Help with inverter battery sizing

mister said:
Does it matter? The batteries are 12 volts

I thought:

parallel: 2 x 102Ah X 12V = 2448Wh
series: 102Ah X 24V = 2448Wh
Click to expand...

It depends on what the inverter requires. If the inverter requires 24 Volt, then no the first calculation even though the numbers are correct is not going to work.

As I said in my post, this particular example allows one to get the right answer even if the calculation is not strictly correct.

Provided the inverter can handle a second bank of batteries you could use 4 batteries in two sets of two each to double up on the standby power available.
 
Geoff.D said:
It depends on what the inverter requires.
Click to expand...

Yes I am aware that some inverters are 12v/24v/48v... my question was more, if you have 2 x 102Ah batteries in series or in parallel, do they provide the same amount of amp-hours?
 
mister said:
Yes I am aware that some inverters are 12v/24v/48v... my question was more, if you have 2 x 102Ah batteries in series or in parallel, do they provide the same amount of amp-hours?
Click to expand...

You can more or less double up on the standby power by having another set of batteries in parallel.

The calculation is then (24 x 102) + (24 x 102) = 4896 w-hr. The limitation is only on what the inverter can charge and then handle on discharge.
 
thechamp said:
Again OP's system is 24V not 12V.
Click to expand...

Here, is this big enough?

Drunkard #1 said:
This is not rocket science:

Battery capacity = 2 x 102Ah x 12V = 2448Wh
Load = 1.669kWh/24h = 69.5W
Duration = 2448Wh / 69.5W = 35h to 100% depth of discharge, or 17 hours to 50%. Now since this isn't too far from the 20 hour battery rating specification, I'm not making any adjustments for that, but you should know that an inverter operating at 3.5% load isn't going to be efficient at all - so a big adjustment is needed there.
Click to expand...

mister said:
Does it matter? The batteries are 12 volts

I thought:

parallel: 2 x 102Ah X 12V = 2448Wh
series: 102Ah X 24V = 2448Wh
Click to expand...

Matters for the inverter, does not matter for the calculation. (and never will)

mister said:
Yes I am aware that some inverters are 12v/24v/48v... my question was more, if you have 2 x 102Ah batteries in series or in parallel, do they provide the same amount of amp-hours?
Click to expand...

Yes, same Ah.
 
Drunkard #1 said:
Here, is this big enough?





Matters for the inverter, does not matter for the calculation. (and never will)



Yes, same Ah.
Click to expand...
Remind me never to accept a quote from your company. The correct way provides some assurance that the supplier does actually know what he is doing.
 
mister said:
Yes I am aware that some inverters are 12v/24v/48v... my question was more, if you have 2 x 102Ah batteries in series or in parallel, do they provide the same amount of amp-hours?
Click to expand...

They give the same amount of watt hours. In series it will be 24V 102Ah and in parallel it will be 12V 204Ah.

For a small home setup it doesn't matter that much, but in general you want to avoid parallel battery banks. Under high current draw some batteries can easily take more load than others in the bank. That brings up special design considerations.

If you want an online UPS, have a look at the Tescom SSPro long run series. Have been using it for a while at different sites, and it has been very stable.
 
Geoff.D said:
Remind me never to accept a quote from your company. The correct way provides some assurance that the supplier does actually know what he is doing.
Click to expand...

Well Mr Smarty Pants, show me when it'll make a difference.

Nuke said:
They give the same amount of watt hours. In series it will be 24V 102Ah and in parallel it will be 12V 204Ah.

For a small home setup it doesn't matter that much, but in general you want to avoid parallel battery banks. Under high current draw some batteries can easily take more load than others in the bank. That brings up special design considerations.

If you want an online UPS, have a look at the Tescom SSPro long run series. Have been using it for a while at different sites, and it has been very stable.
Click to expand...

I'd have phrased it differently... probably used quite a few expletives. For me, 1 string and only 1 string is absolutely, 100% not negotiable, unless you've got R100k to blow on a proper BMS.
 
Last edited:
Drunkard #1 said:
Here, is this big enough?





Matters for the inverter, does not matter for the calculation. (and never will)



Yes, same Ah.
Click to expand...

Please no! It matters whether the batteries are parallel or in series, the amp hours can never be the same for different configurations, in series OP's amp hours will remain 102, at 24v whilst in parallel the amp hour doubles at 12v.
 
