Smart-UPS SUA2200I - Battery Float Voltage

[vivekjm_apc]

This was originally posted on APC forums on 4/8/2016

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Hi,

My nearly 3 year old SUA2200I has a float voltage of 54.5VDC in the PCBE monitoring screen and 55.44VDC (27.72V per RBC which consists of 2 17AH VRLA batteries in series) when measured using a Fluke DMM at the battery terminal. We're fast heading into the summer season where I live where outdoor temps can exceed 40C/104F. The ambient temp in my home is now about 31C/88F and the unit's internal temperature is 35C/95F

I have had to replace 4 pretty expensive batteries on an average once a year, about 2-3 times more frequently as I normally do with my other SUA2200IN unit.

I now realise this is probably because the float voltage is way too high. These batteries (from an APC approved OEM vendor) require a float voltage of between 13.38-13.68 VDC. Once I switch on the aircon the unit detects the drop in temp (internal temp approx 31C) and raises the float voltage to about 27.9VDC (nearly 14V/battery) measured at the terminal. The high voltage is damaging the batteries and will continue to do so indefinitely until the float voltage is corrected.

How can I lower the float voltage. Please help.

Regards,

Viv

[BillP]

This reply was originally posted by Bill on APC forums on 4/11/2016

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Hi,

PowerChute will report the battery string. To my knowledge that unit should have 4 12 volt batteries so the float should be around 54 - 55 volts DC. If the batteries are being over charged then the unit should be replaced. 

If another forum member would like to assist with possible changing out the charger they are welcome to do so. Our policy is the units do not have user replaceable part except for the batteries. However, I do know that other members of this forum will occasionally offer repair tips.

[vivekjm_apc]

This was originally posted on APC forums on 4/11/2016

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Hi Bill,

Yes this is a 4 x 12 V battery model which has a float range between 54.2 and 55.1 VDC as seen on the PCBE screen. Unfortunately the voltage at the battery terminal is higher.

Replacing my UPS with a new SUA unit costing US $600 in my country only because it has a slightly higher float voltage would be a challenge for me.

Though I used to repair consumer electronics including TV sets as a hobby I did not want to risk opening the UPS. I was able to change the float voltage by following a method described on the Internet and a utility called APC-Fix. Luckily this is the older SUA model which permits these changes. 🙂 So, I adjusted the voltage to 27.25V/RBC i.e. 54.5 VDC which matches matching the value in PCBE. I am now a happy camper.

I don't mind if the batteries take a while longer to charge. The city I live in doesn't suffer frequent power cuts or brown outs. This particular UPS just got its 4th set of batteries, (including the factory fitted set) in only 3 years. Moreover, spending over US $100 every 12-14 months on replacement batteries was getting a bit tough on the wallet. Quite a contrast to my 1st SUA2200I (2010 manufacture) which has never cooked the batteries and consistently gives a battery life of about 2.5-3 years.

[vivekjm_apc]

This was originally posted on APC forums on 4/19/2016

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OK, so I proactively replaced the batteries in my 1st (older) SUA2200I unit. After I purchased the batteries (APC OEM approved), they were charged using a temp sensitive external charger and installed in the UPS.

A few hours after installation (to get the UPS up to ambient) I measured the float voltage using a Fluke 177 DMM - 26.6VDC @ an internal temp of 35C/95F. Little wonder this 2010 unit has NEVER cooked any batteries and has run faultlessly (touch wood) so far.  Must appreciate the factory adjustment has held well for so many years. BTW this unit was assembled in the APC plant at Bangalore India, while the 2nd (newer unit and the subject of this thread) was assembled in some other plant in India. I think the Bangalore blokes did a far better job with QC!

This is my 4 or 5th APC UPS having steadily migrated/upgraded every few years starting with the little Back UPS 800 back in 2000-01. An 8 year old Back UPS 1500I is still doing duty with only a single battery change after 5 years. 🙂

[BillP]

This reply was originally posted by Joe on APC forums on 4/20/2016

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Hi Viv,

I've been keeping an old SU2200 alive since about 1998 and I had battery charge problems that I was able to correct by changing out some components that drifted with age.  The NMC in the unit reports the battery floating at 55.05 VDC and is confirmed by an accurate DMM.  Schematics are nearly non-existent and a good eye and a top-notch magnifier were able to help pin point the drifting resistors.

Once during the life of the unit, even though the battery float voltage was 55.05 VDC, the battery assemblies themselves were physically quite hot to the touch indicating that something was going on with them.  Pulling those batteries, APC RBC11s, showed signs of being swollen and slight leakage of electrolyte around the terminals where the fuses were bolted.  The other two or three packs, again APC-branded RBC11s, ran perfectly fine at the 55.05 VDC level.  Do your batteries feel hot to the touch (hotter than the units reported internal temp)?

Just a question, when you say you use "APC OEM approved" batteries, I am assuming you mean APC-branded (APC labels and serial numbers) RBCs?

I've decided that this is the last battery replacement for this venerable old war horse and I will "sunset" it when the installed batteries are gone or the unit finally stops working.  Good luck in keeping yours alive!

[vivekjm_apc · Accepted solution]

This was originally posted on APC forums on 4/20/2016

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Hi Joe,

Actually my UPS batteries have always run a bit warm but never hot to the touch and I live in a tropical country. Luckily none of the batteries have swollen up or the case distorted. I put that down to 2 reasons i.e. low float charge voltage in one SUA unit (the last replacement was in Dec '12, proactive replacement few days back) and yearly replacements in the 2nd unit. More frequent battery replacements means no time for the battery to swell up.

My batteries are not sourced through APC. However, I use the exact same brand & model of batteries that are APC approved and are frequently factory fitted in brand new UPS systems. I save quite a bit of money by buying from after market sources. The batteries carry a 1 year manufacturer warranty.

I am looking to upgrade to the new SMT series some day. But the lack of an Internet "knowledge base" on the revised codes/protocols that can help me tweak the UPS (as I do with my older SUA units) serve as a serious dampener for my upgrade itch.

Cheers!

Viv