Lithium Ah to A.C. Kw conversion rates

[Nigel Crompton]

Is there a formulae/rule of thumb for estimating in advance how many Ah an 'x' Kw device will use ?
If I use a 2kw induction hob for 30 mins what Ah will that take out of the battery ?


I know battery monitors will give instantaneous readings, has anyone a note of such discharge rates?

And I know some inverters are more efficient than others, and cable sizes have an effect.

I can afford 1x200ah or 1x150ah; I have space for 2x150ah but I think the latter is overkill .....

Just trying to get a feel.

 

[Gromett]

I use the nominal 12v value.

So W / V = A

2000 / 12 = 166 Amps.

You then need to add a conversion efficiency loss. I use anything from 10% to 20% depending on how conservative I want to be.

 

[Lenny HB]

Watts/kilo watts is the same whatever the voltage.
So a 2000 watt device will take 2000/12 = 166.66 amps add 10% for inverter efficiency so 183 amps. So if you ran a 2000 watt device for 30 min it would take 92 amps out of your battery.

BUT induction hobs & air fryers pulse on and off, so in practice would probably use less than half that amount of power.

 

[Gromett]

Also worth noting that the chemistry of the battery will affect the real world result as well.
The peukert exponent is higher for a lead acid for example than a Lithium.

In a lead acid the faster you take the power out of the battery the lower the effective capacity.

10. Battery capacity and Peukert exponent

www.victronenergy.com

And a lead acid should never be taken below 50%. So bear this in mind.

 

[Nigel Crompton]

And a lead acid should never be taken below 50%. So bear this in mind.

Thank-you. I am trying to estimate the lithium capacity I need in my conversion.

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[Gromett]

Thank-you. I am trying to estimate the lithium capacity I need in my conversion.

You can pretty much ignore peukert for Lithium when calculating needs. Other factors will be far bigger

 

[Nigel Crompton]

You can pretty much ignore peukert for Lithium when calculating needs. Other factors will be far bigger

My choice is, basically, an affordable 1x200ah (@€650) or a somewhat less affordable 2x150 (€1000) (I'm limited to what the supplier will fit, this is not DIY)

 

[olley]

Don't know a great deal about lithium, but taking around 180+amps out of your 300ah less affordable option, doesn't sound good to the batteries to me. But better than the 200ah option.

 

[Gromett]

My choice is, basically, an affordable 1x200ah (@€650) or a somewhat less affordable 2x150 (€1000) (I'm limited to what the supplier will fit, this is not DIY)

Ah, just noticed you are in Spain not the UK. Was just about to suggest you check out fogstar which are much cheaper than that.

When choosing I would think about this. If you get the 200ah now, and need to upgrade later you can't just add another battery I presume?

If it were me I would be veering towards getting the full setup now, as it will cost less in the long run rather then trying to upgrade later?

Just my two pennies worth.

 

[Tombola]

Had rememebr if you fit 2 batteries as opposed to one, the load is split across the 2 so isn't as damaging.

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[Nigel Crompton]

When choosing I would think about this. If you get the 200ah now, and need to upgrade later you can't just add another battery I presume?

Correct, whereas I could go for the 1x150ah now and add a second 150ah later .... if that particular battery was still available ...

 

[Steve and Denise]

Correct, whereas I could go for the 1x150ah now and add a second 150ah later .... if that particular battery was still available ...

I was told it’s not best practice to add lithium batteries of different ages by Roamer batteries

 

[headlight]

Correct, whereas I could go for the 1x150ah now and add a second 150ah later .... if that particular battery was still available ...

Will a 150AH run a 2000 watt inverter ?
What is the max continuous draw rating of the battery BMS ?
You will need the BMS to be rated at 200 amps continuous draw.

 

[Nigel Crompton]

Will a 150AH run a 2000 watt inverter ?
What is the max continuous draw rating of the battery BMS ?
You will need the BMS to be rated at 200 amps continuous draw.

Good questions ....

 

[Nigel Crompton]

What I'm really looking for is working examples of lithium capacity & usage.

" We have 100ah lithium and 50w solar and do roast beef & Yorkshires for six in the air-frier on rainy days in a farmer's field"

Sort of thing ...

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[suavecarve]

We got through about 50 ah in half hour of 1300 watt air fryer.

