Monthly Archives: February 2015

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How to Power Up

 

 

 

Now I am still waiting for my PCB for the Battery Management System (BMS) so I still have plenty of other things to do. Like working on the problem of cold start the EV. All battery stacks will be self contained and disconnected from the main power rail. Each stack will have its own micro controller (uC) that will measure the total voltage of the stack and control its current flow. The uC will also control the contactor. While the BMS itself will be connected to the individual cells, they can only be put to deep sleep. All the uC however shall be turned off when not operated. They will get their supply from a dedicated power net.

So if everything is off, how can we turn it on?

My solution will be a master battery, that will be hard wired to a mechanical switch. That switch, once pressed, releases current to the contactor of the master battery. This will power up the rest of the controller network and connect the other battery stacks to the power net.

The diagram below might help to visualise the logic: initial on logic

So far for theory, on to the prototype.

Below are the schematics and the first layout on the breadboard.

I picked the IRF 9610 because it can operate on the full stack voltage of 72V and I hope I will be able to find a contactor that will not draw more current that the MOSFET can supply.

latchingSwitch

 

If anyone has a tip on a suitable low power contactor that can sustain 1200A, please leave me a message.

The next step is to draw the layout for the analog part and the digital logic and then to demonstrate its behaviour.

To Display or not to Display

This EV project was held up for quite some time, because of my requirements for the main GUI. It should be flashy, sufficiently big and it should be a fast starter. Instant on is a myth so I settled with a 3 second cold start delay.

That was around 1999.

I had good experience with character displays, connected to a uC, they were very fast start ups. So how hard could it be to add a graphics display?

Very hard as it turned out. I tried it the embedded way, added a dedicated Epson chip, that I was not able to hook up to an LCD. I also tried several off the shelf variants like ASIC, serial displays and others. All failed, either they were slow to draw on or took forever to start (>30 secs) Also the flood of cheap embedded displays did not help, most of those use some kind of ARM with embedded Linux or are simply too small to be used for the main GUI. While Linux is sexy, it is not an option for me. While there is rumor of a super fast loading Linux , most fail to mention that hardware start up and application start up are not considered. Super fast Linux, practically is not below 10 sec, most are still in the 20 sec range.

And there are the “cheaters”. Solutions that never shut off (sleep) or proximity solutions. The later ones seem to be popular with certain car manufacturers. With the transponder, that the driver carries instead of his keys, the car detects an approaching driver and turns on its electronics. This gives you the impression of instant-on, while it is not.  For an EV this is not my preferred solution. Off should be off and not dormant.

In Novemer 2014 I finally found the company 4D that makes a lot of embedded displays. Without any expectations, I ordered a 7″ display for a different project and I was astonished to see that it meets my requirements quite closely. It is sufficiently flashy and it starts within 4 secs, close enough to start my demonstrator and revive my EV project.

DisplayIn the picture you can see the demonstrator. Currently it starts into this screen in under 4 secs, the gauges are moving up and down and the icons blink, there are two touch buttons (did I mention that it also has resistive touch included?) that control some functions.

The protective foil is still on because the display will have to endure rough handling in the future, so the picture looks dull – trust me, it is not 🙂

The next step will be to let it communicate to the outside world. The first gauge that will get information will be the battery indicator on the left, since my current project is to build the BMS (battery management system).

 

Hello world!

Welcome to the eHaflinger Project. Please see the start menu on the top for the motivation and specifications!