Electrical consumption

[TC5]

Hi

I am having a 60foot narrow boat built and my plan is to be gas less and power every thing from a 230v ac system. The ac power will be from either the shore or a 9kva whispergen or a 5kva invertor connected to a 24v 600ah battery.

I am working out the average current consumption for various domestic components and I have some doubt on the following calculation:

A Miele K622 Ui-1 fridge according to the specification has a rated load of 100w, now dividing that by 230v will give me approximatley 0.5 amp, so far so good.

Energy consumption is rated at 230kwh/yr, diving this by 230v gives me 1kah/yr, dividing this by 365days gives me 2.73ah/day. This figure seems to good to be true. Are my calculations logical?

 

Cheers

 

TC

[bottle]

It is logical you will use approx 630watts per day; i.e. the fridge will run for 6.3hrs

 

per 24hrs. BUT this will also depend on the number of times the door is opened

 

and the ambient temperature of the suroundings. The guide consmption I think is

 

probably worked out in ideal conditions.They are a good guide though.

 

Stay cool

 

bottle

[NB Willawaw]

TC5,

 

I have a gas-less boat. I use a Mastervolt Inverter when motoring and have a Whisper6000 genset in the back cabin to drive the washing machine and electric cooker when moored to the towpath.

The fridge load sounds a bit on the light side. I will have to check my fridge power consumption for comparison.

[TC5]

It is logical you will use approx 630watts per day; i.e. the fridge will run for 6.3hrs

 

per 24hrs. BUT this will also depend on the number of times the door is opened

 

and the ambient temperature of the suroundings. The guide consmption I think is

 

probably worked out in ideal conditions.They are a good guide though.

 

Stay cool

 

bottle

<{POST_SNAPBACK}>

[TC5]

TC5,

 

I have a gas-less boat. I use a Mastervolt Inverter when motoring and have a Whisper6000 genset in the back cabin to drive the washing machine and electric cooker when moored to the towpath.

The fridge load sounds a bit on the light side. I will have to check my fridge power consumption for comparison.

<{POST_SNAPBACK}>

 

Mark

 

Thanks for the note, what size domestic battery do you use?

 

Cheers

 

TC

[Richard Bustens]

Hi TC5

How are you going to power the fridge from a 240V supply or from an inverter?

 

If you are going to power it through an inverter which i suspect you are, you will use about 36AH per day @24V.

The fridge assuming it is a grade A insulated one will run for 12 hr per day at best. possibly more.

Also don't forget that 100w is running, and start up will be in the region of 8-900W but only for 1-2 seconds.

 

I also am building gas free and have gone over the top with gen set etc but the cost of putting a bigger one in is not a lot compared with the cost of a small one.

[NB Willawaw]

Sorry not physically on the boat today, so don't have access to the books.

From the top of my head, I think the domestic bank is about 440AH.

[TC5]

Hi Richard

 

Thanks for the information, I have just realised that my calculation of 2.6ah/day is at 230v ac. So 2.6ah x 230v = 598wh. 598wh / 24v dc = 24.9ah/day: say plus 10% for inverter losses 24.9ah + 2.4ah = 27.3ah/day. This is the figure that I would expect.

 

I plan to power the 230v ac system from shore or a 9kva whisper gen or a 5kva inverter hooked up to a 24v dc 600ah battery. The main engine will have a 110amp dc alternator for charging whist cruising. The plan is for the 9kva whisper gen to cut in automaticaly ( between the hours of 0800 - 1800 ) when the battery is 48% discharged. Thus if we moor up for a few days there is no need to run the main engine for battery charging.

 

Cheers

 

TC

[Richard Bustens]

Hi TC

I agree with your calculations now, but have reservations on the fridge only running for 6 hrs a day i have worked on 12 and have been told that that is being optomistic.

But time will tell.

[Amicus]

I can help here. The fridge/freezer here at my home had a kuputen thermostat, as a tempory bodge I used a plug-in timer. 2 or 3 years later this is still in use. Using a thermometer in the freezer I have found that a duty cycle of 30% (15 mins. on 30 off)in the summer, and 25% (15m on 45 off) in the winter is about right. Of course the usage pattern would effect this greatly.