As an aside the 280 ah from fogstar currently at 680 English notes fits under the seat on its side of our fiat and actually gives 304 ah if you can get a funsters delivery service

 

[bigtwin]

Will a 150AH run a 2000 watt inverter ?
What is the max continuous draw rating of the battery BMS ?
You will need the BMS to be rated at 200 amps continuous draw.

This is likely to be the deciding factor. I doubt that a single BMS will handle that sort of current.

Ian

 

[headlight]

This is likely to be the deciding factor. I doubt that a single BMS will handle that sort of current.

Ian

My Fogstar 230AH BMS is rated at 200 amp continuous. I'm pretty sure that the new 230AH, mine is 8 moths old, is rated at 250 amp continuous.

 

[headlight]

What I'm really looking for is working examples of lithium capacity & usage.

" We have 100ah lithium and 50w solar and do roast beef & Yorkshires for six in the air-frier on rainy days in a farmer's field"

Sort of thing ...

Here you go, I have a 230AH Lifepo4, 230 watts solar and a 2,000 watt inverter.
I run a 1400 watt air frier, 1200 watt Panini maker and a 800 watt microwave.
Not all at the same time obviously.
I've just done 17 nights stationary on a site without EHU.
Lowest my battery got was 65%.
Sunshine hasn't been good and the battery only reached 100% SOC twice in the 17 days.
But being Lifepo4 that's not a problem.

 

[Barriesimpson]

Here you go, I have a 230AH Lifepo4, 230 watts solar and a 2,000 watt inverter.
I run a 1400 watt air frier, 1200 watt Panini maker and a 800 watt microwave.
Not all at the same time obviously.
I've just done 17 nights stationary on a site without EHU.
Lowest my battery got was 65%.
Sunshine hasn't been good and the battery only reached 100% SOC twice in the 17 days.
But being Lifepo4 that's not a problem.

That is very good information. I trust you did not exaggerate anything there. So based on this I only need a 230ah LifePo4 to complete my installation. Thank you for that, you have saved me €530 for another solar panel and I can now spend that money on wine.

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[bigtwin]

My Fogstar 230AH BMS is rated at 200 amp continuous. I'm pretty sure that the new 230AH, mine is 8 moths old, is rated at 250 amp continuous.

That’s good then but it, nonetheless, remains a consideration when anyone is spec’ing a system and may be a good reason for choosing two smaller batteries over a single larger battery.

Ian

 

[Nigel Crompton]

Here you go, I have a 230AH Lifepo4, 230 watts solar and a 2,000 watt inverter.
I run a 1400 watt air frier, 1200 watt Panini maker and a 800 watt microwave.
Not all at the same time obviously.
I've just done 17 nights stationary on a site without EHU.
Lowest my battery got was 65%.
Sunshine hasn't been good and the battery only reached 100% SOC twice in the 17 days.
But being Lifepo4 that's not a problem.

Cooking for six ?

Excellent thanks. Real-world data.

 

[bigtwin]

So based on this I only need a 230ah LifePo4 to complete my installation.

Provided that the BMS is capable of handling your inverter’s full rated output.

Ian

 

[Carpmart]

I was told it’s not best practice to add lithium batteries of different ages by Roamer batteries

I thought we established that was because they were trying to upsell you Steve!

 

[Barriesimpson]

Provided that the BMS is capable of handling your inverter’s full rated output.

Ian

Apparently it is. But how would I know that to be sure?

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[Nigel Crompton]

Apparently it is. But how would I know that to be sure?

Ask Fogstar or a dealer, listen to the the horse's mouth

 

[Steve and Denise]

I thought we established that was because they were trying to upsell you Steve!

I’m not 100% sure myself really,

 

[headlight]

That’s good then but it, nonetheless, remains a consideration when anyone is spec’ing a system and may be a good reason for choosing two smaller batteries over a single larger battery.

Ian

I orig

Cooking for six ?

Excellent thanks. Real-world data.

No, cooked for 4 a couple of times though.

 

[Nigel Crompton]

Just looked at the spec sheets for the batteries the fitter supplies, Eleksol. (Made here in Spain)

It's confusing.
Corriente de descarga continua - Continuous discharge current
Corriente de descarga continua máxima - Maximum continuous discharge current

200ah - max continuous current = 100a, continuous maximum 200a, but for how long ?




150ah - max continuous current = 75ah OR 150ah but for how long?


I assume that with 2x150 my max continuous draw should be < 150a (2x75). That how it works ?

 

[bigtwin]

Apparently it is. But how would I know that to be sure?

Look at the battery specifications.

Ian

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