On Fri, 15 Aug 2008 15:48:56 -0500, "N9WOS" > I do see what you're getting at with these hypotheticals. The thing
In this case, debating hypotheticals is only useful if they're at least somewhat practical. It seems that you have *the* solution in search of a specific problem that you've never actually heard of.
Good idea! A word of advice - if someone offers to sell you cheap pot, don't bite, because you won't be able to cook a damned thing in it! Oh crap, now you're going to accuse me of suggesting that people bite each other.
Perhaps you should show a quote to support that contention, which is exactly the type of BS that got you a free parody site. Regardless, how can anything that others write ever help mitigate your posting definitive proof that you don't know Ohms from apple butter?
"Station batteries" are a widely available technology. Single 2.1VDC cells of a wide variety of A-H ratings are commercially available. Probably a size for just about any homepower installation.
True, maintaining batteries is more work than maintaining a grid-connect electric meter. But this is true of *any* battery installation. Then it becomes a question of how valuable your time is, playing Plant Engineer versus buying new batteries every two or three years.
Obviously the customer considered the cost of the UPS against the costs of losing power. Can't speak to that much as I'm not that customer.
We recently 'retired' a UPS at work because a) The cost of replacing the battery every five years was getting kind of expensive (~$9,000) b) the annual maintenance /repair was running rather high and c) the 'fragile' (and costly to repair) computer systems it was protecting had been replaced with cheaper, COTS PC-based computers. The loss of service had never been the issue, but the cost of repairs to the 'fragile' computer system after a power outage. With that risk eliminated, the cost of the UPS was no longer justifiable.
So don't use a submarine battery for a homepower setup. I never actually suggested that you should. I only pointed out that large commercial setups of batteries have always opted for series strings of relatively higher voltage instead of many parallel batteries at low voltage.
When unltra-reliability is an issue, commercial installations will use two strings in parallel. They aren't paralleling the strings for added capacity, they are concerned with *redundancy*.
Of course you don't need as many amp-hours as a commercial UPS operation. But the basic principles are the same, correctly sized cells connected in series to attain the desired working voltage. The TCO of such a setup is lower than massively paralleled systems at low voltage. YMMV.
I'm sure that small research subs and such use all sorts of exotic power schemes. But your basic warship submarine sticks to what works.
And again, I never suggested that a submarine battery was the right battery for a homepower installation. I pointed out that some of the largest capacity battery systems in use do *not* go for multiple parallel strings. So *they* (the ever infamous 'they') have figured out that if you want more capacity, the best way to do it is with larger amp-hour rated cells, *not* paralleling small cells together.
Just glancing around at random,
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seem to run about $1 / Ah with 10 year warranty. Some higher for odd voltages, a couple lower.
For a 'golf cart' battery, the first hit I found was...
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is a bit over $1 / Ah with a 1 year warranty.
Of course this was just a five minute search. I'm sure a more detailed search would be appropriate before jumping on any choice.
True, some commercial installations will use two strings in parallel. But they generally do that for redundancy and reliability. Not for increased capacity. Different reason all together that probably doesn't apply to a homepower installation.
daestrom P.S. Despite our disagreements, it's nice to find someone that is polite about disagreeing :-)
Fair 'nuff. But as I said in another post, UPS designers typically use
*two* (and no more than two) strings in parallel because they are installing a redundancy in case a cell opens up. It's a question of reliability, not increased capacity.
I doubt any homepower installation is thinking about increased reliability when they start thinking of paralleling batteries.
Agreed, and there are a number of factors related to that issue. One, relates to the size of the array, as you mentioned. Another relates to the site and how much actual sunlight will be available to the array, not just the amount shown on an "Insolation" table. Another is the amount of use made of, or demand on, the system. A perfect balance of these factors may be unlikely but a very workable and practical solution can be arrived at that has a minimal impact on the battery bank's longevity. (Keep in mind there will be some using up of any battery system, it's in the nature of the beast.)
And there is always the option of having a generator handy on the occasional totally dead days for local energy production. (Even a combined PV and Wind setup can have a break down that can necessitate a wait for parts. Even micro hydro can dry up or break.) A generator sized for just the job of an "overnight" recharge of your battery bank, and the occasional EQ charge when the local production is marginal, would not be that big, (or such an environmental disaster for the overly sensitive types out there) nor require that much fuel for the rest of us frugal types.
One of the advantages of the Homepower system is that you can go without for a period, if you really need to, and not find yourself hurting that much. If you are a business that may not be the case.
