Re: [EVDL] FW: On the road again.
On Thu, May 28, 2015 at 11:01 AM, Cor van de Water via EV ev@lists.evdl.org wrote: Nope, I have a little experience with charging older style Li-Ion batteries by hand and the resting voltage is typically a rather fixed amount (delta) below the charging voltage, no matter how high you charged them. If you charge to 3.8V then they rest at say 3.65 If you charge to 4.0 then they rest at 3.85 If you charge to the max recommended 4.25 edge then they rest at 4.1 If you overcharge to 4.5 then they rest at 4.35 (they will self-discharge faster but not immediately) So, from measuring the rest voltage it is not clear that they are balanced - you really need to measure each cell to make sure, that is why a BMS is important. What chemistry are you talking about? If you charge LiFePO4 cells like the CALBs that Damon has to 4.25V and the current tapers to near 0A then you are definitely overcharging the cell and damaging it. If you charge a CALB cell and let it rest for 24 hours at room temp and it is resting over 3.38V then the cell was overcharged and you need to cut back your charging a bit. Damon would be best served to bottom balance each cell to about 2.75V. Then hook them up in a pack and stop charging when the first cell goes over 3.65V depending on current. With my 4 pack of 80Ah CALBs I have a 40A charger that is set to charge to 14.2V and shut off when the current drops to about 3A. In one of my packs the smallest cell goes to 3.8V but settles to 3.37-3.36V with no load so I know I'm not over charging it. In my Gizmo with 20 cells and a charger that tapers to essentially 0A the target voltage is 3.455V/cell. All settle to under 3.38V with no load on the pack. No balancing over nearly 4 years and over 12k miles. They haven't drifted as many predicted they would. There are several people who have been running LiFePO4 cells for several years now with no BMS and haven't run into problems. I have heard, however, of several with cell level BMS setups who have had problems from damaged cells to short lived packs. -- David D. Nelson http://evalbum.com/1328 http://www.levforum.com ___ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
[EVDL] FW: On the road again.
Thanks David... for pointing out the forgetfulness factor. Been there, done that. There are a couple of fairly simple solutions to that particular problem. First, a charger that is set at a low enough voltage to limit that danger. So far it has been my experience with this pack that there is not enough of a voltage rise to set a dumb charger up for this function, but I am considering getting a smart charger that will do constant current to a specific voltage then shut off. Another easy solution is a mechanical timer. I have an e-meter on the motorcycle so I know how much energy I have taken out. That makes it pretty easy to set a timer as a fail-safe. I think my e-meter may even have an alarm function that I could use to shut the charger off. I thought the joke about the tarp was clever :) Finally, as Cor pointed out, it is my motorcycle which has the 3.4kwh pack on it now. Since I have not done lithium before I brought out the old test mule from under the tarp so that if I do learn from the school of hard knocks, as is often the case, I will be well educated before investing in a much more expensive lithium for my truck. I don't believe I will do the lithium without a BMS, but that is a decision for some future time. I have two normal scenarios. MWF - round trip to the gym and back 10 miles - opportunity charge for an hour while I get ready for work then 8 miles to the office where I have the full day to charge if I like. Then back home 8 miles. The other two days of the week I do not do the gym first, so overall this pack is getting very light duty. In fact, I think the hardest thing for me to get used to is not fully charging it. I'm so used to charging as much as I can whenever I can that it is a hard habit to break. In this case though, why get close to the danger points? Bad things usually happen to batteries when they are nearing full or empty. Keeping them away from those danger zones makes a lot of sense. The most stress I am likely to put on them will be if I go to visit my good friend John Wayland who lives 17 miles of mostly freeway from me. It's no problem picking up a charge at his house before I head back home, though, so even that should not be too bad. damon To: ev@lists.evdl.org Date: Wed, 27 May 2015 15:52:20 -0400 Subject: Re: [EVDL] On the road again. From: ev@lists.evdl.org On 27 May 2015 at 9:23, damon henry via EV wrote: After 5 years under the tarp, I put my EV motorcycle back on the road this week. You must have been awfully bored, living under that tarp for all those years! ;-) I purchased 16 Calb CA60ah cells which fit well in my existing battery boxes. So if my math is right, ~3.4 kWh. That's the equivalent of about four T-125 golf car batteries (useful capacity 900Wh each). I'm thinking this is going to be a short-range truck, and probably short-lived batteries from working so hard. I do not have any BMS installed, but on such a small pack with good access it is easy to be my own BMS As long as you don't get busy with something else and forget. I know of a guy around here who destroyed an entire set of rare and expensive Saft STM5- 180 NiCd batteries when he forgot he was charging them. I wouldn't even do an E-bike lithium battery without a BMS. But that's me, and I know how forgetful I can be! David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to evpost and etpost addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = ___ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA) -- next part -- An HTML attachment was scrubbed... URL: http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150528/bb9c2e30/attachment.htm ___ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
Re: [EVDL] FW: On the road again.
