# Running for 4hrs calculation

#### Dolby

##### Honorary Master
I know there's a calculation to use - I'm not really sure :/

If I want to power both of these (only) for just over 4 hours - what size UPS would I need ?

It's a Calix GigaHub (the ONT seems passive?) and a Zyxel switch. A guy at work was telling me the switch *may* be an issue, but the Calix is alright with a UPS?
By the way - n00b question ... is a UPS the same thing as an inverter ? Batteries?

#### Dolby

##### Honorary Master
Oh I realize I can make do without the switch on the left! So only need to run the smaller Calix on the left

#### lsheed_cn

##### Expert Member
The left unit needs 55v x 1.3a = 71.5w /hr
The right unit needs 18w / hr.

If you want to keep them running for say 4 hrs.

18w x 4 = 72W
71.5 x 4 = 286W

You'll need a UPS that can provide at least that much power.
Given that most UPS's will have Dead Acid batteries in, you probably want 2x the battery needed.

So 150Whr of battery for the right one.

Given most smaller UPS's have 12v /7ah batteries in, look for something that has at least 2 batteries inside.
12x7x2 = 168w..

*This is simplified, doesn't take into account losses, but good enough.

#### Dolby

##### Honorary Master
Thanks !

So in terms of UPS output - I see they're rated in terms of VA 600VA / 1,000VA / 3000VA ... sorry for the n00b quesion - but how do I do the watts to the VA ?
Also, I notice they have kettle plugs at the back ... so there's some type of converter needed?

#### RedViking

##### Nord of the South
Thanks !

So in terms of UPS output - I see they're rated in terms of VA 600VA / 1,000VA / 3000VA ... sorry for the n00b quesion - but how do I do the watts to the VA ?
Also, I notice they have kettle plugs at the back ... so there's some type of converter needed?

Any UPS should work as it use very little power. But get a UPS maybe with 2 batteries in. So it will probably be a bigger one. Also remember a UPS make a warning beep noise when not plugged in, you will need to mute this, remove the beeper or use the option available on the UPS (if any). Also, not all UPS will switch off, when the batteries are low. Generally you don't want baggeries to go below 30-50% or they won't last long. But you can buy new batteries again.

Check More qualified answer from others. =)

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#### RedViking

##### Nord of the South
A UPS use a 'kettle' plug. Just cut off the normal plug and attach a kettle plug.

#### supersunbird

##### Honorary Master
Thanks !

So in terms of UPS output - I see they're rated in terms of VA 600VA / 1,000VA / 3000VA ... sorry for the n00b quesion - but how do I do the watts to the VA ?
Also, I notice they have kettle plugs at the back ... so there's some type of converter needed?

A 1500VA and up UPS should match what you need with the 1 device.

As to the UPS female kettle plug multiplug, one can make your own, or buy, I have some of the below:
https://titan-ice.co.za/ups-surge-protection/multi-plugs/

#### furpile

##### Expert Member
If you want to only power the hub with the 12V power tou can also look at a 12V UPS. These are typically used for alarm systems. This is much more efficient since you don't have to go from 12v to 220v back to 12v. I have a unit like this powering my adsl router with the same power requirements. Notmally these take the 7Ah alarm batteries, but I added a 45Ah battery that came out of a UPS at work. The power has been off for more than 24 hours and it stays on.

With the 7Ah battery you should still get 2 to 3 hours for the hub. You also get lead crystal batteries in that size that you can completely discharge without damage for a longer backup time. I took the power cable from an old router and connected that to the ups to power the adsl modem, since you don't need the power brick anymore.

The ups unit is about R400, and the battery between R180 and R400.

#### JJRM

##### Well-Known Member
If you want to only power the hub with the 12V power tou can also look at a 12V UPS. These are typically used for alarm systems. This is much more efficient since you don't have to go from 12v to 220v back to 12v. I have a unit like this powering my adsl router with the same power requirements. Notmally these take the 7Ah alarm batteries, but I added a 45Ah battery that came out of a UPS at work. The power has been off for more than 24 hours and it stays on.

With the 7Ah battery you should still get 2 to 3 hours for the hub. You also get lead crystal batteries in that size that you can completely discharge without damage for a longer backup time. I took the power cable from an old router and connected that to the ups to power the adsl modem, since you don't need the power brick anymore.

The ups unit is about R400, and the battery between R180 and R400.
Would you mind sharing where I can get something like this from?

#### Dairyfarmer

##### Expert Member
To work out how long a battery will last or how many batteries you need, use this simple formula:

Hrs = Volts x Ah / Load / DoD x Eff

Voltage = the voltage of your batteries. i.e 12v

Ah = the amp hour rating of the battery. Those little black ones in your gate motor or pc inverter are 7 or 9Ah

Load = the load that you are drawing in watts. i.e. a CFL bulb draws 15w, a geyser draws 4000w

DoD = Depth of discharge. You divide by 2 because you don't want to run your batteries past the 50% depth of discharge. This will shorten the number of times you can recharge the battery (cycles). And it is exponential. An example of a battery spec sheet I saw: if you use 80% of your battery every time you will get 80 cycles (1 cycle per % used). If you only use 50% you will get 300 cycles (6 cycles per % used). 20% and you may get 2000 cycles (100 cycles per % used).

