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Here are six guidelines to follow which will hopefully avoid voltage depression or the memory effect or whatever: (Portions of the following guidelines are from the NiCd FAQ written by: Ken A. Nishimura (KO6AF)) 1. DON'T deliberately discharge the batteries to avoid memory. You risk reverse charging one or more cell which is a sure way of killing them. 2. DO let the cells discharge to 1.0V/cell on occasion through normal use. 3. DON'T leave the cells on trickle charge for long times, unless voltage depression can be tolerated. 4. DO protect the cells from high temperature both in charging and storage. 5. DON'T overcharge the cells. Use a good charging technique. With most inexpensive equipment, the charging circuits are not intelligent and will not terminate properly - only charge for as long as recommended in the user manual. 6. DO choose cells wisely. Sponge/foam plates will not tolerate high charge/discharge currents as well as sintered plate. Of course, it is rare that this choice exists. Author's note: I refuse to get involved in the flame wars with respect to NiCd battery myths and legends --- sam.
(From: Mark Kinsler (kinsler@froggy.frognet.net)). All of which tends to support my basic operating theory about the charging of nickel-cadmium batteries: 1) Man is born in sin and must somehow arrange for the salvation of his immortal soul. 2) All nickel-cadmium batteries must be recharged. 3) There is no proper method of performing either task (1) or task (2) to the satisfaction of anyone.
This applies if the pack appears to charge normally and the terminal voltage immediately after charging is at least 1.2 x n where n is the number of cells in the pack but after a couple of days, the terminal voltage has dropped drastically. For example, a 12 V pack reads only 6 V 48 hours after charging without being used. What is most likely happening is that several of the NiCd cells have high leakage current and drain themselves quite rapidly. If they are bad enough, then a substantial fraction of the charging current itself is being wasted so that even right after charging, their capacity is less than expected. However, in many cases, the pack will deliver close to rated capacity if used immediately after charging. If the pack is old and unused or abused (especially, it seems, if it is a fast recharge type of pack), this is quite possible. The cause is the growth of fine metallic whiskers called dendrites that partially shorts the cell(s). If severe enough, a dead short is created and no charge at all is possible. Sometimes this can be repaired temporarily at least by 'zapping' using a large charged capacitor to blow out the whiskers or densrites that are causing the leakage (on a cell-by-cell basis) but my success on these types of larger or high charge rate packs such as used in laptop computers or camcorders has been less than spectacular. Is my battery charging? ---------------------- If you are trying to substitute a battery of a different type, all bets may be off. For example, NiCd and lead-acid are quite different in operation and termination conditions. Thus, your charger may not be fully charging the new pack for some reason or one or more of the cells may be defective. If you can, monitor both current and voltage into the battery during charging. The voltage should top out somewhat over the marked ratings. The current should work out to around 1.5 times the A-h rating over the charging period. If this is the case, put a load on the battery and see if you get something near the A-h rating out.
In addition to the NiCd cells, you will often find one or more small parts that are generally unrecognizable. Normally, you won't see these until you have a problem and, ignoring all warnings, open the pack. If it is a little rectangular silver box in series with one of the positive or negative terminals of the pack, it is probably a thermostat and is there to shut down the charging or discharging if the temperature of the pack rises too high. If it tests open at room temperature, it is bad. With care, you can safely substitute a low value resistor or auto tail light bulb and see if the original problem goes away or at least the behavior changes. However, if there is a dead short somewhere, that device may have sacrificed its life to protect your equipment or charger and going beyond this (like shorting it out entirely) should be done with extreme care. If it looks like a small diode or resistor, it could be a temperature sensing thermistor which is used by the charger to determine that the cells are heating which in its simple minded way means the cells are being overcharged and it is should quit charging them. You can try using a resistor in place of the thermistor to see if the charger will now cooperate. Try a variety of values while monitoring the current or charge indicators. However, the problem may actually be in the charger controller and not the thermistor. The best approach is to try another pack. It could be any of a number of other possible components but they all serve a protective and/or charge related function. Of course, the part may be bad due to a fault in the charger not shutting down or not properly limiting the current as well.