I don't know of a lithium cell that would be carrying significant capacity at 2 Volts. That voltage would not hurt a Li cell. 2V would be a reasonable low cut off. Higher gives you more leeway if your are far out of bottom balance. If you bottom balance to begin with you are safer for a longer time. A DIY'er can bottom balance, but a pack manufacturer has to devote more time than they are willing to top balancing. The Batt Bridge would warn you if one cell has gone off the reservation. Not which one, but you would know in which half pack and then you check the individual cells. The high cutoff is different depending on the chemistry of the positive electrode. It is very important to get this right because fully charging cells in conjunction with high temperatures the situation that is damaging to Li cells. A chemistry like LiFePO4 has a lower voltage/capacity curve than most other cell chemistries. 3.4V max might be all you want for max voltage on a LiFePO4 system (CALB, others). Other chemistries would be safe at 3.4V or less, but some would not be charging very well at that low voltage. This the upper cut off situation is when you want to know exactly what you are dealing with - and this is probably a hard thing to sort out with uncertain supplier chains you -- importer -- exporter -- Chinese factory for example. Mike On Thu, May 28, 2015 at 2:02 PM, EVDL Administrator via EV ev@lists.evdl.org wrote: On 28 May 2015 at 10:18, damon henry via EV wrote: There are a couple of fairly simple solutions to that particular problem. First, a charger that is set at a low enough voltage to limit that danger. I'm not a lithium expert, but this sounds like it should work well as long as your cells remain balanced. If some are different temperatures, differing efficiency could get them out of balance. I would think you'd also need some kind of over-discharge protection. I wonder if that could be something as simple as a Lee Hart batt-bridge imbalance alarm. http://www.evdl.org/pages/battbridge.html Do lithium cells have enough voltage falloff when flat to make it work as needed here? Sorry about the bike/truck confusion. That one flew right past me. :-\ David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to evpost and etpost addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = ___ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA ( http://groups.yahoo.com/group/NEDRA) -- To invent, you need a good imagination and a pile of junk. Thomas A. Edison http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 585-6737 Land (919) 576-0824 https://www.google.com/voice/b/0?pli=1#phones Google Phone (919) 631-1451 Cell michael.e.r...@gmail.com michael.e.r...@gmail.com -- next part -- An HTML attachment was scrubbed... URL: http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150528/278569ff/attachment.htm ___ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
Re: [EVDL] FW: On the road again.
On 28 May 2015 at 10:18, damon henry via EV wrote: There are a couple of fairly simple solutions to that particular problem. First, a charger that is set at a low enough voltage to limit that danger. I'm not a lithium expert, but this sounds like it should work well as long as your cells remain balanced. If some are different temperatures, differing efficiency could get them out of balance. I would think you'd also need some kind of over-discharge protection. I wonder if that could be something as simple as a Lee Hart batt-bridge imbalance alarm. http://www.evdl.org/pages/battbridge.html Do lithium cells have enough voltage falloff when flat to make it work as needed here? Sorry about the bike/truck confusion. That one flew right past me. :-\ David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to evpost and etpost addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = ___ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
Re: [EVDL] FW: On the road again.
