Re: Rechargeable (2CR5) for PZ-1p
Hi, Doug Franklin wrote: For my crowd, it was a Bic lighter, forceps, a handful of pennies, and a willing flock of bats. You _can_ hear a bat squeal if you motivate him enough. :-) I've never understood this syndome. You meet a person that you find you have a lot of respect for in many ways and then you find that they like stamping on kittens or somesuch nonsense. Is it just because it's possible - in which case, why not do it to kids, or women or smaller men? Really flummoxes me. m - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Rechargeable (2CR5) for PZ-1p
On Thu, 20 Dec 2001 15:43:05 +, mike wilson wrote: I've never understood this syndome. It's called being an 10 year old boy in the time and place in which I was an 10 year old boy. TTYL, DougF - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: Rechargeable (2CR5) for PZ-1p
Hello to All, My brother has been in electronics for over 25 years and he told me there is No Way that a rechargable could damage a camera motor. Rechargables always have a little less voltage than the regular batteries they replace. (1.25 volts to 1.5 volts for instance) To settle the issue, I have been using rechargables in my AA holder on my ZX5n and have had No Problems. A Rechargable Fan, Ryan Somebody wrote: mentioned that the hardness (high current output under big drain) of NiCd or big NiMH might damage the motor or something, is this really true? Although I don't have this camera, I have made batterypacks for almost everything photo-electric I have (mostly using old notebook batteries, a friend tested them and selected the best for me, suprising how they hold), so it's a curiosity-question. Good light, Frantisek - - Check out Yahoo! Shopping and Yahoo! Auctions for all of your unique holiday gifts! Buy at http://shopping.yahoo.com or bid at http://auctions.yahoo.com - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: Rechargeable (2CR5) for PZ-1p
Having been in this field longer than your brother I think you may have not posed the correct question. We aren't taking about voltage but the amount of current a given battery technology can sink across a give load value. A circuit has the same amount of current flow as long as the ohm value of the load and the voltage of the source remain constant. However in a camera the load seen is high (low current) when only the metering is operating. When the motordrive kicks in the power source has to be able to increase it's current flow to power the startup torque and running of the motor. The only way to do this is to suddenly have the battery see a lower load (fewer ohms of resistance). Various battery technologies have different peak current supply capabilities. If the camera maker wants to use this as part of the protection circuitry of the camera they will specify a limited battery type for the camera. Using rechargeables is only a problem in the voltage area if the electronics need to run close to the voltage produced by x number of alkalines or other specified types. If the camera has power regulation down to a something like 4 volts from 4 AA alkalines then 4 NiCads at 4.8 will work. On the otherhand if the camera maker says not to use NiMH or Lithium-Ion batteries it generally means that prolonged use of higher current capable battery technologies will eventually burn out some of the electronics because they were using the source current limit as part of the design process. Especially if the manual says something like use of battery types not specified can void the warranty. Kent Gittings -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Ryan Charron Sent: Wednesday, December 19, 2001 8:48 AM To: [EMAIL PROTECTED] Subject: RE: Rechargeable (2CR5) for PZ-1p Hello to All, My brother has been in electronics for over 25 years and he told me there is No Way that a rechargable could damage a camera motor. Rechargables always have a little less voltage than the regular batteries they replace. (1.25 volts to 1.5 volts for instance) To settle the issue, I have been using rechargables in my AA holder on my ZX5n and have had No Problems. A Rechargable Fan, Ryan Somebody wrote: mentioned that the hardness (high current output under big drain) of NiCd or big NiMH might damage the motor or something, is this really true? Although I don't have this camera, I have made batterypacks for almost everything photo-electric I have (mostly using old notebook batteries, a friend tested them and selected the best for me, suprising how they hold), so it's a curiosity-question. Good light, Frantisek - - Check out Yahoo! Shopping and Yahoo! Auctions for all of your unique holiday gifts! Buy at http://shopping.yahoo.com or bid at http://auctions.yahoo.com - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . ** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.com ** - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: Rechargeable (2CR5) for PZ-1p
