# Power consumption



## loddy (Feb 12, 2007)

Hi Guys

What is the formula to work out how long my Remoska will run for ??

3x100 amph batteries and a 1000 watt inverter and Remoska 650 watt

Loddy suffering from brain down time


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## karlb (Feb 22, 2009)

at 650watts you are drawing over 50amps so it wont be a long time


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## clodhopper2006 (Aug 13, 2006)

loddy said:


> and Remoska 650 watt
> 
> Loddy suffering from brain down time


Hi Looddy, I don't know what the quote above means but to work out battery endurance you first work out the amps by dividing the power by the voltage. So if you are using a constant power of 1650W, at 12v you will have a current flow of 137.5A. Next divide the amps into the Ah (amp hour) and you will see you get 2.18 hours.

Bob


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## loddy (Feb 12, 2007)

The batteries 12v power the Inverter 230v and the Romeska runs off the inverter 650 watt @ 230 volt

loddy


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## karlb (Feb 22, 2009)

clodhopper2006 said:


> loddy said:
> 
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> > and Remoska 650 watt
> ...


the above quote is 650watts so power is voltage multiplied by current

12 times 50 = 600 hence i said over 50 amps!! with overheads running the inverter the current flow is nearer 60 amps not 137.5 so in theory with 3 100ah batterys you might get 5hrs in practice more like 1-2hrs with a current flow of 55-60 amps


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## loddy (Feb 12, 2007)

Thank you

loddy


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## clodhopper2006 (Aug 13, 2006)

karlb said:


> clodhopper2006 said:
> 
> 
> > loddy said:
> ...


But I was answering the OP's question, there are two inverters not one. Total load 1650w divided by 12 = 137.5A not 55-60A.


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## 111154 (Apr 6, 2008)

clodhopper2006 said:


> karlb said:
> 
> 
> > clodhopper2006 said:
> ...


The remoska 650watts appears to be the miniature cooker, not an invertor. :?:


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## karlb (Feb 22, 2009)

clodhopper2006 said:


> karlb said:
> 
> 
> > clodhopper2006 said:
> ...


as i understand it the cooker is plugged into the inverter so hence a load of 650watts+, please confirm loddy.


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## Pudsey_Bear (Sep 25, 2008)

I got 54.1666666666 amps, but I'm totally out of my depth, I'm trying to get to grips with electrickery in Mh's, if only to understand posts like these.

Kev.


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## loddy (Feb 12, 2007)

Yes the cooker is rated at 650 watts at 230 volt and plugged into the inverter which is 1000 watt rated, powered by 3x100amph batteries

Loddy


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## gromett (May 9, 2005)

Also remember the faster that you pull current out of a battery the less there actually is to get. For example my 220AH batteries are rated at that while I am pulling 22A out of it. If I increase that to 40Amps it will drop the battery rating down to around 180Ah. (Peukert's law)

The formula for this is InT=C 
I = the discharge current (in amps)
n = an exponent related to battery construction.
T = The duration of discharge (in minutes)
C = The capacity removed as a result of that discharge.

If n=1 then 100Ah battery always has 100Ah no matter how fast you discharge it but n is never = 1 1.2 is normal but it can be slightly lower in better quality batteries. 

Also remember it is best not to fully cycle a battery. Its best not to take them below 50% if you want a reasonable life span out of them.
Battery life is related to how deep the battery is discharged each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is only discharged to 80%. If discharged to only 10% , it will last about 5 times as long as one cycled to 50% these are just rough figures but show the problem.

My batteries state that all ratings are based on a 10 hour discharge time. So 220Ah if I discharge it at 220/10 = 22Amps/hour. I have 4 of them installed so the max I can take is 88Amps/hour without reducing the effective capacity of them. 88 x 12 = 1056Watts. less invertor efficiency I am looking at probably around 800Watts of usage before my battery capacity starts to be effectively lower.

Anyway, am rattling now and probably going into far too much details and including some rough and ready figures at the same time which is not a good idea.

Karl


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## Pudsey_Bear (Sep 25, 2008)

Crackin rattle Gromett, arf arf.

You'd think when they first made electrickery, they'd have made it a bit more simple like.

Happen now there's a bit of a recession, they'll have a few spare boffins to simplify it all for us numpties, ther could be some money to be made there me thinks.

Kev


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## clodhopper2006 (Aug 13, 2006)

Peukert's law

life, never simple is it  Yes Kev it is 54A


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## 123243 (May 7, 2009)

*batteries*

Hi There
The 54 amps is in the right ball park. Inverters are not 100% efficient, and you need to take into account the output type, i.e. sine or square wave. The manufactures manual will state the efficiency, e.g. 90% in which case you need to add 10% extra current, ≈ 59Amps.

The biggest problem is not the amount you take out of the batteries, it is how long it takes to put it back. RVs and boats all have this problem, The initial current into the batteries will be say 10 amps (depends on the charger) and as the charge comes up and the batteries begin to gas, then the charge rate reduces to a more moderate level, say 5 amps. So you can work it out yourself, a battery stack of 300Ah charging at 10 amps would take 30 hours to reach full charge again, and as the charge rate will reduce long before full charge is reached, the recon on 50 hours.

The more intelligent charges go through a cycle of boost charge / bulk charge / & trickle charge, but they may have problems with a battery stack as the sensor which send battery information back to the charger will be on one battery only, and the other two just have to follow whatever the charger decides to do based on the single sensor.

A further correction is needed to the statements above. Most battery manufacturers calculate the Ah of a battery over a 20 hour discharge rate. A 100Ah battery is given this rating if (100Ah / 20Hrs = 5amps) discharging at a rate of 5 amps per hour (60watts).

This chart shows battery capacity Vs hours discharge

Battery capacity % loss	Hours of discharge
100	20
90	10
87	8
83	6
80	5
70	3
60	2
50	1

The higher the discharge rate, the lower the battery capacity in Ah.

sorry table not showing correctly

hope this helps
Joe


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