Building battery packs - Dewalt lion (a123), NiMH RC packs, PrivateNrg etc..

Thanks! This matches a problem I've been mulling over, how to handle keeping the battery packs equalized in a plug-in lite. There is a 24 pair, connector that should work just fine for what I want to do.

Battery engineering is not a trivial problem. I've only started working with batteries, mostly to try and refurbish weak modules:

I've also seen photos of what happens when batteries are overcharged and it isn't a pretty sight. The biggest problem is the flat charging and discharge profile means there is no voltage clue to the state of charge.

Bob Wilson

 

Atari,
From the link provided:
"Early in 2004, when I had finished assembling the NiMH array, a friend & I put the whole array in the spare-tire wheel-well and you can see for yourself, 18Ah & more can fit down there."

In late 2005, that same friend helped me install the same 18Ah setup in my Prius. I also built a low cost grid charging system. For very short trips, the setup had some merit. But for my (at the time) 25 mile commute, I found no real difference in FE. I removed everything in early 2006 and sold off the components. For me, the $3000 cost would have never paid itself back.

Also note from that link:
"I know a lot of people can get this kind of mileage without extra batteries but, I don't have the patience to go the slow speeds required to do that ... Yet!"

I currently have a 135 mile round trip commute. I drive 60mph for 100 of those miles and 25-45 for the other 35 miles. My MFD currently shows 68 MPG at 400 miles, which is better than the 64.5 mpg shown in the link provided. Just food for thought.

 

I've looked at this. Its not very cost effective right now. A123 and some of their suppliers do custom battery packs. The EV Nova drag car had a custom pack which is probably one we could use or need. I do not know how much it cost though.

 

the price sounds about right. i just figured out that prius oem battery is 6.5ah, and this one guy running his own set up in that one link, is using something like 18ah with limh. you could do 8 packs to get you up to 19.2ah at 288v if you wanted to. you would still need chargers but, it wouldnt weigh very much, about 20lbs.

i wonder if anyone will just use the dewalt packs as is, make some sort of config, so that you can have them all hooked up to be used and charged. even rig up the dewalt 1 hour chargers. it would be golden. just rig up your two custom two adapters, instead of actually having to mess with the battery packs. a battery pack goes bad, just replace it. use dewalts battery packs and chargers.

i think there are two problems though. i believe i read that there is some sort of low voltage cut off electronic device in the battery pack and there is also a fuse made into dewalts tabs that connect all the batteries together. both of these will hinder using it as only a battery pack (more electronics and saftey precautions to cause a problem).

 

In general putting the batteries in is the easy part. Unfortunately, just adding more battery capacity will do very little for MPGs. As an example, the US gov. ran some Gen I Prius to 160k miles. At that point they found the battery capacity was down 50%, but the mileage was unchanged. Under most driving conditions you are not even remotely limited by battery capacity. Adding a grid charger is a crucial first step to better performance, but still in of itself will not result in greatly improved MPGs. In order to really get good numbers from a PHEV conversion you have to get the battery controller to acknowledge that extra charge is available, and the HV controller to use that extra charge. Neither of these is trivial, and really to pull it off requires a custom micro-controller.

In my opinion it makes no sense to go fancy with your batteries and skimp on your control, as the biggest bang for the buck by far is your control algorithm. You are probably much better off with a small lead acid pack with a good controller than a nice Li-ion pack and a switch on the dash.

From the numbers I have seen, a 30 mile PHEV take ~8 kWh of battery. The numbers I've seen for the A123 18650 cells was 3.2V, 1.1Ah. For a 30 miles pack you would need ~2272 cells, at a cost of ~$25,000 at $11/cell. Thats an unfairly low cost, as you will need some sort of sophisticated battery management system to monitor, balance, and protect each and every cell! Incidentally, the Tesla Roadster uses over 6800 of these same cells.

If you are trying to do this on the cheap, I honestly don't think you can do much better than the cal-cars open source recipe. You should be able to get ~10 miles EV, or ~15-20 miles at 100mpg+ for $3-6k. In the long run you might be better off with the Nilar NimH version they are working on, as the batteries should last a lot longer although they cost more up front. This is really about as simple as you can get. There is a big contractor (basically a switch) that connects and disconnects the secondary battery to the primary. There is a controller that monitors all the traffic on the CAN bus between the battery controller and the HV controller and decides when to close the switch to optimize SOC to use as much electric drive as possible. Theres a big lead battery pack, a battery box, some low voltage electronics to keep the car happy about what you're going to it, and a charger.

Its really hard to see where you would get it much cheaper than that, at a guess you're talking about $1000 for the batteries, $800-$1000 for a charger, $500 for the controller, ~$500 for the HV electronics, and another $500-$1000 for low voltage electronics and the materials and hardware to put the whole thing together and have it be safely secured. That would put you in the $3300-$4000 range (ignoring tax, shipping etc). You can also buy the whole kit ready to install with a nice box and retaining spare tire access for ~$6k. You could skimp a bit on batteries, but you'd loose range. You could design your own controller, but that would take a lot of time. Skimping on the HV electronics, low voltage electronics or battery boxes could result in putting the vehicle or its occupants at greater danger.

PriusPlus - EAA-PHEV

Rob

 

The basic cal-cars method is independent of battery technology, but you will be on your own in terms of the battery management system which is in many ways the most complicated part. With lead acid they get away with just not having a BMS, with the Nilar NimH they are working on an open source managment system, though I don't know how far along they are.

The Nilars are pretty nice, not quite as impressive as Li-ion but much easier to work with in many ways. The prices I've heard are ~$200-250 for a 9 Ah 24V module. For a typical cal-car pack I would guess you would want 20 modules, so about $4-5k. I'm guessing that would be good for 15+ miles EV, and cycle life should be much better than lead acid. Pack weight is about 170lbs, so you could even go for 30 or 40 modules and get more range. You still need a BMS, but the pressure sensors in the Nilars simplify that greatly. Plus you would have the support of the open source community.

Nilar - a new way of packaging energy

Rob

 

Hey guys,

Did mwbueno remove the old battery completely and replaced it with his 18 amp battery? Or, was it parallel to the OEM battery?

 

Hey,

Where did you read about the "two problems" that might occur? I like your idea. Are you doing it? If I got some more technical info., I would probably try this set-up during the summer. The Dewalt batteries offer so much power and charge cycle.