UPS Battery Bank Isolation

There is a philosilly basey fundamold that needs to be tackled first:

• Either isolating the battery bank, or switching the unit to bypass, turns an UPS into an IPS.

Why would one want to do this <rhetorical question - NNTR>?

If one were worried about ripple with the battery bank isolated, the safer approach would be to put the unit in bypass instead.

As it is undoubtedly the best source of advice, one presumes the UPS unit manufacturer's telephone number is to hand?

It should be OK as the UPS will static switch straight through ie bypass.

As well as UPS functionality an online UPS is an excelent line filter (if a battery is present.)

Why do you ask?

I would like to know how the ripple content in the UPS output is getting affected if we isloate the battery bank for replacement/capacity testing etc........As clearly indicated by PWSlack,I can get the answer but I wanted to know opinions of the brilliant CR4 enginers wordwide also.(During battery isloation,we don't go to bypass,just let the UPS flow as it is.)Hope my question is here.

Should be OK.

The rectifier will connect directly to the invertor which will ensure a clean sin wave output. (it is true sin and not modified sin right?)

A correctly designed and built UPS will have battery circuit breaker or fuse that when open will not impact operation unless you have a primary power outage of course.

If possible perform these tests when on generator and not grid supply to eliminate risk of outage outside your control. Check how much fuel you have or it could get embarrassing.

In an Online UPS, the Battery is necessary for a good reduction of ripples at the input of the Inverter part. The Output is normally filtered for a true sine wave UPS, but no battery will affect the voltage stability. The output may have extra ripples.

isolating the battery from the UPS is not an improuvement, therefore avoid it if possible.

Also, if the battery is out of circuit, why do you need the online UPS? If the main supply goes off, the UPS will also go off.

Missing some important information here.

What size is the UPS?

Is it dual conversion or online?

How many Battery Strings are we talking about?

What Voltage are the battery strings?

All these questions will impact your approach.
For example if you have two (2) or more battery strings, you may be able to isolate one (1) string at a time safely, without impacting the UPS.

If it is a small office or self contained UPS, you are probably better off just going to by-pass and working on the unit offline.

If this is going to be a long term situation....just take the UPS offline and remove it.
If you are not going to replace the Batteries, the UPS is just a line filter and an overhead cost you don't need, not to mention a new failure point.

Regards,
Sapper

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1.Its 25KVA UPS for DCS & other critical supplies.

2.It's a parallel redundant UPS similar to one shown below.

MY question is how the ripple content is affected when the battery bank is isolated.Battery would come in line only when incomer supply fails.

Thank you Sapper...But my doubt still not cleared.How the ripple content in this UPS output affected when the battery bank is isolated.

Giri,

The Short answer is that the ripple is going to be 50/60Hz at the UPS output.

The output of the UPS is going to be AC at 50 or 60Hz depending on location.

Since the DC from the Rectifier is fully regulated to the DC bus there will be No Ripple left to impact the Inverter. You are only isolating the batteries...Not the DC Bus.

Regards,
Sapper

Sapper,

Extremely sorry for unable to understand the thing that why the ripple goes up in the UPS output if the battery is isolated(curse my mind!).The DC from the Rectifier is always fully regulated irrespecctive of battery in-line or not.

Giri,

The Output of the UPS is AC. Therefore 50 or 60Hz depending on spec or location.

The output of the Rectifier will be 0% or very close, regardless of the batteries.

Regards,
Stuart

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