October 12, 201114 yr There are various modules you could use to monitor each cell and give warning if a cell goes to low in use. Check out hobbyking for the cellog devices or similar, they are cheap and simply plug into the balance leads. With the nano batts it's probably best not to let the cells drop below 3.4v, they are effectively empty at this point and further discharge will cause damage.... --------------------------------- Posted using Tapatalk
October 12, 201114 yr Yep I use the CellLog device which is excellent and will even log voltages of individual cells during a ride. http://www.hobbyking.com/hobbycity/store/catalog/CL8S.jpg See more details here You can then use LogView to plot the results, see here Regards Jerry
October 12, 201114 yr Bear in mind though that the celllog draws 0.5A/h on it's own though, so it's not really suitable for monitoring on the bike permanently. Ok for the first few runs to get an idea of your range but you wouldn't want to keep it connected due to it's constant amp draw.
October 12, 201114 yr You mean it draws 500mA when the alarm port is active! Otherwise it draws <8mA --------------------------------- Posted using Tapatalk
October 12, 201114 yr Bear in mind though that the celllog draws 0.5A/h on it's own though, so it's not really suitable for monitoring on the bike permanently. amigafan2003, I can’t agree with your figures with reference to the CellLog 8S require to operate. The CellLog 8S I use draw about 20mA with the backlight display on and 14mA in sleep mode which is not a problem for monitoring the batteries when in use but I agree could be a problem if you store the batteries for any length of time. I think there are some modifications that can be made to reduce the stand by current drain of the CellLogs down to micro amps. But they certainly don’t draw anywhere near 0.5A/h. I think the 8S are a bit expensive if they are used just to monitor the cell level LVC, although there is a monitor only version, CellLog 8M with alarm available about half the price. HobbyKing R/C Hobby Store : Cell-Log 8M Cell Voltage Monitor 2-8S Lipo There are other cell monitoring meters with LVC alarm available for 6S cells like the BM-6 which are a bit lower in price than the CellLog 8M. HobbyKing R/C Hobby Store : BM-6 Cell Voltage Monitor 2-6S Lipo (New Version) Chris
October 12, 201114 yr Interesting. I note the BM-6 is no good if you use A123 cells as the low voltage limit only goes down to 3.0v whereas the A123 cells go down to 2.0. The Cell-Log monitor looks like it might be good to leave permantly attached to my two 6s1p packs, though that might be over kill. But then they ARE cheap. Regards Jerry
October 12, 201114 yr Author There are various modules you could use to monitor each cell and give warning if a cell goes to low in use. Check out hobbyking for the cellog devices or similar, they are cheap and simply plug into the balance leads. With the nano batts it's probably best not to let the cells drop below 3.4v, they are effectively empty at this point and further discharge will cause damage.... --------------------------------- Posted using Tapatalk Thanks for the info 3.4V seems like a high number if they are full capacity at 4.1V. I checked mine yesterday after about 5-6 miles and they were at 3.7V all roughly the same. Charging took 1.5hrs. Will look into a CellLog
October 12, 201114 yr Thanks for the info 3.4V seems like a high number if they are full capacity at 4.1V. I checked mine yesterday after about 5-6 miles and they were at 3.7V all roughly the same. Charging took 1.5hrs. Will look into a CellLog Lipos are just about empty at 3.7v. They fall off a cliff at about 3.6v, so you shouldn't dare to go below that as they will very quickly go below the 3.3v minimum. It looks like your range is therefore only 5-6miles, which seems rather low. You might try charging to 4.2v for a bit more range.
October 12, 201114 yr 4.1v is only at about 90% capacity so as D8veh said it would be worth charging up to 4.2v for that little bit more range.
