Question about Belkin (f6c900-unv) UPS System

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Belkin UPS F6C900-UNV burns up after replacing the battery.

Normal 0 Has this happen to anyone else? I've had (3) Belkin F6C900-UNV UPS's burn up after replacing the battery - note: (5) others did not burn up after replacing the batteries. Yes, I'm using the same rated battery 12V's, 8Ah. After replacing the battery (red to red, black to black) and plugging the unit back in, after about 10 minutes I noticed the smell (acid smell) and found that the battery was 'cooking'. The first time this happened, I thought that maybe I had hooked the battery up backwards (as in backwards - red to black, black to red), and certainly that would have burned it up. Since the unit was cooking and I didn’t want to be involved with an explosion or acid burn, I moved it to a safe place to cool and disposed of the unit. But then it happened to me 2 more times, I went back to check that they were connected to the battery correctly (I'm sure I did, but I double checked anyway) and they were hooked up correctly, red to red, black to black. What is going on? Why would replacing the battery cause the system to overcharge the new battery and 'cook' the new battery? The second time I had this problem, the unit was in a remote room and I didn't notice it for about 90 minutes. The system was so burned up after 90 minutes that gel cell acid had liquefied and was started to leak out of the unit, not to mention the acid smell from the 'cooking' that lingered for days. This could be a real hazard. We have 20 of these, and I have lost all confidence in the units. I’m to the point that I feel it necessary to report this to my management as a possible building hazard, and I searching the web to see if others have reported this. (I have 20 years experience in maintaining data systems, and I’ve never run into anything like this before).

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  • ray781 Feb 26, 2009

    Some of the Belkin F6C900-UNV units came with two smaller batteries connected in series, and some came with one larger battery.

    The smaller double batteries are labeled:
    12V 4.5Ah
    cycle use 14.6-14.9V
    standby use 13.6-13.8V
    initial current: less than 1.35A

    The single larger battery are labeled:
    12V, 7Ah

    My battery supplier gave me the following for replacement:
    single larger batteries
    12V, 8Ah
    standby use: 13.6-13.8V, initial current 1.2A
    cycle use: 14.5-14.9V, initial current 2.4A

    I can't find anything about 540W/900va listed on any of the batteries.

    did question that adding the two smaller batteries 4.5Ah together would
    yield 9Ah, and the replacement 8Ah was different (but both 12V). And I
    was told that the 9 vs. 8Ah would only affect the run time - that the
    Ah was only a unit of run time, not of electrical characteristics for
    replacement parity.

    Was that information correct?

    sure that I've replaced a few (I think 6 units over the last 2 years)
    with the same replacement batteries, I've labeled the unit with the
    replacement date, so I'll try to pull a couple of units out of use and
    check to see which replacement batteries were used, but I do remember
    that I've always replaced the single and double battery packs with
    single batteries.

    Thanks for your help.

  • Anonymous Mar 19, 2009

    I have the same problem. Two 900VA units that are cooking batteries. I am dealking with Belkin Support right now but it hasn't been much help yet.

  • David Shaub May 11, 2010

    If they came with batteries connected in series and you are connecting thwm in parallel, there is one of the problems.

    2-12 volt batteries connected in series will give you 24 volts, where 2-12 volt batteries connected in parallel, will give you 12 volts.

  • David Shaub May 11, 2010

    It sounds like 1 of 2 possibilities.

    You connected the batteries in parallel but got the charging wires reversed, or you don't have the correct rated batteries. 540w/900va. The Belkin UPS F6C900-UNV has been discontinued.



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I just replaced the batteries on my Belkin F6C900-UNV. They died just short of 3 years of use, which is what I would expect. My unit contained two 12 volt, 4.5 amp-hour batteries that were connected in series. When connected in SERIES (one battery's red terminal is connected to the other battery's black terminal), the two batteries behave as if they were one 24 volt battery. Therefore, this UPS is designed to charge a 24 volt battery. When replacing the batteries, you cannot use a single 12 volt battery. This will fry the battery. You can use either two 12 volt batteries connected in series, or one 24 volt battery.

I measured the charging voltage of my two new batteries (connected in SERIES), and find it charging at 24.6 volts. This is an ideal float voltage to maintain these sealed AGM (absorbed glass mat) lead acid batteries (13.2 volts per battery). The replacement batteries are similar to the originals, each measuring about 2.7x3.5 inches and 4 inches high and rated at 12 volts, 5 amp-hours. They can be purchased for $20 or less each, so for $40 I now have a fully functional UPS, good for another 3 years.

Posted on May 07, 2009

  • Ron Pendleton Nov 12, 2011

    I know this is 2 years old but I wanted to chime in. DaddioDave is correct. If your F6C900-UNV has the two smaller 12 Volt Batteries, you will notice that the two batteries are taped together with a Jumper wire going from Black to Red between the two batteries. This makes them wired in Series and thus it is a 24 Volt Battery at that time. By replacing it with a single 12 Volt Battery, you now have the UPS that is designed to charge a 24 volt battery, (as well as Run off of a 24 Volt battery in BackUp Mode), utilizing a 12 Volt Battery. Total Chaos. Same as putting a 24 Volt Battery in your car, is going to fry everything. So you MUST replace the two batteries with the same 2 x 12 Volt Batteries. Hope that "splains" it for you Old Timers, (as Lucy used to say to Ricky) NOTE: While doubtful , if by any chance you have one of the 12V Battery's test out good and the second tests bad, do yourself a favor, replace the batteries in Pairs. To replace one new one and keep tone old one (even if it tests OK) is just going to cost you more money down the road. Trust me on that.

  • ssturbo May 03, 2013

    Ron, thanks for enlightening us. Ray781, thanks for iterating the problem in the first place.



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