Last edited:
thechamp said:
Please no! It matters whether the batteries are parallel or in series, the amp hours can never be the same for different configurations, in series OP's amp hours will remain 102, at 24v whilst in parallel the amp hour doubles at 12v.
Click to expand...

Correct. :D
Certainly, it is probably not a good idea to have two "strings" of batteries in a simple inverter system, especially in the residential environment. BUT it does not mean it cannot be done. It just requires a more sophisticated battery management system.
Yet you will find quite few suppliers of inverters and battery setups selling this type of system in SA. All connected to a single common positive and negative bus.

And hence why the calcs have to be shown in such a way that highlights this if it is indeed the way in which the desired standby is being realised.

I know of at least one holiday destination in SA where precisely this setup has been installed and where the cabling to the 3 battery banks is far from good enough and if one takes a few simple measurements with a multimeter (;)), you can clearly show that the charging and power draw is not optimal from the 3 banks.
 
Last edited:
Sorry to butt in - its all so harmonious here I couldn't resist :)

Just a quick point. Don't forget the inverter and batteries themselves are a load. So when your discharging particularly at small loads, you will likely not get what you hope for - because say the inverter and batteries will be using 50W too. (Not sure on the numbers I know from experience that cheap UPSs are pretty bad). All that heat has to come from somewhere!

It depends on your batteries and inverter, but may be shown in the spec sheet. The 'efficiency' shown will be at near full use, so hopefully they have one at 10% and 50% use too for you to estimate.
 
richjdavies said:
Sorry to butt in - its all so harmonious here I couldn't resist :)

Just a quick point. Don't forget the inverter and batteries themselves are a load. So when your discharging particularly at small loads, you will likely not get what you hope for - because say the inverter and batteries will be using 50W too. (Not sure on the numbers I know from experience that cheap UPSs are pretty bad). All that heat has to come from somewhere!

It depends on your batteries and inverter, but may be shown in the spec sheet. The 'efficiency' shown will be at near full use, so hopefully they have one at 10% and 50% use too for you to estimate.
Click to expand...

I had mentioned that already, and included in my calculations, but apparently I don't know what the **** i'm doing.
So..
 
thechamp said:
Please no! It matters whether the batteries are parallel or in series, the amp hours can never be the same for different configurations, in series OP's amp hours will remain 102, at 24v whilst in parallel the amp hour doubles at 12v.
Click to expand...

Good thing then that energy isn't measured in Ah.

Geoff.D said:
Correct. :D
Certainly, it is probably not a good idea to have two "strings" of batteries in a simple inverter system, especially in the residential environment. BUT it does not mean it cannot be done. It just requires a more sophisticated battery management system.
Yet you will find quite few suppliers of inverters and battery setups selling this type of system in SA. All connected to a single common positive and negative bus.

And hence why the calcs have to be shown in such a way that highlights this if it is indeed the way in which the desired standby is being realised.

I know of at least one holiday destination in SA where precisely this setup has been installed and where the cabling to the 3 battery banks is from good enough and if one takes a few simple measurements with a multimeter (;)), you can clearly show that the charging and power draw is not optimal from the 3 banks.
Click to expand...

I'd like to see these BMSs that'll suit OPs budget. Good luck.
 
richjdavies said:
Sorry to butt in - its all so harmonious here I couldn't resist :)

Just a quick point. Don't forget the inverter and batteries themselves are a load. So when your discharging particularly at small loads, you will likely not get what you hope for - because say the inverter and batteries will be using 50W too. (Not sure on the numbers I know from experience that cheap UPSs are pretty bad). All that heat has to come from somewhere!

It depends on your batteries and inverter, but may be shown in the spec sheet. The 'efficiency' shown will be at near full use, so hopefully they have one at 10% and 50% use too for you to estimate.
Click to expand...

Unfortunately very few that I looked at yesterday provide that detail in their spec sheets. Some did not even quote any efficiency factors at all.
 
lsheed_cn said:
I had mentioned that already, and included in my calculations, but apparently I don't know what the **** i'm doing.
So..
Click to expand...

You should help us fight the BS brigade. I was sort of waiting for you to come back into the debate on inverter efficiency effects.
 
Geoff.D said:
What a pain you are! If only you would drop your personal attacks. .......
Click to expand...

I become a pain when I detect bull****. And since when is calling people out on bull**** a personal attack?

Maybe if you could back up any of the bull**** you spew, I'd take you seriously.
 
You must log in or register to reply here.
Back
Top
Sign up to the MyBroadband newsletter
X