I've been driving mine for years and several hours after charge the voltage is exactly the same. Like you said self discharge till you reach OCV. Sent from my iPhone On May 28, 2015, at 1:01 PM, Cor van de Water via EV ev@lists.evdl.org wrote: Nope, I have a little experience with charging older style Li-Ion batteries by hand and the resting voltage is typically a rather fixed amount (delta) below the charging voltage, no matter how high you charged them. If you charge to 3.8V then they rest at say 3.65 If you charge to 4.0 then they rest at 3.85 If you charge to the max recommended 4.25 edge then they rest at 4.1 If you overcharge to 4.5 then they rest at 4.35 (they will self-discharge faster but not immediately) So, from measuring the rest voltage it is not clear that they are balanced - you really need to measure each cell to make sure, that is why a BMS is important. BTW, the only thing that I found different between charging and resting voltage was the indication of a bad cell with high resistance, but even those were pretty consistent in just a slight larger delta between charge and rest. Hope this clarifies, Cor van de Water Chief Scientist Proxim Wireless office +1 408 383 7626Skype: cor_van_de_water XoIP +31 87 784 1130private: cvandewater.info www.proxim.com This email message (including any attachments) contains confidential and proprietary information of Proxim Wireless Corporation. If you received this message in error, please delete it and notify the sender. Any unauthorized use, disclosure, distribution, or copying of any part of this message is prohibited. -Original Message- From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Paul Dove via EV Sent: Thursday, May 28, 2015 10:54 AM To: Electric Vehicle Discussion List Subject: Re: [EVDL] FW: On the road again. I disagree. Assuming by your example the OCV of the cell is 3.8v and one charges to 4v. After cycle 1 the OCV will be 22.8v After cycle 2 the OCV will be 19v After cycle 3 the OCV will be 19v Etc. One can tell if there is a bad cell immediately after every charge because the OCV will be lower. Sent from my iPhone On May 28, 2015, at 12:44 PM, Lawrence Harris via EV ev@lists.evdl.org wrote: Just remember to check each cell periodically to ensure they are staying together. If one cell is weak it will drift down each cycle and eventually you will overcharge the good ones and destroy the weak one (this is where fires come from). A little exaggerated perhaps but this is what happens, maybe not exactly cycle by cycle but over time. Your charger is set to chart to 24v and then cut back. cycle 1: 6 x 4v = 24v cycle 2: 5 x 4.1 + 3.5v = 24v cycle 3: 5 x 4.2 + 3.0v = 24v cycle 4: 5 x 4.3 + 2.5 = 24v : eventually the good ones are being charged over their max values and the weak one is being pushed towards zero or negative at the end of each discharge cycle. Now we get heat and overpressure and poof! Lawrence On May 28, 2015, at 10:18 AM, damon henry via EV ev@lists.evdl.org wrote: Thanks David... for pointing out the forgetfulness factor. Been there, done that. There are a couple of fairly simple solutions to that particular problem. First, a charger that is set at a low enough voltage to limit that danger. So far it has been my experience with this pack that there is not enough of a voltage rise to set a dumb charger up for this function, but I am considering getting a smart charger that will do constant current to a specific voltage then shut off. Another easy solution is a mechanical timer. I have an e-meter on the motorcycle so I know how much energy I have taken out. That makes it pretty easy to set a timer as a fail-safe. I think my e-meter may even have an alarm function that I could use to shut the charger off. I thought the joke about the tarp was clever :) Finally, as Cor pointed out, it is my motorcycle which has the 3.4kwh pack on it now. Since I have not done lithium before I brought out the old test mule from under the tarp so that if I do learn from the school of hard knocks, as is often the case, I will be well educated before investing in a much more expensive lithium for my truck. I don't believe I will do the lithium without a BMS, but that is a decision for some future time. I have two normal scenarios. MWF - round trip to the gym and back 10 miles - opportunity charge for an hour while I get ready for work then 8 miles to the office where I have the full day to charge if I like. Then back home 8 miles. The other two days of the week I do not do the gym first, so overall this pack is getting very light duty. In fact, I think the hardest thing for me to get used to is not fully charging it. I'm so used to charging as much as I can whenever I can that it is a hard habit to break. In this case though
Re: [EVDL] FW: On the road again.
