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Member

Join Date: May 2008
Location: McAllen, Texas, USA
Posts: 9

Using a UPS as a continuous inverter.

05/22/2008 4:03 PM

Does anyone out there have experience or practical suggestions in using an APC 3000 watt UPS as a continuous use "full sine wave" inverter powered by a sizeable (800 Ah, 24 volt) battery bank? I recharge the battery bank with 1.8 Kwatts of 24 volt solar panels – and will be adding more solar panels soon.

Currently, I use a 2000 watt modified sine wave inverter to operate some home applications and want to change the APC UPS to run continuous for the sizable 3000 watts.

My main concern is the switching back from inverted AC (from 24 v DC) when even 800 Ah are depleted (bad weather), and eliminating the AC to DC charge circuit in the APC.

I encourage comments and suggestions regarding the feasibility of such an endeavor.

Nick from South Texas.

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#1

Re: Using a UPS as a continuous inverter.

05/23/2008 5:26 AM

Dear Nick

I would suggest that you could look at an option for low cost wind mills too( check the topology of your region and also the winds). The Chinese windmills are cheap and relaible too. I could suggest the details to you based on the geography and total requirments.

This would give you power in the night too.

Do review this option

Regards

ST Choudhary

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Location: McAllen, Texas, USA
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#6
In reply to #1

Re: Using a UPS as a continuous inverter.

05/28/2008 11:25 AM

Thanks for your comments. I do plan to install some wind generators (depending upon city compliance) for the night or bad weather times. Wind conditions are not favorable for a steady supply of wind energy in my area.

My thoughts on the UPS were to use it as a full sine wave inverter for sensitive devices – TV's, computer equipment or other electronics, thus my questions. I already have modified sine wave inverters running.

There are internal relays within the UPS already that switch from "house power" to battery at signal loss, and relays that charge the batteries when power is returned. The main reason for my questions were to find creative ways of employing the UPS – and there are many around – instead of buying more inverters.

I wondered if others had overcome the battery charger problem and could help me.

Thanks for your thoughts.

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#2

Re: Using a UPS as a continuous inverter.

05/23/2008 7:37 AM

Dear Friend,

Why don't you use connecting relays to do the switching. This will enable you switch from utility supply to inverter of from inverter to utility supply or vise viser.This will enable the system change over automatically.

Thank you

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#4
In reply to #2

Re: Using a UPS as a continuous inverter.

05/23/2008 5:56 PM

But is also dangerous and highly illegal.

In any civilized country, you have to have a specific type of changeover switch. It can be manual (cheaper) or automatic (expensive) and it has to be type approved and type approved installed by you local electricity supplier....

This is done so that you will not have the slightest chance of killing a line man trying to do his job!!!!!

If you also want to sell electricity back to the supplier, then an even more expense automatic switching system is needed!!!!

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#5
In reply to #4

Re: Using a UPS as a continuous inverter.

05/28/2008 11:15 AM

Thanks for the comments. I would not attempt to connect to the main grid without a certified Grid-Tie device.

What I want to use the UPS is an intermediate step in providing true sine wave power for TV's, Computers and such. The inverters I use currently are modified sine wave and not recommended for sensitive electronics. They work great for the refrigerator and lights/ceiling fans but a true sine wave inverter is expensive and I have the APC 3000 that I can use.

I wanted feedback on its use.

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Anonymous Poster
#18
In reply to #5

Re: Using a UPS as a continuous inverter.

08/08/2010 9:25 AM

The answer to your problem is very simple. You don't need any sophisticated, expensive devices to use the APC3000 as a full time inverter. The APC 3000, the 5U version, can be powered up three (3) ways: 1)by the internal battery; 2)AC power when utility power is available (at the same time charging the batteries and; 3)an external battery. The APC 3000 has a power connector at the back so you can connect an external power source such as a bank of batteries or an AC/DC charger. The only catch there is that your source should be capable of charging 48 volts. So if you are using a solar panel, you need to build your solar panel in a way that its output is > 48 volts.