When I was doing those Nimh tsts I also mesured the amperage of the cells, the best alkaline battery testd at 1.6V 40~50 ma, a 1600 mah nimh battery was 1.3v 130-140 ma, now remember your puttting 4 of these in a fg battery pack, so 4 regular or rechargable alkalines will provide 160-200 ma to the camera, now 4 nimh or nicads are powering 560 ma to the camera, if they built it to be powered by a higher voltage lower amperage source and you double/triple the apmerage it is only a matter of time before you burn something in it. No rechargables in my MZ-3, the flashes can use them all they want, since I change the AA's in the MZ-3 every 3 months but the flahses nightly --- Kent Gittings [EMAIL PROTECTED] wrote: Having been in this field longer than your brother I think you may have not posed the correct question. We aren't taking about voltage but the amount of current a given battery technology can sink across a give load value. A circuit has the same amount of current flow as long as the ohm value of the load and the voltage of the source remain constant. However in a camera the load seen is high (low current) when only the metering is operating. When the motordrive kicks in the power source has to be able to increase it's current flow to power the startup torque and running of the motor. The only way to do this is to suddenly have the battery see a lower load (fewer ohms of resistance). Various battery technologies have different peak current supply capabilities. If the camera maker wants to use this as part of the protection circuitry of the camera they will specify a limited battery type for the camera. Using rechargeables is only a problem in the voltage area if the electronics need to run close to the voltage produced by x number of alkalines or other specified types. If the camera has power regulation down to a something like 4 volts from 4 AA alkalines then 4 NiCads at 4.8 will work. On the otherhand if the camera maker says not to use NiMH or Lithium-Ion batteries it generally means that prolonged use of higher current capable battery technologies will eventually burn out some of the electronics because they were using the source current limit as part of the design process. Especially if the manual says something like use of battery types not specified can void the warranty. Kent Gittings __ Send your holiday cheer with http://greetings.yahoo.ca - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Rechargeable (2CR5) for PZ-1p
No Way may be correct. However, the relative voltages my not be the issue here. Of more interest at high duty cycles/loads or in case of component failure maybe short circuit current capability, which relates to the internal resistance of the different types of battery cells under high load conditions. Any one know out there happen to have info on the relative short circuit characteristics of NiCd, NiMH, Alkaline, Lithium etc. cells? Cold there be circumstances where one or more of these sources delivers more current than some older designs provided for? Otis Wright Ryan Charron wrote: Hello to All, My brother has been in electronics for over 25 years and he told me there is No Way that a rechargable could damage a camera motor. Rechargables always have a little less voltage than the regular batteries they replace. (1.25 volts to 1.5 volts for instance) To settle the issue, I have been using rechargables in my AA holder on my ZX5n and have had No Problems. A Rechargable Fan, Ryan Somebody wrote: mentioned that the hardness (high current output under big drain) of NiCd or big NiMH might damage the motor or something, is this really true? Although I don't have this camera, I have made batterypacks for almost everything photo-electric I have (mostly using old notebook batteries, a friend tested them and selected the best for me, suprising how they hold), so it's a curiosity-question. Good light, Frantisek - - Check out Yahoo! Shopping and Yahoo! Auctions for all of your unique holiday gifts! Buy at http://shopping.yahoo.com or bid at http://auctions.yahoo.com - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Rechargeable (2CR5) for PZ-1p
I think you are slightly mistaken in your figures (I am being polite). The current of four batteries in series is the same as one battery, but the voltage is 4 times as high. For batteries in parallel have 4x the current but the voltage stays the same as one battery. However, the question of whether rechargeable will hurt the equipment is a matter of whether the manufacture was depending on the internal resistance (high on alkalines, low on rechargeables) for current limiting, or has built current limiting into the circuit (more expensive). A battery will deliver current proportional to its load, and if there is no external load that is the internal resistance. A dead shorted ni-cad AA will deliver about an amp for a couple of minutes. Long enough to melt the battery