October 12, 201114 yr If you you check the discharge curves on the RC group forums you'll see the Turnigy packs are good down to 3.2v the nanos around 3.4v Some of the cheap packs off eBay may well be finished at 3.6v bit the better ones from hobbyking can be taken down to 3.2 or even 3 as an absolute minimum. I know from first hand experience with the Turnigy packs there is plenty more capacity left at 3.7v Charging to 4.1v is a good idea and the cell is going to be just about as full as it will get around 95% or more. --------------------------------- Posted using Tapatalk
October 12, 201114 yr Nrg I have only used up capacity untill the resting voltage is around 3.73v Of which time I always think that the cells are pretty much used up. What additional capacity have you used when you get past 3.7? Obviously when discharging there is voltage say but nothing more than 3.6 per cell. I know lipoly can go to 3v per cell as an absolute minimum. Always weary of dropping them past the 3.7 resting
October 12, 201114 yr Hi Scott, 3.6/7v resting yes but under load I set my BM-6 to 3.2v as the minimum. Its not caused me an issue todate...and just when I try to find the curves I was referring to....I cant Edit: LVC is a moving target though and perhaps I push mine a little hard and maybe 3.4 would be more wise and cover more manufacturers. The Turnigys seem to be very good for the money and stay in balance well and as capacity on a bike is limited I like to get as much out of them as possible. Edited October 12, 201114 yr by NRG
October 12, 201114 yr They do seem to balance fine and I generally charge to 4.18 per cell and there all inline. Its just reading forums for definitive lowest levels of discharge of resting cells there's always a lot of conflicting info. I still try to not use all the capacity just to give the cells an easier time! Thinking of buying another pair of 6s to extend range to 30ish miles.
October 12, 201114 yr Interesting. I note the BM-6 is no good if you use A123 cells as the low voltage limit only goes down to 3.0v whereas the A123 cells go down to 2.0. Jerry the BM6 are Ok with A123 and other LiFePo4 cells like the Headway. They can be set down to 2V LVC alarm, at least the version 3.0 examples that I use work down to 2V although I set mine to an LVC of 2.75V which is around the point that the A123 cells take a dive in performance. The advantage of the CellLog 8 is it can display the value of all the cells simultaneously, where the BM6 can only display a single cell at any one time as it scans each individual cell of the battery. But I have found the BM6 more reliable compared to the CellLog 8S/M as I’ve had a couple with intermittent displays. Chris
October 13, 201114 yr Author I've just done 4 miles and tested the batteries and they are showing 3.9v. Better news, I've also just ordered the cellog 8m so looking forward to getting that. As an aside I've had a fair amount of interest in this bike and a couple of requests to build similar lightweight machines. I may be doing some more.
October 14, 201114 yr Sounds good. I did 9 miles on my pack and the cells went to 3.83v. Another 9 miles later and they only dropped to 3.73v. Look at some of the lipo discharge graphs - voltage drops fairly consistently for the first half of the capacity then it really levels out for the last half, so you barely see any voltage change. http://www.rctoys.com/images/products/extra-description-images/thunder-power-extreme-v2-lipo-discharge-chart.jpg You can see 3.8v is about 50% discharged. 3.6v so only 0.2v covers the next 30/40% of capacity 3.9v is only 30% discharged so I estimate your pack is good for approx 10 miles - sounds like you've got plenty of range in those batteries.
October 14, 201114 yr I want to just add a note of caution here mainly if you are thinking of building an ebike for a general user and encouraging them to use lipos as a power source. Whilst I am well aware that many of you are more than capable of charging and using Lipos safely, please be aware that these cells are not for your average Joe, non DIY ebike user. They can be pretty dangerous/present a fire hazard if not treated with respect. Maybe I am being over cautious but I felt a note of caution would not go amiss. Regards Jerry Edited October 14, 201114 yr by jerrysimon
October 14, 201114 yr That's a good point - I'd never build something that uses lipos for someone else. In fact, I wouldn't build a bike for someone else full stop - tell them to do the research themselves and build it themselves or tell them to buy an off the shelf bike. Having built things like PC's for friends and relatives it's not worth the hassle - they treat you like a 24/7 support line.
