Question about 5 KW BLDC with VECTOR 300 as a range extender w/ regen braking

[Sstargazer]

Hello,

I am designing an open source snowmobile engine that is carbon neutral (runs on biodiesel and/or hydrogen) and has long range, in cold climates, where a battery would not be practical.  For various reasons, such as flexibility (use of AC power) and also reliability, I want the combustion engine driving a motor-generator and charging a small battery / supercap, which then has a separate electric motor with its own controller to drive the vehicle.

For this application I have bought a micro RC gas turbine engine that can deliver 5.1 kW of shaft power at 6000 RPM.  I believe that the Golden Motor BLDC 5kW is a good fit for direct coupling. 

The vehicle drive motor will also be a 5 KW BLDC (I understand in principle this motor should be smaller due to efficiency losses, but there will be other battery charging devices e.g. fuel cells in parallel added later, so the 5 KW is a good fit for the output motor as well.  It is just for a test scale model of snowmobile engine which is usually much more powerful).

From reading the forums I gather that if I drive the 12V brake line on the VECTOR 300 controller high, or short the 5V and GND on the main brake, it will activate the regen braking feature.  Are there any limits to the current (or duration of current) that the regen feature has?  Can it be permanently (continuously) driven in regen mode up to the full current of the motor?

Thanks,

Stefan

[Bikemad]

Hi Stefan andto the forum.

The EBS (regen) is engaged by either grounding the normal Brake wire or supplying 12V to the optional High brake wire.
However, my concern would be the amount of braking force that the motor would apply at lower rpm without producing any regenerative voltage/current.

I don't have any "hands on"experience with the EBS function of the VEC-300 controller and 5kW motor, but my 26" Magic Pie does not produce any noticeable regenerative voltage/current below 15 mph, but the electromagnetic dynamic braking effect below this speed is considerable.
I have the throttle switch on my bike wired in parallel with the brake switches to permanently engage the regen function when it is pressed, which I regularly use as a "Hill descent control" when going down steep hills.
But I suspect that if I pedalled really hard from stationary downhill while the EBS was engaged , I would probably be unable to reach (let alone exceed) 15 mph, therefore no useful regenerative power would be produced for all that effort.

Unfortunately, my biggest concern would be the use of a RC jet turbine for daily use, as they typically run at between 50,000 and 165,000 rpm and often require servicing every 25-50 hours (or possibly less), and jet engines are not exactly renowned for being very quiet. 

Each JetCat has a prescribed maintenance interval. After approximately 25 hours, the
engine should be returned to JETCAT USA (along with the ECU and fuel pump), for
service. The total running time of the turbine can be accessed and monitored through
the STATISTIC menu.

I presume the gas turbine you have in mind already has a substantial reduction gearbox (like a turboprop version) to reduce the output to just 6000 rpm. 

Anyway, regarding your question, the software does allow for maximum voltage and current settings to be entered for the regenerative braking function:



But I have serious doubts as to whether your proposed setup will be very practical to operate. 

I don't mean to rain on your parade, but what I consider to be the negative aspects of your design should be looked into a lot more at this stage. 

Alan
 

[Sstargazer]

Thank you for the reply Alan.  Yes, I am aware of several of the issues with the design.  I have responded below:

- Re: output RPM, the gas turbine I bought is a turboprop variety with a shaft output speed of up to 6500RPM at full power.  (This will be limited to 6000 RPM by setting in the turbine ECU to match the motor max).  The core of the turbine, as you said, is at a much higher RPM.

- Re: dynamic braking.  I understand that not much current will come from the motor at low RPM despite a significant braking force.  Generally, the turbine would not be operated at low RPMs because it is inefficient, both at the turbine and at the electric motor; a suitable control system will be implemented at the ECU to ensure that high RPMs are desired from the turbine, even if this creates a noticeable on/off charging duty cycle (the turbine has electric start and cool-down so cycling losses are not significant).

- Re: reliability, yes that is a major concern for turbine engines, especially the micro RC ones.  My KingTech TP turbine model says a USD300 overhaul every 25 hrs of use.  Keep in mind this is just a scale model of a full sized snowmobile engine, which will use a much more expensive / larger / more reliable turbine in future.  Depending on materials of construction and so on, the reliability of industrial grade / aircraft grade turbines can be quite high, even higher than piston engines or so I have read.

Note that given the high power output I am looking for, in a small package i.e. a snowmobile, neither batteries nor fuel cells will be good enough, and some form of ICE is required, and a turbine has the most flexible fuel source, highest efficiency, lowest size and weight for given power.  Furthermore, when used in parallel with a fuel cell, the engine will not generally need to engage (start) the turbine unless high power draw is required for a sustained period.  In other words, the duty cycle of the turbine in regular use is not expected to be that high, which will reduce the wear on it / increase the length of actual time before the 25hr mark is reached.

- Re: the primary question, about the maximum current, from what you have shown me it seems not to be limited other than by the current of the motor controller (120 AMPS) and the battery bank (48V), plus whatever the software is set to (which I assume can go up to those specs).  So this (mostly) answers my question about the maximum current, and I should not need to go to a bigger motor.

Again, thank you for the info.  I get that the practicality of the current design is limited for sustained use, but with advances in turbine technology and fuel cell addition, the issues you have raised can be dealt with, and this is just a prototype demonstrator.

Stefan