Tire recommendations
04-21-2011, 11:28 AM
#31
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Very nice. Looks like you've put a lot of effort into the BMS/pack already. How about going with 2 parallel packs instead of three for starts, and then add the third string later? Save several grand initially and still have a lot of performance.
I've heard good things about the Headway cells, don't they make a 16AH cylindrical also? A123 is the king, but I haven't heard of anyone using theirs pouch cells yet. I like the pouch cells for packaging. With Headway cylindirclas there's just too much wasted space. I can do a much better job fitting pouch cells into my boxes.
Hmmm, 2 parallel strings would put me at 40ah, more than I have now. What are they 3.2v nominal? Let's see, 3.2 vpc times 96 cells times 40 AH gives me a 12k pack. That still put's me right on the edge of what I'd need for commuting. Fine for racing though. 3 strings give me range but the $$....
I have my motor voltage limit set at 240, but my pack can't deliver any where near that. But the 1000 amp limit of my controller is within reach. Hopefully I'll have my expanded pack going soon and then we'll see how bad the sag is.
Does your BMS work with a charger to signal end of charge? I have a Manzanita Micro PFC-30 that has some ability to respond to commands. They do use a proprietary but open protocol to communicate. If you were to commercialize your BMS it would open you up to a fairly large market. It would be a great feature if your BMS could let all the subs finish charge and then tell the charger to shut down. Plug and play.
Keep me posted on your progress.
Dave Cover
www.evalbum.com/2149
I've heard good things about the Headway cells, don't they make a 16AH cylindrical also? A123 is the king, but I haven't heard of anyone using theirs pouch cells yet. I like the pouch cells for packaging. With Headway cylindirclas there's just too much wasted space. I can do a much better job fitting pouch cells into my boxes.
Hmmm, 2 parallel strings would put me at 40ah, more than I have now. What are they 3.2v nominal? Let's see, 3.2 vpc times 96 cells times 40 AH gives me a 12k pack. That still put's me right on the edge of what I'd need for commuting. Fine for racing though. 3 strings give me range but the $$....
I have my motor voltage limit set at 240, but my pack can't deliver any where near that. But the 1000 amp limit of my controller is within reach. Hopefully I'll have my expanded pack going soon and then we'll see how bad the sag is.
Does your BMS work with a charger to signal end of charge? I have a Manzanita Micro PFC-30 that has some ability to respond to commands. They do use a proprietary but open protocol to communicate. If you were to commercialize your BMS it would open you up to a fairly large market. It would be a great feature if your BMS could let all the subs finish charge and then tell the charger to shut down. Plug and play.
Keep me posted on your progress.
Dave Cover
www.evalbum.com/2149
The problem with adding a string later is I want all the cells in parallel then series the groups, not that difficult with headways as I can design the buss bars with extra room to install the cells, pouches I have no idea how I'm going to assemble it anyways but I don't see an easy way to add some in parallel later.
My charger is out of the norm, instead of having a 340v @ xAmp charger I'm going with 94-96 individual 3.5V (adjustable) dc/dc converters, this lets me feed 48v in and the whole pack gets charged at upto 25A (if I had enough current at 48v that is) The main benifit is virtually eliminating the posibility of overcharging a cell. And the pack balances every charge, I no longer need a signal to turn off the charger, but it will get turned off when the current drops to a certain level. I no longer need any kind of shunt bms to balance the cells and if I have enough current at 48V I can charge pretty quick. If I ever install solar panels I'll have a 48v battery bank that would let me dump current straight into the 48v line and charge the pack quickly. In the mean time I'm using a 3kw PFC power supply (1.5kw if connected to 120v). The BMS is mainly a monitoring system it will let me read each cells voltage with an arduino and take action if I want. It'll also measure discharge current, charging current, battery box temp, eventually it could control heaters in each battery box individually, sound a warning if any box gets too hot, control fans for cooling, monitor heater coolant temp, controller coolant temp, motor temp etc.
The first step is the charging board shown above, then I will design the rest of the system, but that board will charge/balance alone.
There are a few people using the A123 pouches, with the most notable being "Crodriver" and his electric BMW. He switched from the 8ah headways to A123 and said the A123's are 10 times better for racing.
http://www.youtube.com/watch?v=WX-_a...er_profilepage
He's got a bunch of video's and stuff but I grabbed that one because in the last 10 or 15 seconds he's racing an awd 911.
He does love to burn rubber though, and would probably be drastically faster if he would control the launches.
But hey, I'd probably have fun burning rubber also if I had 550whp and 650ft-lbs of torque in a 2310lb car!
04-21-2011, 12:13 PM
#32
Track Day
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I've seen Crodriver before, lot's of fun watching the progress. I wonder what his budget is like?
I still keep heading back to 100ah prismatics like those offered by Manzanita Micro. 80 cells come in just over $10k, add another $2500 from BMS and monitoring. That give me the range I need and should also provide good power. The cells are rated for 1200 amps burst, 400 amps continuous. They'll sag, but not like my NiCads. And I can fit them in my car without too much trouble. It keeps going back to the $s.
Dave Cover
I still keep heading back to 100ah prismatics like those offered by Manzanita Micro. 80 cells come in just over $10k, add another $2500 from BMS and monitoring. That give me the range I need and should also provide good power. The cells are rated for 1200 amps burst, 400 amps continuous. They'll sag, but not like my NiCads. And I can fit them in my car without too much trouble. It keeps going back to the $s.
Dave Cover
