Archive for the ‘technology’ Category

LiPo – Batteries Terms Explained

Electronics, technology | Posted by admin February 28th, 2011

I came across a great article on LiPo batteries on the RC Helicopter web site.  These guys have been using LiPo batteries with a lot of sucess.   Click here to read the full article.  Below are the highlights translated into values which are more to our using.

Below are some of the values you need to look at when designing a pack.

148 volt LiPo pack = 40 cells x 3.7 volts

Ah – Capacity indicates how much power the battery pack can hold and is indicated in amp hours (Ah).

C –How fast a battery can be charged or discharged. A battery with a discharge rating of 2C would mean you could discharge it at a rate 2 times more than the capacity of the pack, a 3C pack = 3 times more, a 20C pack = 20 times more, and so on.

Let’s use our 100 Ah battery as an example; if it was rated at 2C that would mean you could pull a maximum sustained load up to 200 amps or 200 amps off that battery (2 x 100 amps = 200 amps). The higher the C value the higher the cost usually.  What this means to an EV though is how much power you can effectively use.  If the C rating is low, you are going to have to use more cells to increase the voltage so that you use less amperage.  My car can easily pull up to 1000 amps at 168 volts if I am racing.  Taking off from a stop at normal driving speeds can easily require 200 amps.  Many cells will allow you to pull at a higher C rating for a short period of time without damaging the battery.  If the cell is drained too fast, this usually results in heat which can damage the cell.

Internal Resistance – Most decent higher discharge rated LiPo cells will have roughly 2 to 6 milliohms (0.002 to 0.006 ohms) of internal resistance when brand new. To calculate the total internal resistance of a series wired pack, you would then add these numbers together so a 148 cell pack with each cell having 4 milliohms of resistance will show a total internal resistance of about 592milliohms (0.592 ohms).

As packs age, the internal resistance goes up and the warmer they run. Lower discharge rated packs will generally have higher internal resistance readings.

Nissan Leaf Test Drive

technology | Posted by admin February 1st, 2011

Got a chance to visit the Nissan Leaf test drive event in Fort Lauderdale. Nissan had a really nice display which was like a small village they setup out in the Sawgrass Mills parking lot.

The main tent was for registration and also had a number of video displays that helped educate people about electric cars.

After they had a group ready, we were escorted into the next tent which housed a display with the Leaf’s battery pack. The pack is a very nicely organized system of 24 prismatic flat lithium ion modules. Each module houses 4 cells. The total pack is 24kwh of energy.  I don’t know how hard it is to actually get into the pack when it’s on the car, but it looks like it would be pretty easy to change out a bad module if you can get into the pack.

The next tent we were escorted to was a display on the range and iPhone system monitoring and control. For those that don’t have an iPhone there is also a web site. From your phone you can read battery charge and a lot of other car functions. One nice feature is that you can turn on the AC or heat remotely. So if you car is plugged in charging in the garage, you can turn on the AC and the car will cool itself off the garage power and be cool when you unplug it to drive.

From here we were lead out to the cars to drive. We first went through a little course setup in the parking lot with cones and then out on the street. The car performed real well. There is an econo mode which we also tried. In this mode acceleration is really sluggish and the regen is a lot heavier. You can really see how driving in this mode would lead to better economy, but for the average driver, it’s no fun.

The back seat was easily large enough to fit 3 adults, so it really is a 5 passenger car. There was even a nice sized trunk.

Charging the car can be done in two ways. There is the new standard j-1772 connector which can be plugged into a public charging station. The car comes with a cable with one of these connectors and a 120 volt standard AC plug. They recommend having a 240 volt charging station put in your house though. This is around $2k. These methods take from 6-8 hours to charge fully. The other method of charging is through a special high speed charging port which can handle a lot higher voltage and amperage. This would be used by fleet vehicles such as Taxis. This high speed port would allow the car to be charged in as little as 30 minutes.

Overall I was very impressed. Nissan seems genuinely committed to making this technology work. As a side note, all of the dealerships will have charging stations. I wonder if they will be kind enough to share a few electrons with other EVs who come to visit?

J-1772 Charging Connector

Electronics, technology | Posted by admin November 13th, 2010

J-1772 Charging Connector

Thanks to Charles and David from the Gold Coast EAA, I now have a J-1772 charging connector to put into my car.  This new connector is the North American standard developed by the Society of Automotive Engineers for use in all charging stations.  Once public stations are put in, my car will be able to easily get a charge.  The connectors are really nice.  There is a button on the top of the plug that links locks into the charging connector so its not accidentally disconnected.  Simple electronics in both the plug and receptacle do some handshaking to make sure the connection is in place before electricity begins to flow.

J-1772 Connector showing pins

The button on the top has a place where a lock could be inserted

Shelby announces the Aero EV

technology | Posted by admin January 28th, 2009

Shelby, the maker or Ford super cars has announced the Aero EV which it claims will do 0-60 in 2.5 seconds. More importantly the battery pack will charge in 10 minutes and have a 150 mile range.

Shelby Aero EV

Shelby Aero EV

For the full story click here.

The Zilla Controller

technology | Posted by admin January 15th, 2009

Big news came today. Evsource.com emailed me today that my controler is about to ship. The Zilla 1k is a hard to get peice of hardware that is the brains of the car. Though there are other controllers out there, none have the capability of the Zilla controller especially for a DC motor powered sports car.

It’s time to get busy. There is a lot to do to get ready for the controllers arrival. With the brains of the car showing up a moving car isn’t far off in the future. Tonight I study the schematics and start working out the electrical design.

The iPhone

technology | Posted by admin November 23rd, 2008

Just a note about the iPhone. This has been one of my most used tools in this project. The whole project actually started when I was sitting on the beach in Sarasota watching the sunset and surfing on eBay with my iPhone. It was then that I came across the Fiberfab Valkyrie that was for sale in Jupiter, Florida. That dream of taking on Detroit and Tesla and building a cool electric sports car for less took hold of me. One press of the bid now button and the journey began.

Since that time I have used the phone to take photos of what I was doing and email them to friends or experts to get advise or find parts. Without this ability to snap quick photos and carry them easily around the job would be much harder. It is very hard to explain to an autoparts employee what you need without a make and model for a car. But I would pull out my iPhone and show them the project and exactly where the part was going or what it was replacing.

And this blog has been written almost entirely with my iPhone.