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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / December 2007Easy Question: Charging Car Battery Removed From Vehicle?
When you charging a car battery removed from your vehicle, my battery charging owners manual states that you need to "attach at least a 24inch (60cm) long, 6 gauge (AWG) insulated battery cable to NEGATIVE battery post", then later states "connect the black NEGATIVE output clamp to the free end of the cable". Ive used battery chargers in the past, but Ive never done this step before. How important is it to use an insulated cable between the batter charger's negative clamp and the battery's negative post? I tried to google for more information, and I see the same instructions explained here: http://www.battery-chargers.com/charging_instructions.htm (scroll down half way until you find "B. CHARGING BATTERY OUTSIDE VEHICLE". Could anyone explain to me why a jumper cable or insulated battery cable is required to be placed between the charger's negative clamp, and the battery's negative post? How important is it to do this? I have charged batteries in the past and have never done this. What problems could occur if I did not use a jumper cable or insulated cable and instead just attached the battery charger's NEGATIVE clamp to the battery's NEGATIVE post? On Dec 9, 1:03 pm, quentinmacdoug...@gmail.com wrote: > Could anyone explain to me why a jumper cable or insulated battery > cable is required to be placed between the charger's negative clamp, [quoted text clipped - 3 lines] > cable and instead just attached the battery charger's NEGATIVE clamp > to the battery's NEGATIVE post? I should add to this: I removed the car battery from my car for the winter since it is not going to be driven. I wanted to store the battery in my basement connected to a slow charging system to keep the battery alive and well all winter. Should I use a jumper cable between my battery post and batter charger's NEG output clamp as described in the owners manual and website URL posted in my original message? > When you charging a car battery removed from your vehicle, my battery > charging owners manual states that you need to "attach at least a [quoted text clipped - 7 lines] > > ... Perhaps it's for the same reason that it's recommended to connect the negative jumper cable to the engine block instead of directly to the negative post when jump starting...to prevent a possible spark from igniting any gases from the battery? I can't think of any other reason why you'd want to do that. If you connect the charger to the battery and then plug the charger in (or turn it on) you'd probably accomplish the same thing. It's probably just CYA for the charger manufacturer... In article <58b76562-f7a0-4f25-a153-1eddc2b89c6d@p69g2000hsa.googlegroups.com>, <snip> > Could anyone explain to me why a jumper cable or insulated battery > cable is required to be placed between the charger's negative clamp, [quoted text clipped - 3 lines] > cable and instead just attached the battery charger's NEGATIVE clamp > to the battery's NEGATIVE post? It's not "required", it's just fairly intelligent. The purpose of the "extension", whether it be a set of jumper cables, a hunk of insulated wire, or whatever else, is to move the connect/disconnect point away from the battery, so that any spark that may happen when connecting/disconnecting the charging apparatus is distant from the (possible) cloud of explosive hydrogen gas produced by the battery as it charges. The extension cable serves *ABSOLUTELY NO ELECTRICAL OR FUNCTIONAL PURPOSE* beyond moving the physical (dis)connection point away from the battery - omitting the extension will have no effect whatsoever on the actual charging process. On the other hand, omitting it *MAY* result in a trip to the hospital to have pieces of the battery surgically removed from various parts of your anatomy... It's the same principle as when you jump-start a car - You hook up to the positive posts on both vehicles (no particular order - it isn't important), then you connect to the negative post of the "live" battery, and finally, you connect the other end of the negative cable to "someplace as far away from the battery as practical". The last connection made is the one that's going to cause the spark, so you want to make that connection as far away from the batteries as you can. Similarly, the first thing you disconnect is going to be the one that makes the spark - So you want it to be far from the battery and the likely cloud of hydrogen. Thus, you disconnect the "someplace far from the battery" connection first. Once you've done that, the disconnect sequence is irrelevant, although most folks agree that the next one to be removed should be the other end of the negative cable (because doing so makes it impossible to accidentally short the positive and negative clamps on the "far end" of the cable to produce a spark) Whether charing out of the vehicle, or setting up for a jump-start, connecting directly to the battery is perfectly functional, but may be unsafe due to the potential for explosion.  