Just remember to check each cell periodically to ensure they are staying together. If one cell is weak it will drift down each cycle and eventually you will overcharge the good ones and destroy the weak one (this is where fires come from). A little exaggerated perhaps but this is what happens, maybe not exactly cycle by cycle but over time. Your charger is set to chart to 24v and then cut back. cycle 1: 6 x 4v = 24v cycle 2: 5 x 4.1 + 3.5v = 24v cycle 3: 5 x 4.2 + 3.0v = 24v cycle 4: 5 x 4.3 + 2.5 = 24v : eventually the good ones are being charged over their max values and the weak one is being pushed towards zero or negative at the end of each discharge cycle. Now we get heat and overpressure and poof! Lawrence On May 28, 2015, at 10:18 AM, damon henry via EV ev@lists.evdl.org wrote: Thanks David... for pointing out the forgetfulness factor. Been there, done that. There are a couple of fairly simple solutions to that particular problem. First, a charger that is set at a low enough voltage to limit that danger. So far it has been my experience with this pack that there is not enough of a voltage rise to set a dumb charger up for this function, but I am considering getting a smart charger that will do constant current to a specific voltage then shut off. Another easy solution is a mechanical timer. I have an e-meter on the motorcycle so I know how much energy I have taken out. That makes it pretty easy to set a timer as a fail-safe. I think my e-meter may even have an alarm function that I could use to shut the charger off. I thought the joke about the tarp was clever :) Finally, as Cor pointed out, it is my motorcycle which has the 3.4kwh pack on it now. Since I have not done lithium before I brought out the old test mule from under the tarp so that if I do learn from the school of hard knocks, as is often the case, I will be well educated before investing in a much more expensive lithium for my truck. I don't believe I will do the lithium without a BMS, but that is a decision for some future time. I have two normal scenarios. MWF - round trip to the gym and back 10 miles - opportunity charge for an hour while I get ready for work then 8 miles to the office where I have the full day to charge if I like. Then back home 8 miles. The other two days of the week I do not do the gym first, so overall this pack is getting very light duty. In fact, I think the hardest thing for me to get used to is not fully charging it. I'm so used to charging as much as I can whenever I can that it is a hard habit to break. In this case though, why get close to the danger points? Bad things usually happen to batteries when they are nearing full or empty. Keeping them away from those danger zones makes a lot of sense. The most stress I am likely to put on them will be if I go to visit my good friend John Wayland who lives 17 miles of mostly freeway from me. It's no problem picking up a charge at his house before I head back home, though, so even that should not be too bad. damon To: ev@lists.evdl.org Date: Wed, 27 May 2015 15:52:20 -0400 Subject: Re: [EVDL] On the road again. From: ev@lists.evdl.org On 27 May 2015 at 9:23, damon henry via EV wrote: After 5 years under the tarp, I put my EV motorcycle back on the road this week. You must have been awfully bored, living under that tarp for all those years! ;-) I purchased 16 Calb CA60ah cells which fit well in my existing battery boxes. So if my math is right, ~3.4 kWh. That's the equivalent of about four T-125 golf car batteries (useful capacity 900Wh each). I'm thinking this is going to be a short-range truck, and probably short-lived batteries from working so hard. I do not have any BMS installed, but on such a small pack with good access it is easy to be my own BMS As long as you don't get busy with something else and forget. I know of a guy around here who destroyed an entire set of rare and expensive Saft STM5- 180 NiCd batteries when he forgot he was charging them. I wouldn't even do an E-bike lithium battery without a BMS. But that's me, and I know how forgetful I can be! David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to evpost and etpost addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = ___ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
Re: [EVDL] FW: On the road again.
