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This .FAQ file concerns the act of modifying a computer Uninterruptible Power Supply for the purpose of having a longer run-time or faster charging or both. Essentially this covers the idea of taking a UPS and modifying it in a way for protection for blackouts for emergency power.
DISCLAIMER: The author/coder assumes no liability for any damages resulting from the use, misuse, or abuse of the information contained herein, nor for collateral damages resulting from the use, misuse, or abuse thereof. This includes but not limited to equipment failures, lost data, fires, or injuries. You use at your own risk.
Now that the legal stuff is taken care of, I shall explain why I wrote/coded this .FAQ file. Back in the summer of Y2K-2 (1998) in Chicago, our power company warned the Chicago area that rolling blackouts may occur as they had some nuke plants down for maintenance. Because my neighborhood had frequent blackouts I wasn't happy to say the least. Unlike the Jobs(tm) thing, I decided to take matters into my own hands and build an emergency power supply. I did just that. I over time (and some money wastage) built a UPS that has 500 watts and can go for 3 hours. Not bad, eh?
This .FAQ file is the result of my experiences with my machinery and my time in alt.energy.homepower where off-grid power comes up as the topic. As far as I know, I was the first one to intentionally buy a UPS for consumer use to modify it for blackout-proofing. I was always a fan of electrical technology. I always liked playing with electricity and I have a decent safety record for my personal experimentation. Because I tend to "fly by the seat of my pants" so to speak, it's good to know electricity first! :)
Q: What's wrong with normal UPS's?
A: The average UPS for the average consumer is meant for a few minutes of power, just enough to save a file then cut off the computer and the UPS. If that's all you want, that's just fine. You can blow only $90 and get one. You get like 10 minutes of power to the computer which is enough to save a file and then some. As you can imagine, this wouldn't be useful for those "mission-critical" mainframes or the like. But for most people, this will work fine to save a file. However, this only saves the file. But what about sitting around the house bored and sweaty?
Q: So what if you get sweaty?
A: Well, the UPS isn't a UPS, is it? That's why I own a 500 watter that runs for hours! :) I can at least run a fan, as well as a light and my computer... and my car stereo!
Q: OK, I've got this 1,000 watter that has a dead battery and I like this idea. How do I hook up bigger batteries to run for hours?
A: This is why I wrote this .FAQ file. In my case I took an old 500 watt UPS and modified it to use an external battery. First you need to find out the original battery's voltage. In my case I was able to tell my UPS takes 24 volts. I examined the battery pack and figured it out. It took 4 batteries of 6 volts each in series. In early times with a cheap consumer UPS I found it took a 12 volt battery by counting the seams of plastic separating the lead-acid cells of the battery. Most UPS's use lead-acid batteries much like a car but sealed. I took jumper cables and made holes in the case and ran them to the battery in question.
Q: Your current UPS takes 24 volts. How do you make it with batteries?
A: I hooked 2 12 volt marine/RV batteries in series and the UPS has the jumpers coming out of the intentional holes. Thus, I clip the jumpers to the 2 poles nicely. Come a blackout, it runs.
Q: Aren't the batteries a lot bigger than the original?
A: Yes, by a large margin. By my estimates, about 10 times bigger if not more. If I had the money, I'd expand it!
Q: Doesn't the original charger not charge them up right?
A: Yes, that is a problem. This is why I use a car battery charger.
Q: But wait! Doesn't your car charger only charge 12 volts not 24 volts?
A: Yes! That's why I devised a system using relays so as to charge each battery one after a time. I use relays in my system to remote-control the changing of the clips from one battery to the other. That way, I can interface the car charger to the UPS for quicker charging after the blackout. The only problem is that at this time I must manually control the switches that control the relays in question. I have a third relay for blackout simulation, controlled by a separate switch. (webmaster note : electric wheel chairs sometimes have 24volt chargers)
Q: So, why do you like 24 volts?
A: There are two reasons. First, there's that current infrastructure where I get 12 volt parts and that smaller wires are needed for 24 volts at a given power. At 500 watts, you're talking 25 amps assuming some losses while at 12 volts you need 50. Although I use jumper cable wiring, smaller wire can be used at 25 amps and still not overheat.