SignatureDon Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist, or the subject of the message doesn't contain the exact text "PopperAndShadow" somewhere, any message sent to this address will go in the garbage without my ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd> for more info The only reason they tell you to use a extra cable when charging a battery out of a vehicle is safety. If the battery is outside of the vehicle chances are that the battery is indoors and away from air movement. If this is the case explosive battery fumes may be present at the battery itself. If your last connection was made at the battery site the spark resulting may cause an explosion. The use of the extra cable nullifies this scenario by taking the inevitable spark and moving it away from the battery, providing your last connection is the negative charger to the free end of the extra cable. > When you charging a car battery removed from your vehicle, my battery > charging owners manual states that you need to "attach at least a [quoted text clipped - 19 lines] > cable and instead just attached the battery charger's NEGATIVE clamp > to the battery's NEGATIVE post? Make it easy on your self and make sure your battery charger is turned off , Hook up the Battery and then turn it on!!! Don't need to nullify (Sigh) justify or anything else. people sometimes forget to turn off the charger before they unhook them and thats why the recommend the cable. If you wanna go pro on it,,, buy yourself a Battery tender (not a trickle charger) and use that during the storage period. It will save you battery life by not over charging and keep sulfation to a minimum Later Tim PASCO we are your starting and charging specialists 410-546-2041 >Make it easy on your self and make sure your battery charger is turned >off , Hook up the Battery and then turn it on!!! > >Don't need to nullify (Sigh) justify or anything else. people sometimes >forget to turn off the charger before they unhook them and thats why the >recommend the cable. So no spark will occur with most chargers unplugged? Think again. > >Make it easy on your self and make sure your battery charger is turned > >off , Hook up the Battery and then turn it on!!! [quoted text clipped - 4 lines] > > So no spark will occur with most chargers unplugged? Think again. Precisely... A spark *DOES NOT NEED TO BE VISIBLE* to be plenty adequate to touch off a hydrogen explosion. *EVERY* time a circuit is made or broken, *THERE IS A SPARK*. Hooking the final clamp of a charger to the terminal of a battery is closing a circuit, and even if the charger is unplugged, *THE BATTERY* is extremely unlikely to be so dead that it doesn't make at least a micro-spark (small, perhaps even invisible, but perfectly capable of igniting a cloud of hydrogen if it's there) as the connection is made. Likewise, disconnecting the clamp after the battery is charged, even with the charger powered down, or unplugged from the wall, causes a spark as the circuit is broken. At this point, though, the chances are *MUCH* higher of getting an explosion, because the battery has been charged, which has generated hydrogen, which may be hovering around the battery just waiting for something to ignite it. Which, incidentally, is the reason that they'll tell you to charge a battery in a well ventilated location - minimize hydrogen build-up, minimize chance of explosion. SignatureDon Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist, or the subject of the message doesn't contain the exact text "PopperAndShadow" somewhere, any message sent to this address will go in the garbage without my ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd> for more info >> >Make it easy on your self and make sure your battery charger is >> >turned off , Hook up the Battery and then turn it on!!! [quoted text clipped - 26 lines] > in a well ventilated location - minimize hydrogen build-up, minimize > chance of explosion. while all this safety info is mostly true, a good batt charger, not a cheepe, will not spark while off. It does not conplete a circuit as that means that it would discharge the batt if left conected but off. The cheep ones will do that but most comercial ones will not. KB SignatureThunder Snake #9 "Protect" your rights or "lose" them. > >> >Make it easy on your self and make sure your battery charger is > >> >turned off , Hook up the Battery and then turn it on!!! [quoted text clipped - 31 lines] > means that it would discharge the batt if left conected but off. The > cheep ones will do that but most comercial ones will not. KB Actually, the "good ones" contain a diode (or work-alike circuitry) that stops the discharge, but even there, a circuit *IS* being made, and for a tiny instant prior to the diode (or work-alike) "noticing" and operating to cut it off, juice flows. Which means spark is possible. SignatureDon Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist, or the subject of the message doesn't contain the exact text "PopperAndShadow" somewhere, any message sent to this address will go in the garbage without my ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd> for more info >>Make it easy on your self and make sure your battery charger is turned >>off , Hook up the Battery and then turn it on!!! [quoted text clipped - 4 lines] > > So no spark will occur with most chargers unplugged? Think again. I thought again, and the answer is still the same. With the charger unplugged- no spark because the diodes in the charger don't allow reverse current flow through it. > >>Make it easy on your self and make sure your battery charger is turned > >>off , Hook up the Battery and then turn it on!!! [quoted text clipped - 8 lines] > unplugged- no spark because the diodes in the charger don't allow > reverse current flow through it. Once the circuit is completed and everything is up to high enough