Nickel-Cadmium batteries that have shorted cells can sometimes be rejuvenated - at least temporarily - by a procedure affectionately called 'zapping'. The cause of these bad NiCd cells is the formation of conductive filaments called whiskers or dendrites that pierce the separator and short the positive and negative electrodes of the cell. The result is either a cell that will not take a charge at all or which self discharges in a very short time. A high current pulse can sometimes vaporize the filament and clear the short. The result may be reliable particularly if the battery is under constant charge (float service) and/or is never discharged fully. Since there are still holes in the separator, repeated shorts are quite likely especially if the battery is discharged fully which seems to promote filament formation, I have used zapping with long term reliability (with the restrictions identified above) on NiCds for shavers, Dust Busters, portable phones, and calculators. WARNING: There is some danger in the following procedures as heat is generated. The cell may explode! Take appropriate precautions and don't overdo it. If the first few attempts do not work, dump the battery pack. ATTEMPT ZAPPING AT YOUR OWN RISK!!!! You will need a DC power supply and a large capacitor - one of those 70,000 uF 40 V types used for filtering in multimegawatt geek type automotive audio systems, for example. A smaller capacitor can be tried as well. Alternatively, a you can use a 50-100 A 5 volt power supply that doesn't mind (or is protected against) being overloaded or shorted. Some people recommend the use of a car battery for NiCd zapping. DO NOT be tempted - there is nearly unlimited current available and you could end with a disaster including the possible destruction of that battery, your NiCd, you, and anything else that is in the vicinity. OK, you have read the warnings: Remove the battery pack from the equipment. Gain access to the shorted cell(s) by removing the outer covering or case of the battery pack and test the individual cells with a multimeter. Since you likely tried charging the pack, the good cells will be around 1.2 V and the shorted cells will be exactly 0 V. You must perform the zapping directly across each shorted cell for best results. Connect a pair of heavy duty clip leads - #12 wire would be fine - directly across the first shorted cell. Clip your multimeter across the cell as well to monitor the operation. Put it on a high enough scale such that the full voltage of your power supply or capacitor won't cause any damage to the multimeter. WEAR YOUR EYE PROTECTION!!! 1. Using the large capacitor: Charge the capacitor from a current limited 12-24 V DC power supply. Momentarily touch the leads connected across the shorted cell to the charged capacitor. There will be sparks. The voltage on the cell may spike to a high value - up to the charged voltage level on the capacitor. The capacitor will discharge almost instantly. 2. Using the high current power supply: Turn on the supply. Momentarily touch the leads connected across the shorted cell to the power supply output. There will be sparks. DO NOT maintain contact for more than a couple of seconds. The NiCd may get warm! While the power supply is connected, the voltage on the cell may rise to anywhere up to the supply voltage. Now check the voltage on the (hopefully previously) shorted cell. If the filaments have blown, the voltage on the cell should have jumped to anywhere from a few hundred millivolts to the normal 1 V of a charged NiCd cell. If there is no change or if the voltage almost immediately decays back to zero, you can try zapping couple more times but beyond this is probably not productive. If the voltage has increased and is relatively stable, immediately continue charging the repaired cell at the maximum SAFE rate specified for the battery pack. Note: if the other cells of the battery pack are fully charged as is likely if you had attempted to charge the pack, don't put the entire pack on high current charge as this will damage the other cells through overcharging. One easy way is to use your power supply with a current limiting resistor connected just to the cell you just zapped. A 1/4 C rate should be safe and effective but avoid overcharging. Then trickle charge at the 1/10 C rate for several hours. (C here is the amp-hour capacity of the cell. Therefore, a 1/10 C rate for a 600 mA NiCd is 50 mA.) This works better on small cells like AAs than on C or D cells since the zapping current requirement is lower. Also, it seems to be more difficult to reliably restore the quick charge type battery packs in portable tools and laptop computers that have developed shorted cells (though there are some success stories). My experience has been that if you then maintain the battery pack in float service (on a trickle charger) and/or make sure it never discharges completely, there is a good chance it will last. However, allow the bad cells to discharge to near 0 volts and those mischievous dendrites will make their may through the separator again and short out the cell(s).
