How many batteries

[Robin2]

I'm still not sure about this...?

I was hoping for some more knowledgable people to come along ..but here goes :

 

Still can't see your correlation between 240 volt and 12 volt ?

Sorry if I'm being thick...

If you draw 1 amp on 240volts...via an invertor...your invertor will take 20 amps from a 12 volt battery..to produce this 240 volt at 1 amp.

In other words..your 1.4 amp an hour fridge on 240 volt...over 24 hours...will take 1.4 x 24 x 20 = 672 amps from 12 volts.

It appears to me..(actual appearing may vary from description)....that you still need the 'hours' figure worked into this.

I 'think'..but am sorry if I'm wrong....that you think...(they think ?..nah)..that an amp on the 240 volt draws an amp from the 12 volt...but this is not so...

You come back to the wattage again...

Look on the back of your appliance...and see its wattage rating while running..

If its a microwave.....and it says '240 volt...1000 watts'...then it is drawing 4.16 amps while running on 240 volts...divide wattage by voltage = current (amps)

To supply this from an invertor..(ignore loss)...you must take 1000 watts from your 12 volt batteries...

BUT...instead of dividing the wattage by 240 volts..to get 4.16 amps..you have to divide the wattage by 12 volts...

That is a wopping 83 amps......and that is what you are taking (losses ignored)...from the 12 volt batteries..

 

If your mini freezer draws 2 amps while running...( and was continuous) and is 240 volts...that is 240 x 2 = 880 watts...in an ideal hour...

Running that on the invertor...from 12 volts...you divide 880 watts by 12v = 73 amps in an hour...!!

 

PLEASE...is there somebody more inteligent here...can help...a drownng Bob !!

 

 

bob

Gibbo selected a small piece out of this. Let me focus on a different piece.

 

The bit I have highlighted implies that the fridge consumes 336 watts. I'm sure you know this is far too much. Fridges are more likely in the 50 to 100 watt area while they are running and they only average maybe one third of that. Now if the above mentioned 1.4 amps is at 12v (rather than 240) it gives an average of 17 watts or about 50 watts when running if it runs for 20 minutes every hour.

 

On this basis I assumed that all of the amp-hour figures that Julynian quoted were at 12 volts, not 240v.

[Ex- Member]

Hi guys

 

I worked out the amps for the fridge based on it's 240 volt requirement.

 

240v fridge 1.4 amps x 24 hours 33.6amps per day

This does not include any additional power from the inverter.

I took the figures from the manufacturers tech info as follows. A+ energy class (117 kWh per year) 0.32 kwh/24 h energy

I assumed that to be 320 watts over a 24 hour period.

It appears than inverter losses are a lot higher than I imagined Maybe i do need a KW of solar after all

 

ETA 1 chose to divide by 230 volts as it's between 220 and 240 volts

Edited August 21, 2011 by Julynian

[nb Innisfree]

Hi guys

 

I worked out the amps for the fridge based on it's 240 volt requirement.

 

240v fridge 1.4 amps x 24 hours 33.6amps per day

This does not include any additional power from the inverter.

I took the figures from the manufacturers tech info as follows. A+ energy class (117 kWh per year) 0.32 kwh/24 h energy

I assumed that to be 320 watts over a 24 hour period.

It appears than inverter losses are a lot higher than I imagined Maybe i do need a KW of solar after all

 

ETA 1 chose to divide by 230 volts as it's between 220 and 240 volts

 

A good quality inverter would increase 33ah to approx 36ah, not too bad really.

[Ex- Member]

A good quality inverter would increase 33ah to approx 36ah, not too bad really.

 

Hi nb innisfree

 

A near definitive answer

 

 

Thanks for the input on this and every one else. I'm not really this stupid but for some reason getting my head around this has been like trying to eat spaghetti with a butter knife

Edited August 21, 2011 by Julynian

[Gibbo]

117 kWh per year

 

This bit you should take with a pinch of salt. It's the ideal figure under perfect conitions (even though they say it isn't). A bit like the advertised MPG figure on new cars.

 

Multiply it by 1.5 to get something approaching a real world figure.

[Ex- Member]

This bit you should take with a pinch of salt. It's the ideal figure under perfect conitions (even though they say it isn't). A bit like the advertised MPG figure on new cars.

 

Multiply it by 1.5 to get something approaching a real world figure.

 

 

Ok Gibbo I'll recalculate bearing that in mind, better to have a worse case scenario rather than being short. I'll apply the same to the freezer also as it's another annual figure. All the other outputs are from stated wattage.

 

 

[Robin2]

I assumed that to be 320 watts over a 24 hour period.

 

 

This is actually 320 watt-hours over a 24 hour period, or an average consumption of 13.3 watts.

 

I agree with Gibbo's comment about the unreality of the manufacturer's figures - though mine does not seem to be as bad as 50% worse.

