d. 14/04/01 4:54 skrev Erik Richard Sørensen på kml.ers@mail1.stofanet.dk i
artiklen 3AD7BBDC.9D6315B3@mail1.stofanet.dk:
>> [Snipsnippetesnip...]
Jeg fandt engang en artikel om dette emne på nettet (og gemte den til bedre
tider)
Magnus
Well here it goes:
> Which type of rechargeable battery best suits your night cycling needs?
>
>
>
>
> © Marty Goodman September 1997
>
>
>
>
> Folks often ask me about which battery to get with their bicycle lighting
> systems: Lead Acid or NiCd (nickel-cadmium) batteries. This is intended as a
> "canned" first response to such questions.
>
>
> The two most common technologies of rechargeable battery used in bicycle
> headlight systems are Sealed Lead Acid ("SLA") and Nickel-Cadmium ("NiCd").
> Low to medium price ($70 to $150) systems will feature SLA batteries, and
> medium to high priced systems ($140 to $400) will feature the NiCd batteries.
>
>
>
> The Short Version of My Advice:
>
>
>
>
> If you do a great deal of night riding, such as many nightly commutes per
> week, you should get a NiCd battery-based system. If you do only occasional
> night rides, you'll likely do fine with a SLA-based system. But in either
> case, you will probably be very wise to invest in a third-party battery
> charger, and not use the battery charger supplied with the system you buy.
>
>
>
> The Long Version of My Advice:
>
>
>
>
> Battery Characteristics
>
> Costs/Benefits
>
> Lead Acid batteries are about 2 to 4 times less expensive at time of purchase
> than are NiCd batteries.
>
> However, NiCds, if properly cared for (this is a key operative qualification!)
> can be recharged 3 to 5 times as many times before they wear out as can be SLA
> batteries.
>
> Cost of a high quality third party charger for either system is roughly the
> same ($45 to $90). Note that SLA batteries require a different charger from
> that required by NiCd batteries.
>
> Overall, NiCd batteries are at least as inexpensive, and probably actually
> somewhat less expensive a source of power than SLA batteries if you are using
> them frequently, over the course of their total life.
>
> However, if you are using the battery infrequently, for, say, 20 rides per
> year, then the more expensive NiCd will probably die due to its shelf life
> expiring before you use all its available charges.
>
> NiCd batteries are, overall, about 30% lighter for a given amount of power
> capacity than SLA batteries. A significant, but not utterly overwhelming
> difference.
>
>
>
> Storage Characteristics
>
> SLA batteries retain nearly their full charge for two months or more just
> sitting on the shelf, unattached to a charger. NiCd batteries lose about 1% of
> their charge per day when sitting on the shelf, due to internal
> "self-discharge".
>
>
> Discharge Characteristics
>
> NiCd batteries have a flatter voltage vs time curve during discharge than do
> SLA batteries. This means your lights will remain relatively more constantly
> bright during the entire useful discharge life of the battery with a given
> lighting system than would be the case for a SLA battery of comparable amp
> hour capacity and voltage.
>
> This is both good and bad: It is good that they stay bright, but this same
> characteristic means that they give little or no warning when they are about
> to poop out.
>
>
>
> Don't Fully Discharge Either Type
>
> Both NiCd and SLA batteries can be severely damaged by being deeply discharged
> to down below 75% of their rated voltage. With either system one must never
> run the battery "into the ground", letting ones lights go from yellow to
> orange to dim orange. Turn your lights off when they get noticeably yellow,
> else you risk permanantly damaging your battery.
>
> Many ignorant folks claim NiCd batteries are subject to "charge memory". This
> is false. As used by cyclists for night lighting applications, there is no
> "charge memory" problem with NiCd batteries. Period. (See below for details.)
>
> Some manufacturers who supply SLA batteries with their lighting systems (such
> as VistaLite with its VL4xx systems) choose the Hawker Industries (formerly
> called "Gates") Cyclon type SLA batteries. This particular make and model of
> SLA battery is significantly superior to ALL other SLA batteries. If you are
> replacing a SLA battery in your existing lighting system, get a Hawker
> Industries Cyclon battery pack (available in 2.5 amp hour and 5.0 amp hour six
> volt modules). These offer greater useable battery capacity for a given amp
> hour rating, are able to withstand deep discharge somewhat better than
> ordinary SLA batteries, and they last thru more recharge cycles than ordinary
> SLA batteries. Interestingly, the retail price for a Hawker Cyclon SLA battery
> is not all that different from the price of a similar ordinary SLA battery.