Since the nominal (rated) voltages for the common battery technologies differ, it is often possible to identify which type is inside a pack by the total output voltage: NiCd packs will be a multiple of 1.2 V. Lead-acid packs will be a multiple of 2.0 V. Alkaline packs will be a multiple of 1.5. Note that these are open circuit voltages and may be very slightly higher when fully charged or new. Therefore, it is generally easy to tell what kind of technology is inside a pack even if the type is not marked as long as the voltage is. Of course, there are some - like 6 V that will be ambiguous.
For primary batteries like Alkalines, first try a fresh set. For NiCds, test across the battery pack after charging overnight (or as recommended by the manufacturer of the equipment). The voltage should be 1.2 x n V where n is the number of cells in the pack. If it is much lower - off by a multiple of 1.2 V, one or more cells is shorted and will need to be replaced or you can attempt zapping it to restore the shorted cells. See the section: "Zapping NiCds to clear shorted cells". Attempt at your own risk! If the voltage drops when the device is turned on or the batteries are installed - and the batteries are known to be good - then an overload may be pulling the voltage down. Assuming the battery is putting out the proper voltage, then a number of causes are possible: 1. Corroded contacts or bad connections in the battery holder. 2. Bad connections or broken wires inside the device. 3. Faulty regulator in the internal power supply circuits. Test semiconductors and IC regulators. 4. Faulty DC-DC inverter components. Test semiconductors and other components. 5. Defective on/off switch (!!) or logic problem in power control. 6. Other problems in the internal circuitry.
Unless you have just arrived from the other side of the galaxy (where such problems do not exist), you know that so-called 'leak-proof' batteries (even those with fancy warranties and high budget advertising) sometimes leak. This is a lot less common with modern technologies than with the carbon-zinc cells of the good old days, but still can happen. It is always good advice to remove batteries from equipment when not being used for an extended period of time. Dead batteries also seem to be more prone to leakage than fresh ones (in some cases because the casing material is depleted in the chemical reaction which generates electricity and thus gets thinner or develops actual holes). In most cases, the actual stuff that leaks from a battery is not 'battery acid' but rather some other chemical. For example, alkaline batteries are so called because their electrolyte is an alkaline material - just the opposite in reactivity from an acid. Usually it is not particularly reactive (but isn't something you would want to eat). One exception is the lead-acid type where the liquid inside is sulfuric acid of varying degrees of strength depending on charge. This is nasty and should be neutralized with an alkaline material like baking soda before being cleaned up. Fortunately, these sealed lead-acid battery packs rarely leak (though I did find one with a scary looking bulging case, probably due to overcharging - got rid of that in a hurry). Nickel Cadmium cells contain so-called heavy metal compounds which are also bad for you if you feast on them but can be safely cleaned up without harm. Scrape dried up battery juice from the battery compartment and contacts with a plastic or wooden stick and/or wipe any liquid up first with a dry paper towel. Then use a damp paper towel to pick up as much residue as possible. Dispose of the dirty towels promptly. If the contacts are corroded, use fine sandpaper or a small file to remove the corrosion and brighten the metal. Do not use an emery board, emery paper, or steel wool as any of these will leave conductive particles behind which will be difficult to remove. If the contacts are eaten through entirely, you will have to improvise alternative contacts or obtain replacements. Sometimes the corrosion extends to the solder and circuit board traces as well and some additional repairs may be needed - possible requiring disassembly to gain access to the wiring. Don't forget that many batteries do come with explicit or implicit warranties against leakage (and resulting damage) which cover the equipment they are in as well. Thus, you may be able to obtain a replacement device from the battery manufacturer for at most shipping charges. I don't know if this extends to expensive products like palmtop computers :-).