[Richard Bustens]

i hope you are right as it would help my energy audit greatly

[NB Willawaw]

For what its worth, I rarely start my genset when cruising on a regular basis. Even in the winter, I use a solid fuel stove and an Eberspacher for heating and my lights/fridge/pumps/microwave run from the batteries/inverter.

However, the electric cooker and hobs do take a lot of juice, as does the washing machine, so I have to start the genset for large meals like sunday lunch or on laundry day.

In comparison to their electricity consumption, the fridge consumption is minimal and I run that from the inverter most of the time. If I'm going to spend a couple of nights at a mooring, I give the genny a run for 2-3 hours to top everything up.

 

At the moment, I'm stoppage bound and have left the boat in a marina, but usually use their shorepower when I'm onboard.

 

I hate running the genset when stationary. I'm probably just too mean to burn the fuel

[DHutch]

When talking about elcetrical loads/consuption, espcaially when it get complicated, ie, multiply voltages, inverters, charges, gensets etc. it is important to work things out slowly and locially, and to always have a certain reseave, becuase im my (small) experiance with these thing, if you try and cut it too fine, it often ends up not working at all!!!

 

-And watts is a measure of POWER , not energy!! (ie a watt is a joule per second)

 

It is logical you will use approx 630watts per day.

 

Daniel

[bottle]

[quote name=

 

 

-And watts is a measure of POWER ' date=' not energy!! (ie a watt is a joule per second)

 

[/quote]

 

Hi dhutch I bow to your knowledge that watts equal power and that is what

 

the electricity company charges me for Kw/hrs. Therefore the power used by the

 

refridgerater in 6.3hrs is 630watts. this eqates roughly to 0.42amps for 6.3hrs

 

this then equals 2.6amp/hrs.

 

Or am I all charged up over nothing

[Richard Bustens]

Amp:

 

A measurement of the flow of electrical current. One amp is equal to the electric force of one volt acting across the resistance of one ohm.

 

Amp Hour:

 

One amp of electrical current flowing for one hour. Expresses the relationships between current (amps) and time. (OHMS law A=V/R)

 

Volts:

 

A unit of measure of the pressure in an electrical circuit. Volts are a measure of electric potential. Voltage is often explained using a liquid analogy -- comparing water pressure to voltage: a high pressure hose would be considered high voltage, while a slow-moving stream could be compared to low voltage.

 

Watt(s):

 

A quantitative measurement of electrical power. Watts are calculated by multiplying volts times amps. Using a liquid analogy, watts are similar to liquid flow such as liters or gallons. (watts = volts X amps).

 

Watt Hour (W / h):

 

Electrical power measured in terms of time. One watt hour of electricity is equal to one watt of power being consumed for one hour. (A one-watt light operated for one hour would consume one watt hour of electricity.)

[NB Willawaw]

Mark

 

Thanks for the note, what size domestic battery do you use?

 

Cheers

 

TC

<{POST_SNAPBACK}>

 

Got access to the drawings now:

 

4 x 12V 140A/H in parallel = 560AHC

 

TC5, have you done an energy audit on your boat to calculate what power you are going to need ?

[gralyn]

I have some doubt on the following calculation:

A Miele K622 Ui-1 fridge according to the specification has a rated load of 100w, now dividing that by 230v will give me approximatley 0.5 amp, so far so good.

 

Hi I am new to the group and have just seen the thread. I have a niggle at the back of my mind that the calculations must be done using the battery voltage,

 

ie 100 w /12 volts = 8.33 amps drawn from the battery

100 w/24 volta = 4.16 amps drawn from the battery

 

and this is assuming that the invertor is lossless

 

Regards Graham.

[Echo_Wink]

Hi, I too am new to the group (the new group that is). I chose a 240v Fridge because of the advice and posts in the old group, and to save money. I have just replaced this with a 12v Fridge though, for a few reasons. 12v Fridges (at least the more modern good ones) have a soft start motor, which does not draw as much power on start up. The problem I found was that a 240v Fridge draws a lot of power (maybe 8a @ 240v) for a second-ish as it starts up which puts a severe drain on the batteries. I have a 1500w pure sine Sterling inverter, which beeps to tell you when the voltage is getting low, even at 4 in the morning ! The 240v Fridge lasted 2 Days on 700ah batery bank with nothing else running and the inverter on power saving mode, the new 12v Fridge lasts 8 days+. For this reason I would bite the bullet and pay the extra for 12v just because it lasts so much longer. Incidentally when I calculated the difference on paper before I bought the fridge, the 240v looked OK, but there would seem to be no substitute for experience.

