# Social Category > General Chat Forum >  Inverters

## HR Solutions

Can anyone advise me on Inverters please ?  Would like to get one for our Jhb office and home.  For the office we need to run 8 computers (if possible) when there is a power failure.  At home I would like to know if there is one that will run basics such as TV, fridge, freezer and a few lights.  How long do these things last and what sort of cost are they ?

----------


## skatingsparks

Hi there
Think you are after UPS (uninterrupted power supplies). Might want to put on the Electrical Contracting Industry part of the part of the forum.  Your sure to get more answers.
There as quite a few factor to take into account.  The larger the load and the longer you want to stay on for the bigger the battery bank the bigger the cost.

----------


## HR Solutions

I would like sport 4 to 5 hours of use - 4 computers and 4 laptops.

----------


## julies

UPS are generally used to provide short-term power (giving you enough time to save and switch off) and protection against voltage spikes. Some UPS are smart devices and can be set to automatically and correctly shutdown/hibernate/sleep your pc, when there is an input failure, thus preventing damage to your equipment, inverters cannot do this . As mentioned, both UPS and Inverter needs a correctly seized battery bank depending on how long you want to keep the device/s running. UPS and Inverters almost work in the same way, both make use  battery's and both need a way of keeping the batteries charged and both need to convert DC to AC. For the PCs at work you would need to work out the total power (watts) needed per PC and either size you UPS or Inverter for each individual PC or find a big enough unit to handle all the PC's together. Maybe using a generator would be more practical/cheaper, I'm not sure on the various prices

----------


## julies

A deep cycle battery with a inverter could work for your Flat Screen and DSTV. I got the Prices of Deep cycle batteries the other day ranging from R1500 - R2000 for a 12V but gel ("maintenance free") batteries are more expensive. The deep cycle batteries will have a Amp/Hour rate and using this you will be able to workout your viewing time. A car battery is not suitable for this application

Also bare in mind that the batteries in the UPS or using with an inverter also have a limited life span and would need to be replaced later, but then a generator would also need to be serviced from time to time.

----------


## skatingsparks

If you work on your computer using 200 watts plus 70 watts for the LCD (more if its and old school moniter).  Plus your lap top chargers which are minimal, say 30 watts.  You need to run a total of 1200 watts or 1.2Kw.  You always upsize the inverter by about 25% give you space so you could use a 1.5kVA inverter, maybe even go 2kVA.  You need to run for 5 hours so for 5 hours you will consume a total of 5kWhrs (1kw for 5 hours) to get that out of batteries you will need 416 Amp hours worth of battery (if they are 12 volts) (5000watts / 12volts) BUT double it as you really don't want to ever flatten your batteries beyond half way.  As they say above you need deep cycle batteries, not a normal old car battery.  It would work but not for very long.  This is a rough guide line.  There are other factor to take in consideration but you can maybe get quotes based on 1.5kVA or 2VA UPS with 8 x 100 amp hour deep cycle batteries to get an idea of what the price would be. The supplier would give you more advice. Hope it helps.....

----------

HR Solutions (27-Jan-15)

----------


## AndyD

There's two completely different issues you need to assess. Firstly is the load because as pointed out this determines the size in KVA of your UPS/inverter. Secondly is the required running time because this determines the size of the battery bank you need.

I would suggest not oversizing the system by more than 10% or so because it starts getting very expensive. If you want it to carry you through load shedding then 4-5 hours is more than double (probably actually triple) what you need. This amount of redundancy is expensive. 

Also forget the fridge and freezer, they'll stay cold for an hour or two without power and motors are best avoided because their start currents and the highly inductive nature of their load makes them very taxing on any back-up power system.

Stick to running a couple of laptops/notebooks only because they're built to be low consumption, not PC's etc. A few lights are fine as long as they're LED's and obvously your router. Even with a small/medium LED/LCD TV I'd estimate your load would be < 1kW.

Look at the Victron inverter/chargers. They're pure sinewave output and they're also scaleable so you can always add a second one to increase your power if necessary at a later date. You can even connect three single phase units together to give you a 3-phase output and they're capable of having multiple inputs so you can connect solar/wind turbines as well as batteries to them. They have a built-in charger as well. I've installed several of these over the last decade and they're very good. Not cheap but you certainly get what you pay for in this case.

----------


## Justloadit

For running computers, laptops and the 'better quality' LED lighting, you do not need a pure sine wave convertor, and a square wave is more than adequate. After all, these devices convert the AC into a DC signal and then using switch mode supplies, convert the DC to the voltage required, so effectively the cost of the sine wave is totally lost in these applications.

Pure sine wave convertors are suitable to run motors and microwaves, as they place less strain on this equipment, which requires a sine wave to be efficient. 

