Dummy battery load for testing UPS backup system - possible?

Discussion in 'General Electronics Chat' started by RogueRose, Mar 22, 2016.

  1. RogueRose

    Thread Starter Member

    Oct 10, 2014
    I have a 7500 VA 6Kw UPS which I would like to test but I'm not sure if it is possible without the batteries in place. The unit uses 32 12v batteries so it is a big deal to replace all of them. The batteries are run in series in groups of 8 and then I believe those are run in series, or possibly is a 2/2 (2 parallel, 2 series).

    Is there any way I can put something in place of the batteries to test the unit?
  2. Lestraveled

    Well-Known Member

    May 19, 2014
    What is the final voltage that the batteries are configured for? Do you suspect that the batteries are bad?

    A little more information please.
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    You can test up to the current limit of whatever powersupply you have to use.

    If the batteries are in fact, connected in a long series, then you will need a special type of power supply. Voltages higher than 60 V are not cheap and mostly limited to a maximum amperage of a single digit. This means you could test the UPS operation but nowhere near it's full capacity
    Yes a powersupply of any voltage and amperage can be built but cost increases to ludicrous levels vs what lead acid battery can do.
    #12 likes this.
  4. #12


    Nov 30, 2010
    Yes, it's possible, but again, you don't realize how many thousands of dollars your idea will cost to implement.
  5. RogueRose

    Thread Starter Member

    Oct 10, 2014
    I'm sorry I didn't make this clearer. The batteries were bad in the unit and were about 10 year old. I want to test the unit to see if it functions: powers up & charges, but I don't have the batteries to put in to charge. I didn't know if it was possible to put something in place to see if it would send voltage to the batteries - I know I can't power the device on anything I make. The thing is that smaller units (3000VA) won't even power on unless the batteries are in place as it just trips over to a safe mode and beeps like crazy but if batteries are put in, even if they are in poor condition, the device runs but lets you know there is a problem (lights/noise...).

    So I'm trying to see if there is a way to power up the unit without buying 32 new batteries. I've come across similar, but smaller, models where I have tried new batteries only to find out the unit is no good. I'm trying to avoid this.
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    I've got an antique 3 arm knife switch the size of a large textbook rated 250V 4A each arm. 3kW.

    Safety types roaming the factory these days would poop their pampers at the site of a machinist grabbing at one of these to start/stop a machine. HAHA

    Sure, sure. Hook up a high amperage power supply at probably 100 plus volts (10s of thousands $) for testing purposes, so it will need the livewire ends to be loose sometimes. Yeah, that's the ticket. Give it to the techs out in production. And put a plastic guard around that Damn knife switch. :)
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
    Are you concerned about
    (A) the UPS charging the batteries
    (B) the UPS converting battery power to mains voltage
    (C) both A and B
    (D) none of the above
  8. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    Consider fractional capacity battery bank. 12-15 Ahr batteries are cheap and can last for weeks or months in a test role
  9. InspectorGadget

    Active Member

    Nov 5, 2010
    Series connection of 8 x 12V batteries? The big rack mount APC UPS I have uses 48V battery packs 4 x 12V.

    If it's 48V, you can probably scrounge up 4 car batteries to test it with. Rounding up 8 will be difficult.

    But you need to be sure of the battery series/parallel configuration.
  10. RogueRose

    Thread Starter Member

    Oct 10, 2014
    Yeah they are definately 12v and they were in series in a tray of 8 using 10-12g wire to interconnect all the batteries in series. Now as far as the 4 trays, IDK their config but the unit takes 4 trays of the batteries to work.

    As far as the other questions, both A & B but I didn't think B (the UPS converting battery power to mains voltage) would be possible to test so I was mainly asking about A (the UPS charging the batteries)
  11. Tonyr1084

    Active Member

    Sep 24, 2015
    I'm frightened by the idea of not knowing for sure exactly what the battery voltage should be. 8x12=96 VDC. Four racks would mean four times the capacity but I don't know what you're going to do with 96 volts, unless the inverted power is also being boosted to a usable AC Voltage.

    Many years ago I used to service Emergency Power Supplies. MOST of them were the lights you see on walls and poles of grocery stores and the likes of K-Mart. However, there were some bigger systems used in schools where we had banks of wet cell NiCad batteries, each were 1.2 V @ 50 aH. A large string of them (again, emergency lighting) provided 32 VDC for the emergency lights alone.

    Though many we're sealed lead acid batteries either 6 or 12 volts on the order of 20 aH, there were a number of wet cell lead acid 6 and 12 volts. Whenever we had to replace a battery we couldn't wait around for the battery to charge. So what we did (AT THOSE LOW VOLTAGES) was to use starter capacitors as dummy batteries for the purpose of making sure the float voltage (for a 6 volt system) was right at 6.8 volts. (13.6 for 12 volt systems).

    Again, without knowing the final voltage I hesitate to suggest this, but it might be possible to use a capacitor to test the system (as you describe) for voltage to charge the batteries. The capacitor that is coming to mind (for me) is the high voltage capacitor found in microwave ovens. That's on the order of 2000 VDC. Still, I don't know if a capacitor will provide the necessary loading for the charging circuit to see "A Battery". But it IS an idea.

    Perhaps a 1 MΩ resistor across the capacitor. Maybe much lower, I don't know. Watch your voltages and wattages or you can smoke a resistor (not a terrible thing, but still, I hate to leak smoke).
  12. BillB3857

    Senior Member

    Feb 28, 2009
    Maybe a manufacturer and model number of the UPS unit would be of some benefit. At least that my help to answer the input DC voltage to the unit. Is it 32, 48 or 96?