Battery charger

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gadgeteer
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Re: Battery charger

Post by gadgeteer » Fri May 30, 2003 12:20 am

I neglected to mention HYSTERESIS; sorry 'bout that. Generally there is a tiny bit of feedback, so that once the control switches ON, it feeds back a little voltage to your "sense circuit" --- so that (on a car battery anyway) it charges to 13.8-15 volts, then remains off until the battery voltage drops to 11-something. I have a 10-amp auto-charger, and a 1-amp auto-trickler; I suppose I could be talked into opening one up and sketching the circuit. Actually, I NEED to open the 10-amp one, would give me an excuse to fix the "auto/manual switch..."<p>I built a tempering box once for photo developing (but the project died and it's never actually been used). Used a temp-compensated voltage reference, and an op-amp compared a simple thermistor-resistor divider and drove a triac (resistive load, didn't worry about zero-crossing). And a couple of "200watt coffee-cup heaters". Seems like I fed back 1meg or more to the thermistor divider from the op-amp output, so that there is no "chattering" as it reaches set temperature; when the OP-AMP fires it SKEWS the thermistor input, so that the heater SNAPS on and then SNAPS off. "HYSTERESIS". I played with the feedback until the hysteresis produced only ½° variance (99.5°F - 100.0°F).<p>Lemmeknow if you want the circuit from the car-charger...

myp71
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Re: Battery charger

Post by myp71 » Fri May 30, 2003 9:08 am

Hey yeah, that would be great :D <p>Thank you very much :cool: <p>
Also, thanks everyone for posting.<p>Myp71
Ryan

Rodney
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Re: Battery charger

Post by Rodney » Fri May 30, 2003 2:23 pm

Gadgeteer, you are quite a bit off in your statements, especially on NiCads.
Don't take my word for it, consult the experts such as one of the manufactureres or rcbatteryclinic.com. Nicads are not hurt by discharging to zero (reverse charge may damage them and that will happen if you try to discharge two or more cells in series as one will reach zero before the other and then start reverse charging). Also, NiCads do not have a memory, an old myth that seems to live on forever. Again, check with the manufactures for the straight scoop.

k7elp60
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Re: Battery charger

Post by k7elp60 » Fri May 30, 2003 7:02 pm

Rodney is right about the memory effect of Ni-Cads. It is my understanding that the memory effect was caused by the manufacturing process. The process has changed for the better, as there is no longer a memory effect.
As far as taking them to 0 volts, this is valid also. I know of a company that supplies Ni-Cad batteries for orbiting satelites. Seems they make up packs for ten year period. Each pack is used for a year then a new pack is switched in. The packs for suceeding years are sent up with no
charge and at 0 volts.<p>There is a write up on Lead-acid, and more specific gel-cel batteries @http://www.ussc.com/~uarc/Microvolt/1998/nov1998.pdf
Once the 16 page newsletter is downloaded(about 1MB) go to pages 10 thru 15. Since this is in
PDF it requires Acrobat Reader.
Hope this answers some questions.
Ned :roll:

gadgeteer
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Re: Battery charger

Post by gadgeteer » Fri May 30, 2003 11:57 pm

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Rodney:
Gadgeteer, you are quite a bit off in your statements, especially on NiCads.
Don't take my word for it, consult the experts such as one of the manufactureres or rcbatteryclinic.com. Nicads are not hurt by discharging to zero (reverse charge may damage them and that will happen if you try to discharge two or more cells in series as one will reach zero before the other and then start reverse charging). Also, NiCads do not have a memory, an old myth that seems to live on forever. Again, check with the manufactures for the straight scoop.
<hr></blockquote>
Welllll, I won't engage in a lengthy debate; I'll only say that the "memory" is how I learned it, and bears out in experience, I HAVE discharged nicads to ground, through a light-bulb; quite forgot about them until the next day. And they never took a charge again. The cell voltage (after 15 hours of charging) remained at 0.0 volts. I've had success by BLASTING a dead cell with a fraction of a second of very high current --- it will then take a charge, but once it goes dead it's SHORTED again, and no charge.<p>RE "memory" --- again there is the "personal experience". I've used nicads in applications like cordless phones, and in mere months they are short-lived. Bought the folks a special phone with a separate CHARGING BAY (so you can charge one pack in the phone, 2nd pack in the bay); then bought 5-6 packs, so one would always be charged. But Mom refuses to deep-discharge; after much less than a year the score is "TWO PACKS DEAD, one or two good for TEN MINUTES, and two still run for a couple hours...<p>(And in spite of the PLETHERA of packs she insists on keeping them all DEAD...)<p>It'll take me a couple days to take apart the charger and trace the schematic; I don't imagine it will be complicated. But I have no scanner, nor any way to --- wait a minute, I can probably use PAINT, but, well, no place on the web to store it. Might be able to just use "ASCII-characters"...

rshayes
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Re: Battery charger

Post by rshayes » Sat May 31, 2003 7:36 am

I agree with "gadgeteer". Flashlight cells used to be made with a zinc shell covered by a cardboard wrapper and sealed with some kind of tar compound. This construction was abandoned somewhere about 1950 and replaced with "leakproof" designs. I have seen a great deal of equipment damaged since by leakage from batteries that were supposedly "leakproof".<p>As far as memory effects go, earlier data books (about 35 years ago) on nicad batteries don't even mention memory effects. Later books (about 25 years ago) claim that if a cell is subjected to random charge and discharge cycles, that the memory effect will probably not occur. The "memory effect" was represented as being caused by a series of many, practically identical charge-discharge cycles, and that this was unlikely to occur in most applications. About 20 years ago, the battery manufacturers started claiming that they had eliminated the memory effect in ni-cad batteries.<p>The battery manufacturers also claim lifetimes of several thousand cycles. At one cycle a day, this wouuld indicate average lifetimes of 5 to 10 years. Most electronic equipment is replaced in less time than that, so there should be very little market for replacement batteries. Yet the Radio Shack catalog lists hundreds of replacement ni-cad battery assemblies.<p>Whether it is a "memory effect", short circuits, or leakage, the performance of ni-cad batteries in real applications seems to fall far short of the performance indicated on the data sheets.<p>Data sheets can be manipulated to conceal serious problems. Some of the early high-voltage transistors had data sheets indicating that the collector breakdown voltage was over 500 volts. You had to read a fine print footnote several pages later to find out that this voltage was measured at a collector current of 10 milliamps. In other words, a "good" transistor could dissipate as much as 5 watts when it was turned off due to collector leakage current. The failures that this caused were usually pretty spectacular.<p>Maybe the "memory effect" has finally been eliminated, but I've heard that so many times that its hard to believe it anymore.

Will
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Re: Battery charger

Post by Will » Sat May 31, 2003 3:57 pm

Without going in to `who said what ' etc - Ni Cad Memory effect is NOT an old myth. It is real and still exists. What specifically hap[happpens is that as a NiCad discharges the electrolyte molecules change progressively further and further away from the electrodes. I.e. if you only make (say) a 10 % discharge then only the molecules nearest to the electrodes change as they discharge. Consequently if you repeatedly make only partial discharges and then re-charge the molecules furthest away from the electrodes never change and tend to polymerize i.e. to form large clusters of adjacent molecules. This renders said molecules un-useable and it is a permanent, irreversible effect. So, if you only discharge 10% and then re-charge all of the time then, before very long the capacity of your battery is only 10% of the original.
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