As Andy says, first work out your total consumption, add 50% for inefficiencies and to allow the inverters to run at 50% of their rated value, as the full rating figures on most inverters is for short periods, next calculate the number of hours you wish to run on battery power, multiply by 2.5, as you want to not drain your battery's to less than 60% of capacity, to allow over 800 cycles or more out of them, going lower reduces the cycles in logarithmic fashion. Sit back calculate, and then recover from the shock  :Smile: , and work out what you can afford. Get a genny as a back up for the extra time you need, it will be cheaper.

If you are not sure of the final figures, place the numbers here and we will do the final calculations for you.

----------


## CLIVE-TRIANGLE

And do be careful of laser printers...

----------


## HR Solutions

Guys thanks for all your input.
I have no idea of the numbers
For the office - we would def need 3 x desktop computers + 3 x laptops + 1 x router (at a squeeze) - the power outages are becoming more frequent and it is starting to cost money for downtime.  Our girls need access to their computers

For the house we perhaps only need to be able to run a few lights which could be normal bulbs & perhaps the tv and dstv if it can be included

Our power outages are sometimes up to 4 hours so it would be more important for work to be able to operate the computers/laptops for this period.
I suppose home would not be too much of a crisis if we only have a small inverter

----------


## AndyD

> For running computers, laptops and the 'better quality' LED lighting, you do not need a pure sine wave convertor, and a square wave is more than adequate.


I'd suggest take it on a case by case basis it very much depends on how their switch mode supply is built. Some may not play very nicely with modified sine supply especially if it's got actice PFC built into it. You may also find they run very hot, again this would vary depending on the design. If it's hi-fi equipment or TV then any common mode noise that carries though the power supply will result in interference and buzzing.

----------


## Justloadit

PFC works on attempting to fill the blank areas of the sine wave by making a boost switch as opposed to a buck switch during the peaks therby reducing the current draw during this time, so effectively reducing the power factor. The PFC still rectifies the sine wave into a DC voltage, and the PFC attempts to reduce the saw tooth which is characteristic of DC rectification under load, where during the dips, the circuit has to both supply the circuit with power, and charge the capacitors up for the next cycle, effectively doubling up the current draw from the supply.This simply means that the PFC will work better with a square wave inverter with a small dead time between positive and negative half cycles. In the case of electronic equipment, because of the low power they draw, the PFC circuits are relatively light and probably would be happy with the modified sine and square wave with dead time.

With respect to the noise on audio equipment, yes that can be a factor, and especially during a power failure, silence augments the hum and buzzing.

----------


## HR Solutions

I phoned PSS - they are going to give me a quote.  Hopefully they get their sines and peaks in line  :Wink:

----------


## HR Solutions

This just sent to me - can you please give opinions on this ?
Power Caddy Brochure  HT-C-M1000.pdf
￼￼￼￼￼￼￼￼￼￼￼￼￼￼￼￼￼￼￼￼￼

----------


## 3x-a-d3-u5

I've worked with Powerbackups.co.za they have a handy power calculator: http://powerbackups.co.za/index.php?main_page=page&id=1 to work out the size batteries you'd need. But keep in mind as* AndyD* said, you'd be looking for a balance between length of time and amount of equipment.

Sometimes the most reliable and cost effective solution is a combination of generator and UPS. An inverter is part of a UPS. So "A UPS consists of an Inverter, Transformer, Voltage regulator, Charger and Batteries." The UPS kicks in as the power failiure starts giving the jenny time to kick in, or when the jenny runs out of juice, the UPS saves the day long enough to get more fuel...

----------


## HR Solutions

3x - I cannot have a genie due to our office park.  I have to have an inverter, therefore I am looking for guidance on what to get to last me up to 4 hours.

----------


## ians

Your quote for that unit must have been around R5000?

----------


## HR Solutions

> Your quote for that unit must have been around R5000?



Yes .... And I'm wondering how long it will last ? Ie will it last 4 hours ?

----------


## CLIVE-TRIANGLE

I have discovered that re-charge time has now also become critical. That info sheet refers to between 6 and 12 hours, which is probably ok.

I don't know what my UPS is supposed to be, but when we had occasional power-outs it allowed us more than enough time to safely shutdown our NAS (network attached storage) box and then it would happily keep our routers and access points going for about two hours.

Now, when the power goes off it does not hold the NAS box for even long enough for me to shut it down; I would say 3 minutes and it's dead. The unit is less than a year old so I assume the battery is ok. Many (probably most) off the shelf UPS are "online" and so the net charge is minimal. With these rolling load shedding power offs, it has no hope of reaching full charge before the next out.

I mention this because most commercial units are made for developed countries  :Smile:  where power failures are the exception, not the norm, so that issue is suddenly a factor.