[John Orentas]

If your 230 volt fridge draws 8 amps for up to a second, (that seems very high) your inverter / batteries should cope ok as long as the inverter is rated at least 1500 watts* running from say 2 x 110 a/h batteries.

 

*The inverter should easily accommodate the surge current.

 

The current draw will be in the region of 160 amps for that very short time. If the inverter indicates a low input voltage I would suggest it is because of insufficient wiring to the unit, they should be as short as possible and minimum 25 sq mm all the way back to the batteries.

 

As you imply the modern 12 volt fridge is likely to be very much more efficient though considerably more expensive. Electrical efficiency is not seen as a priority on domestic 230 volt fridges.

 

When purchasing a 230 volt fridge you should study the specification plates on the units and buy the one one with the lowest consumption, the standard of insulation is important too as a high standard will allow the unit not to be running as long.

Edited February 14, 2005 by John Orentas

[Echo_Wink]

I think you misunderstand my point a little. The fridge I fitted was AA class efficiency . This is currently the most efficient 230v you can get I think. The reason it was no good was that the heavy current draw on start up flattens the batteries very quickly (Its a bit like starting an engine from your domestic bank 48 times a day), and when there is a heavy load on the Inverter the voltage from the batteries drops momentarily. If the voltage drops below 10.5v then the inverter beeps to let you know. This can be a bit annoying at 4 am. This happens even when the batteries are at 11.5v thus reducing the useable range of power available from the bank considerably. While comparing very favourably on paper to a twelve volt fridge, in practice it sucked. So in conclusion I would say if you are going to run a fridge from a battery bank go 12v.

[John Orentas]

Don't confuse thermal efficiency of a refrigerator with it's electrical efficiency.

 

You cannot equate the start up current of a fridge with the current demand when starting an engine.

 

The voltage may well drop down to 10.5 when measured at your inverter but it certainly will drop to anything like as low as that when measured at a reasonably well charged battery bank. See my previous reply re. cable sizing.

 

If the batteries read less than 12+ volts off load they are either heavily discharged or defective in some way.

[Echo_Wink]

I'm not confused about anything John. I'm just trying to prevent people reading the same advice that I did, about a 240v fridge being OK to run on a boat from batteries (from the old forum) when it clearly is not. The wires I am using on my battery bank are more than adequate exceeding the specs described in the manual, and the wiring for the inverter came with it. I can run my 1500w Hoover and 2000w washing machine without any problems. The point I am making is that even an efficient 240v fridge has no place on a boat as it is not cost effective. You will quickly recoup the money spent on a 12v Fridge because of all the extra money you will have to spend charging up your batteries if you have a 240v Fridge.

I know this information from bitter and costly experience. I am trying to help others not to make the same mistake. John and Carol at Limekiln Chandlers told me they have had the same results from a mains fridge.

I am trying to help people out here, not get into a petty argument.....

[david and julie]

Echo_Wink, sorry if this is slightly of topic, you said you have a 1500watt pure sine wave sterling inverter which runs your washer no problem. I am currently speccing a new build and am uncertain whether to go the inverter route or bite the bullet and go for an electrolux 3.5 kva (mainly for the washer), at the build stage it is easier to fit rather than later on. What sort of washer are you using and is it solely a washer rather than a combined washer/ tumble drier?

[Richard Bustens]

ECOH WINK

 

Rubbish, i am running a fridge and freezer one 110w and the other 120w perfectly ok.

[TC5]

Got access to the drawings now:

 

4 x 12V 140A/H in parallel = 560AHC

 

TC5, have you done an energy audit on your boat to calculate what power you are going to need ?

<{POST_SNAPBACK}>

Mark

Yes I have carried out an electrical energy audit but I am not sure how to include it in this reply.

If you would like to ping me an E Mail on "mail@trevorcole.eclipse.co.uk" I'll send you a copy

 

cheers

 

TC