Inverter power drain

[nb Innisfree]

We used to leave our Multiplus 24-3000-70 switched on 24/7. With zero 240v load consumption was approx 0.5 amps, I once saw it drop to 0.2amps (BMV 501)

Double those figures for a 12v model and worse case 24hr standby would be 24a/h

It never hesitated to power any load whether small or large. 

[Drayke]

Perhaps another reason to go 12v is that it stays on when inverter is off, piece of mind, providing you have power in batteries, but then the inverter would not work if there wasn't.

[Theo]

9 hours ago, WotEver said:

Who knows? Without a spec sheet you'd have to measure it to know, unfortunately. 

That's way everyone needs a clamp meter.

 

N

[Theo]

6 hours ago, sirweste said:

Yer, but typically you've got one of those for the other mod cons onboard e.g. Fan heaters, hair dryers, tumble dryer, kettle, oven and hob etc

If you have that lot you probably need a butty to carry the battery bank and gennie to charge it!

 

N

[Cloudinspector]

So there doesn't seem to be a definitive answer then. 

[rusty69]

7 hours ago, Cloudinspector said:

So there doesn't seem to be a definitive answer then. 

Yes, there is

 

Zero load power = 20W

Zero load power in AES mode =15W

Zero load power in search mode =8W

[sirweste]

8 hours ago, Cloudinspector said:

So there doesn't seem to be a definitive answer then. 

As I did for my system on the second page of this thread (as you know the model and make of your fridge and inverter) you can easily work out the typical consumption. 

Then compare this to the 12 V options and the efficiency figures quoted by the manufacturer - this bit isn't ideal as you don't know what cycle they have done and how comparable it is to the EU spec, but it should give you some idea.

With regards fridge repair, as said previously our family business is white good repairs and sales, typically the only this that's economical to replace in a fridge is the thermostat. If the compressor or insulation has failed then it usually makes more sense to scrap them.

[Cloudinspector]

1 hour ago, rusty69 said:

Yes, there is

 

Zero load power = 20W

Zero load power in AES mode =15W

Zero load power in search mode =8W

You'd have to explain those figures in more detail. Are they per day? What's AES mode? What's search mode?

[Sea Dog]

9 hours ago, Cloudinspector said:

So there doesn't seem to be a definitive answer then. 

Don't use your inverter for essential stuff if you don't have to - even good ones consume energy and keeping your batteries happy is challenging enough as it is.

[rusty69]

5 minutes ago, Cloudinspector said:

You'd have to explain those figures in more detail. Are they per day? What's AES mode? What's search mode?

Have you read the instructions to the inverter /charger you own? 

[Cloudinspector]

2 minutes ago, Sea Dog said:

Don't use your inverter for essential stuff if you don't have to - even good ones consume energy and keeping your batteries happy is challenging enough as it is.

I've always assumed that a 12v fridge is the no brainer option. However reading some of the figures quoted on here that may not be the case. I think the curve ball is that we need the inverter to power the diesel range which is providing our cooking, hot water and heating.

[sirweste]

4 minutes ago, Cloudinspector said:

You'd have to explain those figures in more detail. Are they per day? What's AES mode? What's search mode?

Have a look at my post on page two, you're taking the instantaneous power usage, for example 20 W and then multiplying by time to give you work. Thus 20 W x 24 h gives you 480 W.h  i.e. nearly 0.5 kW.h to put it in domestic electricity bill terms.

I suspect that due to your relatively inefficient inverter the 240 V option will come out poorly

[Cloudinspector]

Just now, rusty69 said:

Have you read the instructions to the inverter /charger you own? 

Yep, several times and I'm still non the wiser as to what those specific figures are telling me. 

[rusty69]

9 minutes ago, Cloudinspector said:

I've always assumed that a 12v fridge is the no brainer option. However reading some of the figures quoted on here that may not be the case. I think the curve ball is that we need the inverter to power the diesel range which is providing our cooking, hot water and heating.

Then the answer for your circumstances is clear(to me anyway)  

Save the extra  money you would have spent on a 12v system and add solar if not already done so. 

Edited May 3, 2017 by rusty69

[Alan de Enfield]

13 minutes ago, Cloudinspector said:

You'd have to explain those figures in more detail. Are they per day? What's AES mode? What's search mode?

You need to take the 'wattage' and multiply it by the number of hours to give you 'Wh'

So for one day usage take 20w x 24h = 480Wh

To convert this to Amp/Hours taken from you battery you divide by 12 (formula is W=AxV) so you are taking 40Ah from your battery.

However - due to inefficiencies in the conversion of 12v to 240v it is 'safer' to use a divider of 10 (instead of 12)

So your 480Wh actually takes 48Ah from your battery.

 

You now need to consider the replacement of this 48Ah, due to the 'laws' and inefficiencies you will actually need to replace the amount used and add (roughly) 20% extra so you now need to actually replace 57Ah.

You may think "this will just take less than an hour with my 70A alternator", however charging batteries does not work like that it is actually the battery SoC that determines the rate of charge, NOT the battery charger / alternator. This is a whole separate subject, but, just to say running your inverter- on its own - for 24 hours at 20w consumption with nothing connected to it, you will possibly need to run your engines for a couple of hours to replace the power it uses.

