12v nightmare,

[Richard Bustens]

Hi that is what i said.

So does that mean that Khayamanzi inverter has a power loss of 120% or what

But it probably explaines why his batteries are going down if a 750W unit is drawing 150 - 200 A

Or am i compleatly on the wrong track.

[ChrisPy]

hi John

So how many amps from a 12v battery then to run it

Is that not the same as i hrs use ie 71.74 ah to run

Is that not what the drawing from battery should be?

<{POST_SNAPBACK}>

Richard,

 

there is always confusion about AH (amp-hours).

 

a gadget which draws 750w uses 3A at 250V before allowing for losses.

 

the same gadget consuming 750W from an inverter which is supplied at 12V draws 750/12 amps before allowing for losses.

 

Assuming 90% of the power that comes into the inverter is usable as power out (90% efficiency) that is 62+6=68A.

 

In one hour that would consume 68AH units from your battery.

 

For a microwave, used for say 5minutes at full power (they don't do that, do they, because they cut in and out) that would be about 6AH of units of power used from your battery.

[John Orentas]

Richard.

 

750 watts @ 12 volts = 62.5 A

 

+ 10% = 69 amps

 

For one hour use. = 69 amp / hours

 

A bit of a modern inovation this amp / hour thing. I think it is American influence. A/h was only used for battery capacicity.

 

Watt / hour is a more sensible and meaningfull unit, it is used extensively in industry as a unit of energy.

 

As an aside, you can now buy watt / hour meters. In the automated mixing of bread dough there was always a problem.

 

A slightly stiff mix would produce enormous amounts of unwanted heat into the dough. Someone came up with the idea of putting so many watt / hours into the mixing with the result that the dough temp is always the same regardless of the mix.

 

John Squeers

[Richard Bustens]

Hi John

In that scenario then John with only that one itim running, what should a amp meeter show as the discharge. 69? or would it be diferent?

[nb maggie]

On a different tack, check the fridge/freezer temp. Often these are set far to low. When I once hired a boat I found that the energy consumption was significantly improved by changing the Fridge Theremostat setting. This is also a real issue for home energy efficiency with fridges using a lot of 'lecy due to poor setting. Stick a cheap thermometer in the fridge and set the fridge so it is a reasonable temp for what you store. It does not need to be so cold for salad, veg, uncooked red meat, cheese, milk, drinks etc. Colder for fish, white meat and cook chill/ready meals. Also how empty is it. An empty fridge or freezer will use a lot more energy than a full one. If the fridge is half empty fill it up with beer!!!

[John Orentas]

Richard.

 

The ammeter on the 12 volts would read 62.5A (it would not see any losses in the inverter)

 

The ammeter on the 230 volts would read 3.6A (some heat given off will make the energy difference)

 

A watt / hour meter would be clicking round like a mileometer

 

John Squeers

[ChrisPy]

Richard.

 

750 watts @ 12 volts = 62.5 A

 

+ 10% = 69 amps

 

For one hour use.  = 69 amp / hours

 

A bit of a modern inovation this amp / hour thing.  I think it is American influence. A/h was only used for battery capacicity.

 

Watt / hour is a more sensible and meaningfull unit, it is used extensively in industry as a unit of energy.

 

As an aside, you can now buy watt / hour meters.  In the automated mixing of bread dough there was always a problem.

 

A slightly stiff mix would produce enormous amounts of unwanted heat into the dough.  Someone came up with the idea of putting so many watt / hours into the mixing with the result that the dough temp is always the same regardless of the mix.

 

John Squeers

<{POST_SNAPBACK}>

 

John, to avoid confusing the masses further we should be more careful about our units. Amp-hour or Amp.hr but not Amp/hr. We'll get them their electrical diplomas one of these days!

 

thanks

[DHutch]

On a different tack, check the fridge/freezer temp. Often  these are set far to low. When I once hired a boat I found that the energy consumption was significantly improved by changing the Fridge Theremostat setting.

 

when our fridge only has the milk in it we turn it down as low as it will go, and then put the milk in the frezer box (sitting on a ice tray so it not accutaly touching the coolent pipes) and like this we can run it for about 3days,

 

daniel

[John Orentas]

NB Magie

 

"An empty fridge or freezer will use a lot more energy than a full one. If the fridge is half empty fill it up with beer!"

 

I don't see the logic in that, please explain.

 

John Squeers

[Paul Evans]

If your fridge is full of cold stuff, it will stay cold longer because the cold stuff - unlike cold air - can't get out when you open the door. There are two problems with the proposed solution - the fridge has to work hard to cool the beer and you can't take the beer out for fear of replacing it with warm air.

 

The best beer cooler I ever came across was a cupboard/wardrobe that had no floor. The beer bottles sat directly on the baseplate - a couple of hours running, even in the summer, and the beer was a perfect temperature. None of that nasty chilled stuff.

[Tommo]

With a microwave, the power consumption is probably double that of the cooking power rating.

 

Tommo

[nb maggie]

When you open a fridge door all the cold air literally 'falls out'. If you have ever used very low temp freezers you can actually see it moving across the floor as soon as you open it.

 

Using beer or anything will both reduce the amount of air that can fall out and hold more cold in the fridge.

 

 

Yes it takes some energy to get the beer cold but this is more than offset by the saving over time.