and maybe the equipment it is in, and that kind of current can destroy integrated circuits in micro-seconds. So, if the manufacture did not design the equipment to use rechargeables you may have a problem, a very real problem. On the other hand sometimes they just tell you not to use rechargeables to limit their liability, or to try and make you buy their own battery pack, and the equipment is perfectly capable of handling them. Ciao, graywolf - Original Message - From: Brendan [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Wednesday, December 19, 2001 10:28 AM Subject: RE: Rechargeable (2CR5) for PZ-1p When I was doing those Nimh tsts I also mesured the amperage of the cells, the best alkaline battery testd at 1.6V 40~50 ma, a 1600 mah nimh battery was 1.3v 130-140 ma, now remember your puttting 4 of these in a fg battery pack, so 4 regular or rechargable alkalines will provide 160-200 ma to the camera, now 4 nimh or nicads are powering 560 ma to the camera, if they built it to be powered by a higher voltage lower amperage source and you double/triple the apmerage it is only a matter of time before you burn something in it. No rechargables in my MZ-3, the flashes can use them all they want, since I change the AA's in the MZ-3 every 3 months but the flahses nightly - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: Rechargeable (2CR5) for PZ-1p
On 19 Dec 2001 at 10:28, Brendan wrote: When I was doing those Nimh tsts I also mesured the amperage of the cells, the best alkaline battery testd at 1.6V 40~50 ma, a 1600 mah nimh battery was 1.3v 130-140 ma, now remember your puttting 4 of these in a fg battery pack, so 4 regular or rechargable alkalines will provide 160-200 ma to the camera, now 4 nimh or nicads are powering 560 ma to the camera, if they built it to be powered by a higher voltage lower amperage source and you double/triple the apmerage it is only a matter of time before you burn something in it. No rechargables in my MZ-3, the flashes can use them all they want, since I change the AA's in the MZ-3 every 3 months but the flahses nightly Hi Brendan (and whomever else is interested), Sorry it doesn't work this way, the batteries are in series, consider voltage as the ~potential~ pressure available to push electrons thorough the circuit, stack the batteries (ie put them in series) and the potential pressure increases (in fact the voltage adds ie 4 x 1.2 for NiMH, 4 x 1.5 for Alkaline or 4 x 1.25 for NiCd) The current flow in any circuit is determined by the potential of the source (ie battery voltage), the internal resistance of the battery (determined by it's short circuit current potential) and the resistance of the circuit which is the load (ie camera, flash, motor etc). The battery and load resistances are always in series (resistances in series add ie create a higher resistance) so the maximum current that can be supplied is governed by Ohms law which is current (amperes) = voltage (volts) / resistance (ohms). Therefore the current can't be forced and usually in any device (excepting a very badly designed one) the current flow is less when used with rechargeable cells as the terminal voltage is lower. Generally (given the same sized cell) the internal resistance of a NiCd cell is lower than a NiMH which is lower than Alkaline which is lower than the old carbon cells, but the difference should only be noted under very large load current requirements (ie a low resistance load approaching what is effectively a short circuit). In short if any electronics engineer designs a circuit that factors the internal resistance of the battery into the design deserves to have a fried circuit on their hands, so it doesn't happen very often (and it would be very apparent in the field as not may users ever RTFM). There might be potential in a badly designed flash gun or motor drive for over-heating due to excessive current flow but it's not common. On the other hand there are now a range of devices on the market (mostly digital cameras) where they are designed specifically for use with NiMH or NiCd rechargable AA cell in which conventional AA Alkaline cells will fry the devices due to their comparatively high terminal voltages (hence they can cause excessive current flow). The battery rating in mAh is simply the absolute charge holding capacity of the battery like MB of hard disk, it has little to do with current flow in ordinary circumstances (ie AA use in photo equipment). It can be used to determine the potential life of the batteries charge for a given current drain, ie if you have a 1600mAh battery supplying a circuit which draws 100mA then the battery should theoretically last for 16hours before it is discharged. BTW the formula for power dissipated in a load is voltage (volts) x current (amperes) = power (watts) therefore power = voltage(squared) / resistance so a small change in terminal voltage has a large impact on power dissipated by the circuit. Sorry about the OT rant but there is no point discussing these sorts of things when there are fundamental misunderstandings of the laws. Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications.html - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Rechargeable (2CR5) for PZ-1p
