Saturday, February 21, 2009

Despite the recent snowfall and subfreezing temperatures, I have managed to stay relatively productive. The most recent developments (as of last night) are a little more progress on my motor controller design. So far, I've completed the isolation circuit for the IGBT driver. I'm using an optocoupler between my PIC's output and then input of my driver IC, and a 5v to 15v isolated DC/DC converter to power it. I'm using a resistor to return the driver to a logical low after the PWM pulse from the optocoupler. All things considered, I'm pretty proud of the circuit. It allows for full isolation (a few kv, need to review the datasheets to be sure) between the high voltage and low voltage systems, while still requiring only one low voltage input and without tapping the high voltage to power the driver circuitry. This keeps the parts count minimal (6 ICs including voltage regulators and stuff) and the price down. The most expensive part on the driver board cost me $8.

Right now I'm trying to come up with an internal precharge circuit. I want to avoid a high voltage tap across the contactor if at all possible. Right now what I have in mind is a circuit that disconnects the caps from the high voltage while the contactor closes, and then reconnects them through a MOSFET or IGBT once it's juiced. That way, the solid-state part of the circuit would take the brunt of the charge current and minimize arcing. Still working out the details.

After that's all taken care of, I'll be working on designing the PCB. I'm hoping to have only one board for the whole controller. This should be possible if I use the same board (with adequate gaps for isolation, of course) for the high voltage cap circuit as well as the low voltage driver circuit. If I do this right, I'm pretty sure I'll only need one internal connection outside of the PCB- the one that goes to the gate of the IGBT. This means less opportunity for failure, more vibration resistance, etc.

Anyway, I'll be doing my best to get this thing ready to test while I'm home over spring break in about 3 weeks, so I'll be staying busy. Stay tuned!


Mike M said...

What we do is precharge the caps through a high wattage resistor. You could probably use a large mosfet for that though we use a contactor. Then once the caps are up to voltage, turn on the main contactor that will handle the large currents. No arcing at all. You could make an easy comparitor circuit to automatically turn on the main contactor once the voltage comes up for very little extra cost.

Andrew Angellotti said...

Yeah, that's basically what I had in mind. Only thing is, I want to keep everything internal- i.e., hook up the battery + and - and you're good to go.

What I'm planning on is doing basically that, only inside the controller. I will probably program a delay so the controller doesn't accept throttle signals until the caps are fully charged. The main contactor will turn on, and then a mosfet will become active and connect the caps through a resistor. Then the controller will become active.


Michael J. said...

I'm thinking about converting an Mazda truck to electric as well, and my brothers and I are pretty inexperienced, so hopefully you could give us some help? We were thinking about buying a 2002 Mazda b2300 model converting it. Is there any problem with using such a "new" car? Or do we need to go with an older model. I've seen sites that say newer models have computers or something that make it harder for them to be converted.

Thanks for your help!

Michael J

Andrew Angellotti said...

Hi Michael- There have definitely been plenty of newer conversions, so it's definitely possible. Some of the electronics might present a little bit more of a challenge than a car with a simpler electrical system, but nothing you can't work around.

I tell everybody to check out and spending some time looking through the old posts and stuff. The collective knowledge on that forum will do you way more good than the information I can give you.

Good luck!

Aminorjourney (Nikki) said...

Hi Andrew,

I know it's a long shot - but would you be interested on taking part in EVcast at some point? I'd love to have you on as a guest for my Saturday show. We record at 1pm Eastern. In fact, would you be interested in coming on tomorrow?


(email nikki @ aminorjourney dot com)

Ricardo M said...

Dear Andrew,
My name is Ricardo, I work for the biggest brazilian newspaper, it´s called Folha de Sao Paulo. I write to teenagers and I think your work with cars is great! I would like to write about it. Can we talk by email? Please, if you want, write to me! or
Thanks and congratulations!

mikey said...

hey Michael! I'm a green car fan and trying to spread good info. Would you be interested in doing a link exchange? And hopefully you'd like to share some stories with our community members?

Let me know how I can reach you via email. thanks!


MakingBoost said...

9 months later, any updates?
Hope all is going well with classes.

Anonymous said...

what kind heart of u..................................................

Kevin said...

you have to keep working hard through the rain and snow

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