potential to forward-bias the diode... Until it hits that potential (Which varies from diode to diode) there is current flowing in the circuit. (Different diodes also have different "response speeds" when it comes to stopping current flowing in reverse, as well) Never mind that any capacitance or inductance in the output circuit is going to "fill up" by drawing from the battery when the connection is made. In both cases, current flow equals possibility of spark sufficient to ignite hydrogen. SignatureDon Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist, or the subject of the message doesn't contain the exact text "PopperAndShadow" somewhere, any message sent to this address will go in the garbage without my ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd> for more info >>>So no spark will occur with most chargers unplugged? Think again. >> [quoted text clipped - 16 lines] > In both cases, current flow equals possibility of spark sufficient to > ignite hydrogen. I just don't buy it. The capacitance of a reverse-biased diode is so tiny that you're talking microamps for microseconds. That would be such a vanishingly small spark that the concentration of hydrogen and oxygen at the point of spark would have to be absolutely PERFECT for ignition. Just aint gonna happen in the real world. The fact that it is theoretically possible at million-to-one against odds is the only reason that the CYA language is there at all in the charger instructions. If some dumb-cluck blows up a battery in his own face by connecting with the charger powered, the language is there to protect the manufacturer. They can say, "see, we TOLD you to use an insulated pigtail and you didn't." Which is as it should be. >> In both cases, current flow equals possibility of spark sufficient to >> ignite hydrogen. [quoted text clipped - 4 lines] >at the point of spark would have to be absolutely PERFECT for ignition. >Just aint gonna happen in the real world. Micramps for a few milliseconds? Have you ever measured the current flow when hooking a unplugged charger up to a charged battery? Diodes are not the perfect switch you seem to imply. In order for a diode to pass large amounts of current it is required to have a minimal resistance in the forward direction. Since a typical power diodes used in battery chargers have about a 10:1 resistance ratio that means it still passes current in the reverse direction. Just not at the same level. You also seem to forget that many chargers have accessory circuits like voltmeters that draw 20 milliamps or so when the leads are hooked up. 20 milliamps will cause a spark. Again, it would be irresponsible to suggest that all one has to do is have the charger unplugged in order to hook a battery up. >>>In both cases, current flow equals possibility of spark sufficient to >>>ignite hydrogen. [quoted text clipped - 7 lines] > Micramps for a few milliseconds? Have you ever measured the current > flow when hooking a unplugged charger up to a charged battery? Since I'm 50 feet from a lab where I can actually make that measurement, and its my lunch hour, I will go do that within an hour. I'll let you know- but I don't think my lab has a meter that can measure that small of a current. > Diodes are not the perfect switch you seem to imply. In order for > a diode to pass large amounts of current it is required to have a > minimal resistance in the forward direction. Since a typical power > diodes used in battery chargers have about a 10:1 resistance ratio > that means it still passes current in the reverse direction. Just not > at the same level. I don't know where you get this "10:1 resistance ratio" business. Its certainly not valid. I have pulled from my shelf and opened on my desk right now the textbook "Solid State Electronic Devices, 2nd Edition" (published 1980- darn I'm getting old) by Ben G. Streetman, presently chairman of the Electrical Engineering department at the University of Texas at Austin. Section 5.3 "Forward- and Reverse-biased junctions" is applicable. Page 150 defines the components of current that can cross a P-N junction (aka a diode), primarily the "drift current," the "diffusion current" and the "generation current" components. All 3 contribute to current flow under forward bias. However, page 151 states clearly: "Under reverse bias, both diffusion currents are negligible and THE ONLY CURRENT (my emphasis) is the relatively small and VOLTAGE INDEPENDENT (my emphasis again) generation current from n to p." Note that the reverse bias current flow across a diode doesn't even depend strongly on the applied voltage, therefore it doesn't even begin to have a curve that looks like a "resistance," and therefore the "10:1 resistance ratio" doesn't even exist at all. "Generation current" is due to the quantum effect of electron-hole pairs spontaneously appearing in the junction region of a diode, and the electron being swept one direction and the "hole" the other due to any applied voltage at all. Photodiodes use the fact that light can cause hole-pair generation, but in regular rectifier diodes its just a probabalistic event, with a super-low probability. The reverse current flow is TINY, up until you exceed the reverse breakdown voltage of the diode... and a 12v battery aint gonna do THAT to a charger rectifier diode. > You also seem to forget that many chargers have accessory circuits > like voltmeters that draw 20 milliamps or so when the leads are hooked > up. 20 milliamps will cause a spark. > > Again, it