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Hi, I've been researching windmills for the last few weeks as a solution to an interesting challenge:
The Problem.
A programmer I employ lives on Koh Tao in the Gulf of Thailand. As the land belongs to the commerce ministry nobody legally lives there so civic services leave a little to be desired. Town power is generated by a couple of huge diesel generators in the main town but they're not up for the job of supplying the island's growing population and swelling visitor numbers. What this means is that the lines deliver lower voltages and interruptions are common.
So, if running a lot of computer equipment the common sense thing to do is get a UPS. Unfortunately the power is so poor that the UPS can't charge up.
So I was thinking, if there's a way to independently generate an offline current, that could be used to maintain the UPS charge, so that it has the juice to run the PCs for 10 minutes rather than a few seconds.
The Challenge.
The first requirement is that the project is as close to zero-cost as possible and can be done with locally sourced parts. My is a very simple windmill (S-shaped sail and car alternator) that charges a car battery which is then used to charge (or replace) the UPS battery. Since this is to be used as an emergency supply (maybe a few minutes a few times a week) low performance is acceptable.
The Question.
The last detail is how to hook the system into the UPS to charge the UPS battery but isolate it from the town-power circuit (as we don't want to feed the grid or burn my friend's house down). I've got some of my own ideas but I'm sure there are right ways and wrong ways to do this, thus I thought I'd ask some experts -- you.
Thanks in advance.
Daniel Cooper
RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495
Posted: 08:24pm 13 Jul 2007
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In this situation, I'd be looking at using three completely discrete parts:
1. An inverter, capable of running the computers. Ie, a sinewave output, rated sufficiently to run 24/7
2. A battery, big enough to run you for the expected interruption period(s)
3. A transformer/rectifier/charger to supply enough current for the inverter, plus a little to charge the battery if required, at a regulated voltage suitable to float the batteries.
This would provide a zero-transfer time UPS, that would be fairly tollerant of mains voltage variations, suitable for renewable energy to supply as and when available (wind, PV, hydro, whatever).
I shouldn't need an inverter as the goal here is just to charge up or replace the battery in the UPS. UPS batteries are usually little motorcycle lead-acid cells so I don't see why I can't replace it with a car battery which is charged from independently generated power.
It's Point 3 that's causing me to hesitate, specifically how I isolate my circuit from the mains power. Otherwise the mains will suck all the power from my battery (since it can't seem to charge one in the first place).
Highlander Senior Member Joined: 03/10/2006 Location: AustraliaPosts: 266
Posted: 06:36am 14 Jul 2007
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Hi chuckygobyebye,
have you tested the batteries in the ups?
Maybe they're stuffed, pull them out and try to charge each one individually.
Maybe you have a few in series and only one is stuffed.
I think you'll find they're sealed l/a not the wet cell, motorcycle type.
What type/model is the ups?
What is the voltage of the bank in the ups?
I went through this a while ago and found a lot of them run on 10 12v batteries in series ie 120v dc.
Only a few of them use 24v and 48v.
Is the ups sinewave?
Edited by Highlander 2007-07-15Central Victorian highlands
I don't have access to the UPS but I'm pretty sure it's the same as most of them here -- the cheapest available. If it's the same as mine it has a single brick inside. It's not exactly the same as a motorcycle battery (I've seen replacements for sale) as it's sealed and the contacts are different. The battery may well be be exhausted but this problem isn't isolated to my mate's setup, it's a common complaint all over the island, which leads me to believe that it's the mains power.
For my UPS I know the input and output voltages but everything else is written in Thai. I do know that it outputs a square wave.
I was having a think last night and it occurred to me that if I was to crack open the UPS, disable the AC charging, replace the battery with my own charging/storage assembly that may do the trick. A cheapie UPS uses a relay to switch to stored power when the AC drops out so that should be isolation enough.
Highlander Senior Member Joined: 03/10/2006 Location: AustraliaPosts: 266
Posted: 08:57am 14 Jul 2007
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Hi chuckygobyebye,
well if your going to try anything like that I can't help you, maybe RossW might.
