobbles up so much electricity ?

 

It may be a useful exercise to conduct an electrical usage audit of YOUR circumstances as they will be somewhat different to anyone else, and you will then know by how much you will have to change your lifestyle.

I suggest you get one of these and monitor each of your big power consumers that you intend to run whilst cruising.

Monitor each item for a day or two and that will show your requirement. If any seem unreasonably high, you can look to change things - for example trying not to open the fridge or freezer door more that a few times per day.

Edited March 15, 2016 by Chewbacka

[Alan de Enfield]

I suggest you get one of these and monitor each of your big power consumers that you intend to run whilst cruising.

Monitor each item for a day or two and that will show your requirement. If any seem unreasonably high, you can look to change things - for example trying not to open the fridge or freezer door more that a few times per day.

 

Good idea but it does not seem to have the right 'plug' for a 12v fridge.

[Dave Payne]

That is real heavy usage!

 

I had two electric 1000 watt heaters running over the winter due to not having a fire, think my average was 40KwHr a week with those, tv, fridge freezer, washing machine and charger....

[MarkHez]

Hell, according to my solar controller, I use 100kwh over 3 months!

[Paul C]

To put 100kWh/week into context, I think this is a typical energy usage for a 4 bedroom house with electric heating and cooking. A 3 bedroom house with gas central heating and cooking typically uses 40kWh/week.

 

I wonder if the "per week" is in fact a "per year" or something?

[David Mack]

I am currently on shore power and we are consuming about 100 kwhrs per week.

Or about 5000 KWhrs per year. I find that very hard to believe. According to my electricity bills I have used 1850 KWhrs in 6 months (July-December) in a substantial detatched stone house in the Pennines. You couldn't possibly use that much on a boat.

[Alan de Enfield]

To put 100kWh/week into context, I think this is a typical energy usage for a 4 bedroom house with electric heating and cooking. A 3 bedroom house with gas central heating and cooking typically uses 40kWh/week.

 

I wonder if the "per week" is in fact a "per year" or something?

 

Maybe the OP can get an idea of how much he uses by how much he pays

 

If the marina is charging 20p per unit then he will be paying £20 per week (getting on for £90 per month).

If he is paying this much then his 'floating flat' lifestyle will have a dramatic change when he 'un-plugs' the umbilical.

[Paul C]

I am suspicious of the unit itself, energy consumption is expressed as kWh typically (no 'per unit time' at the end of it). If expressing as a power consumption, ie per unit time, its normally either W, kW, or kWh/annum. I recently saw a reference to kWh/day but that an exception, not the norm.

[Loafer]

With a name like Blazeaway, I'm wondering if there's some hydroponic 'farming' going on, with sodium lights and all the rest. That might explain the high power consumption

 

Anyone any idea where he's moored?

[Alan de Enfield]

I am suspicious of the unit itself, energy consumption is expressed as kWh typically (no 'per unit time' at the end of it). If expressing as a power consumption, ie per unit time, its normally either W, kW, or kWh/annum. I recently saw a reference to kWh/day but that an exception, not the norm.

 

Surely the only way you / he can express his usage is by quoting the number of Kw used over a period of time (in this case per week)

 

His Kw usage (by the hour) will vary considerably depending on if his heating I on, the time when the immersion is active etc.

 

The OP should have said "100Kw per week" but we all knew what he meant.

[Paul C]

 

Surely the only way you / he can express his usage is by quoting the number of Kw used over a period of time (in this case per week)

 

His Kw usage (by the hour) will vary considerably depending on if his heating I on, the time when the immersion is active etc.

 

The OP should have said "100Kw per week" but we all knew what he meant.

 

Yes but where does the "per week" come from - if weekly readings, then fair enough, but he's effectively made a new unit up, and somewhere (seems the consensus, unless he's doing something abnormally energy intensive) made an error. I am suggesting the "100" bit is correct but the "per week" might not be, that's all.

[Dave Payne]

But meters say kwh ? or at least i think mine does.

[Loafer]

Kilowatt-hours are an accumulation, over time, of energy used.

 

Kilowatts are an instantaneous unit of power, (energy per sec right now) and apply to what's happening this instant.

 

So a meter can show either. A reading of '1.2kW' tells you that your electric fire is using 1200 Watts. Right now! If you turn off the fire, the reading will drop to zero. But if your meter also adds up all the energy you've used, it could say 1.2kWh and stay there when the fire is turned off. It USED 1.2kWh of energy, but REQUIRES 1.2kW to work.

[David Mack]

There's nothing wrong with the OP's units. A kWhr is what is otherwise described as a 'unit' of electricity, and is what customers are billed in. So you can describe your level of usage as the number of units or kWhrs consumed over a period of time - be that a day, a week, a month or a year.

 

Its just the magnitude of the OP's consumption that doesn't look right to me - or is at least VERY extravagant.