> Power Sonic (headquarters in Redwood City, CA) sells Hawker Cyclon batteries.
> Locally in Berkeley, Al Lashers can order and sell these batteries.
>
>
>
> Charger Issues
>
> With the exception of the Nite Rider Digital Pro 6 and Xcell Pro (formerly
> called NiteHawk) lighting systems, virtually all bicycle lighting systems on
> the market supply inexcuseably cheap, often quite destructive to the battery
> type of chargers. The problem is that with most supplied chargers, they charge
> the battery rather slowly (require 10 or more hours to provide a full charge)
> then then keep jamming current into the battery after it's full, heating it up
> and ultimately destroying it. many cyclists have destroyed their $140
> replacement cost NiCd water bottle battery by leaving it hooked up to the
> charger for some days or weeks.
>
> While not a "smart" charging system, the NiteRider Xcell Pro and Digital Pro 6
> systems do have a reasonably safe "set it and forget" charging system, tho
> only when used with their supplied battery. Their system charges the battery
> at a modest rate for 10 hours, then a timer switches over to a 3 times slower
> charging rate for maintanance of the battery. Their system is not a "smart
> charger" in that it does not in any way sense actual battery condition.
>
> It's relatively easy to make a cheap but safe "set it and forget it" charger
> for SLA batteries. All that's needed is a voltage regulator, which adds about
> $1.00 to $2.00 at time of production, or at most $10.00 at time or retail
> sale, to the cost existing bicycling lighting systems. Amazingly, few if any
> commericial systems provide this, and instead provide an unregulated DC power
> supply, which has the potential (liklihood, actually) of destroying the SLA
> battery if left attached. NiteRider MAY provide such a safe SLA charger in
> their new product, the "Trail Rat." I've not yet had a chance to analyze this
> new product on my lab bench.
>
> To more quickly charge SLA or NiCd batteries (full charge in 2 to 4 hours),
> one needs a "smart charger". Such a charger senses battery condition during
> charging, pours current into the battery as long as the battery needs it,
> senses when the battery is full, and then cuts back to a much reduced current
> flow (or pulses of current at intervals) to keep the battery filled without
> harming it.
>
> This kind of a very smart charger is a nice convenience with a SLA battery,
> but not necessary in that a simple voltage-regulated "trickle" charger will
> usually do the job fine for cyclists. Smart SLA chargers can be purchased from
> Power Sonic, at a cost of about $50 to $80 for chargers appropriate to
> existing bicycle lighting systems. You have to add your own cable, of course,
> to attach the charger to your particular system. Tinkerers should note that a
> proper trickle charger for SLA batteries is a regulated power supply set to
> 6.90 to 6.95 volts for a "6 volt" SLA battery, and to 13.8 to 13.9 volts for a
> "12 volt" SLA battery.
>
> NiCd batteries really benefit from a proper smart charger. Unfortuately, one
> has to press into service chargers made for other purposes if one wants a
> smart charger for one's bicycle lighting system. Or make one oneself from
> scratch. I've done both, successfully. Certain DeWalt and Black & Decker power
> tool chargers can be converted into very effective smart chargers for bicycle
> lighting system batteries. The DW9106 and DW9104 in particular are good
> choices. Some cam-corder and cell phone 6 volt NiCd battery chargers may be
> suitable as smart chargers for 6 volt NiCd bicycling batteries. I've built
> from scratch two smart chargers for my battery systems using a Maxim MAX 713
> smart charger controller chip. Both work very well. Some have used the more
> modern 2002 NiCd smart charger controller chip made by Maxim, Benchmarq, and
> Unitrode. Contact me for details if interested.
>
>
>
> The Myth of NiCd "Memory"
>
> Discussion of the MYTH of "charge memory" in NiCd batteries (from a discussion
> on the BikeCurrent mailing list) Date: January 12, 1997 13:59:24 +1300
> From: Steve Christall
> Subject: Re: Charge Memory post (again! arrgh!)
