# Working out power consumption



## MeatandMocha (Nov 3, 2017)

Hello

Does anyone have links or know formulas to work out power consumption.

I'm working out whether its possible to use just leisure batteries to power equipment or have to go generator route. Going gas route adds complications but I know that's possible too.

TIA

Alastair


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## Stanic (Dec 12, 2015)

I can comment based on experience with miss Silvia and meCoffee PID - it would work on 100% power in the first 5-minutes and after the temp has stabilised, it would oscillate between 7-10% power consumption when idle


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## El carajillo (Mar 16, 2013)

It would be helpful if you stated exactly what you wish / want / expect to run from batteries, including their power requirements.

How would you recharge the batteries ?


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## MeatandMocha (Nov 3, 2017)

El carajillo said:


> It would be helpful if you stated exactly what you wish / want / expect to run from batteries, including their power requirements.
> 
> How would you recharge the batteries ?


That's what I am asking basically ....

I shall be running a 2 group machine with grinder and fridge and maybe blender. What I am asking is if anyone can explain the formulas used to work out power consumption over an hourly rate. I have seen it before on I think a solar power website, but can't find it again.

I'm sure there is a formula where you divide volts by watts time amps etc etc to work out hourly consumption to then work out what batteries I will need.

I don't have a definitive list of equipment so hence only looking out how to work it out.


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## Batian (Oct 23, 2017)

Phew! That could be a lot of weight to carry around. That will increase the vehicles running costs.

Something else to consider, it may even put you over the weight limit for the vehicle / licence/road tax?


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## billt (Jul 10, 2013)

The most important thing for this scenario is maximum power, which should be shown on the rating plate of the machine. Your battery/inverter needs to be able to supply the maximum power the machine takes with a bit of margin on top. A single group machine is likely to be about 3 kW.

The size of the battery is determined by the energy used by the machine. Simplistically, if the heater was on all the time that would be 3kWhr for a 3kW heater, but as the heater only needs to operate intermittently it will be much less than this, maybe 0.4kWhr at a guess. You need to measure it for accuracy, there is no meaningful formula to work it out.

The size of the battery you need is determined by the capacity of the battery in Ahr and the battery voltage. Say you use a 100Ahr battery at 12V, the theoretical maximum energy that can supply is V x AHr, or 12 x 100 = 1.2kWhr. However, lead acid batteries will soon die if you discharge them excessively and Leisure batteries aren't really designed for deep discharge, they probably shouldn't be discharged more than 40% for a reasonable life. That reduces your energy capacity to 0.48kWhr; enough to keep our speculative machine going for about an hour.

Short answer, it's not sensible to run a big machine of batteries for any length of time. Use a generator if you can't use gas.


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## MeatandMocha (Nov 3, 2017)

Ah got what I was looking for -

Power = Volts x Amps

Amps = Power/Volts

All amps together = total load

Battery Ah/Total Amps = time to run


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## Jacko112 (Oct 29, 2015)

Batian said:


> Phew! That could be a lot of weight to carry around. That will increase the vehicles running costs.
> 
> Something else to consider, it may even put you over the weight limit for the vehicle / licence/road tax?


This is so important & something most people don't even think about. Since 1991 ( I think) you stopped getting a lot of categories on your licence ie. being able to a minibus or being able to tow. The dvsa will have a field day if you're over the payload & will impound the vehicle.


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## ajohn (Sep 23, 2017)

Probably better off with a motor generator for that lot if you want electric. Lead acid battery capacity isn't that simple - the rate it's taken out varies it a lot. Leisure batteries are intended for relatively low current draws. Car batteries are mainly aimed at engine starting - that one used to be 3min at -40C or there abouts. It's 20hr rate might 40 odd AH. 10hr less and 5hr a lot less.

A better alternative is probably a gas espresso machine and fridge. That just leaves the grinder and blender. Those seem to have the power draw shown on their plate rather than the actual motor output power.

John

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## Thecatlinux (Mar 10, 2014)

MeatandMocha said:


> That's what I am asking basically ....
> 
> I shall be running a 2 group machine with grinder and fridge and maybe blender. What I am asking is if anyone can explain the formulas used to work out power consumption over an hourly rate. I have seen it before on I think a solar power website, but can't find it again.
> 
> ...


not feasible im afraid , the cable sizes from the battery's would have to be rather large to cope with this , hence the main concesous is the maximum inverter size shouldn't exceed 1kw on 12v system , I suppose you could always create a series battery bank to increase to 48volts , this is all possible but costs would be prohibitive.

invest in a silent run generator or run on gas


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## El carajillo (Mar 16, 2013)

Something to bear in mind, the MGW on vans INCLUDES the driver. A colleague of mine was stopped and was informed of this fact.

It cost him £600 fine + points


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## CallumT (Aug 23, 2013)

Conversion losses through efficiencies in the inverters would be costly in a 12v system too meaning you need to generate even more to power same load. Consider LPG / dual fuel machines. I have seen trikes operating solely on banks on leisure batteries but never had any experience on the actual setup unfortunately.


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## MeatandMocha (Nov 3, 2017)

Thanks everyone, now I just need to figure out whether to get a silent generator or to go gas.


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## Batian (Oct 23, 2017)

MeatandMocha said:


> Thanks everyone, now I just need to figure out whether to get a silent generator or to go gas.


 A genny keeps more options open for other uses, but remember most cases of electrocution are caused by portable generators. You do need to be up to speed in their use and understand 'earthing'.

Make sure you or others are not it!

When I had a genny (to run the house because of frequent power cuts) the sparky added to the 'on board' RCDs a plug board with individual RCDs to each socket and an additional earth strap.


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## MeatandMocha (Nov 3, 2017)

Batian said:


> A genny keeps more options open for other uses, but remember most cases of electrocution are caused by portable generators. You do need to be up to speed in their use and understand 'earthing'.
> 
> Make sure you or others are not it!
> 
> When I had a genny (to run the house because of frequent power cuts) the sparky added to the 'on board' RCDs a plug board with individual RCDs to each socket and an additional earth strap.


that I'm happy to say I'm ok on, strangely I'm a facilities engineer right now. And the owner of where I work also owns one of the biggest generator hire companies. I will be picking his brain. And before you ask all his are huge generators the size of mobile homes. I might get discount though !


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## Batian (Oct 23, 2017)

I am surprised you even considered batteries!

Genset do some very quiet, small diesel gennys, but oh so expensive. They are well thought off, by all accounts.


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## MeatandMocha (Nov 3, 2017)

Batian said:


> I am surprised you even considered batteries!
> 
> Genset do some very quiet, small diesel gennys, but oh so expensive. They are well thought off, by all accounts.


Mum good at safety but not that knowledgable on the finer things lol ! I think it was wishful thinking and lack of knowledge of battery power etc it would of been nice to charge them up park up and use battery power all day but then using the formula I started to realise it's dream land.


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## ajohn (Sep 23, 2017)

Gas will probably give you most energy per unit weight on the powering side but leaves the problem of grinder and blender. A suitable battery might be a 6TN

http://www.fcl-online.co.uk/Catalogue/BATTERIES/MILITARY/BATTERY-6TN-ST6TN

That seems to be rather cheap. Many years ago I designed a version of that for a tank. Had to be waterproof and stand submersion. It was interesting that the level it was kept at was some way over the heads of the people in it.

John

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## El carajillo (Mar 16, 2013)

Gas powered jenny? Would run machine + grinder. Less noise , smell and pollution.


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