Can I use a computer backup UPS as external battery power supply?

Discussion in 'General Electronics Chat' started by circuitfreak2000, Jun 12, 2015.

  1. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    I have a 600 Watt / 220 Volt battery backup UPS as you normally use them for a computer and I want it to power an Arduino and a very small aquarium water pump where I don't have access to any mains power.

    If the UPS is charged, it usually provides up to 10 minutes of power to the computer. My idea is to charge the UPS full, disable the speaker inside the UPS that sounds an alarm when the UPS is not connected to mains and use it basically like a battery. With just an Arduino connected and a water pump that runs for 10 seconds every couple days, shouldn't the UPS provide enough power for a long period of time (weeks, months) ?
     
    Last edited: Jun 12, 2015
  2. Reloadron

    Active Member

    Jan 15, 2015
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    The typical UPS outputs a MSW (Modified Sine Wave) unlike normal mains power. So the question is will the pump motor type run on a MSW? How do you plan to power the Arduino?

    Ron
     
  3. ian field

    Distinguished Member

    Oct 27, 2012
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    All the UPS boxes I've seen only kick in if they had mains and then it dropped out while a load was drawing current, some also have an (alleged) energy saving feature that they drop out if the current draw falls below a set level.

    Presumably this is to stop villains using them to power an angle grinder to remove locks - then their only alternative is a portable generator, which sort of spoils the element of surprise.

    Years ago I had a motorcycle lock with a Chubb radial tumbler key, road grit had fouled and worn the lock so one morning the key just didn't work. Since there's no way to run an extension lead to the garage, I found out about the 'safety' feature on the UPS. The small transformer that trickle charges the battery had enough secondaries to bodge in something resembling a blocking oscillator - operating that with a push button was enough to fool it into thinking it had mains that then went off.
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Weeks, probably. Using the 220 V output through a wall wart is not the most efficient way. It probably has 12 V or 24 V batteries. You can direct convert this to 5 V or 3.3 V with a small switching regulator (bought or built) for better efficiency. The battery model number will get you its amp-hour capacity. Subtract 20% for DC/DC converter efficiency. Calculate or measure the arduino board power and the motor power, and you can get some idea of your run time.

    ak
     
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  5. WBahn

    Moderator

    Mar 31, 2012
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    Why couldn't they just use a small battery and inverter?
     
  6. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    The idea is to power the Arduino with a standard 12Volt wall wart and the small aquarium pump has a 220V wall socket plug. The water pump only runs for 10 seconds every couple days. It's very small, about half the size of a hand. It would be awesome if I could get at least two weeks power out of the UPS. That would be sufficient.
     
  7. ian field

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    Oct 27, 2012
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    Some places sell basic inverters with none of the inhibitions of a UPS.

    Run that off a deep cycle leisure battery and you're good to go.

    The Arduino is probably thrifty enough to get away with a linear regulator, a 20VA transformer with a 12-0-12 secondary (used back to frony) and a couple of MOSFETs would probably do occasional pump duty without breaking a sweat.
     
  8. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    I have a UPS here that I don't use. Just thought why not use it as a battery and have a nice looking external power supply with build in regulator, etc. Will give it a try tomorrow. Just hooked it up for charging :)
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    One quick way to tell if your UPS has the undesirable feature that Ian mentioned would be to charge it up, disconnect it and let it sit for a few minutes, then plug a lamp into it and see if it comes on. If you have a DMM you could also just measure the voltage with no load attached. Quick, easy, and the lamp doesn't care about the MSW output (if it's an incandescent).

    When you try it with your pump, first run the pump on a clean supply and make note of how it sounds. Then run it on the UPS and see if it sounds different. If there is much of a noticeable difference, then you might be concerned about the effect of the MSW output on it. But even if it sounds the same and seems to work the same, it's possible that the MSW output is taking a toll that will result in reduced life expectance for the pump.
     