>
> From GE Tech Notes ....
>
>
> "Among the many users of batteries in both the industrial and consumer
> sectors, the idea of a memory phenomenon in nickel-cadmium batteries has been
> widely misused and understood. The term 'memory' has become a catch-all
> 'buzzword' that is used to describe a raft of application problems, being most
> often confused with simple voltage depression.
>
> "To the well informed, however, 'memory' is a term applied to a specific
> phenomenon encountered very infrequently in field applications. Specifically,
> the term 'memory' came from an aerospace nickel-cadmium application in which
> the cells were repeatedly discharged to 25% of available capacity (plus or
> minus 1%) by exacting computer control, then recharged to 100% capacity
> WITHOUT OVERCHARGE [emphasis in the original]. This long term, repetitive
> cycle regime, with no provisions for overcharge, resulted in a loss of
> capacity beyond the 25% discharge point. Hence the birth of a "memory"
> phenomenon, whereby nickel-cadmium batteries purportedly lose capacity if
> repeatedly discharged to a specific level of capacity.
>
> "The 'memory' phenomenon observed in this original aerospace application was
> eliminated by simply reprogramming the computer to allow for overcharging.
> [Note that no mention is made of adding an intentional *discharge* to clear
> the problem - RLM] In fact, 'memory' is always a completely reversible
> condition; even in those rare cases where 'memory' cannot be avoided, it can
> easily be erased. Unfortunately, the idea of memory-related loss of capacity
> has been with us since. Realistically, however, ' memory' cannot exist if any
> one of the following conditions holds:
>
>
> 1. Batteries achieve full overcharge.
> 2. Discharge is not exactly the same each cycle - plus or minus 2-3%
> 3. Discharge is to less than 1.0 volt per cell.
> "Remember, the existence of any ONE of these conditions eliminates the
> possibility of 'memory'. GE has not verified true 'memory' in any field
> application with the single exception of the satellite application noted
> above. Lack of empirical evidence notwithstanding, 'memory' is still blamed
> regularly for poor battery performance that is caused by a number of simple,
> correctable application problems."
>
>
> End of quote ... Basically memory (loss of capacity) due to discharge is a
> myth.
>
> Reduction of your NiCads / NiMH capacity due to overcharging (heating) and,
> cell reversal in voltage depressed battery packs kill your batteries.
>
> ------------------------------------------------------------------------
> Peter Ludwig adds: January 14, 1997 12:09:44 +0002
> From: Peter Ludwig
> Subject: Re: Charge Memory post (again! arrgh!)
>
> Steve wrote about the memory effect:
>
>
> "Specifically, the term 'memory' came from an aerospace nickel-cadmium
> application in which the cells were repeatedly discharged to 25% of available
> capacity (plus or minus 1%) by exacting computer control, then recharged to
> 100% capacity WITHOUT OVERCHARGE." [emphasis in the original]
> To be correct this appeared in a satellite which cycles around the earth, so
> charging & discharging is very precisely the same in every cycle. Temperature
> is very constant through each cycle, and there are absolutely no mechanical
> shocks or vibrations and and and so on.
>
> "This long term, repetitive cycle regime, with no provisions for overcharge,
> resulted in a loss of capacity beyond the 25% discharge point."
> Also to be correct: The memory effect causes a lower voltage from that point
> than otherwise expected. This resulted in an early cut off by the software.
> The cells where by no means empty at this stage, but as we know, when a NiCd
> cell's voltage starts to drop, there is almost no remaining capacity. So the
> real 'loss' was caused by cutoff.
>
> Anyway, there is AFAIK no other confirmed case where the memory effect had any
> influence in an field application.
> ------------------------------------------------------------------------
> Marty Goodman in Oct of 1997 adds:
>
> I believe what Peter was trying to say in the last big paragraph is that
> normally, in the absense of a development of a "voltage knee", when a NiCd
> cell's voltage starts to drop significantly, it's going to die very quickly.
