From: muratlanne@gmail.com   
      
   "Bob La Londe"  wrote in message news:vsujvm$1octb$1@dont-email.me...   
      
   On 4/6/2025 10:06 AM, Jim Wilkins wrote:   
   > "Jim Wilkins"  wrote in message news:vstnuv$s7al$1@dont-email.me...   
   >   
   > For LiFePO4 the current limit is typically the Amp-hour rating or a small   
   > multiple of it, ...   
   > ---------------------------   
   > Which means that a 12V, 100Ah LiFePO4 could ideally power a 1.6 HP motor   
   > for an hour. 16 of them in the BMS maximum 4S4P configuration equals 25HP.   
   > I had such an engine in a Beetle, whose 0-60 time was 15 minutes while the   
   > tranny oil warmed up.   
   >   
   > That was a good excuse to avoid the Autobahn and instead wander through   
   > picturesque little villages on service calls. At the time the Autobahn was   
   > a squareish loop around the edges of Bavaria and cutting across diagonally   
   > was nearly as quick, plus a Jeep or Army truck wasn't much faster and I   
   > couldn't leave them parked outside a Gasthaus overnight.   
   >   
      
      
   From what I have found the only "economical" way to even make good use   
   of a mid voltage motor like the Hyper 9 is to buy used commercial EV   
   cells.  If I ran with something like a 48 volt forklift battery as Clare   
   Snyder suggest I could run multiple LiFePos in parallel, but for higher   
   voltages I'm stuck with used commercial Lithium Ion EV cells.  Well, new   
   cells/modules are available, but they price puts it back in new car range.   
      
   Bob La Londe   
   ------------------------------------   
      
   I think (risky) the reason for the limit to how many you can parallel is the   
   overheating (fire?) risk if the control of one BMS fails and it passes the   
   entire load current, IOW the design margin. Likewise the series limit is the   
   voltage rating of the MOSFETs if one BMS has to sustain the whole pack   
   charging voltage.   
      
   If that's correct you might at least need a fuse or DC-rated circuit breaker   
   for each set of 4 in parallel. The explanation I read wasn't written by/for   
   engineers.   
      
   The prototype EV batch I helped build had 300V Li-ion batteries and I was   
   the tech who had to diagnose (while hot) and fix their problems. Like my APC   
   UPS there was a high current jumper plug to pull out and open the battery   
   circuit to work on it. I am NOT qualified to give detailed design advice.   
      
   The special instruments I bought for high voltage and current are a 1KV   
   Megger to check insulation, a micro-Ohmmeter for cable and contact   
   resistance and a thermal imager to show hot spots. The micro-Ohmmeter found   
   a batch of Chinese cable apparently made from scrap instead of pure metal,   
   with much higher than expected resistance.   
      
   The alternative is passing 1 Amp through the Device Under Test and measuring   
   the voltage drop in milliVolts, which equals milliOhms.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)