Read the whole thing from beginning to end, This report refers to float systems as use for backup in industrial applications and "NOT" home power systems and in fact says that
"This is not a problem for occasional discharges, or for more frequent discharges that are taken to completion. It can become an issue, however for a system that is designed for long discharges, but is subjected to frequent shallow discharges. In this case, the high rate battery will receive the brunt of the cycling duty, and may age prematurely as a result."
Given that in parallel strings one string will always have a higher rate than another string, batteries /cells never being perfectly matched, failure is always an option. The paragraph above gives a pretty good description of a home power system.
Whether you like it or not, no matter how you try to rationalize it, no matter how you twist the words of the author to meet your needs, a home power system with parallel batteries is not a good idea.
The real problem is the Tweedledee's and Tweedledum's of the world spot such a report as this on the net, read the title and jump to the conclusion that it says that parallel strings are ok for a home power system, never bothering to read the article to find out that it describes industrial float systems which may or may not ever be called upon to fulfill its intended use.
Sorry, the report really has nothing to do with home power systems.
Then that definition is as faulty as other definitions from your Telco oriented textbook answers.
In general, a diode is a rectifier, but here are other applications, like current steering. Yes, it prevents reverse current flow, but it is in a DC only application. Then there are 'Protection Diodes', that attempt to outsmart fools who shouldn't be anywhere near electronics. Diodes are used to drop a DC voltage, or provide a reference voltage, both DC only applications. Then we get to LEDs, which are not typically suitable for rectifiers. A Gunn diode turns DC into microwaves. Once again, these are DC only application, and no rectification takes place.
The whole world isn't bands of 2 V telco batteries and refrigerator sided 'Rectifiers' to float charge them.
AFAIK, the term "diode" pre-dates semiconductors by some considerable period. The term was used to describe a valve (tube to our trans-pondean friends) with a cathode and an anode (two in total, hence a diode).
Particular diode designs were designed as "rectifier diodes". That terminology was continued when semiconductors came along, to give "signal diodes" and "rectifier diodes". Eventually, by common usage, the latter was shortened to "rectifier" and the former to "diode".
In general, a rectifier is a diode, not vice versa. Much like a human is a primate but a primate is not necessarily human. The word "rectifier" indicates that the design purpose of this particular diode is some form of power conversion - not some form of signal processing. Not all diodes are rectifiers by definition - because the definition of a rectifier is that of being a diode designed or used for a particular, limited, purpose - that of power conversion.
I'd say the opposite; A diode is a rectifier, but not verse-visa. An LED, for instance, may not be used primarily as a rectifier but it is one. OTOH, synchronous rectifiers are not made from diodes, rather "higher order" semiconductors (e.g. FETs or SCRs).
This is because you are defining all things that rectify as being rectifiers. That isn't how a rectifier was defined. A rectifier was an abbreviation of the term "rectifier diode". It was a particular type of diode. All diodes rectify but not all diodes are rectifiers.
Language evolves. Your definition may easily become the norm. May have already become the norm in certain specialisations. But a purist will always look to the derivation of the word, rather than current usage, when considering definitions.
Ok, all diodes are rectifiers, so all diodes are "rectifier diodes". ;-)
A "rectifier" is something that rectifies.
It *IS* the norm (and your argument doesn't convince me it's ever been otherwise). ...at least has been since I've been around the biz. OTOH, both descriptive and definitive dictionaries both have their problems.
Due to the insane amount of spam and garbage, I block all postings with a Gmail, Google Mail, Google Groups or HOTMAIL address. I also filter everything from a .cn server.
68000 hits on google for "half wave battery charger" That is a fundamental application, and one I have used many times. Direct connection with a wire. Many modern applications of an old circuit. You probably have used them if you ever used an old automotive charger.
Have you ever seen, or even heard of an electrolytic rectifier? It was one of the fist developed, to charge batteries from the AC line. The term Valve was the first low grade vacuum tube rectifier. Then we have the more exotic like thyratrons and Triacs when can adjust the trigger voltage, to almost any conduction phase. there were copper oxide rectifiers, mechanical rectifiers, like those used in a vibrator power supply.. Today, we have synchronous rectifiers, using power FETS, where the gates are driven for the proper half cycle. These are commonly used where the Vf wastes too much power, and the lower Ron of the FET reduces the wasted power, and waste heat.
Have you ever seen an Eimac 15R vacuum rectifier? It was developed for the early airborne RADAR used in W.W.II. It, along with the 15E triode generated the RF pulse for the transmitter section.
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there was an online data sheet for the 15E, but I can't find it right now. It looked like the 15R, but had a pin out the side to connect the grid.
The oldest electronics manuals I have all refer to rectifiers rather than diodes. Some are form the days of spark transmitters, but they are all on another computer that's not accessible on my home network,, right now.
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