Uninterruptible power supply question

[agrid]

Hey we have to run an intrument on a farm for a couple of weeks. Basically its a pump that switches on every half an hour or so and sucks gas over an electrochemical sensor and can log about 3,000 records. There's 4 solenoids as well so when it does a reading cycle it sucks for about a minute, switches to another line sucks for a minute and so on, then goes into sleep mode for half an hour or so.

The power on this farm is a bit flaky and if the power fails, even for a short while, the monitor will reboot to the start menu, it doesn't lose data but it does stop the running program. The the unit is 230 V AC/110 V AC , 50 Hz and the pump specs are: flow rate: 500 ml/min - 1000 ml/min Power: 4.5 V DC, 35 mAh.

I'm thinking I could just buy a cheap-arse UPS from Dick Smith for $129 that claims to be able to run a computer for 43 minutes. I suspect our gas monitor would use way less power than a computer especially as it is in standby mode for 20% of the time.

Does someone that's worked with a UPS think I'm on the correct line of thought? Someone else suggested a car battery and inverter but I'm not sure that would last for two weeks in the field.

[Stoneville]

I wouldn't buy a cheap one, I opted for a 750, and found that I should have gone for a 2.5 or similar, if the power is out for any length of time it will be worth it.

I'm thinking of selling this one and getting a bigger one. You need to cover for the max amount of time possible, it will only cost you another $100 or so, I bought mine from PLE computers in Cannington.

I have the wireless modem, normal modem and the Netstora hooked up to it, managed to stay hooked up to the internet for an hour before she went down, the power was out for 6 hours, unusual I know, but I'd get the bigger size if I were you, best thing I've done for awhile

[agrid]

Hmm, my mate's young bloke works at PLE. The power never goes out for long because the farmer notices. I guess we would have to put in some sort of weather-proof box because it will be sitting in a paddock.

[Stoneville]

They get pretty warm as well, so make sure there is some sort of air flow.

Our power goes out here in Stoneville every second day for 1/2 to 2 hours, hence me getting UPS last year

[Jim621]

Id suggest a car battery and inverter setup would suit you fine for a temporary install - find out what the current draw is from the 'unit' and the inverter you plan to use and work out the total current draw.
are you able to run some tests on the current draw from the 'unit' and pump?

Steve.

[Sonik]

Small UPS and a car battery, disconnect the internal battery and wire up the car battery. The UPS will smooth out any spikes/dips in voltage and the large battery will give you a greater run time without power. If you get stuck you could even hook it up to a generator.

[Desmo]

Why use a 12V battery with a 240V device.
If the power is only out for a matter of minutes, a small UPS will be fine.
I'm sure Mr Agrid is smart enough to work out the current draw of his instrument and extrapolate the expected tinting from his UPS.

[Sonik]

A small UPS uses a sealed lead acid 12v battery and depending on how long the interruptions in mains power are and the importance of this testing the car battery is extra insurance against failure. Just a ghetto way of having a UPS with a long backup time without having to fork out heaps on a large UPS.

EDIT: car battery and inverter is the same sort of thing but doesn't have the capacity to run on mains power or charge the battery.

[agrid]

Yeah I suppose a UPS is just a car battery charger, a car battery and an inverter in a box. I just wonder if they have some sort of standard decay rate or something and shut down after a prescribed time even though the current draw has been low. Just seemed odd that the $129 UPS gave 43 minutes and the $149 one 53 minutes. So precise.

[Sonik]

Most likely a number calculated from the battery life @ a UPS' max rated load. Going off experience with traffic light UPS backup they last longer after the signals are changed to LED (significantly less load) but they are a lot bigger than the average home PC UPS and inverters do use some power. Does seem a little odd that it's a precise number (myself I would have rounded to the nearest 10 mins).

[busa_bloke]

Why use a 12V battery with a 240V device.
If the power is only out for a matter of minutes, a small UPS will be fine.
I'm sure Mr Agrid is smart enough to work out the current draw of his instrument and extrapolate the expected tinting from his UPS.

240VAC batteries are getting rare these days. I blame global warming.

;^)

[agrid]

I purchased a cheap ($99) one from PLE computers. It claims to be able to run a computer for 25 minutes after power failure. Units with longer run times were much larger and defeated the purpose of a portable gas monitor. I charged it for 8 hours as required and it ran our gas monitor for 5 hours. I would have thought it would run longer but there you go, perhaps there is a drag on the batteries by the inverter even though the monitor in sleep mode can only be drawing minuscule power.

Interestingly I installed the UPS management software on a netbook computer so I could monitor battery capacity and disable the loud alarm that runs when it is on battery power. This seemed to interfere with things, maybe the UPS thought the only thing it was driving was the laptop so it did weird things like force a shutdown on the laptop which in turn forced a shutdown on the UPS even though there was still batter capicity remaining. No worry because there won't be a computer plugged in in the field.

Thanks for your comments.

[kayne]

Interestingly I installed the UPS management software on a netbook computer so I could monitor battery capacity and disable the loud alarm that runs when it is on battery power. This seemed to interfere with things, maybe the UPS thought the only thing it was driving was the laptop so it did weird things like force a shutdown on the laptop which in turn forced a shutdown on the UPS even though there was still batter capicity remaining. No worry because there won't be a computer plugged in in the field.

The Software forces the shutdown to prevent lost information etc to the PC and damage to the batteries if getting near 100% exhausted

[agrid]

That's what I figured but when I restarted both the computer and the UPS it showed 50% capacity. There's a bunch of options in Chinglish about forcing shutdowns and so on, it can eve send an email to let you know what its about to do. Seems pretty sophisticated but we just need a dumb battery backup.

The gas monitor is a cheap Indian one, its pretty funny how they structure the menus and so on e.g. it asks for confirmation that you would like to download data but doesn't for erasing data! The dumbest thing is that they set it up to be able to store thousands of readings but when you set the number of read/sleep cycles they only allowed a two digit number, so 99 cycles is going to use about 1% of its storage memory. When I point stuff like this out to them they always reply "Thank you very much, we have discovered this also, and will fix the issue in the next model". Nothing better than getting your buyers to do your beta testing.