What's he building in there?

[mauswerkz]

Today's progress:

Description: "A quick demonstration of my prototype battery management system (BMS) polling the cell voltages of a pack of A123 lithium batteries. There are 18 in series and 4 in parallel. This is approximately 1/5 of a larger high voltage battery pack that I have built to test my 3-phase motor controller at high loads. At the moment, it takes about 7mS (that's 0.007 seconds) to read each cell's voltage. Lower value pull-up resistors on the optocouplers will allow this to be increased significantly. The system is also capable of reading cell temperature, but it is not implemented on this test pack.

Bypass capacity is 1A @ 4V.

The modular design allows the BMS to be used on any type of lithium cell so that pack replacement and/or upgrades in the future do not require a new BMS to be purchased. Only appropriate adapter boards would be needed."

[Crazy2287]

Blinkies! It's good to see these little squares working. Are you going to add temperature monitoring for the test pack before you use it?

[starletkid]

man when i seen this thread, it reminded me of this song..

it made me laugh how much it reminded me of this....
http://youtu.be/nMqxNPsfN50

[mauswerkz]

Blinkies! It's good to see these little squares working. Are you going to add temperature monitoring for the test pack before you use it?

Nah, not going to bother monitoring temps on the test pack. It's not really that nessecary. I've only included it as a feature because that's what the competition has.

man when i seen this thread, it reminded me of this song..

it made me laugh how much it reminded me of this....
http://youtu.be/nMqxNPsfN50

Finally, somebody got the reference!

[starletkid]

yeah man,
if ppl knew the song more it would have been perfect!
good for those covert jobs.
lol

[mauswerkz]

Finally got the battery management system (BMS) installed on this test-pack. As before, there's 98 cells in series, 4 in parallel. The battery pack will be used for testing my EV motor controller. Eventually, the BMS, motor controller, and a few other products will be for sale to people who want to do their own electric car conversions.

Here's a pic of the system fully installed on the battery pack.


For those not clear on the purpose of a battery management system, here's an example. On the left is the voltages of each cell in a 40-cell series string of batteries. You can see clearly that they are all different and not "balanced" with each other. On the right is that same string of batteries after charging with my BMS installed. Notice how every cell's voltage is very close to the rest. They are well balanced.


If I had attempted to charge that string of batteries without a BMS, the highest cells (69,79,81) in the string would become overcharged before the lowest cells became fully charged. This would cause damage to the batteries and shorten their lifespan. The battery pack in the photo above cost $1000, but a battery pack big enough for an electric car can cost $10-15,000 or more. A BMS is essential to protect such expensive parts.

[GakkenGod]

I'm just curious what is the estimated cost of your project. It is very motivating.

I have looked into tesla roadsters and such and am very impressed with the advances in tech.

Also do you know what motor you plan to use?

[Jenga]

That's really cool dude, did you make the PC software that outputs the different cell voltages? And I'm assuming you're charging the batteries in mini-banks of 3 cells (since it's 3.6V)

[mauswerkz]

I'm just curious what is the estimated cost of your project. It is very motivating.

I have looked into tesla roadsters and such and am very impressed with the advances in tech.

Also do you know what motor you plan to use?

Estimated cost of parts is listed below:
Car: $5000 (my 1992 BMW 318is)
Motor: $1850 (details here: http://forums.mightycarmods.com/show...l=1#post102659)
Controller: $???? (I'm designing it myself and development has been very expensive/time consuming. Retail price will be around $4000)
Batteries: $9000 (Current plan is for a battery pack that will get roughly 100km range
Charger: $800 (Not sure if it will be an off-the-shelf one, or my own design. Will likely give it a shot myself so that it can talk to the BMS and other components designed by me)

That's really cool dude, did you make the PC software that outputs the different cell voltages? And I'm assuming you're charging the batteries in mini-banks of 3 cells (since it's 3.6V)

I wrote that software, yeah. It's done in Visual Basic, though I'm more comfortable with C than Basic these days (Was good with Basic when I was much younger). I haven't had a good play with Visuall C++ yet, so I'm using what I know for the moment.

I'm charging the batteries with the rectified output of a 0-280vac 2.5kW variac. So far I've charged them in strings of 40 cells in series, 4 cells in parallel (that's what the screen shots above are from). Once I get the packs mounted safely and properly wire up, I'll be able to charge the entire 320v string at once with my variac. It requires supervision at the moment as the output is not regulated and it fluctuates as the mains voltage varys. Initial current is 6A, reduced to 250mA (well within the BMS's bypass capability) once the first cell reaches full charge. This is done manually by me at the moment, but will be done by a proper charger eventually. Luckily, it only takes about an hour to charge the pack this way, so no big deal.

[Dreamz]

speed controller for an electric car

PS: your pic chip is missing from the socket

you beat me too it marty .. i knew as soon as i seen it..
been racing rc cars since i was like 12

[brent012]

I wrote that software, yeah. It's done in Visual Basic, though I'm more comfortable with C than Basic these days (Was good with Basic when I was much younger). I haven't had a good play with Visuall C++ yet, so I'm using what I know for the moment.

So you are going to be using an actual PC with it? How about using Embedded C so you can have a microcontroller? Might have to read this whole thread lol, i saw the photos before but never took the time to read all the pages.

[mauswerkz]

So you are going to be using an actual PC with it? How about using Embedded C so you can have a microcontroller? Might have to read this whole thread lol, i saw the photos before but never took the time to read all the pages.

Embedded C is the reason I'm so comfortable with C ;-)

There are 99 microcontrollers being used in that system (not kidding, one on each cell managing the cell's voltage during charging, and one polling the rest for their data and doing all the calculations). It's scalable up to 250 cells. The before/after picture is a shot of the serial stream coming directly from the main microcontroller. I've hooked an LCD up to it (simple 2x16 one) before and that's how it will be in the car for showing critical information (low cell voltage, high cell temperature, state of charge, etc).

[tekkentool]

So curious question, how many KM's of range did you design and plan the battery cell in this to last for? What is the ballpark you're aiming for?

[mauswerkz]

So curious question, how many KM's of range did you design and plan the battery cell in this to last for? What is the ballpark you're aiming for?

The pack I've built here is only 1.25kW-hr. It's just a "high" voltage, high current power source for short full-power tests of my motor controller (sized with dyno runs in mind). If I put it in a car, I would get about 7-8km on a charge at 60kph.

The pack that will eventually end up in the car will take me 100km on a charge at 100kph average speed. More at lower speeds and probably another 5-10% thanks to regeneration when braking and going down hills. That pack will be 19.2kW-hr, more than 15 times the size of this one.

[tekkentool]

Yikes! I knew EV batteries were expensive but damn. Even the DIY route isn't cheap.

Like anything I guess the cost will drop and efficiency increase...I mean look how far mobile phones have come in 20 years.