While it is tempting to want to use your car's battery as a power source for small portable appliances, audio equipment, and laptop computers, beware: the power available from your car's electrical system is not pretty. The voltage can vary from 9 (0 for a dead battery) to 15 V under normal conditions and much higher spikes or excursions are possible when loads like the radiator fan or air conditioner are switched on or off. Unless the equipment is designed specifically for such power, you are taking a serious risk that it will be damaged or blown away. Furthermore, there is essentially unlimited current available from the battery (cigarette lighter) and 20 A or more without blowing a fuse. This will instantly turn your expensive CD player to toast should you get the connections wrong. No amount of internal protection can protect equipment from fools. My recommendation for laptop computers is to use a commercially available DC-AC inverter with the laptop's normal AC power pack. This is not the most efficient but is the safest and should maintain the laptop's warranty should something go wrong. For CD players and other audio equipment, only use approved automotive adapters. For something like a CD player that runs on a 9VDC wall adapter, even if the droid at Radio Shack says it will work without dropping the voltage, proceed with caution. The 3 V difference isn't the only problem - you might get away with that though I would recommend against it (measure the open circuit voltage out of your AC adapter - it is probably closer to 12 V or more anyhow). It is the other nastiness of the automotive power. Putting 4 diodes (e.g., 1N4002) in series with the power would drop the voltage to be closer to 9 V but the spikes will sail right through If it were mine, I would probably add some filtering to the 12 V - maybe 10,000 uF, 35 V, and then use a 7809 or LM317 regulator to drop it to 9 V. This isn't a guarantee but is much better than ignoring the issues entirely. See the section: "Adding an IC regulator to a wall adapter or battery". However, there is a one more minor problem - when starting, the voltage can easily drop to 9 V or less. With the regulator, the output would be closer to 7 V which may or may not be enough. So, the player may quit while starting but I suppose there are more important things to worry about! As with a laptop, another option is to use a small 12 VDC to 115 VAC inverter, perhaps $25. This would definitely protect the player (assuming the adapter doesn't mind the squarewave it puts out) but would not be very efficient. I received a dead CD player with an auto adapter included. It was supposed to run on 3 V. Guess what? There was no circuitry in the adapter! That was probably a Radio Shack recommendation as well :-). Just because the plugs match doesn't mean it will work and not blow up!
There is a graded width resistance element that gets connected when you pinch those two points. It heats up - substantially, BTW. Some sort of liquid crystal or other heat sensitive material changes from dark to clear or yellow at a fairly well defined temperature. Incidentally, since the current is significant, repeated 'testing' will drain the batteries - as with any proper under-load battery test! This isn't an issue for occasional testing but if the kids figure how to do this.... Personally, I would rather use a $3 battery checker instead of paying for throw-away frills!
A variety of motor types are found in audio and other electronic equipment. For the additional information on the specific types of motors used in VCRs and CD players, see the documents: "Notes on the Troubleshooting and Repair of Video Cassette Recorders" and "Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives". Types of motors: 1. Small brush-type permanent magnet (PM) DC motors similar to those found in battery operated appliances. Such motors are used in cassette decks and boomboxes, answering machines, motorized toys, CD players and CDROM drives, and VCRs. Where speed is critical, these may include an internal mechanical governor or electronic regulator. In some cases there will be an auxiliary tachometer winding for speed control feedback. These are usually quite reliable but can develop shorted or open windings, a dirty commutator, gummed up lubrication, or dry or worn bearings. Replacement is best but mechanical repair (lubrication, cleaning) is sometimes possible. Also see the section: "General tape speed problems - slow, fast, or dead". Additional info on these types of motors can be found in "Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives". 2. A low profile or 'pancake' brushless DC motor may provide power for a in some Walkman type tape players, direct drive capstans and general power in VCRs or tape decks. Since these are electronically controlled, any non-mechanical failures are difficult to diagnose. In some cases, electronic component malfunction can be identified and remedied. 3. AC induction motors - shaded pole or synchronous type used in inexpensive turntables. These motors are extremely reliable and are easy to disassemble, clean, and lubricate. Just do not lose any of the spacer washers on each end of the shaft and make notes to assure proper reassembly. 4. Miniature synchronous motors used in mechanical clock drives as found in older clock radios or electric clocks powered from the AC line, appliance controllers, and refrigerator defrost timers. These assemblies include a gear train either sealed inside the motor or external to it. If the motor does not start up, it is probably due to dried gummed up lubrication. Getting inside can be a joy but it is usually possible to pop the cover and get at the rotor shaft (which is usually where the lubrication is needed). However, the tiny pinion gear may need to be removed to get at both ends of the rotor shaft and bearings.
