• Content count

  • Joined

  • Last visited

Community Reputation

54 Excellent

About MJSfoto1956

  • Rank
    Advanced Member

Recent Profile Visitors

853 profile views

MJSfoto1956's Activity

  1. MJSfoto1956 added a post in a topic eZuma   

    So if I ditch the BabyBloc balancers (one per parallel module) and replace them with a traditional BMS, what might that look like?
    In particular, what might it look like if I max out the capability of a PowerVelocity controller which is limited to 100V? 
    Well, this is what it would look like. Basically swapping one form of complexity for another. No free lunch folks.
    I might add that 84V 150A relays are not cheap...

    • 0
  2. MJSfoto1956 added a post in a topic eZuma   

    And lest you think this is the end of the evaluation, here is a "spreadsheet" comparing how upping the battery bank Voltage reduces overall "stress", thereby lengthening the life of the battery pack. Of course, higher voltages come with their own issues. 
    The plot thickens...

    • 1
  3. MJSfoto1956 added a post in a topic eZuma   

    Lesson 1: the relationship of battery pack size to electric motor size
    For those of you new to how to calculate lithium battery pack sizing vs. electric motor sizing here is what I am using for my build.
    Basically, I have decided on an 8000W hub motor with the goal of achieving 100kph top speed on level ground. Additionally since this is a scooter, I am somewhat restricted to a 20s16p 18650 battery pack which just happens to fit into my existing battery tray (i.e. a lithium battery pack consisting of 20 serialized sets of 16 cells in parallel, total 320 cells). But how did I come to this setup? For the best results, one must match one's battery pack to the motor. So for starters, we need to convert the 8000W to Amps. Since I will be using 72V (i.e. 20 series @ 3.6V = 72V) the math is easy:
    8000W / 72V = 111AFrom the equation above, I conclude that in order to make best use of this 8kW motor, my battery pack must be able to supply 111 Amps to it on demand. Since I am using a 20s16p pack one of the most-powerful, most-reliable battery cells I can pack into that space is a Panasonic 18650B Li-ion battery which delivers 3400mAh each. That leads to the next calculation:
    16p @ 3400mAh = 54.4AhOk, my pack can deliver 54.4 Amp hours -- so far so good. But how do I "convert" Amp hours into "Amps"? Well, we need to know the max discharge rate of the cells. In general pretty much any lithium cell these days can discharge @ 1C. So at a constant rate an "ordinary" 3400mAh 18650 20s16p battery pack could theoretically deliver:
    54.4Ah @ 1C = 54.4AWhich is only half of what the motor is capable of. Put another way, if I only use "ordinary" 3400mAh cells, I might as well limit myself to just a 4000W motor. So I either need to double my battery pack or use cells that can discharge @ 2c. It turns out that Panasonic 18650B Li-ion batteries can indeed discharge @ 2c. Thus we have:
    54.4Ah @ 2C = 108.8AWhich is darn close to what the motor is asking for. As a side note: the battery life would be much better @ 1c than 2c due to heat and stress, but this being phase 1 the numbers add up nicely and I am going with it. Eventually however, I will likely attempt to double the battery pack size in the future.
    Lesson over. Any questions?
    • 1
  4. MJSfoto1956 added a post in a topic eZuma   

    That would be a wine-bottle bush! :P
    • 0
  5. MJSfoto1956 added a post in a topic eZuma   

    This is what she looks like now:

    • 1
  6. MJSfoto1956 added a post in a topic eZuma   

    It took a while for the parts to arrive from China, but I finally have the rear-end parts/mods sorted out. The list of mods includes the following:
    Installed rear fairingRemoved rear fender with Dremel but kept original license plate mounts and reflectorsInstalled one-arm tire hugger/fenderAdjustable aluminum swing-arm (this will be key to allow me to install a much taller tire on a 13" rim)Adjustable progressive clevis-end shocksUpgraded leaking turn signals with a proper pair from Baja Designs 

    Next up is to install an upgraded programmable controller...
    • 0
  7. MJSfoto1956 added a post in a topic Had a bad crash yesterday   

    yikes. hope all is well.
    • 1
  8. MJSfoto1956 added a post in a topic I gotta have one of these   

    Dubai Police, Amputee Division.
    • 2
  9. MJSfoto1956 added a post in a topic What are u listening to tonight?   

    The Tubes rock. Don't touch me there!
    • 0
  10. MJSfoto1956 added a post in a topic What are u listening to tonight?   

    I figure Piston would appreciate this: 
    • 1
  11. MJSfoto1956 added a post in a topic eZuma   

    Pondering an alternate battery scheme using 200 20700 Li-ion cells instead of 320 18650 cells as shown previously. This layout would require mods to my frame, but would be "pluggable" (assuming I built a 2nd one).

    • 0
  12. MJSfoto1956 added a post in a topic What are u listening to tonight?   

    that's some pretty serious guitar work.
    • 0
  13. MJSfoto1956 added a post in a topic eZuma   

    I don't need to do all four holes -- just the one that I will actually be using. 
    What kind of grease should I use? And how do I keep the grease "in there"?
    • 0
  14. MJSfoto1956 added a post in a topic What are you drinking tonight?   

    Well, that's kind of what happened -- we had 36 between us! :P
    P.S. shucking is a real art. Thankfully my friend is an expert.
    • 0
  15. MJSfoto1956 added a post in a topic eZuma   

    I need some advice. My Chinese CNC swingarm has provision to attach the rear shocks at various points as shown in the photo below. So far so good. However, the ID of the mounting holes are an odd-to-me 8.9mm (0.035"). And therein lies the problem. My shock's clevis mount uses M8 threads (8mm). That leaves 0.9mm for the shock to rattle around, which over time would destroy the swingarm mounting point. I ordered some 10mm "shoulder" bolts which are grade 12.9 and are designed just for this kind of thing. Should I ream out the 8.9mm holes to 10mm? Should I turn the 10mm shoulder bolt down to 8.9mm? Or should I try something else? 

    • 0