Hello everyone!

I have the following goodies:

• 8 x 15 kW brushless motors
  • 70 V max
  • max continuous current = 300 A

The idea is an 8 wheel ATV. For a half hour at 15 kW I will need over 260 kg (575 lbs) of high grade Li-Ion batteries @ 3.28 US$ per cell (5200 of them). Simply put I will be too heavy and long gone bankrupt. However I also have the following:

• A 120+ kW Subaru internal combustion engine. Only weighs 115 kg (250 lbs)
• 2 times/of 50 kW brushless motors. Which also only weighs 12 kg combined (27 lbs)

Now that leaves a large amount of weight to perform:

• the mechanical coupling of combustion engine to 2 big motors
• Fuel for more than a half hour of operation.
• And perhaps rectification.

So my question is whether it is possible to rectify the three phase output of the 2 huge motors (yes now generators) to power the 8 smaller ones.

The big motors are wired at 55kV and rated for 120 Vmax and 500 amps.

My question is if it is even possible to rectify the combined 1000 amps at 120 V and then step the dc voltage down to the 70 required for the eight smaller motors.

The power discrepancies are due to rated and peak maxima and bad supplier labeling. Also the coupling of the 2 big motors (hopefully generators) to spin at the 6600 rpm required to gen the 120 V is rather easy for the Mechanical engineer side of my life.

I should mention that the 8 motors and the ICE are for free so I need to use them. But I have to either pay for the 2 big motors and rectifying circuits or for the batteries. Batteries are more expensive by a factor of 7 excluding charging gear. Perhaps another option is to make my own higher voltage generator and use off the shelf rectifiers (1600 V 100 A units are on ebay for cheap cheap)

Can this be pulled off?

Thanks in advance.
Bretto

 

The big motors are wired at 55kV and rated for 120 Vmax and 500 amps.

"The big motors are wired at 55kV"
What does the 55Kv refer to.?

Apart from attempting to reduce the generated output of the generators, there is the issue of controlling the 8 brushless motors, not to mention the wheel slip detection and synchronization of all 8.
Max.

 

Yeah definitely, but apart from everything else my question is to viability of the power electronics. Do you know if it is possible and if so viable?

 

Possible but not practical. The basic numbers say you want to put something like 150 HP to the ground which in relative propulsion terms is what a fair sized field tractor or bulldozer or semi truck puts to the ground in normal operational actions.
So, unless your ATV is the size of a small bus and has to drive up 40+ % grade slopes at several 10's of miles per hour or will be pulling a 16' field plow at 8+ MPH I have doubts you need the power.

 

It will be used to pull a test bed that will have draw bar loads in excess of several tonnes. So the power has been carefully specified. Lets forget the terramechanics and the vehicle dynamics.As an example if I were to build a huge drone, and wanted air time that excluded the use of batteries only but requires the range extending ICE, would the power electronics (specifically the rectifier and dc-dc conversion be possible) ??

 

It would be possible but if any degree of high power pulling with accurate control over the speed and pull force are needed for extended periods basic hydrostatic drive will beat home made multistage engine over electric drive system any day for simple implementation control and overall operation costs.

For that matter a good old farm tractor or fair sized pickup or small commercial truck set up with a load cell on the drawbar and a basic ground speed monitoring system tied into a basic control system to regulate the throttle to maintain the speed and or pulling force will beat what you are proposing hands down in every aspect.