Otis Wright, Jr. Wrote: Any one know out there happen to have info on the relative short circuit characteristics of NiCd, NiMH, Alkaline, Lithium etc. cells? Cold there be circumstances where one or more of these sources delivers more current than some older designs provided for? I can't speak to theoretical stuff like this, but I can speak practically. From past experience, I know that ordinary flashlights burn brighter with NiCad cells than with fresh alkaline cells. Flashlights are not running near the maximum current limit of the cells, but the internal resistance of the cell is a significant part of the power calculation for them. Things like motors tend to run a lot closer to the current limit of the cell when starting. While this may not be much of a problem for the motor itself, the control circuitry may not be able to handle the extra current without overheating. However, all this aside, I find it unlikely that the designers of the camera went so far as to use bench power supplies that emulated the internal resistance of a battery. Since a bench power supply can source tons more current than a typical small battery cell, there probably is a safe voltage at which the camera can be run no matter tha battery technology. No? later, patbob ([EMAIL PROTECTED]) - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Rechargeable (2CR5) for PZ-1p
Well put and never, ever, under no circumstance, should anyone lick a light socket. :) - Original Message - From: Rob Studdert [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Wednesday, December 19, 2001 5:22 PM Subject: RE: Rechargeable (2CR5) for PZ-1p On 19 Dec 2001 at 10:28, Brendan wrote: When I was doing those Nimh tsts I also mesured the amperage of the cells, the best alkaline battery testd at 1.6V 40~50 ma, a 1600 mah nimh battery was 1.3v 130-140 ma, now remember your puttting 4 of these in a fg battery pack, so 4 regular or rechargable alkalines will provide 160-200 ma to the camera, now 4 nimh or nicads are powering 560 ma to the camera, if they built it to be powered by a higher voltage lower amperage source and you double/triple the apmerage it is only a matter of time before you burn something in it. No rechargables in my MZ-3, the flashes can use them all they want, since I change the AA's in the MZ-3 every 3 months but the flahses nightly Hi Brendan (and whomever else is interested), Sorry it doesn't work this way, the batteries are in series, consider voltage as the ~potential~ pressure available to push electrons thorough the circuit, stack the batteries (ie put them in series) and the potential pressure increases (in fact the voltage adds ie 4 x 1.2 for NiMH, 4 x 1.5 for Alkaline or 4 x 1.25 for NiCd) The current flow in any circuit is determined by the potential of the source (ie battery voltage), the internal resistance of the battery (determined by it's short circuit current potential) and the resistance of the circuit which is the load (ie camera, flash, motor etc). The battery and load resistances are always in series (resistances in series add ie create a higher resistance) so the maximum current that can be supplied is governed by Ohms law which is current (amperes) = voltage (volts) / resistance (ohms). Therefore the current can't be forced and usually in any device (excepting a very badly designed one) the current flow is less when used with rechargeable cells as the terminal voltage is lower. Generally (given the same sized cell) the internal resistance of a NiCd cell is lower than a NiMH which is lower than Alkaline which is lower than the old carbon cells, but the difference should only be noted under very large load current requirements (ie a low resistance load approaching what is effectively a short circuit). In short if any electronics engineer designs a circuit that factors the internal resistance of the battery into the design deserves to have a fried circuit on their hands, so it doesn't happen very often (and it would be very apparent in the field as not may users ever RTFM). There might be potential in a badly designed flash gun or motor drive for over-heating due to excessive current flow but it's not common. On the other hand there are now a range of devices on the market (mostly digital cameras) where they are designed specifically for use with NiMH or NiCd rechargable AA cell in which conventional AA Alkaline cells will fry the devices due to their comparatively high terminal voltages (hence they can cause excessive current flow). The battery rating in mAh is simply the absolute charge holding capacity of the battery like MB of hard disk, it has little to do with current flow in ordinary circumstances (ie AA use in photo equipment). It can be used to determine the potential life of the batteries charge for a given current drain, ie if you have a 1600mAh battery supplying a circuit which draws 100mA then the battery should theoretically last for 16hours before it is discharged. BTW the formula for power dissipated in a load is voltage (volts) x current (amperes) = power (watts) therefore power = voltage(squared) / resistance so a small change in terminal voltage has a large impact on power dissipated by the circuit. Sorry about the OT rant but there is no point discussing these sorts of things when there are fundamental misunderstandings of the laws. Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications.html - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Rechargeable (2CR5) for PZ-1p
On 19 Dec 2001 at 20:38, Doug Franklin wrote: On Wed, 19 Dec 2001 12:10:00 -0500, Otis Wright, Jr. wrote: Any one know out there happen to have info on the relative short circuit characteristics of NiCd, NiMH, Alkaline, Lithium etc. cells? A six-cell pack of 1400, 1600, or 2000 mAh Sub-C NiCD (Sanyo or Panasonic) cells is reputed to deliver 100A or more of dead-short current for a _very_ short time. Within five to ten seconds, the cells overheat to the point they can give you a 2nd degree burn and they violently start venting gas (don't know what type of gas). [Sub-C cells are slightly smaller than a C size alkaline battery.] I've seen this happen several times in the 1:10 scale electric R/C cars. In a controlled test several years ago, an acquaintance measured a specific six-Sub-C 1600 mAh pack dead shorting a bit over 100A for less than five seconds. The current delivered dropped off to zero over the next thirty or so seconds as the internal structure self-destructed from the heat and and the chemical system was depleted by the venting. :-) Keen, I just checked the specs for the 1600mAh AA NiMH cells that I use in all my gear, the shirt circuit current is 7.75A for 2 seconds max, the cells internal resistance when fully charged is 25 mOhm. see: http://users.skynet.be/bs137713/DATASHEET/pdf/VH1600AA.PDF AFAIK NiMH cells have a higher energy density than NiCd cells but NiCd have a far higher short circuit current in most cases. I believe that some aircraft use NiCd batteries for starting? In school we used to use charged AA NiCd cells to heat up the pocket clips on old Parker ball point pens before sending across the room via air vbg Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications.html - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Rechargeable (2CR5) for PZ-1p
On Thu, 20 Dec 2001 14:50:01 +1000, Rob Studdert wrote: On 19 Dec 2001 at 20:38, Doug Franklin wrote: In a controlled test several years ago, an acquaintance measured a specific six-Sub-C 1600 mAh pack dead shorting a bit over 100A for less than five seconds. The current delivered dropped off to zero over the next thirty or so seconds as the internal structure self-destructed from the heat and and the chemical system was depleted by the venting. :-) Keen, I just checked the specs for the 1600mAh AA NiMH cells that I use in all my gear, the shirt circuit current is 7.75A for 2 seconds max, the cells internal resistance when fully charged is 25 mOhm. see: http://users.skynet.be/bs137713/DATASHEET/pdf/VH1600AA.PDF AFAIK NiMH cells have a higher energy density than NiCd cells but NiCd have a far higher short circuit current in most cases. I believe that some aircraft use NiCd batteries for starting? In school we used to use charged AA NiCd cells to heat up the pocket clips on old Parker ball point pens before sending across the room via air vbg Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications.html - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: Rechargeable (2CR5) for PZ-1p
Howdy, folks, First of all, sorry for the Oops. I accidentally hit the send button before composing my reply. :-( Oh well. At least it wasn't a bug in my production code. :-) On Thu, 20 Dec 2001 14:50:01 +1000, Rob Studdert wrote: On 19 Dec 2001 at 20:38, Doug Franklin wrote: [...] they can give you a 2nd degree burn [...] In retrospect, maybe I should explain the (US) burn scale (as far as I can recall it): 1st degree: Pain with skin reddening but no blistering 2nd degree: Blistering up to skin ablation (burning off) 3rd degree: Ablation and charring of skin, muscle, etc. Flaking away of exposed skin and muscle. [...] they violently start venting gas (don't know what type of gas). Oops. That should have been start violently venting gas. When I've seen it happen, the venting is at very high pressures and flow rates. At least as high, and probably a good bit higher, than a tea pot whistling. I'm guessing (without much basis at all) that the exit velocity of the gas approaches 20 m/s through the .75 mm vent holes in the battery's can. Since I