SUA3000XL 12v or 24V?

[Anonymous user]

We have a SUA3000XL that is blinking the replace battery light. I have checked the voltage on the two batteries, and they show 24v. Which brings up two questions. The batteries look good at 24v, so why is it indicating batteries are bad? And the recommended battery replacements are 12v. The batteries we have test at 24v?

[BillP]

Hi,

The batteries are wired in series. When wiring in series the voltage is increased. That system has 2 banks of 2 X 12volt batteries. Check out this YouTube video that discusses wiring 12volt batteries is series https://www.youtube.com/watch?v=m_fRQOBoLEg. 

A good 12volt battery should read 2.25v to 2.27v per cell. Each12 volt batteries has 6 cells so the individual batteries if good should read 13.5v to 13.62v. When measured in series the 2 X 12volt batteries should read 27v to 27.24v

NOTE: I have removed your second post on the subject as it is a duplicate of this post. 

[Anonymous user]

I think you for your reply. I understand what you say. But the batteries are measuring 24v out of the system on my bench. So one battery 24v. Also I only see 2 batteries accessible through the door at the front. Are there 2 more inside the UPS? How do I get to them? We do have the extra battery unit SU48XLBP, that contains 4 batteries accessible through 2 doors at the front. But that is disconnected at the moment. I am just trying to get the base SUA3000 working first. Does the SUA48XLBP battery unit take 24v batteries? Is it possible I have inadvertently switched the batteries between the add-on pack and the UPS. hence why they measure 24V? We moved recently, so all batteries were removed. Maybe I have put them in teh worn units?

[BillP]

That SUA3000XL ships with RBC55 which is 2 sets of 2x12v batteries. The 12v batteries are stuck together and wired to output 24v DC. 

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On 4/1/2020 2:46 PM, Chris said:

Does the SUA48XLBP battery unit take 24v batteries?

No. The SUA48XLBP is 2 RBC55 

[Anonymous user]

Ok so if I understand correctly the dual battery should read 24v out of the APC? And the SUA3000 UPC and SUA48XLBP add on unit, both use the same RB55 batteries? So if I have a dual battery unit that measures less than 24v on my test bench, that battery unit needs to be replaced? I do appreciate you rhelp.

[Anonymous user]

Just looking for the correct way to determine which batteries need to be replaced. If they measure less than 24v out of the APC, they are bad?

[Brad_C]

On 2/4/2020 3:52 AM, Chris said:

If they measure less than 24v out of the APC, they are bad?

Depends on how long the piece if string is.

If they are fresh out of the UPS and fully charged, then if they are below 24V the answer is yes.

If you really want to know if they need to be replaced then you need to charge them fully and subject them to a load/capacity test. The RBC55 is ~17AH at a C/20 rate (so after a constant current discharge of 850mA for 20 hours the terminal voltage should be 10.5V/21V (one/two batteries) or higher).

I have some here that are down to less than ~3AH, yet when they are freshly charged the voltage is correct. They are no good and the UPS knows they are no good (it looks at the terminal voltage while under load performing a self test). If I relied on the multi-meter test then I'd be blaming the UPS as they hold their unloaded terminal voltage just fine.

The other thing to look at is the voltage of each battery in the 4 battery set. When new, they are very evenly matched. As they age the no-load voltage starts to show significant imbalance.

[Anonymous user]

Thanks that is a very detailed reply. So it seems, when the replace battery light blinks, there is no easy way to work out which battery is the problem. Or, if in fact, it is the APC at fault. So both dual-unit batteries have to be replaced? And for the add-on unit, that means replacing all 4 batteries as well? That is going to be expensive. I thank you all for your advise. Is invaluable.

[Brad_C]

On 3/4/2020 2:38 AM, Chris said:

So it seems, when the replace battery light blinks, there is no easy way to work out which battery is the problem. Or, if in fact, it is the APC at fault

If you don't have test gear, then there really isn't. I can offer one bit of hard-won experience though. Excepting for quite rare early life battery failures, if one battery has failed then the rest in the pack are not far behind.

How old are the batteries? My record for an RBC55 is 6 years, but 3-5 seems normal depending on environment and cycles. I've regularly seen as low as 2 in hot climates.

On 3/4/2020 2:38 AM, Chris said:

So both dual-unit batteries have to be replaced?

If you mean do you replace all 4 batteries (stuck in pairs) at the same time, then yes. If you don't then as the unit recharges the "deader" batteries charge up first, and their terminal voltage slowly climbs until the overall battery voltages reaches the UPS float voltage, slowly cooking them and leaving the new battery(ies) undercharged and quietly sulfating away.

You don't have to replace the batteries in the external cab at the same time, and often batteries in external cabinets tend to last longer as they don't have the heat of the UPS keeping them above ambient temperature. You just need to replace all 4 in each string together. Having said that, the red light indicates the combined capacity of the batteries (both internal and external) is insufficient, so they're probably all dead.

If there was any suspicion about the viability of the UPS itself, I'd replace the batteries in there, disconnect the externals and run some tests and a calibration before splashing out on new externals also.

The other thing you could do is take the batteries to someone who has test gear (like an auto-electrician perhaps) and have some basic tests run on each battery (you can peel back the covers and access each 12V battery individually.

Frankly if they are 3 years or older, the balance of probability is the batteries are duff.

On 3/4/2020 2:38 AM, Chris said:

That is going to be expensive.

Potentially. All the RBC55s I've seen have been CSB GP12170 batteries. I have a local supply of those, so I now just replace the batteries.

When you replace them, you should get the red light to go out after a self test, but you'll need to do a runtime calibration to get the UPS to really recognise the new batteries capacity.

[Anonymous user]

I thank you for your insight. I think I need to replace all of the batteries in the APC and the external, total of 6 batteries stuck in pairs or 12 singles. I have seen some equivalents on Amazon for under $200 for wired up pair. I have no idea how reliable they are though. Anyone any experience? Or should I only buy APC branded batteries?

[Brad_C · Accepted solution]

On 3/4/2020 11:27 PM, Chris said:

I have seen some equivalents on Amazon for under $200 for wired up pair.

It's always a risk if you don't know what you are buying. There are lead acid batteries, and then there are lead acid batteries.

On 3/4/2020 11:27 PM, Chris said:

Or should I only buy APC branded batteries?

APC don't make batteries. They buy known and tested batteries and put an APC sticker over the manufacturers label.

Having said that, APC don't put their name on batteries that are likely to make them look bad, so with the extra level of QC, plus the warranty and after-sales service you can't generally go wrong. You do pay for that though.

What is the potential business risk if your load drops?