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Anonymous Poster
#3

Re: Using a UPS as a continuous inverter.

05/23/2008 12:30 PM

Is the APC 3000 charge circuitry interfering with you charging the battery pack from your solar panels using a seperate charge controller ?

If not then why bother removing or bypassing the circuitry when it can be used to charge the batteries when you have AC Hydro power ?

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#7

Re: Using a UPS as a continuous inverter.

05/28/2008 2:22 PM

While I question your overall scheme, I'll answer just your specific question. I used to be in the UPS business.

Consumer grade products such as everything made by APC, are NOT rated for continuous use. They are limited duty cycle devices, intended to provide simple backup power so that users can accomplish an orderly shutdown. Using the invertersection continuously will likely result in its premature failure.

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#8
In reply to #7

Re: Using a UPS as a continuous inverter.

05/30/2008 11:04 AM

This is more to the point of my post. I did consider this limited duty cycle of operation.

My thoughts co-mingle with your statement regarding this issue. Non-the-less, I would employ a ups at 50 to 60% utilization to avoid over stressing and would add ventilation fans that the ups does not have.

Your point is well taken and it may be the reason I do not find much experimenting in the way of using the vast number of used UPS's out there. In the recycling areas I find many UPS's that have battery failure and are just junked instead of replacing the batteries.

Thanks you for your suggestion. I'll take it to heart.

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#9
In reply to #8

Re: Using a UPS as a continuous inverter.

05/30/2008 6:00 PM

A 50% derate will certainly help, but even if the power devices are under less stress, the control boards are also not necessarily designed to operate continuously. Still, if you are picking up scrap material for pennies on the dollar, I think you have a decent chance of success. Good luck.

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#10
In reply to #8

Re: Using a UPS as a continuous inverter.

06/02/2008 8:39 AM

I cannot agree with post# 7 or your thinking that it is correct.

I have made and used a UPS of this type for about 7 years now, all I did was to design my own charger (albeit a hobby of mine) and attached it to a leisure battery of 100 Amp/hours, feeding an inverter that I bought with a proper Sine wave output....and a high efficiency!

Nothing has broken in all this time and it allows me to shut my PC down in an orderly way if a power cut happens. Which is only twice for me......so it probably was not really worth the effort....but it gave me a lot of fun and allowed me to test my caravan charger design for a number of years in an easy way......I do of course actually cause "power cuts" myself, intentionally and watch current usage and battery voltage most carefully....

In all that time, I am still using the same leisure battery and it has not had to have even distilled water added, a sure sign of misusage......so my design would appear to be quite good!!! No, I am not giving away free copies.....sorry.

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#12
In reply to #10

Re: Using a UPS as a continuous inverter.

06/05/2008 9:47 AM

You seem to have good working experiance with this type of application. Much like your post, I want to use the UPS circuitry for the Sine wave output for the more sensitive devices. I use modified Sine wave outputs from market inverters for the bulk of the house power (refrigerator and lights).

I am impressed with your cut-over idea. When I cut out the PV circuits to make modifications, I am always thinking of how to maintain power output. You have just given me a great solution.

The PV panels are running through a Morning Star Charge controller (60 amp, 24 volt)for the batter chargeing. That is why I am interested in removing (or by-passing) the built in charge circuit from the UPS.

Thanks for the tip and if you have other constructive suggestions I'm all ears...

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#14
In reply to #12

Re: Using a UPS as a continuous inverter.

06/05/2008 7:08 PM

The ones that switch from the mains to the inverter and back again, often make a small (but important) blip in the mains voltage while switching over. This can cause sensitive equipment to fail. This is the reason that I did not follow that route personally as I simply could not find a way to stop it!

