# Interest group forums > Energy and Resource Conservation Forum > [Question] Assistance Calculating UPS Size

## AmithS

Hello,

Please assist me with calculating UPS size for my home fish tank to get some pricing / budget in place.

Option 1
Run 8 watt filter motor only for 48 hours continuously.

Option 2
Run 8 watt filter motor + heater 50% of time + lights 25% of time = Total 200 watts continuously for 48 hours.

Any brand / UPS model / type is also welcome.

Thanks in advance.

----------


## Alfred M

Just to clarify why 48 hours are you working on worst case scenario for load shedding ? First of all would you have backup (genset or solar) should you be without mains power for more that 48h. Your load is fairly small but for 48 hours you will need a continuous rated ups not a pc backup ups. What is your budget approximately? Type of backup batteries used is going to be determined by your budget(lead acid,gel lithium Ion)

----------


## Dave A

The starting point is to take your figures and extract the required kWh.

Option 1:
8W x 48 hours = 384Wh = .384kWh

Option 2:
200W x 48 hours = 9600Wh = 9.6kWh

Step two is to consider the depth of discharge of your battery. 

The relationship between lifespan of the battery and depth of discharge is quite a long story. The short version is that the less you discharge as a percentage of capacity for each cycle, the longer the battery will last and you will need to replace them less often.

Gel batteries should not be discharged below 50% without significantly impairing the lifespan of the battery.
So double the kWh figure arrived at in step one and anything larger should meet your needs.

Lithium (LiFePo) will let you discharge to 20%, but one should try to keep that the exception and work on the basis of a DOD of 50% as the regular limit.

----------


## AmithS

Hi, the area I am in has frequent outages. Last week 65 hours continuous with no electricity. No other backup systems, just for the fish tanks. No specific budget - trying to get an idea if it is worth my while to look at these options... It is also more so if we are not at home to actually manage the situation.

----------


## AmithS

> Just to clarify why 48 hours are you working on worst case scenario for load shedding ? First of all would you have backup (genset or solar) should you be without mains power for more that 48h. Your load is fairly small but for 48 hours you will need a continuous rated ups not a pc backup ups. What is your budget approximately? Type of backup batteries used is going to be determined by your budget(lead acid,gel lithium Ion)


Hi, the area I am in has frequent outages. Last week 65 hours continuous with no electricity. No other backup systems, just for the fish tanks. No specific budget - trying to get an idea if it is worth my while to look at these options... It is also more so if we are not at home to actually manage the situation.

----------


## AmithS

> The starting point is to take your figures and extract the required kWh.
> 
> Option 1:
> 8W x 48 hours = 384Wh = .384kWh
> 
> Option 2:
> 200W x 48 hours = 9600Wh = 9.6kWh
> 
> Step two is to consider the depth of discharge of your battery. 
> ...


Thanks Dave, will definitely keep this in mind. I know our alarm & gate batteries frequently need changing because of them draining out completely.

----------


## GCE

Hi 

Further to Dave's calculation above 

For option 1 a Gel battery 100AH will a small inverter would do the trick and only discharge to around 30% - Would be in the region of R8K depending on inverter, battery box and battery  

For Option 2 a would say lithium as lead Acid would require to many batteries and a bigger inverter to handle the recharge current and time. At the required 9,6KWH needed and using 30% depth of Discharge , I estimate 26 batteries would be needed and they would need to be replaced every 5 years .
Gel batteries - 26 x R 2 500.00 + inverter estimate 10K + battery housing ? ) = +/-75K - The release of gases on charging and discharging the batteries would need to be taken into account.

Lithium - inverter 10K + 3 x 3,2KWH Lion batteries ( 51K )  = +/- 61K and could go to 150K depending on the quality and requirements from a software point.


A gel battery Depth of discharge ( DOD) to cycles normal sits around 

15% DOD - about 2000 cycles 
30% DOD - about 1500 cycles 
50% DOD - about 1000 cycles 
80% DOD - about 500 cycles 

Once Gel has cycled to the 80% or lower mark , once or twice you will be replacing within 2 years - You do get decent small inverters that can cut power when the Gel gets to 50% - 

The prices tossed in above are estimates and there are various qualities of material around - It is figures I normally throw out there when I get calls so that I can get to a budget that they are prepared to spend .

If I was doing that for myself I would through some PV panels ( 40K to 100K )  in and use the inverter and batteries to store and supply other , what I deem ,critical items and then manage if there was a prolonged outage .

----------

AmithS (24-Mar-22)

----------


## AmithS

> Hi 
> 
> Further to Dave's calculation above 
> 
> For option 1 a Gel battery 100AH will a small inverter would do the trick and only discharge to around 30% - Would be in the region of R8K depending on inverter, battery box and battery  
> 
> For Option 2 a would say lithium as lead Acid would require to many batteries and a bigger inverter to handle the recharge current and time. At the required 9,6KWH needed and using 30% depth of Discharge , I estimate 26 batteries would be needed and they would need to be replaced every 5 years .
> Gel batteries - 26 x R 2 500.00 + inverter estimate 10K + battery housing ? ) = +/-75K - The release of gases on charging and discharging the batteries would need to be taken into account.
> 
> ...


Thanks a million, really appreciate the detail you have provided. Gives me a good idea on my options.

----------


## Alfred M

All advice and calculations above are sound but the big problem not to loose track off is the period without any mains power 64 hours. If you want to do it properly with the least amount of batteries($$$) is to use solar array with hybrid inverter incorporated with mppt charge controller and battery backup then you would be assured you will always have your fishtanks and premises powered and batteries protected to last.Get a solar specialists in your area to come and do an assessment and quotation.

----------


## AmithS

> All advice and calculations above are sound but the big problem not to loose track off is the period without any mains power 64 hours. If you want to do it properly with the least amount of batteries($$$) is to use solar array with hybrid inverter incorporated with mppt charge controller and battery backup then you would be assured you will always have your fishtanks and premises powered and batteries protected to last.Get a solar specialists in your area to come and do an assessment and quotation.


Thanks, so much will definitely get a professional opinion.

----------

