----- Original Message ----- From: "Roger Stockton" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Wednesday, September 25, 2002 10:41 AM Subject: RE: Conversion Concept Musings
> Jon "Sheer" Pullen wrote: > > > > A stopwatch and a clear section of flat road? ;^> > > > > Tests done tonight indicate you are correct.. after driving > > the car 90 miles today, I did a 0-60 test and got about 13.5s > > with just me in the car. There may be some error in that > > number, as the road was not exactly flat [maybe 1% uphill > > grade], but it's probably close enough to validate your point. > > > > I genuinely thought she was faster. Ah well.. > > Wait a minute; unless what you wrote is a typo, the only thing your test > validated that I wrote is that a stopwatch and clear section of road is > all you need to test your 0-60 time. ;^> Sorry - no, I'm saying that you were correct in your earlier statement that I do not meet the speed requirement when fully loaded and at the end of a charge - it's likely that with four passengers, that number would be somewhere around 17 secondxs. I was apologizing for having overestimated my car's acceleration at low SoC. > > > But they do warm up somewhat on discharge, and if they > > > start off in a 90-100F+ ambient, you could very well > > > require some cooling before you 90-100F+ could > > > safely plug them in to charge immediately upon reaching your > > > destination. > > > > I still don't follow you - if you're exceeding the temp > > limits for the pack while driving, that's a problem while > > driving, not while charging. > > OK, let me try again: the car is sitting in a 90-100F+ ambient, you get > in and make some sort of trip, drawing sufficient current to heat the > batteries further. When you park at your destination and immediately > plug in, the batteries are still too hot to permit charging unless you > have a thermal management system working to keep them at an appropriate > temperature the whole time. > > Remember, the manual states the max temperature for discharging > (driving) as 60C (140F), but the limit for charging is specified as just > 35C (95F), so quite a bit of heating can occur while driving before it > becomes a discharge problem, but it doesn't take much to cause a charge > problem. (Even in Vancouver summertime temperatures can get warm enough > that a pack of Evercels could exceed 95F at the end of a drive.) [looks up with some suprise] Um, can you send me a copy of the spec sheet where you found this number? I'm confused, because I have temp correction curves for charging that go all the way to 130F, which would seem to imply that the batteries can be charged all the way to 130. I'm sure that you're correct, at least I'm sure that evercel has at some point stated that you can't charge them when they are warmer than 95F - but I'm going to confess that I've done exactly that many times, and nothing seems to have gone *pop* yet. > In any event, it is not so much of a concern to me whether the heating > is a driving or charging issue; either substantiates the need for a > proper temperature management system for these batteries if an EV using > them is to be widely usable and satisfy the plug-and-play requirement of > this exercise. I'm not convinced that they need a thermal management system. As usual, like the stubborn person I am, I want to test. However, testing is going to require waiting until summer and then relocating my car to somewhere that is about 100 degrees ambient, so you're going to have to wait a little while for the results of same. > And note that NiCd, NiMH, PbA also all need thermal management of some > sort too; I am not singling out NiZn here. If anything, I am singling > out NaNiCl as an example of a battery that has simpler thermal > management issues (heating only), and includes the solution as part of > the package that you buy. I understand this - however one of the beauties of NiZn that has made me think of it as a serious contender in the battery world is the lack of a need for thermal management in many parts of the country - if it turns out that my assumptions are wrong, then I need to reconsider this. However, I'm not sure that they are. I'll ask Elio for his opinion on the subject. > > The batteries cool off pretty > > quickly once you take a load off them - 40 lbs just isnt that > > much thermal mass - so I really don't see this as a issue. > > Ah, but you don't have a single 40lb battery with air circulating all > around it, do you? You have a bunch of them packed more or less tightly > together in some sort of box, forming ~440lb blocks of thermal mass > (assuming 22 model 100s evenly divided between 2 boxes). I'm just telling you what I've observed. The batteries cool off quickly (they're at ambient in less than 2h) when the load is removed. > With respect to plug-and-play, it doesn't help that they cool 'quickly' > if it means that when you get to your destination you can't just plug > in, but have to leave the car sit for some amount of time, then return > to confirm that the temperature has dropped acceptably so it is safe to > charge. Well, obviously, one of the goals of the BMS (which as you'll recall I included in the price tag earlier) would be to turn on the charger when the batteries had cooled off below a certain threshhold. Given that my BMS is rather microcontroller based, adding this feature would be fairly trivial. > > Yes. The suspension upgrade also increased my aero losses > > slightly. I'm hoping that adding a belly pan will get me back > > some of the loss, but I haven't gotten that far yet. > > Can you explain what your suspension mods were, and how they increased > aero losses? Rolling losses I would expect, but impacting on aero > losses is a bit of a surprise. Let's just say that I had done the equivilant of lowering my car about a inch and a half, and the suspension mods undid this. [They included new springs] > > Those are the numbers I was givin by evercel. Real world > > testing has not bourne them out > > Does that mean you achieve more than the 89Ah value, or that you have > achieved more than the 50 cycles without the capacity dropping to 83Ah? > Both? Neither? Unfortunately, I haven't been tracking capacity every cycle, so I'm not positive if I've experienced the capacity drop or not. The batteries have definately 'broken in' insofar as they no longer get nearly as hot.. [actually, in 80 degree ambient weather I drove the car at 80 mph from my house to EV parts (about 15 miles), to discover that the batteries had gained about 6 degrees F. As they age, they're getting dramatically less hot under load] One of the problems is that I don't know if 'half-cycles' count. Just by looking at my milage, you can tell I haven't gotten 50 full cycles in.. I've done a lot of little cycles.. Based on the kwh counter on my inverter, I surmise I'm getting about 98 AH out of my evercels right now.