The previous units I had were supported by a standby generator. I suspect the generator's voltage regulator was really dodgy because it killed the UPS units pretty quickly. I changed  from desktops to laptops with external monitors and wireless keyboards and mouse so that the laptops' battery became the UPS and at least the computer hibernates and ultimately does a soft shutdown when that battery gets low.

I am afraid there is no way out; if it is important that you work through power outages and more importantly, you value your data, you have no choice but to throw money at it.

If your desktops are recent powerful beasts, the power supplies are almost certainly 300 watt units and if so then I doubt the unit you posted will be adequate.

----------


## Justloadit

Hi Clive,

I am in no doubt that the battery in your UPS is dead. This happens when low cost batteries are used. Most suppliers, to keep the cost of the UPS as low as possible to compete, use the low cost batteries.
You will need to open the inverter, and replace with what is called a deep cycle battery. Will probably cost 3 times more than the low cost units.
The main problem with UPSs are that they continuously trickle charge the battery, and this kills the battery over time. One should also at least once a month run the UPS off the battery, so that the battery can cycle and keep the electrolyte going. Also for a full charge, you need a 24hour cycle.

With respect to the generator killing UPSs, it is simply too small for the application, making the generator hunt around the 50Hz excessively, making the UPS switch in and out attempting to maintain a constant power to your computers, this hunting, causes excessive voltage to be developed which takes out the UPS protection (MOVS or surge arresters).

If a generator hunts up and down, stop and get a larger one. Just remember up here on the highveld, you lose 40% of the generator capacity because of the thin air, add to it that it will be a Chinese made in whcih the specs have been inflated, and divide the rating by 50% to get a rough idea of its true capacity.

----------


## CLIVE-TRIANGLE

> Hi Clive,
> 
> I am in no doubt that the battery in your UPS is dead. This happens when low cost batteries are used. Most suppliers, to keep the cost of the UPS as low as possible to compete, use the low cost batteries.
> You will need to open the inverter, and replace with what is called a deep cycle battery. Will probably cost 3 times more than the low cost units.


I will certainly give that a try. This is kind of like a packaged unit with a battery very similar to those attached to alarm systems. Do you get "deep cycle" batteries in that format?




> The main problem with UPSs are that they continuously trickle charge the battery, and this kills the battery over time. One should also at least once a month run the UPS off the battery, so that the battery can cycle and keep the electrolyte going. Also for a full charge, you need a 24hour cycle.


This I am sure is part of the problem. Our shedding schedule so far has come every 18 hours.




> With respect to the generator killing UPSs, it is simply too small for the application, making the generator hunt around the 50Hz excessively, making the UPS switch in and out attempting to maintain a constant power to your computers, this hunting, causes excessive voltage to be developed which takes out the UPS protection (MOVS or surge arresters).
> If a generator hunts up and down, stop and get a larger one. Just remember up here on the highveld, you lose 40% of the generator capacity because of the thin air, add to it that it will be a Chinese made in whcih the specs have been inflated, and divide the rating by 50% to get a rough idea of its true capacity.


At that stage I had a 1KVA ups supported by a 3.5KVA generator. The generator certainly was a Chinese product, that's all I could get at the time. The symptoms you describe are spot on!!
Bugger....

----------


## Justloadit

Hi Clive,

Yes deep cycle batteries are available in the 7.2A size

----------

CLIVE-TRIANGLE (10-Dec-14)

----------


## IanF

> Hi Clive,
> 
> Yes deep cycle batteries are available in the 7.2A size


Thanks for that I will bookmark as I am sure my alarms at work and home will need batteries shortly thanks to the power blackouts.

----------


## Yahy

Hello guys,
I am new to the forum. Since you guys are discussing inverters I wish dome one will be able to help me. At home I have a three phase electrical supply and wish to install an inverter to overcome the load shedding. I have two single phase 5KvA inverters with 24X12V (105 AH) batteries. Will it be possible to connect these to the three phase circuit. I only require to run phase A and phase B of the three phase setup. How do I do it.

Thank you
Yahya


Sent from my iPad using Tapatalk

----------


## Justloadit

It depends on what load you wish to run. If your loads are all single phase, but you have a 3 phase supply purely for load balancing, then you can use single phase inverters on each line you wish to back up.

The question is, what do you want to happen when there is a power failure?
Your reply will guide the answer.

----------


## Yahy

Thank you Justloadit for the prompt reply. My requirements are simple. When there is a power failure I want my  the following to continue to work 

1  the lights 
2 the home alarm
3 the fridge (2)
4 the freezers (2)
5 the router
6 computers
7 the TV (2)
8 Electric kettle
9 2 x toasters

----------


## HR Solutions

I would suggest you read this thread from the beginning and you might find some answers

----------


## Justloadit

Running kettles and toasters on inverters is a no no.
Even a fridges and freezers on inverters is a no no.

The problem is that these devices are power hungry when it comes to stored power to do any work.