 

PS. I have just done a 'net search on the above points and there is loads of advice for govt type energy efficiency bodies and manufacturers that supports this. Actually the correct advice is don't get a bigger fridge than you need.

 

Doesn't seem that is has to be beer though ... Sshh don't tell anyone I said that, I have kidded my family for years

 

Neil

[DHutch]

The best beer cooler I ever came across was a cupboard/wardrobe that had no floor. The beer bottles sat directly on the baseplate - a couple of hours running, even in the summer, and the beer was a perfect temperature.

 

yeah, we once left a pan of curry boilers base plate (which is welded to the base plate via the steel batterns) and it was fine for days, not a great place if the boilers lit though!!

 

 

daniel

[Big COL]

NB Magie

 

"An empty fridge or freezer will use a lot more energy than a full one. If the fridge is half empty fill it up with beer!"

 

I don't see the logic in that, please explain.

 

John Squeers

<{POST_SNAPBACK}>

 

 

John

 

Your tugging on legs again The logic in this only applies if the freezer or fridge is loaded with pre-frozen or pre-chilled food, otherwise any energy saved is used up freezing or chilling the goods down to temperature. Fridge economy can be obtained overnight by turning the stat up higher, the contents have given off the required heat to reach normal settings, and the heat loss overnight will be minimal as the door is closed for this period. Any heat gain will be offset by the colder contents, and the stop starts (short cycling) will be reduced.

Short cycling is the main cause of a power drain, the start up currents are high and if this occurs too often the power drain is considerable. Thermostat temperature differentials tend to be around 1 degree C which to my mind is too short, if they were at 2 degree C you could halve the start ups where the high current draw occurs.

This is where the gas fridge scores over the electric fridge, as it has no compressor to run, but I still wouldn't have a gas fridge for all that.

[John Orentas]

Neil.

 

No still don't see the point. There is not much energy required to cool a couple of cubic feet of air on the other hand there is a lot required to cool several cans of beer.

 

John Squeers

[timboharticus]

The heat capacity of air is very low so the air which spills out when opening the fridge is insignificant.

 

I suggest it is a good idea to get some glycol packs in the fridge to reduce the cycling of the compressor. These could also be used in a (non- electric)coolbox etc. if required.

 

Microwaves, fridges, breadmakers- whatever next.

[khaffra]

Having checked the consumption of power on my microwave a while ago it was found to pull 100 amps out of the batteries via the invertor. The cooking power of the microwave is 750W but the electrical power useage (on the backplate) is 1200W at 240V. Although this is a high current it is rare it is used for more than a couple of minutes so total battery drainage is not great.

 

The 1500W invertor running with no load is approx 2.5 Amps so this is a considerable amount if left switched on permanently so is swithed off overnight.

 

The fridge on my boat is large and seems to be very inefficient it draws 10 amp when run on 12V or 12.5 amp on 240V (including invertor) and I think it runs almost constantly and gets very warm above it. I am going to try and give it more ventilation and see if it is anymore efficient.

[John Orentas]

Hi Khaffra

 

I assume you have a fairly sophisticated battery charging system. The consumption figures you quote a pretty much in line with what you should expect, though the fridge does seem very inefficient, the way you describe it, it is an absorbtion type like an Electrolux.

 

The off load current useage of the innveter is not un-typical though few people bother to measure it.

 

Are you having any particular bother with your system.

[khaffra]

The fridge is a electrolux gas/12/240 fridge and full size, seems to struggle to get down to temperature and I have been told that they require quite a lot of ventilation to work correctly and due to this one getting quite warm I suspect it needs more ventilation.

 

Battery system has 660AH of Batts 90AH alternator and Adverc Alt controller, We do not live aboard and generally cruise quite a bit each day so have never really had any battery problems.

[Richard Bustens]

The no load reading for the inverter seems a bit high.

Victron quote 10w which is less than 1/2 Amp @24v.

[John Orentas]

Richard.

 

Victron quote that figure but have you actually measured it.

 

1/2 amp is right at the bottom end of what is attainable.

[John Orentas]

Your fridge is really manufactured as an absorbtion type gas fridge, the facility for running it on electricicy is very much a secondary option, it fact it is no more than heating elements which mimic the effect of the gas flame.

 

I would assume that the functions are the same as it's smaller counterpart so there will not be a controlling thermostat though the gas system does have multiple settings. If I was in your position I would certainly run the fridge on gas, though there is a fashionable anti-gas movement going at the moment. If you go along with that a more efficient compressor type fridge should be considered.

Edited December 30, 2004 by John Orentas

[Richard Bustens]

Hi John

As well as Victron quoting 10w Mastervolt quote .5w in standby and 5.5 in the on position and sterling quote 1-25w adjustable.

All these are well under 2.5A and neglible to say the least.

And no i have not tested any of them but surley if they put it in print it must be right. 2.5a @ 12v is 30 w and 60w @24v

[John Orentas]

Hi Richard.

 

I did a lot of research on inverters for an article in Waterways World, I found some inverters will take up to 2 amp and others as low as 0.2 amp. I did make a note however that many manufacturers had a prefix 'Nominal' or 'Typical'.

 

Richard, it's about time you learned to be cynical and suspicious.

[Richard Bustens]

LOL I do try John but it has always been my downfall, if i had been a bit less trusting i would have been very rich by now

But i have learnt one thing and that is dont trust Scouse business partners, as they empty the bank account and run off with it all leaving me to pick up all the tabs.