October 14, 201114 yr Certainly true. But it should not be discounted if you like tinkering about with various setups. Like I noted above I do miss some ease of use and portability with a pre-made battery and charger + BMS as it negates the need to worry about any of the hazards. But you are right its not for the faint hearted and you'll need a few basic electronic tools and building skills required. I was a complete novice to anything electrical untill i came onto this forum on Feb this year. 9 months later and I think I have virtually got my head round the basics and the terminology. I'm now trying to work out what each component in the controller now does and why... But I equally don't think people should be to scared of Lipo. Ok your using the cells in a very raw format with huge amps to play with but Kids play with RC gear and as long as your not rough with it, overcharge it, over discharge it or puncture it then most people wil lbe ok. Its jsut making sure all your connections are good and that you don't mistakenly do something silly. If in doubt do what I do and keep a large 9 litre water fire extinguisher near...
October 14, 201114 yr If in doubt do what I do and keep a large 9 litre water fire extinguisher near... Water is zero use for a lipo fire - you want 10kg of sand :-)
October 14, 201114 yr Water is zero use for a lipo fire - Does the trick ok if the pack is dropped into a quantity of water. The fish hate it though.
October 14, 201114 yr Again I'm not convinced about all the folkllore concerning lipos. I've heard of loads of people that let their lipos go down too far without catching fire when they charge them. Most chargers are current limited. which helps. I've also seen some explode when they were being charged on a charger without HVC. So, everybody is right to be cautious. I'm still convinced that the biggest risk is from short circuits. Each time you connect and disconnect them and remove them from your bike, there's a chance that the wires can get pulled or chafed, or, if they're not properly supported/protected when riding, the wires can wear through especially the thin balance wires. Once the bare metal touches, it's game over. I've heard of many (mainly in aeroplanes) that spontaneously caught fire, which I'm sure is because of shorts, especially after a few bumpy landings. To help prevent the possibility of a short circuit, I lay all the wires flat against each cell pack and tape them so that there isn't any direct tension on the solder joints and they can't rub against each other. Then I connect the cell packs together making sure that all the wires lay flat on the outside and then I tape them again. If you're going to put them in a pannier, it would be smart to give extra protection. Mine banged against a rack fixing screw, which wore through the pannier, the tape , the heatshrink and the pouch to expose the stuff inside the cell and I was lucky - no fire - just a compromised cell pack. I think I've learned from my near miss. Like my headmaster said to me once, "Clever people learn from other people's mistakes; average people learn from their own mistakes; thickos never learn: Let's hope that you're in the second category, because it's obvious you're not in the first otherwise you wouldn't be here!". So, all you clever people can learn from the mistakes of a not so clever person.
October 14, 201114 yr Ok now the public health warnings are out the way Getting back on topic this little monitor/alarm looks interesting. Cheap and small enought to be left perm on my packs. It seems support both Lipo and LiFe packs ? Lipo battery Voltage Indicator voltmeter monitor Alarm | eBay http://i.ebayimg.com/00/$%28KGrHqZ,!hoE2sHWPWCnBN701RKw-w~~0_12.JPG I am not sure if the display cycles through each cell voltage or displays the total pack voltage ? I have emailed the seller. Regards Jerry Edited October 14, 201114 yr by jerrysimon
October 14, 201114 yr Ah question answered after looking at this UK sellers listing. ON-BOARD Lipo BUZZER INDICATOR 1 to 6 cell METER UK | eBay Regards Jerry
October 14, 201114 yr I have a couple of those. They do what they say. The alarm's quite loud, but high pitched. In the end I decided that it was a bit complicated to keep connecting/disconnecting them for charging . Now I monitor overall battery voltage with a wattmeter, which works for me. I always balance charge my lipos and check the cell voltage before starting to charge, and everything is always normal. I try to not go below 37v o my 36v pack and 45v o my 44v packs. I theory it's possible to have a problem o one cell, but I think I'd notice something unusual on the meter like the time I forgot to charge half the pack.
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