RE: (ET) Converter losses

[Larry Elie <lelie ford com>]

David replied to Allan...

----------
From:   David Roden (Akron, Ohio, USA)[SMTP:roden ald net]
Sent:   Friday, July 09, 1999 1:39 PM
To:     elec-trak cosmos5 phy tufts edu
Subject:        Re: (ET) Converter losses

> I have been considering rebuilding the controls on an E20 ... 
> with newer technology, and have some questions:

;Allan, I don't yet have direct experience with adding transistor control 
;to an ET.  I've looked into it, though, as it's one of my long term 
;projects.  Here's how I see it right now:

> 
> 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.

;There are thousands of 36v golf cars running Curtis and other transistor 
;controllers.  No problem.

> 
> 2. How much power loss is there in using a converter [solid state 
> controller] for motor control? 

;Very little.  Voltage drop across modern devices is a few hundredths or 
;tenths of a volt.

That's only partly true.  What Allan is describing is the voltage drop 
across a bipolar 
system, which is typically .6V period.  What you are describing is an FET 
or IGBT 
based control in something like a solid state relay.  Yes, the on 
resistance can be 
20 milli-ohms or less BUT you have to provide a gate voltage above the Vcc 
voltage 
of the device that will be closing.  There is a way around this, but it 
isn't on the market 
yet (I have a patent pending on such a device).  So, for now, if you were 
to try to use 
a FET or IGBT to fully turn on or off a 36V 200A system, you would have to 
provide 
a control voltage of something like 38V at .05 amps.  I could go into the 
details of the 
other approach, but the company lawyers would kill me.  Think about it; if 
you could 
just drop an FET or IGBT puck into the system, why wouldn't ALL relays, 
contactors 
and solenoids be obsolete; they are more expensive than the solid state 
counterparts.  
So, unless there is something that our Ford folks haven't seen that the 
golf-cart guys 
are using, it just isn't that simple.

Larry Elie