don't know what gas (gasses?) is (are) vented, I can't estimate the mass flow rate. The current delivered dropped off to zero over the next thirty or so seconds as the internal structure self-destructed from the heat and and the chemical system was depleted by the venting. :-) It's really quite spectacular if you've never seen it. Since the batteries are full of cadmium, I would only do a controlled test under a fume hood, though, even though I'm not sure what gasses are being vented. :-) I guess I should have also mentioned the specifics: six 1600 mAh sub-C NiCd cells, wired in series. The load was a dead-shorted (unmoving) DC electric motor. One characteristic of a dead-shorted DC electric motor is that it draws current in inverse proportion to the internal resistance of the motor (which is often near the wire resistance of the wire in the armature windings). So you're looking at 9.6VDC drawn across a load measured in milli- or microamps. Since V=IR, I=V/R=9.6V/10^-3 or less ohms, that's a lot of current. :-) Keen, I just checked the specs for the 1600mAh AA NiMH cells that I use in all my gear, the shirt circuit current is 7.75A for 2 seconds max, the cells internal resistance when fully charged is 25 mOhm. The manufacturers always seem to quote fully-charged internal resistance. I suspect that means that internal resistance increases in a normal discharge cycle. I'd love to see the graphs their labs have of current/internal resistance during a catastrophic discharge like a dead-short. You _know_ they do those tests. My suspicion is that events unfold something like this: 1) The dead short is applied. 2) The battery (multiple cells wired in series and/or parallel) see a load near 0 ohms. 3) The battery starts delivering (even more) current by the bushel. 4) The current flow begins heating the cells of the battery. 5) As the individual cell temperatures catastrophically increase, their internal structure starts to degrade, causing their internal resistance to decrease. 6) Decreased cell resistance increases the overall current flow. 7) Increased overall currently flow causes more heating and more degradation. Go To Step (3). 8) At come critical point, the cell's internal temperature rises to the point that there's enough ambient energy to fuel the endothermic chemical processes that produce the gasses. 9) Shortly thereafter, the gas pressure inside the cell overcomes the rating of the valves on the cell body, and gas is vented (at spectacular rates). 10) The gas venting decreases the chemical potential of the cell's contents. 11) At some point, the decreased resistance of the (melting) internal structure is offset by the decreased chemical potential due to vented gasses and, over time (a few seconds) you end up with (effectively) an open circuit across the battery (cell). This train of thought makes me a little skeptical of the 7.75 A dead-short current per cell spec they list. :-) Unless you're only talking about the first handful of seconds of a catastrophic discharge. Just from Mark-One-Mod-Zero-Eyeball measurements, I can guarantee that the physical process ramps up for about five to ten seconds before gradually subsiding. AFAIK NiMH cells have a higher energy density than NiCd cells but NiCd have a far higher short circuit current in most cases. I believe that some aircraft use NiCd batteries for starting? I'm not sure about the APUs (Auxiliary Power Units, used to fire jet ignitions, among other things), but NiCd definitely can deliver more current (maybe not power) per unit volume than alkaline or wet-cell. I don't know about NiMH. My understanding is that NiMH is about midpoint between NiCd and alkaline in (almost?) all useful measures. In school we used to use charged AA NiCd cells to heat up the pocket clips on old Parker ball point pens before sending across the room via air vbg For my
OT: Re: Rechargeable (2CR5) for PZ-1p
On Thu, 20 Dec 2001, Doug Franklin wrote: I'd love to see the graphs their labs have of current/internal resistance during a catastrophic discharge like a dead-short. You _know_ they do those tests. How would a curious person go about trying this at home? :) Is there a nice and easy way to make a battery do this? chris - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: OT: Re: Rechargeable (2CR5) for PZ-1p
