(ET) Converter losses

[Allan <allanhv worldnet att net>]

I have been considering rebuilding the controls on an E20, which, at the
very least, needs several relays replaced and the charger repaired.  I
have been thinking about updating the controls and/or charger with newer
technology, and have some questions:

1. Has anyone attempted this with a 36V system?  I'd rather not convert
my tractor to 24 or 48 if I don't have to.

2. How much power loss is there in using a converter for motor control?
It seems to me that replacing the mechanical contactors with a
solid-state equivalent (transistors of some kind) would result in a
voltage drop across the solid-state devices.  Is the loss significant?
I would guess something like 2V * 50A * 2 devices = 200 Watts?

3. Who makes appropriate controllers and how expensive are they?

4. Has anyone considered using an AC drive motor with an appropriate
converter?