Of course you expect your audio equipment to be absolutely silent unless told to perform. Motor noise should not be objectionable. However, what if it is? There are several kinds of noise: rotating noise, vibration, and electrical interference: If the noise is related to the rotating motor shaft, try lubricating the motor (or other suspect) bearings - a single drop of electric motor oil, sewing machine oil, or other light oil (NOT WD40 - it is not a suitable lubricant), to the bearings (at each end for the motor). This may help at least as a temporary fix. In some cases, using a slightly heavier oil will help with a worn bearing. See the section: "Lubrication of electronic equipment". For AC motors and transformers, steel laminations or the motor's mounting may be loose resulting in a buzz or hum. Tightening a screw or two may quiet it down. Painting the laminations with varnish suitable for electrical equipment may be needed in extreme cases. Sometimes, the noise may actually be a result of a nearby metal shield or other chassis hardware that is being vibrated by the motor's magnetic field. A strategically placed shim or piece of masking tape may work wonders. If the noise - a buzz or whine - is actually coming from the audio output but only occurs with the motor running, the interference filter on the motor power supply may have failed. This is often just a capacitor across the motor terminals and it may be defective or there may be a bad connection.
In many cases, motors are fairly standardized and you may be able to find a generic replacement much more cheaply than the original manufacturer's part. However, the replacement must match the following: 1. Mechanical - you must be able to mount it. In most cases, this really does mean an exact drop-in. Sometimes, a slightly longer shaft or mounting hole out of place can be tolerated. The pulley or other drive bushing, if any, must be able to be mounted on the new motor's shaft. If this is a press fit on the old motor, take extreme care so as not to damage this part when removing it (even if this means destroying the old motor in the process - it is garbage anyway). 2. Electrical - the voltage and current ratings must be similar. 3. Rotation direction - with conventional DC motors, this may be reversible by changing polarity of the voltage source. With AC motors, turning the stator around with respect to the rotor will reverse rotation direction. However, some motors have a fixed direction of rotation which cannot be altered. 4. Speed - for tape players and turntables - this may not be feedback controlled. With a little care you should be able to determine the normal rpms of the motor. For example, with a cassette deck, knowing the tape speed (1-7/8" inches per second is standard), it is straightforward calculate the motor shaft speed based on simple measurements of pulley and capstan diameter ratios. MCM Electronics, Dalbani, and Premium Parts stock a variety of generic replacement motors for tape decks, Walkmen, boomboxes, and CD players.
The ubiquitous electromechanical relay is a device that is used in a large variety of applications to switch power as well as signals in electrical and electronic equipment. Operation is quite simple: An electromagnet powered by an AC or DC coil pulls on an armature having a set of moving contacts which make or break a connection with a set of stationary contacts. Most common relays can be characterized by three sets of parameters: 1. Coil - voltage; resistance, current, or power consumption; and whether it is AC or DC. For AC coils only, the VA (volt-amps) rating may be used instead of or in addition to power consumption due to the inductive coil. Typical coil voltages range from 5 V to 480 V (AC or DC) - and beyond. Current and power consumption depend on the size of the relay. 2. Contact configuration - number of sets of contacts and whether they are their type. The designation will be something like SPST-NO, DPDT, 4PST-NC, 6PDT, etc. The first two letters refers to the number of sets of simultaneously activated contacts (S=1, D=2, numbers are usually used for more than 2 sets of contacts). The second two letters refers to the contact configuration (ST=NO or NC but no common terminal, DT will have a common - there will be both an NO and NC terminal). Where contacts are ST, the last two letters indicate NO or NC. An almost unlimited number of variations are possible. Typical relays have anywhere from 1 to 6 or more separate sets of ST or DT contacts or a mixture of the two. 3. Contact ratings - this may be specified for a number of types of applications. For example: in amperes at a particular voltage for DC resistive loads, or in horsepower at various voltages for AC inductive loads. Like fuse ratings, these are maximum ratings and lower values are almost always acceptable. Small relays may be able to switch only a few hundred mA at 32 V while large industrial contactors can switch 1000s of A at 1000s of V. Even the contactor in your automobile's starter must control hundreds of amps to the starter motor. The common (C) contacts connect to the normally closed (NC) contacts when the coil is unpowered and to the normally open (NO) contacts when the coil is powered. Miniature and subminiature relays are used to switch phone line signals in modems, fax machines, and telephone answering machines; audio amplifier speaker protection circuits; multiscan monitor deflection components; and many other places. Small relays control power in lighting equipment, TVs and other home appliances, automotive systems and accessories, and the like. Large relays (often called contactors) are used for the control of central air conditioning systems (compressor and blower motors), all types and sizes of industrial machinery - as well as in the starter of your automobile.
