Setting up a UPS

Kassem

Hey guys,

I've recently bought a new desktop computer and I'm starting to regret it because of the damn power! My only option now is to set up a UPS that could keep it on for around 3 hours when the power is out. So what do I need to know about my computer and what UPS/batteries should I have?

BashLogic

3hrs? buy a generator! its cheaper than buying a 3hr supporting ups!

Kassem

mmm so that's not a viable solution? I used to see this kind of setups in internet shops... They used a large UPS (I have a 600 watts UPS by the way) with a bunch of large batteries. That's why I thought I could something similar, but on a smaller scale... It doesn't need to be for 3 hours, maybe an hour would be enough. Possible?

J4D

easy, your UPS should function on a 12V battery. Get a normal Car battary, some 70Ah and a proper charger for it . Hook it up properly, and you should have something that lasts around 2-3 hours :) .
I would be glad to help.

arithma

Car batteries are not made to be discharged (car battery were designed under the assumption that they will not go below 80% charge).
A decent UPS system should be based on deep cycle batteries (heavy gel batteries) that are made for exactly reasons like yours.
A better yet alternative would be if you were able to get a power supply unit in your tower that has an internal battery. That way things can be optimized (the same way lithium batteries can be for laptops) to deliver constant low voltages directly from the battery (using a buck or boost converter).

I'd recommend searching for a battery backed up power supply (make sure it has an output for your monitor) since it probably is cheaper than a gel based battery.

MegaCool

I had the same issue as you when i bought my pc, almost regretted it because of the damn electricity, it was literally raping it, so I bought a 1000V UPS and a 150Am truck battery, it can last me up to 4-5hours easily plus connected a lamp and a fan too...

nuclearcat

Well gel is obsolete, especially in hot climate like Leb.
AGM is good. Or at least just deep discharge.

Math is simple:
Usual UPS efficiency 85%
Battery efficiency on 6h discharge cycle , if battery rated at 20hr - 70%

Computer usually consumes around 70W and 17LCD around 20W = 90W
90 / 0.85 / 0.70 = 151W (Around 59% efficiency)

151W*3h = 453Wh = 37.75 A*h, now count this is full discharge. To keep your battery to have at least 1000 cycles you need to not discharge it lower than 50% level. If you discharge for example to 25% level - lifespan will be around 500 cycles.
Means 75.5Ah at least. So UPS with usual 70Ah battery will work.

Very important: this is assumptions, because some values will change equations on logx() or exp() level, if some of variables different (especially higher load, higher temperature and etc) - my assumptions will not be correct.

Small 600VA UPS sold in supermarket with 7Ah battery stands max for 10-15 minutes. Why?
First of all capacity is 84Wh. This means 30 minutes discharge cycle. On this short discharge cycle battery is VERY inefficient. Means maybe 20-40% of whole capacity.

julien_saadeh

nuclearcat, there is nothing like "battery efficiency". but indeed there is "battery life-time"
Even if you discharge a battery to empty, it doesnt mean that you are killing it. There are some limits.
Batteries are designed to discharge in a matter of 1 hour or more.
Means you can consume 7A out of a 7AH battery while being totally on the safe side.
But everyone knows that typical UPS batteries last only 15 minutes while the PC is on. And STILL it lives for 3 years (because of the fact below). You kill a battery when you cause a full discharge in less than 5 minutes (and in this case you are actually overloading the battery AND the UPS that it would shut off sometimes).

UPSes are made to cope with the required load. For ex. if you need 500W out of your UPS, the battery will recharge (reconstruct is a better word) after the first discharge accordingly to provide the current. And there is no difference between car battery and UPS 7ah battery. Both work the same way.

Note: If you want to add external batteries to an ordinary UPS, you have to get super high-power diodes (these are huge) and add them to get the UPS consume-only from and not recharge the external batts as you are going to add an external charger.

rolf

Kassem wroteHey guys,

I've recently bought a new desktop computer and I'm starting to regret it because of the damn power! My only option now is to set up a UPS that could keep it on for around 3 hours when the power is out. So what do I need to know about my computer and what UPS/batteries should I have?

If you want I have little book on the topic:

"Hacking and recompiling your UPS kernel and firmware"

Seriously though :) I dont plug my monitor into the UPS, it does make a little difference. Dont know if it's an option in your case.

nuclearcat

julien_saadeh wrotenuclearcat, there is nothing like "battery efficiency". but indeed there is "battery life-time"
Even if you discharge a battery to empty, it doesnt mean that you are killing it. There are some limits.

You are giving very evil recommendations. Please read how battery chemistry works and why deep discharge killing it.

Batteries are designed to discharge in a matter of 1 hour or more.

They are not designed for "hour and more", most of them designed to operate in wide limits.
They have vendor capacity with specific discharge rate. They have also limits of discharge rate caused by connectors and internal resistance. Sure there is temperature limits and etc.

Means you can consume 7A out of a 7AH battery while being totally on the safe side.

Watch this picture:
http://www.mpoweruk.com/images/dod.gif

But everyone knows that typical UPS batteries last only 15 minutes while the PC is on. And STILL it lives for 3 years (because of the fact below). You kill a battery when you cause a full discharge in less than 5 minutes (and in this case you are actually overloading the battery AND the UPS that it would shut off sometimes).

