Holy crap! Mattio79 - no one is going to invest in an unproven device. You'll need to post some of your prior work, a CAD model of the battery pack, or at least a napkin sketch - it just sounds like you have a good amount of spare time and an internet connection at this point. If you want to get funded, do attempt to make a sketch and try kickstarter.com!
You are dabbling in so many fields - composite manufacturing to boot! Have you done any fiberglass or carbon fiber lay up in the past? at the bare minimum, we'd like to see the type of encasement you'd make as this is one of the main issues with current lifepo4 battery packs in this field.
I wasn't able to read through your swarm of posts but there are a few issues that I think you should expand upon:
->How do you plan to assemble the cells in the 4s-4p or 4s-3p configuration? The best method is to spot weld them, but you either need a professional spot welder or make your own capacitive discharge welder which will still cost you $$. Soldering them is possible but not recommended due to the method of prolonged heat transfer and reliability.
->I gathered that you wanted to wrap 26650 cells for this pack in carbon fiber? How are you electrically isolating them as carbon fiber will conduct? If any salt water finds a way in there (and it will!) what do you think will happen...
->Who is going to create the low voltage protection logic circuit with isolation switch - are you using an off the shelf model or fabricating it yourself? This will need to be a solid component as a false positive will put you dead in the water - we will need to know confidently that you have tested this in ALL conditions commonly ridden!
->I see you have mentioned the low voltage alarm - have you ever used one of these? I have and they are cheaply fabricated 90% of the time and I've gotten plenty of false positives as it measures each cells voltage and if any cell is bad is too low it throws a red light and buzzes - however after attaching my fluke to the balance cable the indicated cell was fine, and my balance charger agreed! I've attempted to use them in high powered light assemblies that run off lipo cells to warn the user but the false positives and nature of light use (either bike riding or pedestrian use) necessitated reliability over annoyance. They are also loud as
and equally annoying (they are meant to be though) but you can't exactly do anything about a low battery out on the water - you need a voltage indicator with some type of easily identifiable universal scale, may it be an RGB led that uses 3 PWM circuits to change color or a set of 3 or 4 led's that indicates power level like a battery bar meter on your phone. You mentioned something like this or someone else did in one of your posts.
->I think you and jMike may be onto something with the prismatic cells however the ~9 inch length is not desirable and getting custom cells made requires extremely large volumes to be ordered if you want them ESR matched - which is typically a good thing with battery packs. I interviewed with a company using them in deep see submersibles (10,000ft) and they were working on a robust backup battery for Apache chopper's navigation system. The deep sea unit was encased in a polyurethane block while the Apache unit had an aluminum case around said block for puncture resistance.
We may be utilizing them [prismatic cells] in our school's formula SAE electric race car this year as they have excellent power density if you can deal with the length and width.
Reply if you want, but if you think of something else to say within a day or less after posting the reply - please use the EDIT button - it's there for a reason!
After seeing the pictures from
superjetjim - it seems that there is a great amount of improvement that can be done on these batteries, just need some solid ideas...