But first test the batteries, you can't charge them with any means if they are buggered.
How old is the unit?
If you think its the mains power, test it.
Edited by Highlander 2007-07-15Central Victorian highlands
domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873
Posted: 06:13am 23 Jul 2007
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chucky,
Mains isolation is easy at least with the meter boxes supplied here in Oz with an auxiliary power point. To switch in your UPS, simply switch the ON/OFF switch in the meter box OFF. This disconnects the grid. Now you must have a power point in the meter box. As the power point is connected to the house circuit and the grid is disconnected you are safe to connect the output of the UPS to the power point and feed the house this way.
Car alternators are free or cost very little (second hand) BUT have the disadvantage that they use electricity for the magnetic field, this is why they are often modified by placing magnets on the rotor. Another disadvantage is that they need to be switched in once the wind is strong enough.
Another disadvantage of car alts. is that they need very high RPMs to generate any useful electricity. Old tractor generators are better than modern alternators. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.
Winston Churchill
RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495
Posted: 06:27am 23 Jul 2007
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Whoa there buddy, hold off on that one!!!
We call the lead you use there a "SUICIDE LEAD" for good reason - you have a 3-pin MALE PLUG at EACH END.
If the UPS will cold-start, and you have the cable plugged into the UPS but NOT plugged into the powerpoint, you have a NON-ISOLATED, NON-FUSED, NO-RCD, LETHAL BARE WIRE EXPOSED 240V connection there.
Not only is doing this illegal, its downright dangerous.
There is also, no interlock to ensure "someone" doesn't accidently turn ON the main switch while the inverter or genset is plugged in.
The only "right" way to do it is with a proper double pole two (or three) way isolator switch. This will properly isolate AND INTERLOCK the two supplies.
I think if you check the codes, you will probably still require some protection circuitry between the UPS and the rest of the system. I know you do for a generator, not certain about a UPS though.
Well, I'm not talking about powering a household off the UPS system, just one or two machines, which is why I think a car alternator would work as this system won't require much overall charge. Ideally, I'd like to see the UPS power supply charged by the mains power where possible and topped up by the co generation.
domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873
Posted: 06:14am 25 Jul 2007
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RossW,
You are quite right, this is dangerous for any linesman working on the supply, which is then powered up should someone switch the mains switch on, etc.
Desperate circumstances lead to desparate measures. Having seen photos of mains supply in Hanoi or Russians wiring their own supply from distribution points I know that standards are not always as good as they should be.
Good idea to suggest a double pole double throw switch. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.
Winston Churchill
domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873
Posted: 06:19am 25 Jul 2007
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Chucky,
As a cheap solution I have also been thinking about the same system. Mains and mill charging car batteries and when the mains fail, then use the UPS.
Just be careful!
Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.
Winston Churchill
thefinis Regular Member Joined: 23/08/2006 Location: United StatesPosts: 53
Posted: 03:23pm 25 Jul 2007
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If the batteries are good in the UPS and you have a system already charging a big 12 volt battery and the UPS works as it is supposed to then I don't see why paralleling two batteries of the same voltage won't work. There would be the same concerns as when using a battery bank with dissimilar batteries. There should be a diode or switch in the UPS to prevent back feeding the grid. A UPS should not backfeed but not sure what effect a brown out would have on it.
A couple of the cheap flexible solar trickle battery chargers might work to keep a big 12 volt charged unless you have to use it too often. It could be switched/disconnected till charged and then switched back on to parallel operation. Not sure why your UPS doesn't charge the battery unless it is trying to use the battery so often that it never gets it to charge up. I would not have the two charging systems using the same battery just for this reason. The UPS battery may not keep a charge if it is held in a depleted state too long and too often.
FinisTexas born and bred
RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495
Posted: 08:29pm 25 Jul 2007
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There are certainly some "gotchyas" here. These won't apply to all UPSs, in all conditions, but they will apply to some UPSs in some conditions. DON'T expect the manufacturer to tell you which ones are which.
