UPS remake?

Discussion in 'General Electronics Chat' started by haamer, Oct 24, 2010.

  1. haamer

    Thread Starter New Member

    Sep 20, 2010
    I want to connect to regular APC CS500 UPS a 40 Ah battery to reach 3 hours of backup time on 150W load(13A on battery).

    But I have found, that small UPS-s are switching off after 15 minutes, regardless of battery size. I have one APC and one GE UPS and both behavior is similar.

    What makes matter worst is, that all is controlled by special APC chip, which I cant modify.

    Only thing I noticed, that on freerun(0.5A on battery) it works longer.

    Does someone know, how UPS measures its load, and how to simulate UPS, that there is no load.

  2. DonQ

    Active Member

    May 6, 2009
    "Isn't the purpose of a UPS to give one a cushion of a few minutes to shut down in the interest of not losing current work / data..."

    Another interpretation of an UPS (Interruptable Power Supply) is to convert battery power to the format you're using (120VAC) until the battery runs down. That's the interpretation I prefer. This allows them to be used for running things like low-power lights during blackouts, etc, that have nothing to do with computers.

    Running till the battery is depleted, or nearly so, seems obvious to me. I can imagine UPS developers hard-coding in a time limit so that you will have to buy a larger unit from them rather than merely getting a bigger battery like normal humans would want to do. In overstressed smaller units this may be a good idea, but should not be present in larger units.

    Some UPSs have external connections for additional batteries. These may be interpreted differently from the internal battery connection. This would be the way I would go. If there isn't an external connection, maybe there are un-used connections inside the unit.

    Realize that when you're messing around with higher current components like those present in UPS, including the battery, things can go really wrong really quickly! Wear eye protection, etc.
  3. DigitalReaper


    Aug 7, 2010
    Could it be a thermal shut down? The cooling may be insufficient for continious running beyond what the original battery is capable of. The heatsink may or may not be live, so be careful if measuring temp or replacing it.
  4. PackratKing

    Well-Known Member

    Jul 13, 2008
    Now that you mention it.... the thought of those heatsinks being chassis-live, is a real mind number.....

    I had the good fortune to stumble upon a dumpster full of scrapped Minuteman UPS, a/w/a a good small pick-up bed full of PC equipment of every stripe imaginable by a local firm that had just upgraded their entire system..

    I didn't try to fire any of this up, since no batteries went with it, I just netted a small fortune in useable components to add to my packrat inventory :D
  5. haamer

    Thread Starter New Member

    Sep 20, 2010
    Definetly no thermal shutdown. On 150W heatsinks are barely warm. Yes indeed they are live.
    I have found some service manuals, if I get printed these on A3, I´ll start thinking, what can be done.