Do I need a pure sine wave inverter?

[gotchanisa]

I have a UPS at home - for the whole house. However, every time there is a power outage, my computer restarts. It does not restart when the power returns! I had an old computer UPS that I had that I connected to the computer. Now when the power goes, the computer does not restart - but the computer UPS does not 'recognize' the power coming from the main House UPS. So instead of a 5 hr back up - that the house UPS gives me, I only have a 15 min back up that the computer UPS can give me. I have talked to UPS manufacturers who say they need to fit a 'filter' which will solve the problem. They said something about a pure sine wave output- not sure if I understood. They also said the later versions of computer UPS - like APC will recognize the power coming from an existing UPS. I am skeptical

Does anyone know of a cost effective solution to my problem?

 

[eblc1388]

Does anyone know of a cost effective solution to my problem?

An AC connected 12V or whatever voltage battery charger, positive output connects in series with a diode, to top up your computer UPS tiny battery and prevent it from discharging. In another word, the battery charger is there to supply all the computer loading and DC/AC inverter loss.

This charger only powered up after the main house UPS has changeover to the internal power.

 

[gotchanisa]

I'm not sure if I understood Is this an explanation as to why the computer does not restart when the power returns? I'm sorry, but I don't see the solution

 

[eblc1388]

Your house UPS is not up to its task in transferring the power, or has difficulty to start up in a short time after main fails.

When power returns, it does not cause a computer restart because its circuit can time the exact moment to transfer the power from internal to external because both sources are available. Nearly every UPS can do that easily.

 

[eblc1388]

This came to me in the form of PM by the OP but I think it would be better for the OP to get different feedback from others:

How can I use a battery charger to do the job? What exactly do you mean when you say battery charger? Other than the inverter itself that charges the huge truck batteries, the only other battery chargers that I know are the 1.5 volt chargers that charge nickel cadium batteries that can be used for a discman, cd players and the like. If the battery chargers in the computer UPS does not recognize the AC power coming from the house UPS, are there other battery chargers that will?

Please let me know more ....

The battery charger can in fact be a DC power supply, with sufficient current rating. I spoke of battery charger instead because it is more easy for someone to get at what is actually needed.

In fact, it can be a self built or commercial off the shelf DC power supply of 13.8V, with about 10A of output current. I would suggest a commercial 120W one for simplicity.

Rest assure that nearly but all DC power supplies will work happily with AC from your house UPS.

 

[audioguru]

The UPS is made too cheaply. It takes a long time to switch off the mains, switch on its output and turn on.

a more expensive UPS has its inverter running all the time so that when the mains power fails then it doesn't switch, it just begins using battery power to run.

 

[HiTech]

Most consumer computers operate well from a modified sinewave AC signal. Pure sinewave AC is reserved for sensitive medical life support equipment. Virtually all consumer grade UPS have modified sinewave (MSW) outputs. Pure sinewave units are expensive.

 

[gotchanisa]

So does everyone recommend Mr. Chung's solution as the best?

Now let me throw in another observation I've made - If I switch of the power by manually turning off the mains, the computer does not restart. (I am only using the House UPS at this stage.) The UPS manufacturer demonstrated this to me. But when the power goes off on its own, the computer restarts..... now something more interesting...... this does not happen EVERYTIME the computer restarts....! only sometimes.

The house UPS is on the 3rd floor. My computer is on the second floor. From my limited understanding of Mr. Chung's diagram, I will need a long wire from before the power enters the house UPS to my battery charger downstairs. Is that right? Unlike the house UPS batteries, the computer battery is inside the UPS unit. What I am still unclear about (sorry!) is why we cant use the charging mechanism in the computer UPS. How will this charging mechanism differ from the recommended charger.

Please bare with me

 

[gotchanisa]

Oops the last sentence should read - please bear with me

 

[eblc1388]

What I am still unclear about (sorry!) is why we cant use the charging mechanism in the computer UPS. How will this charging mechanism differ from the recommended charger.

If the charging mechanism of your computer UPS is functional when using house UPS then you would not have had the problem in the first place. Your computer UPS does not reckon that a healthy AC power supply is present so insists on using up all the juice of your UPS battery.

Now you have told us the locations of the two UPSs, I have modified my suggestion to ease your wiring situation.

The difference is now the DC power supply always powered ON and is producing 12.6V output instead of the 13.6V shown previously. The lower voltage used is that it won't mess with your existing computer UPS's own battery charging circuit.

 

[gotchanisa]

If the charging mechanism of your computer UPS is functional when using house UPS then you would not have had the problem in the first place.

Thank you for your patience
Just to ensure we are on the same page, the computer UPS works fine (charges fine) when outside power is supplied (not from house UPS). Its only when there is an outage that it does not charge - even though there is power supply from the house UPS.

So according to your design, the new charger will have to be connected to the small battery inside my computer UPS - in the manner shown. Have I got this correct? I'm assuming if I show this diagram to someone who understands them - they will understand what needs to be done. Is there anything else they would need to know?

I know I must be causing you to bang your head on the wall by now.... but I really appreciate your patience.

 

[eblc1388]

Its only when there is an outage that it does not charge - even though there is power supply from the house UPS.

