Hiya Ronrule,
I'd like to make some comments on your last post and I'm not trying to be argumentative, I'm just trying to pass along some tried and true information from people who have a lot more experience and knowledge than I have. I'd also like to mention that I'm not completely inexperienced either. I am a graduate from a 2 year electronics program at a local community college and I have had a business in the past dealing with a small electric vehicle called the Electric Ox, a multi-purpose electric tractor. All that being said, I am far from an EV expert but I have been paying attention to the industry for about 15 years now. My focus lately has been with an online TV show called EVTV. They have been converting cars to EV's since 2008 and have been documenting their successes and failures online in a weekly webcast. I also stay in touch somewhat with what is going on at EV West of whom I consider one of the leadig edge EV conversion shops ( one of the partners in EV West worked at EVTV for a while ). You have some excellent advice here but I would like to add some food for thought to those who are thinking of EV conversions.
Ok, here we go:
1) About kits. There are a number of companies who have put together "kits" and I agree they are base on components that they have figured out what works together well out of the countless number of products that are on the market today. The reason they call the kits is that they have been through the ringer trying different component packages and have done the "homework" of trial and error for us. They are a good place to start if you are totally new to the business of EV conversion. If you are knowledgeable and experienced you can pick and choose from the array of components out there and put together your own kit. It's like hot rodding and ICE vehicle. Those with experience with parts and products knowledge probably pick and choose the components that they like for their own reasons for their own car. Look at track records of these companies to see how legit they are and use your own judgement.
2) I have never converted a car or have had to buy parts from an EV conversion company but I do know that some of them do stock components ( I have actually bought some electrical parts for my tractor, but not many). I also know of one business that rewrites manuals from the original manufacturers so you can actually use their products when you buy them from them. They have gone through the process of "figuring out" how the products work for themselves and have put their knowledge down on paper for the rest of us ( and they were in the publishing business for years so they are good at it) . Getting what you order is a nightmare according to some stories that I have heard in the EV conversion e-business. It's a shame and very discouraging for anybody starting out. This is where you have to do your due diligence and scope out your dealer. Buyer beware!
3 & 4) BMS's...A very hot topic amongst EVers indeed. What if I told you that there are numerous cars out there driving around without BMS's on LiFePO4 batteries? Would you believe it? Do not use lithium based batteries until you learn about them! But who do you trust for info about them? Why not ones who use them daily and document their challenges with them and study them like they have to pass a university exam about them? Those are the people who I would trust. A BMS system adds a lot of complexity and cost to a system and they have been known to cause fires in battery packs. If you want to avoid problems with LiFePO4's, learn their limits and avoid them. It's that simple. Don't overcharge, don't under discharge and don't try to charge them below freezing. Also bottom balance your cells individually to the same level before making them into a pack. I could go into more detail about batteries, but once again, I am far from an expert on the matter. It may sound like I am typing myself smart here...no...I am just a student observer in this matter and this is what I see is working in real life situations.
You even mention in #4 a good reason not to use a BMS when you talk about expense and connection problems yourself. Think about it, your are putting an inexpensive little device ( the BMS circuit ) between two very expensive and powerful devices ( your battery cells ) plus all the spaghetti wiring that is associated with allowing them to all talk to the main BMS board. Sounds like a great place for failure to me.
5) Yes, LiFePO4 batteries are the enabler for the DIY EV converter. They are of the safest of the litium chemistry batteries out there and give you way better range and performance than lead acid batteries. They are expensive, that is a given, but the expense is worth it. The battery pack in my electric tractor was great at first and I was very careful with charging, checking their specific gravity and watering them. But even with this care they predictably lost their runtime and performance in a matter of a few years. If you give the same care, not watering of course, to a LiFePO4 pack and it will reward you with many years of service.
6) When you're done with your own successful EV conversion you will have a pretty good working knowledge of motors and electrical systems. You will be your own mechanic and will be able to fix most of your own problems, ( perhaps with a little help from your parts dealer or the internet, but hey, you wouldn't have gotten yourself into an EV conversion if your weren't a DIYer, right? ). I agree, I wouldn't go into this blindly unless you have a lot of patience and/or money to spend on blown parts. It's a rewarding challenge if you're up for it.
7) Doing bench tests is a good idea. You're right it's a lot easier to solve a problem before you bury your motor under the hood and run wires all through the car.
8) True, heat and water are the enemy of electronics. Water ( or liquid cooling of some sort ) can be a friend to take care of the heat though. More modern motors have liquid cooling for the motor and controller in the case of AC or PMAC ( Permanent Magnet AC ) motors. Look for those if you think you are going to tax your motors heavily and put a good heat exchanger/radiator cooling system in to keep things cool.
9) Yeah, pack voltage conversion to run 12V accessories is a needed PITA in EV conversions. The auto industry unfortunately has been built around 12V products and that is what we have to deal with. Whether you use a DC-DC conveter, a separate 12V battery or a alternator connected to the motor, you're gonna need 12V. Hey, there's a market for some up and coming electronic entrepreneur...design car components that run on various pack voltages instead of 12V so you don't have to use a converter! ( Yeah, I know, sounds outrageous...just me thinking out loud, lol )
So...there's my 2¢ for what its worth.
Ronrule, seriously though, you should examine the BMS thing. Either confirm or prove me wrong. You could save yourself a lot of money, time and confusion if you don't use a BMS. I'm not saying, don't monitor your cells, just look into how to do it without a BMS. It has and is being done safely in many cars and boats every day for years now.
Good luck with your build Ronrule and keep us informed of your progress!
Cheers,
John
