Battery Backup Systems Or UPS - 2 Batteries - In Series Circuit - Bad?

Hello. I have a question about battery backup systems or UPS where now they have a sealed pack of 2 numbers of batteries as 1 battery.

I know that having a second battery will increase either voltage or capacity, depending on how they are wired. Hooked
up in series will increase the voltage, so if a battery is 12V, then your will have a 24V system or unit. Parallel wiring will increase the capacity and thus run-time.

Now, if the the 2 connected batteries ARE tied together as one unit, and the batteries ARE wired in a "SERIES" circuit, HOW CAN 24 volts ANYWAY improve run-time versus 12 volts? (BECAUSE THAT IS HOW I AM FINDING THEY ARE WIRED -- IN "SERIES"; IT DOESN'T MAKE ANY SENSE.) Can it provide ANY positive effect to run-time? Doesn't it REALLY NEED to be wired in PARALLEL in order to increase run-time?

Please reply.

Thank you!

 

I'd have to look at the schematic for your unit, but it may be a moot point - the unit must output 120 volts (at least here in America), so there may be different ways (series, parallel, or series/parallel) to achieve that goal. It all depends on the manufacturers' equipment designs.

 

Hello. Thanks for your reply.

Yes, it sounds odd; you say debatable. A series circuit can increase run-time, hmmm...

I am looking at 1 of 2 units to buy. Respective tech reps. have told me from both manufacturers that their units I'm interested in are indeed series and not parallel. The are the APC Back-UPS RS Pro 1000 Website: http://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=BR1000G&tab=models

...and the CyberPower CP900AVR. Website: http://www.cyberpowersystems.com/pr...R.html?selectedTabId=overview&imageI=#tab-box

If you can make reason why or even how series circuits can produce a longer run-time, that would much be appreciated.

I am an American, so yes I have 120 V standard at my home.

Please reply.

Thanks for your interest.

 

Understand that 2 (or 3, or 4, or whatever) batteries in parallel or series is still just one battery. The individual batteries become, in effect, "cells" of the one battery, even though each battery may have several cells too. The voltage alone does not determine the run time. The amp hours (Ah) and load play major roles too. Note that many UPS use four 6V batteries as cells, while another UPS with the same capacity and runtime may use two 12V. There is nothing really that says one is better than the other - although replacing four 6V batteries probably cost more than replacing two 12V.

Since the DC is converted to AC, it really does not matter how they do it. You just need to pay attention to the published specs. How they achieve that is more a matter of curiosity, rather than quality.

 

Hello. Thanks for the reply.

I was failing to see that both series and parallel circuits have the SAME wattage when converting from DC to AC. I was getting hung up on the differences between wattages and consequently the amperes impact on runtime. There is no difference between circuits. However during runtimes, you would discharge the cells twice as fast in a parallel circuit than a series circuit, correct? However, comparing total runtime to discharge between a parallel and series circut -- they would be the same total runtime?

This required some thinking.

Example:
You need to draw 10 amps from a 12 volt system to get 1 amp at 120 volts. You need to draw 5 amps from a 24 volt system to get 1 amp at 120 volts.

Makes sense?

Please reply.

Thank you!

 

You are getting hung up on the wrong facts. Once again, as I said previously, the Ah specifications of the batteries as well as the load are significant factors in determining run times too. If you are looking for an UPS, look at the specs of the UPS, not the batteries inside.

 

@Digerati:

Thank you for your reply. Please help me.

Okay, you say that I should be looking at the UPS and not the battery. WHAT EXACTLY in terms of facts for the UPS unit should I be looking at to get a fair and true estimates of what information I need?

I am looking at the runtime graph of the APC unit, I assume that is something I need to look at. The Cyberlink I am insterested in does not have a runtime graph, so I cannot tell here. What other facts do we need to look at?

Please reply.

Thank you!

 

APC has a UPS calculator, you can use that. Or you can use the eXtreme PSU Calculator Lite to determine your minimum power supply unit (PSU) requirements. Then add power consumption of your other components you want to support to that power supply value and that should be your minimum UPS size. Note that runtime is not normally that critical. Most power outages only last a few seconds. Outages that last longer usually last much longer. So all you really need is a UPS to run long enough to save any open files, close applications, gracefully shutdown Windows, and power off the computer.

And note, like power supplies, there are good ones and not so good ones.

 

@Digerati and all:

Thank you for you replies.