Thanks for your detailed response, David. I do have the tech manual you referred to. I understand the single-battery charging regime.
My concern is equalization. The person I got these batteries from fried individual batteries -- I mean internally melted! -- by charging them to spec in a 144V string! So needless to say, I want to take excellent care of what may end up being lifetime batteries. (This vehicle will get only about 3,000 km/year.) > Unlike some of Saft's other NiCds, I'm pretty sure these were designed for > road-going electric vehicles... They were also used in E-buses back in the > 1990s. Some of > the used ones on the market a few years ago came from those buses, but be > careful, those buses worked their batteries hard. These apparently came from busses, but were renewed to SAFT specifications before distribution. > They're really easy to charge, but the profile is very different from other > batteries, so you need a flexible smart charger. Maybe the Brusa chargers > can still do it... I've looked into Brusa chargers, and they no longer support these batteries with their new chargers. > Othewise you may have to make your own charge controller. But as I said, > the profile isn't tough to implement. That's why I'm interested in the open-source Electric Motor Werks chargers. But they strongly suggested a BMS to avoid equalization issues. > You don't need individual cell or battery regulators. NiCd batteries love > to be overcharged and are happy when they're gassing freely as long as they > don't overheat. "As long as they don't overheat" seems to be the rub. My source showed me batteries that contained a molten mess inside, after charging to spec in a 144V string. That made me think individual cell voltage and temp sensing was necessary. But perhaps I'm being paranoid, and he simply misused them somehow. (The ones I'm getting were NOT part of that experiment!) > There are two tricks... that time plays a role, so the charger has to keep > track of it. This is why I'm leaning toward the open-source Electric Motor Werks chargers. They are open-source, and use a commonly-available and easily-programmed Arduino control processor. Does anyone have experience with these chargers? 12 kW for ~$1,000 (kit) sounds darned good! > ... the threshold voltage for a change to phase 1 to phase 2 > has to be adjusted for battery temperature, so you need a temp compensating > charger... The EMW charger has a TTL-level turn-off, but I'm not sure if it has a user-accessible temp-comp coefficient. Again, I'd LOVE to talk to someone who has actual Electric Motor Werks charger experience! > There should be a pocket in the side of the case of each module (battery) > somewhere for the temperature sensor. Thanks for that "heads up!" I didn't even realize that the batteries come in "left" and "right" versions, so you can design bus-bars appropriately. I'm planning to use flattened 3/4" schedule "L" copper pipe for bussing, which has a cross-section area as big as 2/0 copper wire. This way, I can alternate left and right versions, and minimize the bus-bar length as well as minimizing the amount of welding cable (at $5/foot!) that I need to buy. I was going to implement a "single wire" BMS, but all I've seen are specialized for lithium voltages and temperature needs. > ... If your pack is split, you might want to use two > sensors and average them. I'm still nervous of anything but "per-battery" monitoring. There seem to be series "one-wire" BMSs available, but they all seem to be hard-wired for lithium, with implied assumptions (~3V per cell, etc.) > Be sure to follow the manual's procedure for watering! I have the components for the original system's automatic watering system. I plan to implement this as two strings of seven batteries, and one of ten, which will optimize my available "left-right" combination of cells while keeping each watering string at or under ten batteries, as stated in the manual. > NEVER use any watering equipment that you've ever used for lead acid > batteries. Traces of acid will destroy your NiCd battery. Roger that! Don't need to destroy this investment! > ... these are very sturdy batteries and will > serve you well for many years if you take good care of them and charge them > properly. That is my take on it, and their availability is the ENTIRE reason I decided to proceed with this project at this time. I didn't want to do yet another lead-acid project. But I'm a bit paranoid about these cells, since the previous owner fried a few of them by following SAFT's recommended charging regime in a 144V series string. > ... You're lucky to have found > them, IMO. I hear you! And I want to eliminate "luck" as a factor in their longevity! Thanks in advance for any advice offered, especially from those familiar with the Electric Motor Werks chargers. :::: I will probably be ridiculed up one side of Manhattan and down the other for writing this, but I say that the modern large city is a dinosaur, economically and environmentally, and people are slowly beginning to realize it. The extended village is the wave of the future. I look at those energy-sucking skyscrapers and I see very tall tombstones. -- Gene Logsdon :::: Jan Steinman, EcoReality Co-op :::: _______________________________________________ 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)