To boil water in a kettle requires approximately 1Kwat for about 10 minutes. This translates to 250watts of energy. If you have a 5Watt LED, it means that the 5 W LED would run for 50 hours on the energy it took to boil your kettle. See what I mean. Now lets look at what the battery has to do, if you take 1Kw or 1000watts at 12V, because that is where you start from, the battery has to supply 83 Amps for 15 minutes (1000w/12V = 83Amps) continuously. Even a 100Amp deep cycle battery will not survive this abuse. It is equivalent to cranking your car engine for 15 minutes non stop, would your car battery work after that time?

Large loads are best suited to a generator.

----------


## Yahy

Thank you justloadit I have taken note of your answer. Now that I have equipment what would you suggest

----------


## AndyD

> I have discovered that re-charge time has now also become critical. That info sheet refers to between 6 and 12 hours, which is probably ok.


 Battery charging against time on a graph isn't a flat line. Depending on the type of batteries and the type of charger it can take 30% of the battery charging time to complete the last 10% of the charging process. So, if you charge a battery for half the time that's stated for its full charge the chances are at least 75% of the charging process will already be complete. 




> I don't know what my UPS is supposed to be, but when we had occasional power-outs it allowed us more than enough time to safely shutdown our NAS (network attached storage) box and then it would happily keep our routers and access points going for about two hours.
> 
> Now, when the power goes off it does not hold the NAS box for even long enough for me to shut it down; I would say 3 minutes and it's dead. The unit is less than a year old so I assume the battery is ok.


 Agree with previous comments, it's almost certainly batteries at their end of life. You can try putting the batteries on a charger like an 'optimate' which is touted as having a 'de-sulphating cycle', it might improve their performance. 

Batteries are a major issue. Standard car type lead acid batteries aren't suitable for back-up solutions, if you're going to buy this type of battery for a UPS or inverter, yes it will be much cheaper that a deep cycle battery but you may as well just drop it straight in the dustbin when you get it home. Car batteries are designed to be discharged less than 10% during use, the deeper they get discharged the shorter their lifespan. An inverter or UPS is going to discharge its batteries at least to the 50% mark, some of the cheaper units will be even more harsh. I'd be surprised if car batteries last more than a couple of months under those conditions with the frequency of the power outages at the moment.

Battery chargers are equally critical to battery life as the battery itself. A good charger will go through at least 6 or 8 distinct stages of charging where the voltage and current is specifically taylored to the point the battery is at in the charging process (the charger I use in my workshop is a 16 stage). A half decent charger will have at least a 3 stage charging process followed by a trickle to maintain, this is the minimum I'd recommend for fairly good battery life. Cheap chargers are not adaptive to the state of charge of the battery, this type of charger will destroy a battery quickly. Unfortunately the poorer quality UPS's have cheap dumb-assed chargers as well as standard lead acid batteries which is the worst possible combination.

----------


## CLIVE-TRIANGLE

AndyD, thanks for your input. This is an off the shelf UPS and is way too small to have anything more than a typical sealed ni-cad type battery. The unit is relatively new and has only died since the daily load shedding. Previously outages presented no problems.

As I write, it has been more than 24 hours since the last outage. By Thursday morning it will be about 40 hours. I would like to say I will test it  :Roll Eyes (Sarcastic):  but I will wait for Eksdom do it for me, and I will post the outcome. I actually only need about 3 minutes to shut down my NAS box and thereby save some very fancy hard drives.

Judging from the press releases, back up power in whatever shape or form is going to be a big issue and I don't want to be caught napping.

----------


## AndyD

I wish you luck and hope you're never in the bathroom when the power outages occur  :Wink:

----------


## ians

Been through this battery story tooo many times. Being a bass fisherman and a "power fisherman" battery power is a critical asset if used correctly.

Some tips: (deep cycle batteries, these should be the only ones used with an invertor)

1/ Always store your battery in a cool place
2/ Never discharge the battery below 10.5 volts or less than the percentage rated for that battery ie 80 or 50 % depending on the make and type. If discharged below a the percentage will shorten the life of the battery or destroy it if discharged to much.
3/ Always use a charger rated at least 10 % the amp/hr of the batery ie 100 amp/hr should be charged with a 10 amp charger, not only will a smaller unit damage the battery it will also take that much longer to recharge. Your battery could still be flat by the next load shed.
4/ The gas (hydrogen) is extremely explosive while charging the batteries.
5/ if used incorrectly batteries or old batteries can explode.

----------

Dave A (11-Dec-14)

----------


## Justloadit

Never allow a discharged battery to stand for more than a day, charge immediately, as flat battery's tend to destroy themselves if left in the discharged state.
Unused battery's should be charged to 80% of their capacity every few months to avoid the above. An unused battery self discharges and needs to be topped up every few months.

----------

flaker (14-Dec-14)

----------