Exactly. The "computer UPS" is relying on the battery power to power the your computer. Even though there is house UPS AC power(non-sinewave), the "Computer UPS" does not accept it to be a good AC source so would not want anything to do with it. It just keep on draining the internal battery giving you 15min backup time.

So according to your design, the new charger will have to be connected to the small battery inside my computer UPS - in the manner shown. Have I got this correct? I'm assuming if I show this diagram to someone who understands them - they will understand what needs to be done. Is there anything else they would need to know?

Except that it will now be a DC power supply(output 12.6V, about ??A, ???W) instead of a battery charger. Its role is to "takeover" the power from the battery and prevent the battery from draining down below +12V. If the battery voltage don't drop below +12V, then the "Computer UPS" will keep on working because it senses the battery voltage to determine when to terminate the backup. No voltage drop, no termination.

I know I must be causing you to bang your head on the wall by now.... but I really appreciate your patience.

No problem. This is a standard problem solving method here in the forum. I just wish others will give their opinions to you too.

Perhaps there are other options available.

 

[eblc1388]

They also said the later versions of computer UPS - like APC will recognize the power coming from an existing UPS. I am skeptical

On second thought, the option of a new UPS, if working, is a much better solution. You have to work out the cost of the these two options and decide.

You get a new UPS for your computer, confirms it really work with you house UPS or return it for your money back.

You can even specify on your purchase invoice a clause that "UPS must be compatible with non-sinusoidal AC main input" as a condition of purchase.

 

[gotchanisa]

Thanks for your time..... I will let you know about what solution I used as soon as I follow up on this.

Thanks again!

 

[pbraju123]

going by the subject line; I am wondering why one needs a pure sine wave wave for running a PC. As far as I can think of every PC has an SMPS at input power stage. SMPS coverts all the AC (Sine, square, Trapeziod, Modified sine) to a DC voltage after rectification. There is good amount of filtering done to remove all the noise component (Harmonics and distortion). In that case pure sine wave shouldnt be the constraint.
I think it is just a marketing gimmick. Any waveform will do unless and untill it doesnt have too many spikes (sharp pulses).
This will not work for inductive devices as fans, refrigerators, Motors. Here I agree that they need pure sine wave to operate efficiently.

 

[Reloadron]

You would likely do better starting a new thread (discussion), however, to answer your question to back up a home PC you don't need a pure sine wave output from a UPS. My home systems run just fine using a UPS outputting a modified square wave.

The UPS units I have supporting my systems only need to support them for about 10 seconds before my generator is online not that it matters. However, they do work just fine on several PCs.

Ron

 

[audioguru]

A 120VAC sine-wave has a peak voltage of 170V.
A 120VAC sine-wave (with a peak voltage of 170V) produces exactly the same power in a resistance (incandescent light bulb or heater) as a 120V peak square-wave. The main filter capacitor filtering the bridge rectifier charges to 168VDC, not 120VDC.

The peak voltage of a 120VAC square-wave is 120V so an SMPS circuit not designed with a lot of voltage regulation will have an input voltage much too low.

 

[tcmtech]

Most devices with a SMPS work just fine on DC inputs as well. IF they have the universal voltage capability 80 - 250 VAC they also will usually work on 120 - 360 VDC with out any problems as well.


Most CFL lights are SMPS based now and will run on a wide range of DC input voltages too.

 

[Reloadron]

I think if we go back to the very beginning of the thread before the recently added question that Audioguru covered it with his reply:

I have a UPS at home - for the whole house. However, every time there is a power outage, my computer restarts. It does not restart when the power returns! I had an old computer UPS that I had that I connected to the computer. Now when the power goes, the computer does not restart - but the computer UPS does not 'recognize' the power coming from the main House UPS. So instead of a 5 hr back up - that the house UPS gives me, I only have a 15 min back up that the computer UPS can give me. I have talked to UPS manufacturers who say they need to fit a 'filter' which will solve the problem. They said something about a pure sine wave output- not sure if I understood. They also said the later versions of computer UPS - like APC will recognize the power coming from an existing UPS. I am skeptical

Does anyone know of a cost effective solution to my problem?

Audioguru:

The UPS is made too cheaply. It takes a long time to switch off the mains, switch on its output and turn on.

a more expensive UPS has its inverter running all the time so that when the mains power fails then it doesn't switch, it just begins using battery power to run.

Even without the more expensive inverter UPS a good UPS should switch over before the supported system shuts down. Apparently the original poster's system was shutting down and restarting.

The only other thing that may figure into the original problem would be the original poster's PSU in their system. A good PSU has a hold up time when it meets the design specifications for a PSU.

3.2.11. Voltage Hold-up Time
The power supply should maintain output regulation per Section 3.2.1 despite a loss of
input power at the low-end nominal range—115 VAC / 47 Hz or 230 VAC / 47 Hz—at
maximum continuous output load as applicable for a minimum of 17 ms.

I never bothered to actually test and measure the transfer time of the UPS units I have around here. They all work fine with the systems they support so that works for me.

Anyway, as to the original problem I see AG as having answered the problem. The OP likely had a really lousy UPS or a lousy UPS combined with a lousy PSU in a system set to restart following a power failure (frequently a BIOS or Power Settings setting.

Ron