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  #1  
Old 07-27-2007, 01:30 PM
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Default Re: Speed controller project

I don't have much time right now to look it over, but
one possible critical problem on the layout is the
position and wiring of the bus caps. Typically you
want these as close to the MOSFETs and diodes as
possible (like in the same parallel plane. You would
preferably have a positive bus plane on the top and
negative on the bottom to minimize voltage overshoot
during switching. It appears as if you may have an
issue with parasitic inductance. Before you crank up
the current, monitor the voltage across the FET's and
see how much voltage overshoot you get during
switching. Before you even attempt to power it, I
would implement the good suggestions that Lee
recommended earlier.
Great to see somebody actually building something!
You will learn far more by experimenting (although it
certainly helps to get suggestions here first!).
Rod
[quote]--- Ian Hooper <xxx@xxx.xxx.au> wrote:

> Hi all,
>
> I built a little speed controller for an electric
> trolley this week,
> and since there's often discussion on home-brew
> speed controllers on
> here I thought it might be useful if I documented
> the design for
> others to peruse/critique/copy:
>
> http://zeva.com.au/speedy/
>
> So far it seems to work a treat! Hopefully might be
> of some use to
> others out there working on their own controllers,
> and I'm always
> open to any constructive criticism on the design
> from the experts
>
> -Ian
>
>
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  #2  
Old 07-27-2007, 01:30 PM
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Default Speed controller project

Hi all,

I built a little speed controller for an electric trolley this week,
and since there's often discussion on home-brew speed controllers on
here I thought it might be useful if I documented the design for
others to peruse/critique/copy:

http://zeva.com.au/speedy/

So far it seems to work a treat! Hopefully might be of some use to
others out there working on their own controllers, and I'm always
open to any constructive criticism on the design from the experts

-Ian
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  #3  
Old 07-27-2007, 01:30 PM
EVDL List EVDL List is offline
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Join Date: Jul 2007
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Default Re: Speed controller project

[quote]Ian Hooper wrote:
> Hi all,
>
> I built a little speed controller for an electric trolley this week, and
> since there's often discussion on home-brew speed controllers on here I
> thought it might be useful if I documented the design for others to
> peruse/critique/copy:
>
> http://zeva.com.au/speedy/
>
> So far it seems to work a treat! Hopefully might be of some use to
> others out there working on their own controllers, and I'm always open
> to any constructive criticism on the design from the experts

This is an excellent first controller, Ian. Your MOSFETs, diodes,
capacitors, and gate driver IC are good choices.

As you noted, it lacks current limiting. Even that little Baldor 0.7hp
motor will draw 100's of amps at stall, so it would be a good idea to
add a fuse, sized to blow if the motor remains stalled for more than a
few seconds.

Your circuit also didn't show any main contactor to turn it all off.
This is necessary because sooner or later the controller will fail, and
you don't want a runaway vehicle when it does!

I'd use even thicker wire to interconnect the MOSFETs, diodes, and
capacitors. Again, these parts could easily be asked to carry 100's of
amps under some conditions. Copper sheet metal strips are convenient.

For low voltage controllers like this (24v), schottky diodes are a
better choice, as they have about half the voltage drop.

15v zener diodes across the MOSFET gates are a good idea. They protect
against transients over 20v or so that could blow the MOSFET gates.
Likewise, a high value resistor from gate to source insures that the
gate can't float high if the gate driver IC is off or becomes disconnected.

I'd add a series resistor and separate filter capacitor to power the
voltage regulator ICs. When the motor switches off, you can get huge
voltage spikes on the battery leads due to their inductance. These
spikes can exceed the regulator's peak input voltage spec.

Hopefully, your microcomputer's software has some fail-safes in it to
detect a broken throttle pot, out of range battery voltage, etc. There
should also be a watchdog timer, enabled so it will shut things off if
the software crashes.
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
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  #4  
Old 07-27-2007, 01:30 PM
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Default Re: Speed controller project

Thank you very much for posting that and the good documentation. Ill
deffinitely use your page as a reference. I use a contactor for now but
when Im in school Ill have time to try to make one.
Paul

> Hi all,
>
> I built a little speed controller for an electric trolley this week,
> and since there's often discussion on home-brew speed controllers on
> here I thought it might be useful if I documented the design for
> others to peruse/critique/copy:
>
> http://zeva.com.au/speedy/
>
> So far it seems to work a treat! Hopefully might be of some use to
> others out there working on their own controllers, and I'm always
> open to any constructive criticism on the design from the experts
>
> -Ian
>
>
Reply With Quote
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