A question I ask myself now and again is if it is technically feasible to build battery powered construction equipment, like large excavators - say 250kW motive power at the shaft of the central hydraulic power pack.
I'm not an electrical engineer so I'm not sure how the motor, battery and everything in between would look like. It doesn't seem trivial:
250 kW motive power is roughly 280kW electrical power. Most batteries deliver single digit voltage and are connected in series to deliver 12V or whatever is needed. DC motors at this power seem to need between 420 and 800V, depending on speed and torque. So I'm either talking about stacking quite a lot of battery units (with their internal resistance!) or using a DC-DC converter (do these exist for 280kW? How (in)efficient are they?) or looking at a different motor.
Provided a 250kW 12V motor exists, I'd be talking at about 23kA current. This seems quite collosal to me (but maybe I'm wrong).
Another way could be to mount several motors on one shaft, but then the inactive motors would likely act as brakes and add their own headaches (or not).
In short, for me as a non electrical engineer it's not trivial to envision such a power train. How could it look like?
An answer should:
- provide a workable solution, not neccessrily the best - proof what is optimal is surely bexond the scope of an answer
- list all the major components - motor, battery, converters, other major stuff I forgot - with effiencies in this particular use case
- provide a decent estimate of overall efficiency (input: charging battery, output: motive energy provided)
- Energy density of battery and smallest viable battery to deliver the power
- ballpark estimates of weight and cost of major components are appreciated but not neccessary