Nope, I have a little experience with charging older style Li-Ion batteries by hand and the resting voltage is typically a rather fixed amount (delta) below the charging voltage, no matter how high you charged them. If you charge to 3.8V then they rest at say 3.65 If you charge to 4.0 then they rest at 3.85 If you charge to the max recommended 4.25 edge then they rest at 4.1 If you overcharge to 4.5 then they rest at 4.35 (they will self-discharge faster but not immediately) So, from measuring the rest voltage it is not clear that they are balanced - you really need to measure each cell to make sure, that is why a BMS is important. BTW, the only thing that I found different between charging and resting voltage was the indication of a bad cell with high resistance, but even those were pretty consistent in just a slight larger delta between charge and rest. Hope this clarifies, Cor van de Water Chief Scientist Proxim Wireless office +1 408 383 7626 Skype: cor_van_de_water XoIP +31 87 784 1130 private: cvandewater.info www.proxim.com This email message (including any attachments) contains confidential and proprietary information of Proxim Wireless Corporation. If you received this message in error, please delete it and notify the sender. Any unauthorized use, disclosure, distribution, or copying of any part of this message is prohibited. -Original Message- From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Paul Dove via EV Sent: Thursday, May 28, 2015 10:54 AM To: Electric Vehicle Discussion List Subject: Re: [EVDL] FW: On the road again. I disagree. Assuming by your example the OCV of the cell is 3.8v and one charges to 4v. After cycle 1 the OCV will be 22.8v After cycle 2 the OCV will be 19v After cycle 3 the OCV will be 19v Etc. One can tell if there is a bad cell immediately after every charge because the OCV will be lower. Sent from my iPhone On May 28, 2015, at 12:44 PM, Lawrence Harris via EV ev@lists.evdl.org wrote: Just remember to check each cell periodically to ensure they are staying together. If one cell is weak it will drift down each cycle and eventually you will overcharge the good ones and destroy the weak one (this is where fires come from). A little exaggerated perhaps but this is what happens, maybe not exactly cycle by cycle but over time. Your charger is set to chart to 24v and then cut back. cycle 1: 6 x 4v = 24v cycle 2: 5 x 4.1 + 3.5v = 24v cycle 3: 5 x 4.2 + 3.0v = 24v cycle 4: 5 x 4.3 + 2.5 = 24v : eventually the good ones are being charged over their max values and the weak one is being pushed towards zero or negative at the end of each discharge cycle. Now we get heat and overpressure and poof! Lawrence On May 28, 2015, at 10:18 AM, damon henry via EV ev@lists.evdl.org wrote: Thanks David... for pointing out the forgetfulness factor. Been there, done that. There are a couple of fairly simple solutions to that particular problem. First, a charger that is set at a low enough voltage to limit that danger. So far it has been my experience with this pack that there is not enough of a voltage rise to set a dumb charger up for this function, but I am considering getting a smart charger that will do constant current to a specific voltage then shut off. Another easy solution is a mechanical timer. I have an e-meter on the motorcycle so I know how much energy I have taken out. That makes it pretty easy to set a timer as a fail-safe. I think my e-meter may even have an alarm function that I could use to shut the charger off. I thought the joke about the tarp was clever :) Finally, as Cor pointed out, it is my motorcycle which has the 3.4kwh pack on it now. Since I have not done lithium before I brought out the old test mule from under the tarp so that if I do learn from the school of hard knocks, as is often the case, I will be well educated before investing in a much more expensive lithium for my truck. I don't believe I will do the lithium without a BMS, but that is a decision for some future time. I have two normal scenarios. MWF - round trip to the gym and back 10 miles - opportunity charge for an hour while I get ready for work then 8 miles to the office where I have the full day to charge if I like. Then back home 8 miles. The other two days of the week I do not do the gym first, so overall this pack is getting very light duty. In fact, I think the hardest thing for me to get used to is not fully charging it. I'm so used to charging as much as I can whenever I can that it is a hard habit to break. In this case though, why get close to the danger points? Bad things usually happen to batteries when they are nearing full or empty. Keeping them away from those danger zones makes a lot of sense. The most stress I am likely to put on them will be if I go to visit my good friend John Wayland who lives 17 miles
Re: [EVDL] FW: On the road again.