 

By the way are you using a fancy editor to create your posts or do you just enjoy the masochism of putting different font codes etc on each line?

[nb Innisfree]

This bit you should take with a pinch of salt. It's the ideal figure under perfect conitions (even though they say it isn't). A bit like the advertised MPG figure on new cars.

 

Multiply it by 1.5 to get something approaching a real world figure.

 

Mind you I have monitored our 100 litre Lec 24v and it works out in the region of 16-18ah per day which is quite near it's claimed consumption.

 

Edited double post

Edited August 21, 2011 by nb Innisfree

[Gibbo]

Mind you I have monitored our 100 litre Lec 24v and it works out in the region of 16-18ah per day which is quite near it's claimed consumption.

 

Edited double post

 

But that's not a 230 volt fridge.

[Ex- Member]

This is actually 320 watt-hours over a 24 hour period, or an average consumption of 13.3 watts.

 

I agree with Gibbo's comment about the unreality of the manufacturer's figures - though mine does not seem to be as bad as 50% worse.

 

By the way are you using a fancy editor to create your posts or do you just enjoy the masochism of putting different font codes etc on each line?

I really don't know, sometimes I copy and paste quotes and stuff for speed, although it hardly makes a difference My screen font size sometimes changes also, I'm just clumsy I think, keep dropping the mouse and the lap top I suppose lounging in a big easy chair with lap top on left arm and mouse on Right arm doesn't help along with a ciggy and cup of tea see it just happened again I really didn't do a thing

 

 

 

 

 

 

[nb Innisfree]

But that's not a 230 volt fridge.

 

True, I got a bit off track there, and I'm sober.

[ditchcrawler]

This bit you should take with a pinch of salt. It's the ideal figure under perfect conitions (even though they say it isn't). A bit like the advertised MPG figure on new cars.

 

Multiply it by 1.5 to get something approaching a real world figure.

Mine runs at ABOUT 550 watt/hrs per day with a duty cycle of 25%

[Gibbo]

Mine runs at ABOUT 550 watt/hrs per day with a duty cycle of 25%

 

That's a more realistic figure. Round about what most people seem to get in the real world as opposed to lab tests.

 

<pedant>

 

(should be watthours - it's watts X hours not divided by)

 

</pedant>

[WotEver]

Just one thing if you divided by 10 instead of 12, that would roughly take care of the losses you ignored.

As I've been going through this thread I've been hoping someone would have said this. It's a great rule of thumb to work by.

 

Tony

[Robin2]

But that's not a 230 volt fridge.

 

The only difference between a 230v and 12/24v fridge is the inverter loss which has nothing to do with the manufacturer's estimate of annual energy consumption.

[Gibbo]

The only difference between a 230v and 12/24v fridge is the inverter loss...

 

No it isn't.

 

I ran a pile of tests on the two different types of fridges. I tested about 20 in total. The 12 volt ones were a lot more efficient. I didn't get as far as looking into why but can only assume it was something to do with either better insulation or the compressor itself being better. Whatever the reason, the reality is that the 12 volt fridges were more efficient.

[smileypete]

This bit you should take with a pinch of salt. It's the ideal figure under perfect conitions (even though they say it isn't). A bit like the advertised MPG figure on new cars.

 

Multiply it by 1.5 to get something approaching a real world figure.

That is only partially true.

 

It depends on ambient temperature, ventilation, door opening and chilling items put in.

 

Here's some real world figures for my 'D' rated mains fridge with 2 star ice box:

 

Fridge

-------

3/1 start

1/2 11.53kWh/29 days = 0.398kWh/day (16.6w av.)

1/3 22.57-11.53=11.04kWh/29 days = 0.380kWh/day (15.9w av.)

1/4 35.08-22.57=12.51kWh/31 days = 0.403kWh/day (16.8w av.)

1/5 49.05-35.08=13.97kWh/30 days = 0.466kWh/day (19.4w av.)

1/6 68.49-49.05=19.44kWh/31 days = 0.627kWh/day (26.1w av.)

1/7 87.69-68.49=19.20kWh/30 days = 0.640kWh/day (26.7w av.)

1/8 107.64-87.69=19.95kWh/31 days = 0.643kWh/day (26.8w av.)

1/9 129.44-107.64=21.80kWh/31 days = 0.703kWh/day (29.3w av.)

1/10 148.26-129.44=18.26kWh/30 days = 0.627kWh/day (26.1w av.)

1/11 163.51-148.26=15.25kWh/31 days = 0.490kWh/day (20.5w av.)

1/12 176.97-163.51=13.46kWh/30 days = 0.489kWh/day (18.7w av.)

1/1 187.53-176.97=10.56kWh/31 days = 0.341kWh/day (14.2w av.)

 

Notice the winter consumption is half that of high summer...

 

So the question is, how do we size a solar array to avoid having wasted solar power?

 

 

The only difference between a 230v and 12/24v fridge is the inverter loss which has nothing to do with the manufacturer's estimate of annual energy consumption.

