This will be a fun one. All kinds of folks "in the know", or self-proclaimed experts are going to start to chime in about lithium battery chemistries and how you must have a complex and expensive BMS system, and how LiFePO4's are so much more stable than lithium-ion, etc., etc.
What's funny about this is that these people who sound off either have never done a conversion or have bought into all the crap BMS system manufacturers have put out there to sell their product that they were too scared to try a pack with lithium-ion batteries and no BMS. My point is if you never tried it, how do you know it doesn't work?
Here's what I do know as one that has tried it and to a level that most have not. Here are links to two videos. The first is a walk-around of a speed boat conversion where I bought a brand new 2016 Bayliner 175 Bowrider, pulled a brand new 3.0L Mercruiser motor and replaced it with HPEVS AC34X2, 147 HP Dual AC Induction motor. It has a top speed of 53 MPH. It cruises nicely at 20 MPH. The battery pack consists of 10, 54v, 100 amp cont., 150 amp peak, Smart Car modules made by Tesla. The chemistry is lithium-ion because of it's power density. The modules are wired 5 in parallel and 2 in series. I do NOT use a BMS. I simply bottom balance the modules upon the initial install.
Here is my secret to managing the packs. First, regarding overcharging, I take a simple approach. I do NOT fast charge. I use a 110v charger with a max discharge of 12a. Yes, it can take up to a full day to charge, but I don't care. The intent was to go out on the water for a couple of hours, then charge overnight in the slip. The charger has been programed to shut off when pack is fully charged. Simple. With respect to over-discharging, simply don't do it. There are a number of SOC meters that will tell you exactly where your at with current draw. I know exactly where to be. The modules are 100 amp continuous rated, I have 5 in parallel, I do not exceed 500 amp continual pack draw. I usually draw between 350 and 400. Even after long continuous runs, the batteries never get warm to the touch. I ran this boat an average of twice a week last year and have experienced less than a 2% loss. The Model S modules have a 500 amp continuous rating and a 750 amp peak.
I originally convinced myself, as many have, that I needed a BMS system and had no problem paying for one. When I went to get pricing on the kit, which really wasn't a big issue at the time, the tech folks told me that a BMS system was simply more trouble than it was worth. This advice was given to me by arguably one of the best EV conversion shops in the world.
My point is simple. Don't let anyone talk you out of something you can see makes could performance and point of purchase sense because they bought into the chicken little syndrome.
Here are the links:
https://www.youtube.com/watch?v=my0TX3INjSk&t=33s
https://www.youtube.com/watch?v=BRqcp4Tzzrg
Scott
Posted by: smasterson2@gmail.com
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