UPS as inverter

[dor]

I've got a 750 VA inverter with pretty well shot batteries. The battereis are sealed gel batteries, 6 volt but wired in pairs in series to give 12V working voltage.

 

Can anyone think of a reason why I can't dump the batteries in the UPS, link the terminals to my boat 12V system and use the UPS circuitry as an inverter?

 

It seems to me that (charging circuits aside), that is all the UPS is doing when the AC supply is interrupted, which is what it thinks is the situation if no AC is supplied.

 

Taking it a stage further, if I did have an AC shoreline, it could also act as a battery charger.

[John Orentas]

Dor.

 

What is a UPS.

[dor]

John

 

Uninterruptible Power Supply.

[John Orentas]

John

 

Uninterruptible Power Supply.

27760[/snapback]

 

 

Are we talking about a 12 d.c. supply with 230 volt input. And what current.

[dor]

A UPS is used to provide backup power for computers.

 

It sits between the ac supply and the ac input to the pc. If power fails, then it maintains the ac to the PC. there are two types, on-line & off-line. One type supplies the ac contiuously from the batteries, with the batteries being constantly recharged, the other switches the ac supply over from the input to battery when it senses an interuption. The former give less disturbance to the ac supply, the latter relies on the fact that most pcs can stand a few hundred milliseconds interuption before dying.

 

The UPS is rated at 750 VA, so presumably could supply about 3 amps, drawing 60 amps from the battery, i.e. what you would expect for a 750 VA inverter.

[DHutch]

I cant see why the inverter in an UPS system couldnt be used on a boat.

- Infact, if you just added a few extra batterys to it, you could just use the ups unit as a combi unit (charger/inverter)

- Only down side is the charger might not be a very powerfull one? But other than that ive often thought it would work well.

 

(all this assumes the UPS unit uses 12v batterys as yours seams to)

 

 

Daniel

[John Orentas]

All the ingredients should be in there to do what you describe, the only question is whether it is continuously rated and that will depend on which of the two types it is, a similar question applies the the charger, can it supply the full 30 amps indefinitely or does it merely trickle charge the internal batteries.

 

You really need the specification for the unit.

[Guest]

I would be concerned about the rating, i.e. is it for a short term supply or continuous? Our Striring inverter works exactly as you describe using a UPS mode, but this of course is purpose built. If your UPS supply is continuously rated, then you have a bargain inverter.

[dor]

I assume the 750VA is a continuous rating, as it is supposed to be able to supply that power for at least 30 minutes continuosuly (based on the built-in batteries). It is pure sine wave as well. I would think that if I disconnect the internal batteries and connect the boat battereis, it will just think that there has been a power cut and supply the mains power. I don't know what the quiescent current would be though, which is where I was hoping someone might have had experience of doing this. I can always bench-test it first under vairable loads to see what it draws. I

 

t just makes me think - how many UPSs get chucked out when the batteries have died when they contain a perfectly servicable good quality sine wave inverter.

[Alan Saunders]

I've got a 750 VA inverter with pretty well shot batteries. The battereis are sealed gel batteries, 6 volt but wired in pairs in series to give 12V working voltage. . .

27756[/snapback]

I have wondered for years why this option has not been pursued. I was not prepared to buy one as they do not specify the battery voltage. If it is 12v as you say then this seems to be viable as an inverter on a boat (etc) at a very competitive price! A 750VA (600W) UPS is usually much cheaper than an inverter. You have the kit, try it out!

 

Miffed at missing a business opportunity! - Alan

 

PS With a Marine rating it would be £1,000 - with an Aeronautical rating, £4,000!

[dor]

Looks like a bench test is on the cards Alan. I'll let you know how I get on.

 

Any further observations gratefully received.

[DHutch]

Looks like a bench test is on the cards. I'll let you know how I get on.

Yeah, i too would be very interested.

 

There are loads of used UPS system for sale though ebay

- A 2500va ones has just gone for £64 "Batterys tired, but otherwise fully functional"

 

 

Daniel

[DHutch]

Just to revive a very old topic, did anything actaully happen with this dor?

[Gibbo]

I've got a 750 VA inverter with pretty well shot batteries. The battereis are sealed gel batteries, 6 volt but wired in pairs in series to give 12V working voltage.

 

Can anyone think of a reason why I can't dump the batteries in the UPS, link the terminals to my boat 12V system and use the UPS circuitry as an inverter?

 

It seems to me that (charging circuits aside), that is all the UPS is doing when the AC supply is interrupted, which is what it thinks is the situation if no AC is supplied.

 

Taking it a stage further, if I did have an AC shoreline, it could also act as a battery charger.

 

Sort of.

 

They are usually not continuously rated. They tend to overheat after 30 to 45 minutes and shut down. Even at only 50% capacity.

 

They are nowhere near as efficient as a standalone inverter. Usually in the region of 70% or so.

 

The chargers in them are rubbish. Usually nothing more than an unregulated trickle charger.

 

But they do vary and some APC ones are actually not too bad.

