Battery question: (254 X 1.5V) vs (32 X 12V)

[CostasV]

Hello,

we have a UPS system that uses 254 batteries if 1.5V in order to give 380V DC. My question is why not 32 batteries of 12V.


Thanks in advance

Costas

 

[mpparent]

I guess the question you need to ask yourself is, "Do I want a wet cell system, with ongoing maintenance, high reliability, long service life, etc. or a valve-regulated system, with low maintenance, short service life, and depending on the battery, questionable reliability"?

Mike

 

[itsmoked]

That would work too! It was probably set up that way for cost and the amount of storage capacity. And the battery chemistry. This sounds like Nickel Cadmium(cell voltage) and they OFTEN came as sigle cells in a case.

 

[MikeHalloran]

Your UPS uses 254 _cells_. They can be diagnosed and replaced individually.

It could use 32 _batteries_ of 8 cells each.

Individual cells in a battery are hardly ever individually replaceable, and are often not even provided with access for individual cell testing. It is often the case that only one cell in a battery actually becomes unusable, but monolithic battery construction forces you to discard the remaining good cells with the bad one.

You are better off with individual cells. Someone probably paid extra to have the UPS constructed that way.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[alehman]

The total required battery capacity can dictate the type of cell packages (units). Larger amp-hour capacities are commonly available as single cells. Smaller capacities are commonly furnished as multi-cell units. As noted above, individual cells will increase the cost of small capacity systems.

 

[rbulsara]

It is safe to assume the UPS is feeding really critical loads then should not be interrupted even momentarily. So the most important criteria of all is the 'reliability' of the battery system and not the technically it will work or not.

Wet cells with 2.0V nominal (they are not 1.5V) per cell have proven their reliability in telecomm industry over a century now. (How often have you lost telephone service due to a power outage? I am speaking for USA or similarly developed nations)

The 12V batteries you are referring to sounds like car batteries...how many times have you seen/experienced a car battery die?..so there lies the answer.

 

[CostasV]

Thank you all for your replies.

As I see from the messages of mpparent and rbulsara, reliability is one difference between 1.5V (or 2V) cell and 12V battery. The reason, if I understand correctly, is in battery chemistry as itsmoked wrote.

Q1. Is there a comparative measurement regarding reliability of various types of batteries? Any link, or even personal measurement would be appreciated. To rbulsara: In order to compare the batteries of the telecom industry with the batteries of the vehicle industry, I guess we need numbers like [failed units / total units], average and standard deviation of operation time before failure etc.

Q2. I thought that the common practice was NOT to change individual cells/batteries when some are found unusable. We supposed to change the whole series of batteries. How, individual testing/replacing is an advantage for the 1.5V cell?

Thanks again for any input.

Costas

 

[itsmoked]

Hello Varsamidis.

Q1 There is often quoted opinions on which batteries can cycle the most, float the longest, be discharged the most but in reality the way batteries are cared for trumps all the standard opinions.

If one's charger brutilizes the batteries they will die quickly. If the ambient temp is too high or too low they will die quicker. If they get cycled they will die quicker. If they etc etc.. So to answer your question is very hard since it even varies with your UPS usage.
Your failure numbers are almost impossible to state because of this.

As for type of batteries, automotive batteries are specially designed to provide whopping currents briefly for cheap. They are utterly worthless for UPS duty.

AS for Q2: Yes and no you can replace batteries one at a time. With that many batteries in series it is harder. But often a single battery fails in a group that large. Go ahead and replace it. You MUST replace it with the same type/capacity/voltage/chemistry thou!! Once they start to fail more often say 3~5 in a year instead of say..one or two it would be better to change out all of them as they are all going to reach end of life.