There is also the compressor and refrigerant, both of which make a big difference.

 

cheers,

Pete.

Edited August 22, 2011 by smileypete

[Gibbo]

That is only partially true.

 

It depends on ambient temperature, ventilation, door opening and chilling items put in.

 

Of course it does. And the tests used to arrive at the lovely figures ensure that all those conditions are perfect.

 

A bit like the figures for my car reckon I can get 62 MPG out of it. Bollocks.

[Chris Pink]

 

So the question is, how do we size a solar array to avoid having wasted solar power?

 

 

 

You can't, all you can do is take a point on the bell curve and say "there", mine's April.

 

In January diddly-squit, in June twice as much (on a good day) as I need, but bear in mind now that 'high' summer is tending to be overcast and spring and autumn are the sunniest times.

 

As my cage has been rattled can the people confusing themselves by using 'amps' when they mean 'amp hours' please desist.

 

ps 1kwh = 83.3Ah @ 12V

[soldthehouse]

[Ex- Member]

Fridge

-------

3/1 start

1/2 11.53kWh/29 days = 0.398kWh/day (16.6w av.)

1/3 22.57-11.53=11.04kWh/29 days = 0.380kWh/day (15.9w av.)

1/4 35.08-22.57=12.51kWh/31 days = 0.403kWh/day (16.8w av.)

1/5 49.05-35.08=13.97kWh/30 days = 0.466kWh/day (19.4w av.)

1/6 68.49-49.05=19.44kWh/31 days = 0.627kWh/day (26.1w av.)

1/7 87.69-68.49=19.20kWh/30 days = 0.640kWh/day (26.7w av.)

1/8 107.64-87.69=19.95kWh/31 days = 0.643kWh/day (26.8w av.)

1/9 129.44-107.64=21.80kWh/31 days = 0.703kWh/day (29.3w av.)

1/10 148.26-129.44=18.26kWh/30 days = 0.627kWh/day (26.1w av.)

1/11 163.51-148.26=15.25kWh/31 days = 0.490kWh/day (20.5w av.)

1/12 176.97-163.51=13.46kWh/30 days = 0.489kWh/day (18.7w av.)

1/1 187.53-176.97=10.56kWh/31 days = 0.341kWh/day (14.2w av.)

 

Notice the winter consumption is half that of high summer...

 

That's really interesting. We've put cooling fans in the floor under the fridge that draw cool air from the bilge and direct it to flow over the back of the fridge, in the summer mainly of course.

 

Clearly the ambiant temperature drops in the boat during winter, and on the figures above by quite some way if saving between 200kwh/day and 300kwhday a fair wack of energy. I always thought the fans I fitted might help as the air they draw is pretty cool. If they achieved cooling to the effect shown from November to may that's a saving of well over 150 watts per day through the summer months. Quite significant really.

 

Of course you would have to deduct fan energy, but the fans I use are only 0.1 amp each.

 

Just a point on manufacturers stats. Surely they have to prove within a reasonable percentage thay the figures the attest to are correct. These figures after all are all to do with the Eco rating system and are awarded ratings as such.

 

Although as Gibbo says MPG from some manufacturers has been proven to be unachievable especially on one of the newer Mercedes models.

[ditchcrawler]

That's a more realistic figure. Round about what most people seem to get in the real world as opposed to lab tests.

 

<pedant>

 

(should be watthours - it's watts X hours not divided by)

 

</pedant>

Yes, I don't know why I wrote it like that, I almost put 1/2 Kwh maybe that is where the / came from

[Gibbo]

Just a point on manufacturers stats. Surely they have to prove within a reasonable percentage thay the figures the attest to are correct. These figures after all are all to do with the Eco rating system and are awarded ratings as such.

 

That's half the problem. It comes down to "Standards" again. The standards are often (mostly?) drawn up by idiots. The "standards bodies" define the tests (which are usually nothing like reality and utter bollocks) then the manufacturers run the tests as they are told to.

 

It does have the advanatage that everyone is testing to the same standards so it's easy to compare one fridge against the next, but it has the disadvantage that the figures produced cannot be relied upon to be in any way related to reality.

[jelunga]

That's half the problem. It comes down to "Standards" again. The standards are often (mostly?) drawn up by idiots. The "standards bodies" define the tests (which are usually nothing like reality and utter bollocks) then the manufacturers run the tests as they are told to.

 

It does have the advanatage that everyone is testing to the same standards so it's easy to compare one fridge against the next, but it has the disadvantage that the figures produced cannot be relied upon to be in any way related to reality.

 

Plus they design the product to give excellent results using the "standard test", but actually give crap results in real life. For example, who drives at a constant 56mph? Chance would be a fine thing eh?

[Gibbo]

Plus they design the product to give excellent results using the "standard test", but actually give crap results in real life.

 

I'd never even thought of that but it makes perfect sense!