> And this is why control software in those satellites was written to shut them
> down when the voltage dropped below such and such. However, if a voltage knee
> has developed (as was the case) you have a situation where the voltage goes
> rather low relatively quickly, but it will stay at that low level with power
> drain for a long time... the total power output (amps time volts = watts) you
> can get from a cell with a voltage knee is not decreased, just the voltage at
> which it will put out that power. Thus, the control software was, sort of,
> needlessly and improperly shutting down the satellite (because it didn't
> "know" about voltage knees, and thought that these were normally discharging
> batteries that were about to be drained so deeply that they might hurt
> themselves permanantly due to cell reversal).
>
> But the bottom line is that "charge memory" does not exist for virtually all
> intents and purposes of applications of NiCd batteries here on earth. In those
> extremely unusual cases where the phenomenon that ignorant folks call "charge
> memory" occurs, this phenomenon does not involve loss of total power capacity
> of the battery, but rather involves the battery delivering its full power
> capacity at a somewhat lower voltage during most of the discharge cycle.
> Hence, the phenomenom is more correctly termed "development of a voltage knee
> in the discharge voltage vs time curve" than "charge memory".
>
> But for uses of bicycle lighting sytems, cell phones, cam corders, and lap
> computers "charge memory" does not exist, despite what ignorant salepeople and
> writers of ads for these products may tell you.
>
>
>
> WHY has the myth of "Charge Memory" in NiCd batteries persisted so strongly,
> given how false the concept is?
>
> It is true that NiCd (and SLA type, too) batteries do in some situations
> benefit from being "cycled" (discharged nearly completely, then recharged). If
> a NiCd battery is injured by virtue of having been shorted out and discharged
> down to zero volts and kept there a little while, it MAY experience some
> degree of recovery if it's "cycled". Similarly, NiCd (and SLA) batteries that
> have been stored for a long time on the shelf and lost some of the their
> capacity may gain some or all of their capacity back after being cycled two to
> four times. Thus, there ARE reasons in some cases to "cycle" a battery down to
> a moderate degree of discharge, then charge it up, in order to "condition" it.
> But this is the case only in special situations, not routinely after each
> ordinary discharge. And it's not a function of "charge memory" (which, again,
> does not exist) but rather of other more complex issues.
>
> NOTE that such "cycling" has to be done very carefully!!! NiCd batteries
> likely will be harmed by being discharged all the way down to zero volts.
> Proper cycling involves using a device that discharges the battery only down
> to a certain voltage (typically 1.0 volts per cell, or there abouts, for a
> NiCd battery pack, which means down only to 10 volts for a nomonial 12 volt
> NiCd pack).
>
> Limiting the voltage you discharge a SLA battery down to during cycling is, if
> anything, even more important (a limit of about 1.8 to 1.9 volts per cell
> works well with moderate discharge rates). For SLA batteries are even more
> vulnerable than NiCds to being harmed if brough all the way down to zero
> volts: doing so will most likely destroy the SLA battery right then and there.
> So, if you try to "cycle" a battery, use equipment designed to do this
> properly and safely... do not just hook some load to the battery and walk
> away, and come back hours later or the next day!
> NiCd batteries can be (I believe most often are) injured by overcharging. They
> can self desctruct due to growth of internal shorts ("dendrites") while left
> on the shelf. They can be harmed by repeated too deep discharge to more than
> 85% of their rated capacity (some others alledge this is the most common cause
> of premature death of NiCd batteries). The point is that there are lots of bad
> things that commonly happen to NiCd batteries. And what has happened is that,
> over the years, whenever someone has a NiCd battery that has died or lost most
> of its capacity, folks have tended to say "Ah! This battery is suffering from
> "charge memory", when in fact (a) "charge memory" does not exist and (b) the
> battery was destroyed by one of the above mentioned situations, usually one
> that would be preventable one knew the real cause.
>
> It is, I believe, for the above reasons that the myth of "charge memory" has
> persisted. This phantom, false explanation has been invoked any time anyone
> has had a problem with a NiCd battery. Sadly, this false "knowledge" has kept
> folks from recognizing the real causes of problems with NiCd systems, and
> doing things about them.
>
> © Marty Goodman September, 1997
>
>
>
>
> Marty has been good enough to let me transfer this document into HTML form and
> post it. I also did a bit of editing and added a few links here and there.
>
> Sheldon Brown
>
>
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