[ausev] DIY controller?

[m. howse]

If a person knows what they are doing with their controller design they  
obviously
don't need to learn how to build a controller and can save a lot of cash.

marv

On Sat, 14 Jun 2008 23:11:45 -0500, Chris Robison <chris at chrisrobison.org>  
wrote:

> Charlesvsi at aol.com wrote:
>> Basic functions off the top of my head:
>>  1. sensors monitoring the relationship between accelerator pedal and   
>> phase,
>> amplitude,etc. of current going into motor, while monitoring phase  
>> shift  of
>> back emf  that indicates how fast electric motor armature is going   
>> around.
>
> In general when people talk about making their own controllers, they're
> talking about DC motor controllers for series-wound motors, which are
> vastly simpler in design, and don't require most of the (apparently
> inductive AC related?) considerations you've listed here. They don't do
> regenerative braking, don't require feedback from the motor beyond an
> RPM sensor for safety and user feedback, and in general consist of just
> a single MOSFET or IGBT switch. Charging and battery management
> functions are also not generally included in DC controllers.
>
> So, the short list of necessary features for a DC controller:
>
> A) Accept a throttle reading of some kind (0-5k pot is most common)
> B) Translate that into a PWM duty cycle
>
> Some things that are not necessary but are a Really Good Idea:
> C) sense motor speed and cut power at or above a set value (many
> commercial controllers don't even do this)
> D) sense controller internal temperature and cut back current in
> overheat condition
> E) sense pack voltage and provide programmable Warn and Stop thresholds
> F) provide programmable battery and motor current limits, and motor
> voltage limit
> G) provide warning light (UI) outputs for the dash
> H) provide a computer interface of some kind for programming
>
> And then there are other issues, like your choice of switching device;
> do you go with MOSFETS which are cheaper, or IGBTs that are more
> efficient at EV power levels but can't normally be paralleled (forcing
> the use of larger more expensive devices)?  If your control electronics
> are powered via a 12V input, how will you maintain electrical isolation,
> and still provide enough power for your gate drivers (which can be
> significant, to overcome gate capacitance and keep your switching time
> short)?
>
> It seems like a very simple thing on the surface, to make a DC motor
> controller. And to a certain extent it can be simple to make one that
> works, but making one that's safe, reliable, sufficiently powerful,
> efficient, and fails in a predictable and controllable fashion takes a
> bit more work.  Most people that I've talked to who have gone to the
> trouble of building their own will tell you that they ended up spending
> a LOT more money in the process, than if they'd bought one off the
> shelf.  Build one if you want to teach yourself about power electronics;
> it can be a great way to learn.  But don't do it to save money.
>
>    --chris
>
>
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