Eff =Is for your inverter efficiency. Normally 0.85. You will never get 1 unit in and 1 unit out. The inverter needs to convert from AC (Eskom) to DC (battery) and back to AC (load). This results in losses (via heat). Some inverters are very efficient, but most lose 15%.

So a 12v 7Ah battery running 100w (18w + 71.5w = 89.5w or call it 100w) load on the inverter would give you 21 minutes. You would need 80Ah of battery or 12 x 7Ah batteries connected in parallel. That would not be very practical, but a single 85Ah or 100Ah battery would be better (and a lot cheaper).

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#### HeftyCrab

##### Expert Member
To work out how long a battery will last or how many batteries you need, use this simple formula:

Battery voltage x Ah / load (watts) / 2 x 0.85

Voltage = the voltage of your batteries. i.e 12v

Ah = the amp hour rating of the battery. Those little black ones in your gate motor or pc inverter are 7 or 9Ah

Load = the load that you are drawing in watts. i.e. a CFL bulb draws 15w, a geyser draws 4000w

2 = you divide by 2 because you don't want to run your batteries past the 50% depth of discharge. This will shorten the number of times you can recharge the battery (cycles). And it is exponential. An example of a battery spec sheet I saw: if you use 80% of your battery every time you will get 80 cycles (1 cycle per % used). If you only use 50% you will get 300 cycles (6 cycles per % used). 20% and you may get 2000 cycles (100 cycles per % used).

0.85 is for inverter efficiency. You will never get 1 unit in and 1 unit out. The inverter needs to convert from AC (Eskom) to DC (battery) and back to AC (load). This results in losses (via heat). Some inverters are very efficient, but most lose 15%.

So a 12v 7Ah battery running 100w (18w + 71.5w = 89.5w or call it 100w) load on the inverter would give you 21 minutes. You would need 80Ah of battery or 12 x 7Ah batteries connected in parallel. That would not be very practical, but a single 85Ah or 100Ah battery would be better (and a lot cheaper).

This should be made a sticky somewhere.

My high school science lessons are coming back to me now.

#### RedViking

##### Nord of the South
This should be made a sticky somewhere.

My high school science lessons are coming back to me now.
What high school science lessons. All I remember was a fire.

#### Venomous

##### Honorary Master
Thanks !

So in terms of UPS output - I see they're rated in terms of VA 600VA / 1,000VA / 3000VA ... sorry for the n00b quesion - but how do I do the watts to the VA ?
Also, I notice they have kettle plugs at the back ... so there's some type of converter needed?

I would recommend an rct 2000va/kva ups.
Then you'll need 1 to 2 plug adaptor as it already can accomodate a single south african plug.
Do not plug your PC into it if you want the UPS to last a whole CoJ loadshedding cycle.
It also takes 6-8 hours to recharge. Recharge time is often overlooked by many. Some UPSs require approx.18 hour recharge time and on stage 4 schedules we do not have 18 hours inbetween meaning the batteries become compromised and very soon they do not last.

#### Venomous

##### Honorary Master
A UPS use a 'kettle' plug. Just cut off the normal plug and attach a kettle plug.

View attachment 636330View attachment 636332View attachment 636334

You do know you can buy the bits and assemble the cable. Will be safer than that mvguyver job.

Female kettle plug, short electrical cable and then one of those extention cord ends that you can buy to replace the end on a normal extention cord should it go faulty. And if you're terrible with a screwdriver then you buy one like in the attached pic... Would be safer and simpler.

#### RedViking

##### Nord of the South

You do know you can buy the bits and assemble the cable. Will be safer than that mvguyver job.

Female kettle plug, short electrical cable and then one of those extention cord ends that you can buy to replace the end on a normal extention cord should it go faulty. And if you're terrible with a screwdriver then you buy one like in the attached pic... Would be safer and simpler. View attachment 637276
No need to waste waste money if I already have everything you need.

But sure, if you can't hold a screw driver it is better to spend more money and buy something rather.

#### furpile

##### Expert Member
Would you mind sharing where I can get something like this from?
Got mine from Security Mecca. Communica also sells them.

#### Geoff.D

##### Honorary Master
So that device on the left 55Volts?? What is it?
That is bordering on dangerous for a DC voltage!
Sure it is not 5.5 Volts?

#### Geoff.D

##### Honorary Master
The formula Dairyfarmer posted is a composite of a number of other basic formulas. I have been working on a simple one-pager to use as a ballpark explanation of all of this, but it is actually not that easy to come up with as one would think.

#### Dairyfarmer

##### Expert Member
The formula Dairyfarmer posted is a composite of a number of other basic formulas. I have been working on a simple one-pager to use as a ballpark explanation of all of this, but it is actually not that easy to come up with as one would think.
That is why, when i put in my inverter I calculated the maximum load, then used double that for equipment. ATM it is spot on. I can either add more onto it or have it run longer. You also have to take into account that batteries will degrade over time. So what is 125% of what you need today, maybe 98% in a few years time.

#### lsheed_cn

##### Expert Member
So that device on the left 55Volts?? What is it?
That is bordering on dangerous for a DC voltage!
Sure it is not 5.5 Volts?
Its not dangerous. Its the amps that matter, not the voltage.

55v @ 1.3A = 71.5W

Seems inefficient for a switch @ 70W but its not outrageous, or "bordering on unsafe".
Still classed in the ULV range - Ultra Low Voltage.