Edited May 3, 2017 by Alan de Enfield

[rusty69]

2 minutes ago, Cloudinspector said:

Yep, several times and I'm still non the wiser as to what those specific figures are telling me. 

You could always measure the consumption, then you would know for sure. 

[Cloudinspector]

4 minutes ago, Alan de Enfield said:

You need to take the 'wattage' and multiply it by the number of hours to give you 'Wh'

So for one day usage take 20w x 24h = 480Wh

To convert this to Amp/Hours taken from you battery you divide by 12 (formula is W=AxV) so you are taking 40Ah from your battery.

However - due to inefficiencies in the conversion of 12v to 240v it is 'safer' to use a divider of 10 (instead of 12)

So your 480Wh actually takes 48Ah from your battery

Perfect. I can now make some sense of it all, thanks.

[Cloudinspector]

13 minutes ago, sirweste said:

Have a look at my post on page two, you're taking the instantaneous power usage, for example 20 W and then multiplying by time to give you work. Thus 20 W x 24 h gives you 480 W.h  i.e. nearly 0.5 kW.h to put it in domestic electricity bill terms.

I suspect that due to your relatively inefficient inverter the 240 V option will come out poorly

That's what I suspected however the inverter needs to be on for some periods of the day to power the diesel range which is providing our cooking, heating and hot water. Also don't forget we are off grid with built in diesel generator and 300w of solar due to be fitted.

[Robbo]

21 minutes ago, Alan de Enfield said:

You need to take the 'wattage' and multiply it by the number of hours to give you 'Wh'

So for one day usage take 20w x 24h = 480Wh

To convert this to Amp/Hours taken from you battery you divide by 12 (formula is W=AxV) so you are taking 40Ah from your battery.

However - due to inefficiencies in the conversion of 12v to 240v it is 'safer' to use a divider of 10 (instead of 12)

So your 480Wh actually takes 48Ah from your battery.

 

There is no conversion, as we are talking about the inverter power consumption itself.  So the multiplus will use 40Ah not 48Ah, however in practise it uses alot less.

[Alan de Enfield]

1 minute ago, Robbo said:

There is no conversion, as we are talking about the inverter power consumption itself.  So the multiplus will use 40Ah not 48Ah, however in practise it uses alot less.

Yes - correct - I was getting ahead of myself. Thank you.

[Cloudinspector]

The replacement A++ rated replacement Liehberr fridge is quoted at 0.255 kw/h per day.

using Alan de Enfield formulas that would take 25.5 ah from the batteries. Add that to the 48ah taken by the inverter and you have 73.5 ah compared 66 ah for the 12v waeco. Given that we need the inverter on for some periods of the day to power the range it would appear that sticking with 240v is the answer.

any comments on my conclusions? Maths and electrical stuff isn't my strong point so I may have got something wrong.

[rusty69]

8 minutes ago, Cloudinspector said:

Add that to the 48ah

40Ah (worst case) 

8 minutes ago, Cloudinspector said:

Given that we need the inverter on for some periods of the day to power the range it would appear that sticking with 240v is the answer

As said above, particularly if you have an inbuilt diesel generator, the answer is clear. 

Edited May 3, 2017 by rusty69

[Alan de Enfield]

4 minutes ago, Cloudinspector said:

The replacement A++ rated replacement Liehberr fridge is quoted at 0.255 kw/h per day.

using Alan de Enfield formulas that would take 25.5 ah from the batteries. Add that to the 48ah taken by the inverter and you have 73.5 ah compared 66 ah for the 12v waeco. Given that we need the inverter on for some periods of the day to power the range it would appear that sticking with 240v is the answer.

any comments on my conclusions? Maths and electrical stuff isn't my strong point so I may have got something wrong.

If you wish to convince yourself further and 'make the figures look better', you could actually apportion the Inverter consumption to the other appliances and deduct it from the 'fridge total'.

It is just playing with numbers and doesn't affect the actual total AH from the battery.

Its probably swings & roundabouts in this particular instance.

[Sea Dog]

1 hour ago, Cloudinspector said:

I've always assumed that a 12v fridge is the no brainer option. However reading some of the figures quoted on here that may not be the case. I think the curve ball is that we need the inverter to power the diesel range which is providing our cooking, hot water and heating.

If your inverter is on 24/7 anyway, you're already bearing it's internal losses and, effectively, the more it powers the less it's overhead in percentage terms. In the summer, when your heating becomes less of a dominant issue, solar will be an option to cover the drain of your mostly idling inverter. 

The difficulty comes when you have essential services like heating and fridge on your inverter and it goes duff - then either you're cold or your beer is warm! Neither of these scenarios is a good thing.

[sirweste]

4 hours ago, Cloudinspector said:

The replacement A++ rated replacement Liehberr fridge is quoted at 0.255 kw/h per day.

using Alan de Enfield formulas that would take 25.5 ah from the batteries. Add that to the 48ah taken by the inverter and you have 73.5 ah compared 66 ah for the 12v waeco. Given that we need the inverter on for some periods of the day to power the range it would appear that sticking with 240v is the answer.

any comments on my conclusions? Maths and electrical stuff isn't my strong point so I may have got something wrong.

Yep you're bang on there pal. Stick with 240 V. Put the money saved by not buying a 12 V unit towards more solar or in a savings pot towards a better inverter