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    UPS external battery mod.

    Recently I ran up on a couple of APC brand uninterruptable power supplies. They both worked, its just the batteries were dead due to age. Rather than try and source a replacement battery, I did something I have wanted to do for a while, and that is rig one up so it can be connected to an external battery for when the power goes out and actually have it run for more than a few minutes at a time since the power goes out quite frequently around where I live. Every time it turns really cold, or the wind blows, or some idiot takes out a light pole so its at least an hour before it comes back on again. I don't really need a lot of power, just enough to run a light bulb or two and to power my DSL modem and router so that I can keep an eye on radar when storms are threatening.

    The model of the UPS I used was an APC-500es, supposedly good for 300w for a few minutes. Here are a few shots of the PCB:







    I'm sorta unimpressed at the MOV's... they are 230v rated (I believe) 14mm diameter blue things (manufacturer unkown). Honestly for a surge protector I would expect something a bit more beefy. At some point in the future I might add on another PCB in the battery chamber and put in some higher joule rated ones and perhaps a gas discharge tube or two for some additional protection against lightning. The caps are mostly pannys for the little bitty electrolytics, and jamicon for the larger ones. I didn't think it would be necessary to yank them out and test them so I just decided to let them be.

    If your wondering what the hell the wires are coming off the PCB, I will explain that in a minute.

    A shot of the PCB sitting in the housing:



    Cover installed:



    To run the wire to the external battery all I did was drill a couple holes in the side of the battery compartment cover and run some cable in. I'm not sure what gauge it is, but its pretty heavy stuff, its some scraps I got out of the boat that I used to connect a deep cycle battery to my trolling motor. I used a couple heavy brass terminal blocks I had laying around to make the connections and a small piece of plexiglass to keep the wires separated. Initially I wanted to use rubber grommets for where the wires ran in, but basically said to heck with it since I couldn't find them amongst all my junk.

    If your wondering what the switch is for, its an audio alarm silencer. Basically when the power goes kaput or there is a problem a buzzer will start beeping and gradually speed up as the backup battery gets depleted. Nice feature, but annoying as hell if you intend to run the UPS on battery for an extended amount of time. So what I did was simply relocate the buzzer to the battery compartment... that is what the wires coming off the PCB were for. This will save my sanity, but it won't tell me how much juice my battery has left.

    What I came up with to work around this shortcoming is to try and use the other side of the switch to power a LED. Unfortunately I have no clue what voltage or amperage the buzzer is rated for. This is important because not knowing those two variables I can only guess what current limiting resistor I need. Measuring the voltage or amperage is out of the question because my DMM is too slow to keep up between beeps. I do know couple things about it, and that one it is not a self buzzing buzzer... it has to have an AC input signal. The other thing is that the resistance measures around 138 ohms with my DMM, and hooking it to a 9v battery it draws about 60ma of current. I'm assuming that the actual working voltage is probably lower, like 3-5 volts since most buzzers I see near it's size are rated for a maximum current draw of less than 20ma and based upon its resistance anything more than that seems like it would be way too much. Therefore went ahead and stuck a 160 ohm current limiting resistor for the LED and will see how that works. If it blows, no biggie I got a whole bunch more of them in my parts bin.

    And finally the unit right side up with the cover on:



    When the switch is in the up position, the buzzer is used. With the switch in the middle, both the buzzer and LED are off. When the switch is down, the LED is operative only.

    Going to hook it to a battery when the sun comes up and see what it does... maybe it won't blow up.

    #2
    Re: UPS external battery mod.

    Beware that some UPS units have the battery at mains potential.
    My first choice in quality Japanese electrolytics is Nippon Chemi-Con, which has been in business since 1931... the quality of electronics is dependent on the quality of the electrolytics.

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      #3
      Re: UPS external battery mod.

      I wasn't aware of that regarding the battery but I do know that as long as there is a battery connected any UPS should be considered live.

      Anyways just got back from hooking it up to my lawnmower battery just to see what it would do. Put a 40w light bulb on it for a load and well the good news is that output regulation seems to be pretty decent, bad news is it is a bit low at 97v. Not for sure if its a bad battery connection (just used some big gator clips), an out of spec or bad cap somewhere, something to do with the non-sinusoidal output waveform causing funky multimeter reading, or the feedback loop simply needs tweaking a bit. And the LED mod seems to work OK (yay mo beeping while on battery power!).

      Now to go dig some decent battery lugs out of the shed and see what it will do when properly hooked up.

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        #4
        Re: UPS external battery mod.

        it will burn up at full load.you want the old steel cased apc units.that one is trash.firmware has a timer anyway.
        the low reading is normal for a stepped square unit.
        i guess you can experiment till the smoke comes out.

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          #5
          Re: UPS external battery mod.

          Originally posted by Evil Lurker View Post
          Put a 40w light bulb on it for a load and well the good news is that output regulation seems to be pretty decent, bad news is it is a bit low at 97v. Not for sure if its a bad battery connection (just used some big gator clips), an out of spec or bad cap somewhere, something to do with the non-sinusoidal output waveform causing funky multimeter reading,
          That last option is most likely. I have put a scope on a similar UPS. That 120 volt output was 200 volt square waves with a spike of up to 270 volts. Ideal perfect power for all electronics. And harmful to some motorized appliances and power strip protectors. If your meter is not RMS type, then it is trying to measure the best it can.

          Now, what is battery voltage when powering that 40 watt light bulb? If above 11.7 volts DC, then the UPS is outputing its best voltage and waveform. Measure the battery. If nearly at or above 12, then the UPS has all in the input power it wants.

          Comment


            #6
            Re: UPS external battery mod.

            I have done this. I have a tripplite UPS connected to a small deep cycle maintenance free battery. Mine will run my computer and 2 monitors for 45 minutes. The UPS is fan cooled.
            "...off the record, unnamed government sources
            alluded to unsubstantiated innuendos about
            alleged indiscretions and insinuated that they
            are rumored not to be without basis for further
            speculation..."

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