I agree with Cor's comment on charging versus resting voltage - I mean a cutoff voltage to be the resting voltage. On Thu, May 28, 2015 at 2:18 PM, Michael Ross michael.e.r...@gmail.com wrote: I don't know of a lithium cell that would be carrying significant capacity at 2 Volts. That voltage would not hurt a Li cell. 2V would be a reasonable low cut off. Higher gives you more leeway if your are far out of bottom balance. If you bottom balance to begin with you are safer for a longer time. A DIY'er can bottom balance, but a pack manufacturer has to devote more time than they are willing to top balancing. The Batt Bridge would warn you if one cell has gone off the reservation. Not which one, but you would know in which half pack and then you check the individual cells. The high cutoff is different depending on the chemistry of the positive electrode. It is very important to get this right because fully charging cells in conjunction with high temperatures the situation that is damaging to Li cells. A chemistry like LiFePO4 has a lower voltage/capacity curve than most other cell chemistries. 3.4V max might be all you want for max voltage on a LiFePO4 system (CALB, others). Other chemistries would be safe at 3.4V or less, but some would not be charging very well at that low voltage. This the upper cut off situation is when you want to know exactly what you are dealing with - and this is probably a hard thing to sort out with uncertain supplier chains you -- importer -- exporter -- Chinese factory for example. Mike On Thu, May 28, 2015 at 2:02 PM, EVDL Administrator via EV ev@lists.evdl.org wrote: On 28 May 2015 at 10:18, damon henry via EV wrote: There are a couple of fairly simple solutions to that particular problem. First, a charger that is set at a low enough voltage to limit that danger. I'm not a lithium expert, but this sounds like it should work well as long as your cells remain balanced. If some are different temperatures, differing efficiency could get them out of balance. I would think you'd also need some kind of over-discharge protection. I wonder if that could be something as simple as a Lee Hart batt-bridge imbalance alarm. http://www.evdl.org/pages/battbridge.html Do lithium cells have enough voltage falloff when flat to make it work as needed here? Sorry about the bike/truck confusion. That one flew right past me. :-\ David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to evpost and etpost addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = ___ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA ( http://groups.yahoo.com/group/NEDRA) -- To invent, you need a good imagination and a pile of junk. Thomas A. Edison http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 585-6737 Land (919) 576-0824 https://www.google.com/voice/b/0?pli=1#phones Google Phone (919) 631-1451 Cell michael.e.r...@gmail.com michael.e.r...@gmail.com -- To invent, you need a good imagination and a pile of junk. Thomas A. Edison http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 585-6737 Land (919) 576-0824 https://www.google.com/voice/b/0?pli=1#phones Google Phone (919) 631-1451 Cell michael.e.r...@gmail.com michael.e.r...@gmail.com -- next part -- An HTML attachment was scrubbed... URL: http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150528/b55f62bd/attachment.htm ___ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
Re: [EVDL] FW: On the road again.