  10. korchoi

    Member

    Jun 5, 2015
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    you can try opening up the ups and bypassing the inverter for the arduino. This way, the inverter and arduino will be in parallel. Thus you get 2 voltages:
    The modified sine wave from the inverter and the 12v or 24v straight from the battery. Plug the 12v into a regulator and you have a guetto power pack.
    Just be careful with these lead batteries, they were not made for long, weak cycles. Just like car batteries, they fail sooner if you discharge them below half their capacity or something like that. Unless your UPS uses Lithium Ion batteries.In that case, the longer it stays still(no load), the faster it loses capacity and the sooner it fails.
     
  11. ian field

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    Oct 27, 2012
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    Not so sure its an undesirable feature to foil burglars who want to power an angle grinder to cut the lock off my shed.

    The one I modified/bodged to release my motorcycle from the faulty lock will never be re-assembled as a UPS or plugged into the mains again. To get the job done I used whatever batteries were around at the time.

    One or more florescent strip light PFC capacitors in parallel with the output may help smooth out the MSW.

    The TS could overcome the difficulty with a basic power out alarm circuit and a monostable to pulse a blocking oscillator. that generates an excitation voltage in the transformer that's sensed for "mains was present". Maybe even count a few pulses to trigger a "fail to restart" alarm.

    The one I modified had convenient secondaries on the sensed transformer to bodge a blocking oscillator - but the blocking oscillator could just as easily be built with an external transformer with twin 9V secondaries. All you need is generate enough voltage to fool the UPS to think it was plugged in.
     
  12. WBahn

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    Mar 31, 2012
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    "Undesirable" was in the context of the TS's objectives. What is desirable in one instance is undesirable in another.

    Still don't see how it is much of a foil for burglars. Again, what's to stop them from using a battery and inverter, both of which would probably end up being smaller and lighter than most UPS units since they don't need it to last nearly as long? Or why can't they use any of the many battery-powered portable tools on the market?
     
  13. ian field

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    Oct 27, 2012
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    For the Yale front door locks, all they need is a cordless drill and suitably sized drill bit.

    It mashes up the tumblers, and there's no shortage of torque to turn the barrel once its free.

    Angle grinders are pretty noisy so its not exactly a stealth tactic. But I'm sure some crims would go that route if the 'safety' feature didn't prevent it.

    Its also much easier to get hold of a UPS cheap, or even free - most people don't bother doing anything about it when the SLA battery deteriorates, with a bit of effort any crook can scrounge up another battery. Not many angle grinders weigh in at less than 600W, and inverters with that kind of rating tend to have professional kit price tags.
     
  14. WBahn

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    Home Depot has 500 W inverters for $30 and 1000 W inverters for $62. Harbor Freight has 750 W inverters for $38. Don't see that being a big stumbling block.
     
  15. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    Hi guys. I have now tested the UPS as a battery power supply, running without connection to mains and with the alarm speaker removed. Everything worked great, except one thing. The Arduino runs fine, the water pump works as well, however the UPS shuts down itself after appr. 10 hours and I have to press the power button to turn it back on. Then it runs for another 10 hours or so before it shuts itself down again. The battery inside the UPS is still nearly fully charged, but the shut down occurs automatically :(

    Does anyone know a way to prevent the automatic shutdown of the UPS?
     
  16. circuitfreak2000

    Thread Starter Member

    Apr 7, 2015
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    Update: I created a workaround. The Arduino is now powered directly from the 12 V battery inside the UPS. The Arduino turns on the UPS via an optocoupler for 10 seconds to power the water pump and then turns the UPS off again. Works like a charm :) Let's see how it holds up over long time. The cool thing is that the UPS is off and only turned on for a short time to power the pump. This should provide an even longer operation time.
     
    Last edited: Jun 14, 2015
  17. Reloadron

    Active Member

    Jan 15, 2015
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    Great and glad the pump works well.

    Ron
     
  18. WBahn

    Moderator

    Mar 31, 2012
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    Must be either a small pump or a big UPS. My UPS's only power my computer and monitor for a few hours before they crap out.

    But glad you found a work-around.
     
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