T-Pain Is On A Boat: Re: [Electric Boats] MARS BLDCmotor

Wednesday, August 5, 2009

Re: [Electric Boats] MARS BLDCmotor

Generally speaking, BLDC PM motors like this work pretty well as efficient 3 phase alternators. The problem is that they aren't easy to control when used as an alternator, as there is no way to control the output directly, as there is with a separately excited 3 phase alternator (like a standard automotive one).

The output can be controlled by using a switched mode type controller though. One way to do this using largely off-the-shelf parts might be to rectify the 3 phase AC to DC, using a suitably rated three phase rectifier, then using the output from this to drive a brush motor controller, modified internally so that the throttle control input is driven by the battery voltage, as a charge regulator (this needs a bit of simple electronics to convert the measured battery voltage to a throttle input feedback signal). This would provide the right sort of voltage regulation that the battery bank needs, whilst still being pretty efficient. The controller output might need some smoothing, depending on the possible sensitivity of the batteries to high frequency pulse charging.

Technically it should be possible to combine the rectification and voltage regulation capability into a single synchronous three phase rectifying controller (similar to the way regeneration works), but this would be harder to do using off-the-shelf parts, I think.

Alternatively, it might be possible to build an electronic regulator that measures the battery bank voltage and alters the diesel motor throttle to maintain the appropriate charge level. This would only need a three phase rectifier, plus the throttle control electronics.

The advantage would be the freedom from brushes, with their maintenance and spark/safety concerns. Cost wise I doubt it's cheaper than a similarly rated big rotor field current modulated alternator.

I'm no expert on this, it's just my view based on some knowledge of the basic building blocks needed for such a system.

Jeremy

--- In electricboats@yahoogroups.com, Paul Beaurain <beaurainpaul@...> wrote:
>
> Denny,
> What are the chances of using that motor to couple to a diesel engine without a controler and some sort of a bridge rectifier to generate DC to charge a 48 volt battery bank driving a Etek RT.
> Paul.
>