Total nonsense. And for your information UPS doesn't discharge battery till zero.
Overload case partially correct, but more often shut off happen because of high battery resistance and high voltage drop because of high load. Most of backup UPS have artificial limit on running time. Note: cheap ups have cheap microcontroller and cheap,basic logics. As i know majority of them cannot sense flowing current thru them.

UPSes are made to cope with the required load. For ex. if you need 500W out of your UPS, the battery will recharge (reconstruct is a better word) after the first discharge accordingly to provide the current. And there is no difference between car battery and UPS 7ah battery. Both work the same way.

The most nonsense thing i heard last month.
UPS battery usually gel. If you put in car battery charger - you will blow it and it will be irreversibly damaged.
Car battery have very short lifespan on deep discharge cycles.
AGM battery is the best one, but provide lower current, cause of higher internal resistance.
Watered lead-acid deep discharge batteries (usually sold in Leb for UPS) - can be used also in cars, but not always, they can provide lower current.
Basic chemistry is same, but operation and important points is VERY different.

Note: If you want to add external batteries to an ordinary UPS, you have to get super high-power diodes (these are huge) and add them to get the UPS consume-only from and not recharge the external batts as you are going to add an external charger.

For your information in UPS except diodes many other parts used. Start from FET transistors, ends with zener diode(not always used) and current regulators.

Even you put huge diodes, it will not help current regulator, used there. Best case your battery charge time will be too slow (especially it is designed for gel battery, and you use deep cycle watered lead acid), in worst case your current regulator will generate a bit smoke. It is all depends on UPS schematics.
Battery charged just by transformer and diodes will be busted very soon.

zaza

you can always use a laptop - if you have one -
that is what i do

julien_saadeh

Man you have a lot of info but 0 experience ;)

Practically what I said is totally right. And diodes are NOT TO RECHARGE the ext batteries. They are to make the current unidirectional as to PREVENT to UPS ITSELF to RECHARGE the BIG EXTERNAL BATTERIES. External charger is the only responsible of recharging them. A relay can be used also to do this instead of the diodes.

And I did not talk about diodes that are INSIDE the UPS. I am suggesting to BUY diodes to use "outside". So, there is nothing about current regulation in my statement. It is simple on-off where required.

Plus, read on 7AH batteries and see what is written about Standby Use and Cyclic Use (do you know the difference?) and different voltages are there for what? So as I said, it is the way you recharge the key for battery efficiency. Also, I have been using a CAR charger for 7AH batteries for ages.

xterm

Yeah, I agree with...

I have no idea.

nuclearcat

julien_saadeh wroteMan you have a lot of info but 0 experience ;)

Practically what I said is totally right. And diodes are NOT TO RECHARGE the ext batteries. They are to make the current unidirectional as to PREVENT to UPS ITSELF to RECHARGE the BIG EXTERNAL BATTERIES. External charger is the only responsible of recharging them. A relay can be used also to do this instead of the diodes.

If you will put diodes, then you have also to take care of many other things.
Probably it will work, but most probably not proper way, it depends on UPS circuitry. One of the effects - house in fire.

And I did not talk about diodes that are INSIDE the UPS. I am suggesting to BUY diodes to use "outside". So, there is nothing about current regulation in my statement. It is simple on-off where required.

Then it is partially correct.

Plus, read on 7AH batteries and see what is written about Standby Use and Cyclic Use (do you know the difference?) and different voltages are there for what? So as I said, it is the way you recharge the key for battery efficiency. Also, I have been using a CAR charger for 7AH batteries for ages.

Probably your batteries not gel, or car charger don't provide enough high current to blow battery.
The way you recharge important, but not only. Deep discharge much more important, because on deep discharge you loose capacity of battery. Also temperature important, because on high temperature you loose capacity too. Overcharge is evil too, but slow charging won't harm, in case if till next cycle battery will have time to be fully charged.

Cyclic use and standby use most probably not technical, it is one "marketing" terms for dumb consumers.
They usually means that standby use is when you can charge battery slowly and you use it occasionally , and cyclic use is when you need to charge battery fast.

They key in battery charging is:

Charger should be multistage, must control battery temperature(it is rate to be implemented) and other parameters, to prevent battery from overheat and generate gases. The best one so called "3stage" chargers. They have bulk, absorption and float(also called trickle/maintenance) charge modes.
That's it.

Kassem

@nuclearcat: Thanks for all the info man, but unfortunately that wasn't very helpful, why? Because I seriously do not understand anything of what you've said :) makes me regret not paying attention in my physics classes back in the school days lol.

Anyway, I was talking to some guy about the issue and he asked me do you have a big UPS or an APS? Then I did not know what to reply because I wasn't sure... Now I've checked the "device" and I read "APS" on it, so I assume it's an APS... Does that make any difference?

Note: I used to power a D-Link router + a landline phone set + a lamp + a 24" TV using this APS. Does that mean I could use it to run the desktop PC (instead of the lamp and the TV)?