would be irresponsible to suggest that all one has to do is > have the charger unplugged in order to hook a battery up. If I'm a corporate lawyer knowing that some goober will hook it up live, backward, or whatever, then I force my tech writers to put in the requirement for a long insulated lead to cover my company's a.s. Someone WILL blow up a battery with one (or more) of the chargers my company sells, so its imperative that I make it clear that my company explained all precautions, both reasonable and unrealistic. On the other hand if I'm out in my garage and all I care about is my own life (which I value greatly) then I have NO problem hooking up with the charger unplugged, because the odds of me getting hit by lighting inside my garage are FAR greater than the odds of connecting this way causing the battery to blow up. IOW, a rational and competent user only cares about the REALISTIC precautions. >> Micramps for a few milliseconds? Have you ever measured the current >> flow when hooking a unplugged charger up to a charged battery? [quoted text clipped - 3 lines] > know- but I don't think my lab has a meter that can measure that small > of a current. Measurement complete. Interesting results, actually. The first test I did was with a 10-amp fully automated (fast then maintain) electronic battery charger that's about 10 years old. Its got dual-color LEDs on front to indicate "charging" or "charged." The LED turns amber ("charging") when the charger is unplugged but connected to the battery, so I knew it was going to have a measurable reverse current because that is what lights the LED. It did- 17 milliamps. Personally, I consider that completely safe to connect while unplugged- the probability of a spark that could ignite hydrogen from the battery would be vanishingly small. But there IS a current. I turned out all the lights and tried to see a spark- no dice. The second charger I measured was a newer fully automatic fast/maintain charger. It was even better than I claimed- when connected to a fully charged battery but unplugged from the wall, it showed a whopping 0.2 MICROamps of reverse current. Yes, 200 NANOamps. The meter I was using only goes down to 10ths of a micro-amp, so really the measurement's at the limit of the meter's- it could be even less than that. Absolutely ZERO chance of that charger causing a spark if you connected it (while its unplugged) to a fully charged 12v battery. Finally, I dug up the oldest-style charger we have. Its a semi-automatic Dayton, meaning that it charges until it senses 13.8 volts, then shuts off (a mechanical relay clicks open) and won't kick back on until the voltage falls WAY down to something like 11. It also has a 55-amp "start" setting. When unplugged, it draws about 30 mA reverse current from a fully charged 12v battery, and that might, conceivably, remotely, create a spark when hooked up unplugged. Yet its instructions don't say *anything* but pretty much hook it up, positive first and then negative" and then plug it into the outlet. Nothing about a long insulated lead or anything. Since Dayton is still in business without having killed or maimed any users, and this was the "worst" reverse current of the chargers I had on hand, I think I will rest my case here. >Measurement complete. Interesting results, actually. > [quoted text clipped - 8 lines] >be vanishingly small. But there IS a current. I turned out all the >lights and tried to see a spark- no dice. At 20ma I can see a spark in the dark. At 17ma I would suggest you look again. >The second charger I measured was a newer fully automatic fast/maintain >charger. It was even better than I claimed- when connected to a fully [quoted text clipped - 17 lines] >maimed any users, and this was the "worst" reverse current of the >chargers I had on hand, I think I will rest my case here. I have made connections to batteries also without blowing anything up. It just makes more sense if you completely remove the possibility by 'use of the extra cable. >>Measurement complete. Interesting results, actually. >> [quoted text clipped - 37 lines] >It just makes more sense if you completely remove the possibility by >'use of the extra cable. Modern auto and marine battery chemistry is such that not a lot of "gassing" occurs unless seriously overcharging.. not the case here and second, the vents are ususally equipped with some sort of flame trap type arestor in the openings. I used to work at a shop where oddball sized, heavy duty, lead acid batteries were "rebuilt", and before leading the terminal connections or heating the tar that was used in those days to seal the cells into the case, the tech used to wave the torch over the open cells to get any little hydrogen "pop" out of the way so that it wouldn't startle him later on!. In my opinion (only), the danger of a hydrogen explosion is MANY times greater after the battery has been on charge, has reached full charge, is gassing freely and the charger is REMOVED without turning off the power... creating a spark when there would likely be gas in the vicinity of the battery terminals. This "extra lead on the negative terminal" sounds like someones idea of a legal CYA more than an absolute requirement if common sense is used around a lead acid battery that has been gassing. Bob >>>> Make it easy on your self and make sure your battery charger is turned >>>> off , Hook up the Battery and then turn it on!!! [quoted text clipped - 22 lines] > In both cases, current flow equals