Tricking UPS systems

[dark666]

Hi to all.

As i mentioned in another post i'm repairing several UPS systems.

Most UPS system won't work without a good battery inserted.
I came across an UPS that didn't work because of the damaged battery.
When tested with a good battery it worked so i bought a new battery.

Some UPS systems have several batteries 3 or more.
The batteries are dead and wont charge on an external charger.
I suspect that the UPS systems won't work without a good battery.

For example one of the UPS system has 6 batteries of 12V 7ah serial connected they are all damaged and won't charge as they are very old.
I don't want to buy 6 new batteries without knowing if the UPS problem is just the batteries.

Can I replace the batteries by a transformer of 72V 7Ah to trick the UPS into thinking that the batteries are pluged in?
Using 2 diodes on the transformer to prevent the current from entering it?

Basicaly I want to trick the UPS into thinking that it has batteries.

Thanks to all

 

[magnatro]

it's for testing rite? then it will work.. i think

 

[dark666]

Yes. For testing.
If the ideia of using a transformer to trick the UPS into thinking it has batteries for testing.
If the UPS works without a problem I will then buy the required batteries.

Thanks

 

[Reloadron]

The units I have tried this on have worked just fine. I use a 120 VAC variac connected to a 35 amp full wave bridge rectifier and just run the variac up to the desired voltage.

Something to watch is how the batteries are actually configured. Most 1.5 KVA systems I have worked on use a pair of 12 volt batteries in series for 24 VDC. I had one that used 4 batteries but configured as two pairs in series / parallel for 24 VDC.

I have had good results but that does not mean every UPS is configured the same so just be careful when using that method.

Ron

 

[magnatro]

yes, it will work... ! but use a filterd dc for the checking purpose OK?

 

[dark666]

basically I will use a transformer to transform 220v AC to the nedded DC voltage and test the UPS.

Now I have two questions.

Does the transformer need to be rectified?
And for magnatro, "but use a filterd dc for the checking purpose OK?" What do you mean by this? (sometimes i have to translate to my native language to understand some terminology)

Thanks

 

[Reloadron]

Yes, the output of the transformer needs to be rectified as you need DC.

As to filtering, I just have a 10,000 uF cap across my full wave bridge which does good enough. Just make sure you get the voltages correct.

Ron

 

[dark666]

Ok. I understand that the transformer have to be rectified from AC to DC, in the previous post when i said rectified i meant stabilized. Again something was lost in translation inside my head. lol

So for the UPS with 6 12v serial batteries i need 220VAC to 72VDC.
Im having trouble in finding such transformer.

Is there another way?
I think i have 220VAC to 90VAC after i rectify from 90VAC to 90VDC, how do i lower to 72VDC?

Thanks

 

[Reloadron]

So for the UPS with 6 12v serial batteries i need 220VAC to 72VDC.

That assumes all 6 batteries are in series. As I mentioned earlier I have seen units and worked on units that used a series / parallel combination. Look closely at how the batteries are configured.

Ron

 

[dark666]

All the 6 batteries are in series im sure of that.

The problem is how to transform 220VAC to 72VDC.

 

[Reloadron]

All the 6 batteries are in series im sure of that.

The problem is how to transform 220VAC to 72VDC.

I mentioned how I do it using what I call a variac also known as an Autotransformer which is like having an adjustable transformer. Here we have 120 V mains but they are also made for 240 V mains.

I don't know of any off the shelf transformer that will step down 240 VAC to 72 VAC off hand. The next option would be to string a combination of transformer secondaries together (in series) to derive 72 VAC which would not be easy or practical. If you do enough of this type of work then investing in a small (maybe 5 KVA) auto transformer is a viable way to go.

Ron

 

[dark666]

"string a combination of transformer secondaries together (in series) to derive 72 VAC which would not be easy or practical"

How you i do that?

 

[dark666]

I searching for a box filled with transformers that i have store somewhere.
I know i have several multiple output transformers.

Lets say I find a transformer with 4 outputs, being, 20VAC, 30VAC, 10VAC and 12VAC.
Can I connect the 4 outputs in a way to achieve 72VAC?

Or even if i find 2 tranformers one with 50VAC output and another with 22VAC output.
How would I serial connect the outputs?

 

[Reloadron]

I searching for a box filled with transformers that i have store somewhere.
I know i have several multiple output transformers.

Lets say I find a transformer with 4 outputs, being, 20VAC, 30VAC, 10VAC and 12VAC.
Can I connect the 4 outputs in a way to achieve 72VAC?

Or even if i find 2 tranformers one with 50VAC output and another with 22VAC output.
How would I serial connect the outputs?

You connect the outputs (secondaries) in series and the primaries in parallel.

Ron

 

[dark666]

What about the amperage of the serial output?
Will the amperage be the total sum of the serial connected ouputs?

And the main question is, if i manage to serial connect several transformers to get the required voltage will this still be ok for replacing/tricking the UPS into thinking it has batteries?

Thanks

 

[Reloadron]

What about the amperage of the serial output?
Will the amperage be the total sum of the serial connected ouputs?

And the main question is, if i manage to serial connect several transformers to get the required voltage will this still be ok for replacing/tricking the UPS into thinking it has batteries?

Thanks

First a little about the current. If I connect six 12 volt 7 Amp hour batteries in series what I effectively have is a 72 Volt 7 Amp hour battery. When batteries are placed in series only the voltage increases. On the other hand if I connect those same six batteries in parallel I now have a 12 Volt 42 Amp hour battery.

Now not all UPS units are created the same. That is why I told you to make sure about the battery configuration. Many, especially larger better made units actually have an LED to tell you when the batteries are bad. They look at the voltage and the batteries ability to take a charge.

A good Google of Lead Acid batteries (cells) will bring up a wealth of information on exactly what the voltages should be and all about charge and discharge. It has also been discussed in this forum many times. Your main concern is not current but voltage in the ability to simulate the presence of good batteries. Also you don't want to destroy the charging system!

Generally on failed units I just test the batteries, though I have simulated them but that isn't the rule.

Ron

 

[magnatro]

you can do this, for a transformer you can eighther buy an auto transformer, or you can design one on your own and wind it for your use...!

the first option is prefrable.

i have attached the files for your concern.

 

[dark666]

Another crazy idea.
Iv'e managed to achieve the needed 72v by serial connect several old batteries that wont charge above 3V~10V.

Will this work in testing the UPS for a couple of seconds?

 

[Reloadron]

I guess in theory it should. Long as you have 72 volts. That's the bottom line.

Ron