On Thu, 20 Dec 2001 00:32:09 -0600 (CST), Chris Brogden wrote: On Thu, 20 Dec 2001, Doug Franklin wrote: I'd love to see the graphs their labs have of current/internal resistance during a catastrophic discharge like a dead-short. You _know_ they do those tests. How would a curious person go about trying this at home? :) Is there a nice and easy way to make a battery do this? OK. And no shitting. Step one is to get a _very_ efficient fume hood. Do some research and see if someone has published exactly what comes out of those bad boys when they vent, but you're _going_ to vent the crap out of the cell (battery) doing the test. It may be harmless gasses, but I would _NOT_ bet on it, since the cell is full of cadmium, nickel, and/or some other biochemical nasties. Step two is the equipment under test. Part two.one is a NiCd cell or battery (cell makes the computations easier). Part two.two is a piece of #8 AWG (or larger) copper or silver wire long enough to connect the cell's (battery's) positive and negative terminals. [I've seen a battery pack burn #12 AWG stranded copper wire clean through. You might want #4 AWG or larger.] You need wire that can take a couple of hundred amps of continuous current for up to a minute or two, for safety's sake. Step three, if you're interested in real measurements, is the measurement apparatus. You're going to have to measure cell (battery) internal resistance indirectly by measuring the current through and voltage drop across the cell (battery) as the test progresses. I don't know enough electronics to say much more than that. My guess is that you need a couple of integrating scopes that can tell you the area under the voltage and current curves and record the data they capture during the test. Step four is some cannon fodder (e.g., the next-door neighbor's idiot kid who's after your daughter) to actually hook up the dead short wire and the measurement probes. :-) Step five is to connect the wire across the terminals of the cell (battery) and get the hell out of the way while the scopes record the data. Step six is to analyze the recorded data to calculate the cell (battery) internal resistance changes over time. I'd caution _strongly_ against breathing any of the gasses, vapors, or anything else emitted from the cell (battery). Let it burn down until it's not only ceased any electrical activity but also cooled back down to human temperatures. I've never measured it, but I've seen a shorted pack draw blisters on the pit crew's hands before. Entomb the remains in the most chemically resistant container you have and take it to a battery recycler. Radio Shack will recycle batteries, but I doubt they'll take a plastic bag full of cells, juice, and emitted solids. :-) TTYL, DougF - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: Rechargeable (2CR5) for PZ-1p
I don't think anyone would design a camera or other piece of equipment to deliberately short out the power source. As long as you meet, and don't exceed, the required operating voltage for a piece of equipment, it's internal resistance will limit current flow to that amount determined by Ohm's law. I've run 12-volt/200ma walkie talkies on lead acid car batteries meant to provide 200+ amperes of current to start large engines, with no problems unless I exceeded the duty cycle of the walkie talkie. You can exceed the duty cycle with small batteries as well as with big ones. If you do, it will fail in either case, though the failure may release more smoke with the big batteries. :-) For the guys that don't know, duty cycle refers to the amount of time that the device can be on before you must shut it down to give it a chance to cool down. Normally the duty cycle for a transmitter will be given as a percentage, with 50% being pretty common. It was also given in terms of transmitting time versus off time. 50% meant that if you transmitted for the given max transmit time, you had to let it rest for the same amount of time before the next transmission. Camera drive motors have some sort of duty cycle too. The good ones are usually enough so you can fire off a 36-exposure roll of film and the time spent unloading the film and reloading the next will be enough to satisfy the duty cycle of the drive motor. Len --- -Original Message- From: Kent Gittings [mailto:[EMAIL PROTECTED]] Sent: Tuesday, December 18, 2001 8:00 AM To: [EMAIL PROTECTED] Subject: RE: Rechargeable (2CR5) for PZ-1p The only other case I can think of is a power design that lacks any kind of current limiting circuitry. In such a design the power source then would have to be based on something that had a maximum output that couldn't exceed a particular value due to inherent design. Something like the type or chemical process of the battery. In that case switching to an alternate source of power that had no current limiting of its own (by design or the technology) could effectively burn it out if the true ohm value of the load was such that it produced a much higher current if the power course could flow that much current. Kent Gittings Somebody mentioned that the hardness (high current output under big drain) of NiCd or big NiMH might damage the motor or something, is this really true? Although I don't have this camera, I have made batterypacks for almost everything photo-electric I have (mostly using old notebook batteries, a friend tested them and selected the best for me, suprising how they hold), so it's a curiosity-question. Good light, Frantisek - - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