I had one cell go bad early on and I knew it the first day because my voltage was lower the next morning after charging. Sent from my iPhone On May 28, 2015, at 1:09 PM, Paul Dove via EV ev@lists.evdl.org wrote: I've been driving mine for years and several hours after charge the voltage is exactly the same. Like you said self discharge till you reach OCV. Sent from my iPhone On May 28, 2015, at 1:01 PM, Cor van de Water via EV ev@lists.evdl.org wrote: Nope, I have a little experience with charging older style Li-Ion batteries by hand and the resting voltage is typically a rather fixed amount (delta) below the charging voltage, no matter how high you charged them. If you charge to 3.8V then they rest at say 3.65 If you charge to 4.0 then they rest at 3.85 If you charge to the max recommended 4.25 edge then they rest at 4.1 If you overcharge to 4.5 then they rest at 4.35 (they will self-discharge faster but not immediately) So, from measuring the rest voltage it is not clear that they are balanced - you really need to measure each cell to make sure, that is why a BMS is important. BTW, the only thing that I found different between charging and resting voltage was the indication of a bad cell with high resistance, but even those were pretty consistent in just a slight larger delta between charge and rest. Hope this clarifies, Cor van de Water Chief Scientist Proxim Wireless office +1 408 383 7626Skype: cor_van_de_water XoIP +31 87 784 1130private: cvandewater.info www.proxim.com This email message (including any attachments) contains confidential and proprietary information of Proxim Wireless Corporation. If you received this message in error, please delete it and notify the sender. Any unauthorized use, disclosure, distribution, or copying of any part of this message is prohibited. -Original Message- From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of Paul Dove via EV Sent: Thursday, May 28, 2015 10:54 AM To: Electric Vehicle Discussion List Subject: Re: [EVDL] FW: On the road again. I disagree. Assuming by your example the OCV of the cell is 3.8v and one charges to 4v. After cycle 1 the OCV will be 22.8v After cycle 2 the OCV will be 19v After cycle 3 the OCV will be 19v Etc. One can tell if there is a bad cell immediately after every charge because the OCV will be lower. Sent from my iPhone On May 28, 2015, at 12:44 PM, Lawrence Harris via EV ev@lists.evdl.org wrote: Just remember to check each cell periodically to ensure they are staying together. If one cell is weak it will drift down each cycle and eventually you will overcharge the good ones and destroy the weak one (this is where fires come from). A little exaggerated perhaps but this is what happens, maybe not exactly cycle by cycle but over time. Your charger is set to chart to 24v and then cut back. cycle 1: 6 x 4v = 24v cycle 2: 5 x 4.1 + 3.5v = 24v cycle 3: 5 x 4.2 + 3.0v = 24v cycle 4: 5 x 4.3 + 2.5 = 24v : eventually the good ones are being charged over their max values and the weak one is being pushed towards zero or negative at the end of each discharge cycle. Now we get heat and overpressure and poof! Lawrence On May 28, 2015, at 10:18 AM, damon henry via EV ev@lists.evdl.org wrote: Thanks David... for pointing out the forgetfulness factor. Been there, done that. There are a couple of fairly simple solutions to that particular problem. First, a charger that is set at a low enough voltage to limit that danger. So far it has been my experience with this pack that there is not enough of a voltage rise to set a dumb charger up for this function, but I am considering getting a smart charger that will do constant current to a specific voltage then shut off. Another easy solution is a mechanical timer. I have an e-meter on the motorcycle so I know how much energy I have taken out. That makes it pretty easy to set a timer as a fail-safe. I think my e-meter may even have an alarm function that I could use to shut the charger off. I thought the joke about the tarp was clever :) Finally, as Cor pointed out, it is my motorcycle which has the 3.4kwh pack on it now. Since I have not done lithium before I brought out the old test mule from under the tarp so that if I do learn from the school of hard knocks, as is often the case, I will be well educated before investing in a much more expensive lithium for my truck. I don't believe I will do the lithium without a BMS, but that is a decision for some future time. I have two normal scenarios. MWF - round trip to the gym and back 10 miles - opportunity charge for an hour while I get ready for work then 8 miles to the office where I have the full day to charge if I like. Then back home 8 miles. The other two days of the week I do not do the gym first, so overall this pack
Re: [EVDL] FW: On the road again.