For substantially over-sized battery banks:
1. Trickle-charge current may excede the UPSs ability to supply, resulting in under-charged batteries, or burned-out charger in the UPS
2. Some UPSs monitor trickle current and will declare the battery "stuffed" if out of specs. Some even shut down.
3. Most UPSs do an intermittent battery test. Batteries of excess capacity MAY damage the battery condition test circuit in the UPS.
The smarter the UPS, the higher the chances its own internal parameter checking and monitoring will consider the extra battery bank to be "batteries out of spec" and shutdown.
Also, as has been mentioned before, most UPSs are not designed to run 24/7, and if run at or near their full rated output for more than about 10 minutes (depends on make and model) a very real danger of damage to UPS or simply shutdown on overtemperature exists.
YMMV.
domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873
Posted: 02:00am 26 Jul 2007
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RossW,
Many thanks for that. As you know a lot about UPSs and as you have a black belt in electrickery may I ask you the following:
If my UPS has an input requirement of 12.2 A, 240 VAC and has a rating of 1500W, 2000VA and sports four IEC connectors for four PCs, would you be able to calculate/guess what sort of Ahours my 36V car battery bank setup can be to be safely charged by this UPS??
Thanks.
Regards,
Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.
Winston Churchill
domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873
Posted: 02:05am 26 Jul 2007
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RossW,
One more thing. On my UPS a PC-like fan starts once mains power fails and cools the bank of FETs. If this does not happen in Chucky's case, then a cheap PC fan from the power supply can be installed - BUT make sure the UPS is not plugged in while you are adding a fan!!
Regards,
Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.
Winston Churchill
RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495
Posted: 02:30am 26 Jul 2007
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Hah, can fool some of the people some of the time :)
Well, 12.2A is presumably its "maximum" current. I hope it's got a 15A plug on it :)
12.2A @ 240V = 2928 VA.
If its output is stated as 1500W (2000VA) they're saying in effect, they expect up to 40 degrees powerfactor! That, or they're "cheating". Most loads will be much closer to 0.8 to 0.85 powerfactor (30 degrees).
Lets assume their 1500 watts is accurate, lets also assume for a moment that their nominal full-load run time is 8 minutes, and that the inverter is 80% efficient.
At full load, you will be sucking (1500/80%) = 1875W from the batteries. At 36V, that is 52 amps.
For 8 minutes, that is 0.133 of an hour, or 7 amp-hours
If we assume that the batteries are "dead flat" at the end of this, then lets say they are only 7AH cells.
A standard charge rate is 1/10C for 14 hours, and UPSs are not designed to "rapid-charge" - they usually just trickle the batteries up, so I would be surprised if a charger would do more than 700mA charge current. Lets be generous and say they could manage 1A, and I don't think that would be too far off the mark.
Do your own calculations, but I think that 1A would provide "maintenance" charge for your car battery bank, but unlikely to charge them from flat.
Lets assume you have 100AH cells. If they discharge nominally at 2%/day. Thats two amp-hours per day, or close enough to 100mA trickle.
domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873
Posted: 06:10am 27 Jul 2007
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Thanks, RossW. I hope this info is also of interest to Chucky as I butted into this topic as I intend to get my feet wet first with a "cheap" system before I court a divorce by buying expensive deep cycle batts.
You are right, I had to buy a 15A IEC plug for it from RS Components as they are most unusual and our local Jaycar/Dick Smith/Alltronics does not carry them.
Regards,
Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.
Winston Churchill
domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873
Posted: 06:28am 27 Jul 2007
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RossW and others:
One more thing Chucky and others with UPS systems + car batts. like myself face:
UPSs trickle charge only up to 13.4 V for SLAs and not up to 14.5 or 14.7 as for car batteries. Another thing is that some UPSs (mine!) only "hot-start", i.e. mains have to be connected and ON to start the UPS on later power failure.
Now we have a case of a mill wanting to charge to 14.5 V max. with a charge controller installed and the UPS being connected to it trickling the batts. up to 13.4 V. Is this going to be a problem? Does a UPS switch off once the max. float voltage is reached? Or will it switch off due to overvoltage and become useless?
So many questions, so little time!
Thanks.
Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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