A relay without a pin connection diagram can usually be identified with a multimeter and variable power supply - or by eye. Many have the critical information printed on the cover. However, for detailed specifications, referring to the manufacturer's databook (or WEB page) really is best! (The following assumes a subminiature (DIP) relay. Lower coil resistances, higher coil voltages, and other variations may exist for larger relays.) 1. If the case of the relay is transparent or you can pop the top, examine the pole piece of the electromagnet. If there is a (copper) ring around half the pole piece, the relay coil is designed for AC (usually line frequency - 50 or 60 Hz) operation. An AC relay operated on DC will overheat very quickly but can be tested on DC. 2. Determine the coil pins. Use your eyeball if possible or your multimeter on the low resistance scale. For a small relay, the coil will most likely be a few hundred ohms. All other combinations of pins will be zero or infinity. If the resistance is under, say, 100 ohms, you may have an AC coil rather than a DC coil. 3. Power the relay from a variable DC supply (I am assuming it has a DC coil which is likely for a DIP relay. You can still do this with an AC coil but it will heat up quickly). Start at zero and increase the voltage until you hear the contacts close. This will probably be at around 3 volts (for a 5 V coil) or 8 volts for a 12 V coil - this will be roughly 60% of nominal coil voltage. If you do not hear anything, reverse the polarity of the coil and try again - you may have a latching relay. Alternatively, put your multimeter on the resistance scale across one of the pairs of pins that measured zero ohms as it is likely to be a NC set of contacts. This will change to infinity ohms when the relay switches. 4. Now that you can switch the relay on and off, you can use your multimeter on the resistance scale to determine which contacts are normally open (NO) and which contacts are normally closed (NC). (Normally here means unpowered.) 5, The power rating of the contacts can be estimated by their diameter (if they are visible). Rough current estimates (resistive loads): 20 A - 5 mm, 10 A - 3 mm, 5 A - 2 mm, 1 A - 1 mm. These must be derated substantially for inductive loads. For latching relays, the polarity of the coil voltage determines whether the relay is switched on or off. In other words, to switch to the opposite state requires the polarity of the voltage to the coil to be reversed. Other types are possible but not very common.
If the relay is totally inoperative, test for voltage to the coil. If the voltage is correct, the relay may have an open coil. If the voltage is low or zero, the coil may be shorted or the driving circuit may be defective. If the relay makes a normal switching sound but does not correctly control its output connections, the contacts may be corroded, dirty, worn, welded closed, binding, or there may be other mechanical problems. Remove the relay from the circuit (if possible) and measure the coil resistance. Compare your reading with the marked or specified value and/or compare with a known working relay of the same type. An open coil is obviously defective but sometimes the break is right at the terminal connections and can be repaired easily. If you can gain access by removing the cover, a visual examination will confirm this. If the resistance is too low, some of the windings are probably shorted. This will result in overheating as well as no or erratic operation. Replacement will be required. Relay contacts start out bright and shiny. As they are used, arcing, dirt, and wear take their toll. A sealed relay used at well below its rated current with a resistive load may work reliably for millions of cycles. However, this will be significantly reduced when switching high currents - especially with inductive loads which results in contact arcing. One speck of dirt can prevent a contact from closing so cleanliness is important. Excessive arcing can result in the contacts getting welded together as well. The resistance of closed contacts on a relay that is in good condition should be very low - probably below the measurable limits on a typical multimeter - a few milliohms. If you measure significant or erratic resistance for the closed contacts as the relay is switched or if very gentle tapping results in erratic resistance changes, the contacts are probably dirty, corroded, or worn. If you can get at the contacts, the use of contact cleaner first and a piece of paper pulled back and forth through the closed contacts may help. Superfine sandpaper may be used as a last resort but this is only a short term fix. The relay will most likely need to be replaced if the contacts are switching any substantial power.Go to [Next] segment
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