I disagree. Assuming by your example the OCV of the cell is 3.8v and one charges to 4v. After cycle 1 the OCV will be 22.8v After cycle 2 the OCV will be 19v After cycle 3 the OCV will be 19v Etc. One can tell if there is a bad cell immediately after every charge because the OCV will be lower. Sent from my iPhone On May 28, 2015, at 12:44 PM, Lawrence Harris via EV ev@lists.evdl.org wrote: Just remember to check each cell periodically to ensure they are staying together. If one cell is weak it will drift down each cycle and eventually you will overcharge the good ones and destroy the weak one (this is where fires come from). A little exaggerated perhaps but this is what happens, maybe not exactly cycle by cycle but over time. Your charger is set to chart to 24v and then cut back. cycle 1: 6 x 4v = 24v cycle 2: 5 x 4.1 + 3.5v = 24v cycle 3: 5 x 4.2 + 3.0v = 24v cycle 4: 5 x 4.3 + 2.5 = 24v : eventually the good ones are being charged over their max values and the weak one is being pushed towards zero or negative at the end of each discharge cycle. Now we get heat and overpressure and poof! Lawrence On May 28, 2015, at 10:18 AM, damon henry via EV ev@lists.evdl.org wrote: Thanks David... for pointing out the forgetfulness factor. Been there, done that. There are a couple of fairly simple solutions to that particular problem. First, a charger that is set at a low enough voltage to limit that danger. So far it has been my experience with this pack that there is not enough of a voltage rise to set a dumb charger up for this function, but I am considering getting a smart charger that will do constant current to a specific voltage then shut off. Another easy solution is a mechanical timer. I have an e-meter on the motorcycle so I know how much energy I have taken out. That makes it pretty easy to set a timer as a fail-safe. I think my e-meter may even have an alarm function that I could use to shut the charger off. I thought the joke about the tarp was clever :) Finally, as Cor pointed out, it is my motorcycle which has the 3.4kwh pack on it now. Since I have not done lithium before I brought out the old test mule from under the tarp so that if I do learn from the school of hard knocks, as is often the case, I will be well educated before investing in a much more expensive lithium for my truck. I don't believe I will do the lithium without a BMS, but that is a decision for some future time. I have two normal scenarios. MWF - round trip to the gym and back 10 miles - opportunity charge for an hour while I get ready for work then 8 miles to the office where I have the full day to charge if I like. Then back home 8 miles. The other two days of the week I do not do the gym first, so overall this pack is getting very light duty. In fact, I think the hardest thing for me to get used to is not fully charging it. I'm so used to charging as much as I can whenever I can that it is a hard habit to break. In this case though, why get close to the danger points? Bad things usually happen to batteries when they are nearing full or empty. Keeping them away from those danger zones makes a lot of sense. The most stress I am likely to put on them will be if I go to visit my good friend John Wayland who lives 17 miles of mostly freeway from me. It's no problem picking up a charge at his house before I head back home, though, so even that should not be too bad. damon To: ev@lists.evdl.org Date: Wed, 27 May 2015 15:52:20 -0400 Subject: Re: [EVDL] On the road again. From: ev@lists.evdl.org On 27 May 2015 at 9:23, damon henry via EV wrote: After 5 years under the tarp, I put my EV motorcycle back on the road this week. You must have been awfully bored, living under that tarp for all those years! ;-) I purchased 16 Calb CA60ah cells which fit well in my existing battery boxes. So if my math is right, ~3.4 kWh. That's the equivalent of about four T-125 golf car batteries (useful capacity 900Wh each). I'm thinking this is going to be a short-range truck, and probably short-lived batteries from working so hard. I do not have any BMS installed, but on such a small pack with good access it is easy to be my own BMS As long as you don't get busy with something else and forget. I know of a guy around here who destroyed an entire set of rare and expensive Saft STM5- 180 NiCd batteries when he forgot he was charging them. I wouldn't even do an E-bike lithium battery without a BMS. But that's me, and I know how forgetful I can be! David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to evpost and etpost addresses will not reach me. To send a private message, please obtain