For battery charging, there's an issue of some UPS's being sensitive to external chargers. With my setup, only half the battery cache is on charge at any time. Cheap UPS's will often trip off if you apply external charging. I adopted 24 volts as a standard as it's rather common and you can by a center-tap adapt 12 volt stuff. Just be careful about grounding. :)
Q: Can you set up a bigger system for better run-time?
A: Yes, and I'm planning on upgrading. I want a run-time of 10 hours at full power. That'll take care of the garden-variety blackouts nicely. It's probably best to design for a full-power run-time of half a day at least. Except for extreme cases, that'll handle most blackouts nicely.
Q: Can you parallel batteries in a large battery bank?
A: Yes and no. When possible, it's best to avoid paralleling battery caches. Instead, it's better to buy the batteries with the desired
amp-hour rating in the first place. For large ratings, you'll have to get industrial batteries, like the ones used onboard electric forklifts. These are some MASSIVE "muthuhs". One case where you have no choice but to parallel is the case of an apartment dweller. After all, you have to get the batteries up the stairs. Depending on your strength, a 70 pound cell should be manageable. For 24 volts, figure on carrying 12 cells up the stairs to assemble the battery on-site. Future movers will HATE you!
Q: Do landlords allow large batteries?
A: So far, us UPS'rs are rare, so the default Lease has nothing to prevent it. This is unlike waterbeds, which most leases ban.
Q: What about the actual weight of the battery pack?
A: This is a good question. This is a good concern as it would be rather embarrassing to have your battery cache fall through the floor! Happily, the average apartment will handle quite a bit of a weight load. For best results, you place the battery cache against a load-bearing wall. The average human weighs 200 pounds, and the average car battery or equivalent weight battery will weigh 70 pounds. You get 3 batteries to the human, so if you can have 5 humans you can have 15 batteries easily. :) The biggest problem is getting the cache up the stairs (and later moving).
Q: What are the best UPS's/inverters to get?
A: I use the cheapest gear I can find, due to my chronic money shortage. If you have a good money supply, you should get a clean sinewave inverter. If you have a chronic money shortage, you will have to settle for a dirty inverter/UPS. A dirty inverter means having to adjust to the requirement of watching out what you buy however. Except for clocks (and things with clocks) most stuff run fine on a dirty (modified sinewave) inverter. I like dirty inverters but if I had a money well pumping out Susie B solid dollars by the barrel I would go with a clean one. My UPS is very dirty, 40 HZ squarewave!
Q: Do computers run on dirty power?
A: Yes. The average PC will work nicely on a dirty inverter. However, beware of laser printers. Those like LOTS of clean power. If you can afford a laser printer, chances are you can afford a clean inverter.
Q: Do Lead-Acid batteries have a "memory" problem like nickel-cadmium (NiCd) batteries have?
A: Yes and no. Lead batteries do have a "barrier effect" when the lead plates are spiked with antinomy. The type spiked with calcium do not have a "barrier effect" problem. What happens is that as you keep a lead battery float-charged a barrier builds up and upon the blackout the device fails. This happens with cheap UPS's in a case of reasonably reliable power. It also would happen onboard submarines were it not for the fact that Navy people prevent it! What the Navy does is to have the batteries discharge by a resistor and always charge it up again periodically.
What I do is I purposely simulate a blackout once in a few months for a short while then recharge immediately after the intentional discharge. I call this a "dive". I thus exercise the battery cache and recharge to maintain full blackout readiness. I also never float-charge batteries. Upon completion of a "dive" I will recharge upon "surfacing". A typical "dive" may be from anywhere from 15 minutes to an hour with my 3-hour battery cache. I normally do this when I feel power is reliable so as to know I can "surface". I took the Navy procedure as I found out in sci.chem.electrochem.battery and adapted it for my UPS machinery. :) A "dive" can be fun! :) I normally do a dive when I'm drinking on a Saturday for some reason.
Q: Can you use a microcontroller (i.e. a BASIC Stamp) to manage a battery bank?
A: Yes, you can. You can even in theory solve the problem of paralleling batteries in your cache. If you can program in BASIC and interface the embedded system to relays, you can do nearly anything. Although I haven't done it yet as of coding this .FAQ I already know how to do it with my present knowledge. I managed to interface relays to a Commodore 64 so as to build a light show machine. I used to use the machinery for Christmas light shows. All you have to do is get creative with the relays to manage a battery cache. You will have to use automotive relays and interface it with the embedded system.
Bloody Viking 10/03/99 http://www.wwa.com/~nospam/