The problem being really twofold:-

1) No warning is given that the mains will fail, till it fails, and therefore the inverter must already be up and running AND FULLY IN SYNC WITH THE MAINS TO ALLOW A PROBLEM FREE SWITCHOVER. This makes everything far more complicated and does not allow any real power savings with regard to having the inverter switched off, as it has to be on all the time anyway.

2) Depending on where you live and what equipment is running at the moment the mains drops near to you, you can get huge spikes from some inductive equipment (motors and transformers etc) on the failing mains, more than large enough to damage or hang anything like a computer etc...

Furthermore, I believe I mentioned it before, while running and connected to the mains, all spikes are given directly to your PC still.

With the simpler battery charger, battery to inverter, these spikes are filtered out by the charger and battery....completely!

But each should make his own choice on the matter!!!!

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#11

Re: Using a UPS as a continuous inverter.

06/05/2008 8:10 AM

Dear Nick

You ahve two questions to be answered 1) Can you use the Inverter continuously : Yes you can use now how do you use it the only ay to use it change the wiring a) one that comes from Ext. Power ( the local city source) and the one coming from battery. The wiring drng will be sent to you in my next post.

2) Do you have a charger ckt saperate in the UPS if it is so (YES) then you can easily do whats written in 1).

3) however if the same is not so then you would have to do a bit of external charging and the wirirgn would differ. I shall forward you the change in wiring schemes for both.

Kindly bear with me for a day

Regards

ST Choudhary

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#13
In reply to #11

Re: Using a UPS as a continuous inverter.

06/05/2008 9:52 AM

Thank you. I'll certainly enjoy looking at your wiring diagram for clues regarding circuit changes.

I use a Morningstar TriStar solar charger (60 Amp, 24 volt) for the charging of the batteries. Thus I want to disable the UPS charging circuit.

There was a point made regarding the UPS installed relays and that has given me an idea. I'll just have to look at the circuit again. Does anyone have schematics for UPS's?

Thank you.

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#15
In reply to #13

Re: Using a UPS as a continuous inverter.

06/05/2008 7:09 PM

It depends on the UPS method used, but a search on the web may turn up the info you want....

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#16
In reply to #15

Re: Using a UPS as a continuous inverter.

06/09/2008 9:45 AM

Thank you Andy, for your comments regarding the phase matching aspects of UPS system's as well as the inductive "surge" voltages that often occur during power outages.

My application is to reverse that engineering of the UPS system. I maintain a moderate sized battery array with (daylight) charging via photovoltaic arrays.

What I want to do is maintain UPS inverter function until battery voltage is at minimum value (before battery damage) and before UPS cuts inverter function. I have an idea to use the LED charge indicator as the trigger and "switch" to house current just before the UPS would normally "shut down" because of "low battery voltage" level. This should allow for synchronized switch over, as when house power outage has been detected and the UPS moves to battery operation and then house power is restored. At this point the UPS matches phase and switches back to house power – as well as starting a charge cycle to the batteries. Thus, avoiding the dangerous inductive spikes you mentioned.

Thus, I want to start from a power outage state and allow the UPS to work as a load inverter (up to 3000 watts) until a low battery condition occurs – usually at night. Just before this condition a "low voltage limit" – circuitry would intervene and force the UPS to switch back to house power – as well as disable the "built in" battery charger. Disabling the battery charger would be a factor so as to allow the photovoltaic array to charge the batteries when daylight is available.

My "green" goal is to use as little house power as needed and use as much "green" PV array power as possible, yet maintain power to selective appliances.

Your continued comments are welcomed.

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#17
In reply to #16

Re: Using a UPS as a continuous inverter.

06/09/2008 6:10 PM

OK, I believe I have understood your requirements, I can see where you are coming from completely....

Using a Laptop (instead of a PC) with battery backup should solve most problems I feel that you want to avoid....

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Users who posted comments:

Andy Germany (5); Anonymous Poster (3); JRaef (2); Nick Morales (6); STChoudhary (2)

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