possibility of spark sufficient to > ignite hydrogen. OMFG!!! I work for a company that sells and maintains batteries all day long and TRUST me there's no science to it any more!!! The only time I have ever seen a battery "explode" was when a crew hooked up a bettery reversed polarity with a bad alternator putting out 22V. Don't make it hard on a person who is just trying to get general info... just give them the basics... I've been doing this for years. Just make sure the switch is off before hookup. And besides if you want to scare the hell out of someone who is trying to save money by doing it themselves,,, why don't you tell them if there battery has a short in it ,, it could sizzle, smoke and really cause a fire! The best bet is make sure you have a good battery charger!!! At PASCO, We are the Charging and Starting Specialists >>>Make it easy on your self and make sure your battery charger is turned >>>off , Hook up the Battery and then turn it on!!! [quoted text clipped - 8 lines] >unplugged- no spark because the diodes in the charger don't allow >reverse current flow through it. A diode will stop all current flow? I thought only a open circuit could do that. >>>>Make it easy on your self and make sure your battery charger is turned >>>>off , Hook up the Battery and then turn it on!!! [quoted text clipped - 11 lines] >A diode will stop all current flow? I thought only a open circuit >could do that. diodes only conduct in one direction. > >>>>Make it easy on your self and make sure your battery charger is turned > >>>>off , Hook up the Battery and then turn it on!!! [quoted text clipped - 13 lines] > > diodes only conduct in one direction. True, but only *AFTER* the circuit has "charged up", so to speak. For a brief instant, they conduct either way. Once the circuit hits *ROUGHLY* (exact number varies by diode type) 2 volts, they stop conducting in reverse until the voltage exceeds the diode's back voltage. (At which point, all the "magic smoke" usually leaks out of the diode) Don't take my word for it, though - Set up a rig so you can watch things happen on a fast oscilloscope. Start with the O-scope set to the highest input impedance it can do, then connect the unplugged charger's positive cable to the battery's positive terminal, the O-scope ground to the battery's negative terminal, and watch the display as you touch the O-scope probe to the (still unplugged) charger's negative cable. The momentary reverse voltage will show up "loud and clear" as the circuit formed by touching the probe to the cable "charges up". (You may need to do some tweaking to get it in a range where you can see it - start with lots of attenuation so you don't blow the 'scope, and if you can't see the spike the first time around, start dialing down the attenuation until you get it into a range the 'scope can display) SignatureDon Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist, or the subject of the message doesn't contain the exact text "PopperAndShadow" somewhere, any message sent to this address will go in the garbage without my ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd> for more info >True, but only *AFTER* the circuit has "charged up", so to speak. For a >brief instant, they conduct either way. Once the circuit hits *ROUGHLY* >(exact number varies by diode type) 2 volts, they stop conducting in >reverse until the voltage exceeds the diode's back voltage. (At which >point, all the "magic smoke" usually leaks out of the diode) I don't think so. There is a certain FORWARD voltage required for turn-on.... the diode remains nonconducting until the forward voltage is about 0.6V. But nothing will make it conduct in reverse. if you don't believe me, look at the I/V plot on the diode data sheet. >Don't take my word for it, though - Set up a rig so you can watch things >happen on a fast oscilloscope. Start with the O-scope set to the highest >input impedance it can do, then connect the unplugged charger's positive >cable to the battery's positive terminal, the O-scope ground to the >battery's negative terminal, and watch the display as you touch the >O-scope probe to the (still unplugged) charger's negative cable. I bet you see a big FORWARD inductive kickback, if the charger doesn't have much shunt capacitance. --scott Signature"C'est un Nagra. C'est suisse, et tres, tres precis." >>True, but only *AFTER* the circuit has "charged up", so to speak. For a >>brief instant, they conduct either way. Once the circuit hits *ROUGHLY* [quoted text clipped - 7 lines] > remains nonconducting until the forward voltage is about 0.6V. But > nothing will make it conduct in reverse. For all pracitcal purposes, you're right. There is a tiny reverse leakage current that can practically be measured in number of electrons per minute, which is for all intents and purposes zero. And there IS the "junction capacitance" that Don is talking about, but its a tiny, tiny, tiny capacitance. Not enough to produce a spark- because the capacitance of the air gap as you move the charger lead up to the battery post (right before you connect it) is comparable to the diode junction capacitance and appears in series with it- in essence the diode "charges" before the physical connection is even made. >For all pracitcal purposes, you're right. There is a tiny reverse >leakage current that can practically be measured in number of electrons >per minute, which is for all intents and purposes zero. In this case yes, but the leakage on a diode can actually be