 

Gibbo

 

Edited to fix broken fingers

Edited August 17, 2008 by Gibbo

[twocvbloke]

I'd say go ahead and try it, I've run a Kirby off my largest UPS on batteries (the UPS hummed a fair bit though!!!), and at 750VA (Which is infact 750 Watts, Volts X Amps = Watts, and VA stands for Volt-Amps, just to confuse you!!!) it's a pretty good bit of kit!!! I wouldn't use it often though, UPS' aren't as tough as a proper dedicated inverter, but if you need that little extra power, by all means have a go...

 

Just wear protective safety equipment and keep a fire extiguisher handy!!!

[Gibbo]

I'd say go ahead and try it, I've run a Kirby off my largest UPS on batteries (the UPS hummed a fair bit though!!!), and at 750VA

 

Here we go...........

 

(Which is infact 750 Watts,

 

No it isn't

 

Volts X Amps = Watts,

 

No it doesn't.

 

Gibbo

[twocvbloke]

Here we go...........

 

 

 

No it isn't

 

 

 

No it doesn't.

 

Gibbo

 

Are you positively sure about that?

 

http://en.wikipedia.org/wiki/Wattage#Mathe..._electric_power

[Gibbo]

Are you positively sure about that?

 

Absolutley, 100%, completely, totally, and utterly certain. No question or doubt whatsoever.

 

http://en.wikipedia.org/wiki/Wattage#Mathe..._electric_power

 

You have to read (and understand) the whole article not just post a link.

 

Note (from the link you posted) ......

 

"In direct current resistive circuits, instantaneous electrical power is calculated using Joule's Law, which is named after the British physicist James Joule, who first showed that heat and mechanical energy were interchangeable.

 

P=VI"

 

(bold is mine)

 

Gibbo

[bottle]

TwoCVbloke

 

You have only been here one day, so you are not to know but just so you know with whom you are discussing.

 

Have a look here http://www.smartgauge.co.uk/technical1.html it is Gibbo's site.

[DHutch]

I see you have met Gibbo!

 

While they certainly are loosly compairable, he is right in so much as that they arent nessarally the same when considering AC, and can only be used interchangable with purely resistive loads such as incadecent lamps and heaters etc where there is no reactive (inductive/capacitive) load.

 

 

Daniel

[twocvbloke]

Absolutley, 100%, completely, totally, and utterly certain. No question or doubt whatsoever.

 

 

 

You have to read (and understand) the whole article not just post a link.

 

Note (from the link you posted) ......

 

"In direct current resistive circuits, instantaneous electrical power is calculated using Joule's Law, which is named after the British physicist James Joule, who first showed that heat and mechanical energy were interchangeable.

 

P=VI"

 

(bold is mine)

 

Gibbo

 

Well, whatever you're reading, I don't see it, what I've been taught is what I know, and if it's wrong, there's a very unsafe fully qualified electrician out there...

 

 

I see you have met Gibbo!

 

While they certainly are loosly compairable, he is right in so much as that they arent nessarally the same when considering AC, and can only be used interchangable with purely resistive loads such as incadecent lamps and heaters etc where there is no reactive (inductive/capacitive) load.

 

 

Daniel

 

I have, I think I need a drink already!!!

[Gibbo]

Well, whatever you're reading, I don't see it, what I've been taught is what I know, and if it's wrong, there's a very unsafe fully qualified electrician out there...

 

If there's a qualified electrician around who thinks V x A = Watts then he must have cheated in his exams. Sorry but that's just reality.

 

Gibbo

[Nickhlx]

Well, whatever you're reading, I don't see it, what I've been taught is what I know, and if it's wrong, there's a very unsafe fully qualified electrician out there...

 

 

Hi Twocvbloke ..... and welcome to the forum...

 

A baptism by fire I would say... as Bottle says.... Gibbo is (one of) the main men on the forum when electrics are concerned and if he says something is wrong, it's wrong... but he is stretching a point a little ( because you are new... ? ) and giving the rest of us a bit of a reminder ...

 

After you have read his website (it's fascinating) you will be in no doubt of his depth of knowledge, so it's pretty fair to say

that he won't make a mistake when helping us lot out with comments and suggestions....

 

Nick

[Gibbo]

If anyone wants to actually understand the difference between Watts and VA as opposed to blindly (and incorrectly) believing them to be the same they could always read this.............

 

http://www.smartgauge.co.uk/watts_1.html

 

Gibbo

[Justme]

A couple of questions came to me reading that.

 

1, How is my electric bill calculated? IE watts or VA, I can see that if the returned power is still billed then equipment with a low PF cost a lot more to run than the consumption figures suggest.

2, You mention transformers & that they consume no power whilst under no load (due to returns). Have I read that right? If so why are we told to turn off things like phone chargers whilst not in use (and they get hot too so must be consuming some thing)?

 

 

Justme

 

PS I understood that VA & watts are not the same after looking at generators & also my plug in power meter which will measure both & the VA is nearly always a lot more than the watts except on resistive loads where it is much closer.