a useful thing in high-Z circuits. If you look at an anti-knock sensor, for instance, it usually has a FET front end with a reverse-biased diode fabricated on the same substrate, to provide a very teeny path to ground for the FET gate. Piezo element flexes, voltage on the gate changes, and the ground path is enough to keep the FET biased right when it's idle but not enough to sink much of the tiny low-current signal from the piezo. >And there IS the "junction capacitance" that Don is talking about, but >its a tiny, tiny, tiny capacitance. Not enough to produce a spark- >because the capacitance of the air gap as you move the charger lead up >to the battery post (right before you connect it) is comparable to the >diode junction capacitance and appears in series with it- in essence the >diode "charges" before the physical connection is even made. Junction capacitance can be pretty large on huge selenium stacks, like your local theatre used to use for projection arcs. Now it's a non-issue except in the RF world. --scott Signature"C'est un Nagra. C'est suisse, et tres, tres precis." >>For all pracitcal purposes, you're right. There is a tiny reverse >>leakage current that can practically be measured in number of electrons [quoted text clipped - 19 lines] > non-issue except in the RF world. > --scott > Junction capacitance can be pretty large on huge selenium stacks, > like your local theatre used to use for projection arcs. Now it's a > non-issue except in the RF world. > --scott And there are all kinds of cool things to do with junction capacitance in the RF world. Since capacitance is related to reverse bias voltage, a reverse-biased diode makes a handy voltage-controlled capacitor (Varactor diodes are optimized for that purpose). Which is the technology that gave us radio and TV tuners without knobs or other moving parts. >True, but only *AFTER* the circuit has "charged up", so to speak. For a >brief instant, they conduct either way. Once the circuit hits *ROUGHLY* bullshit. When reverse biased, they never conduct; when forward biased, silicon diodes have a 0.7V drop. >>>>>Make it easy on your self and make sure your battery charger is turned >>>>>off , Hook up the Battery and then turn it on!!! [quoted text clipped - 13 lines] > >diodes only conduct in one direction. Usually by a ratio, not infinity. >>>>>>Make it easy on your self and make sure your battery charger is turned >>>>>>off , Hook up the Battery and then turn it on!!! [quoted text clipped - 13 lines] >> >>diodes only conduct in one direction. >Usually by a ratio, not infinity. cite, please. The conduction in reverse is close enough to zero that you can ignore it. a few microamps don't matter in an automotive charging circuit. >>>diodes only conduct in one direction. > [quoted text clipped - 4 lines] >The conduction in reverse is close enough to zero that you can ignore it. >a few microamps don't matter in an automotive charging circuit. Take any electronics coarse and you'll see that a typical diode has as low as a 10:1 forward to reverse resistance. Any resistance less than infinity can cause a spark across a voltage source. It would be irresponsible to say that all one has to do to hook up a battery is to just have the supply turned off. > >>>diodes only conduct in one direction. > > [quoted text clipped - 10 lines] > irresponsible to say that all one has to do to hook up a battery is to > just have the supply turned off. Precisely... Which is *EFFECTIVELY* what the original poster was asking about - "Why does it say to do the hookup by connecting an extension to the negative post, then connecting the charger to the far end of the extension?" The answer, when boiled down, is "To get the inevitable spark away from the stuff that it could ignite, causing the battery to blow up in your face." How well or poorly a diode conducts, in which direction, or at what voltage, has little or nothing to do with it. When you make or break a connection to the battery, even if what you're (dis)connecting is an unplugged charger, THERE WILL BE A SPARK. That spark MAY be enough to ignite the cloud of hydrogen that could be hovering around the battery. So you want to make/break the connection at a distance from the battery. SignatureDon Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist, or the subject of the message doesn't contain the exact text "PopperAndShadow" somewhere, any message sent to this address will go in the garbage without my ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd> for more info > >>>>>>Make it easy on your self and make sure your battery charger is turned > >>>>>>off , Hook up the Battery and then turn it on!!! [quoted text clipped - 22 lines] > The conduction in reverse is close enough to zero that you can ignore it. > a few microamps don't matter in an automotive charging circuit. The point is that even a small amount of current can cause a spark - and it doesn't matter which way the juice is flowing. And even a small (invisible to the naked eye) spark can be sufficient to touch off the hydrogen explosion that's the reason behind the method originally being asked about. SignatureDon Bruder - dakidd@sonic.net - If your "From:" address isn't on my whitelist, or the subject of the message doesn't contain the exact text "PopperAndShadow" somewhere, any message sent to this address will go in the garbage without my ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd> for more info |
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