RE: (ET) 48v ET

["Elie, Larry \(L.D.\)" <lelie ford com>]

You are right Chris, but GE DID sell the kit, and someone on the list had 
it.  BTW, ratings get 
exceeded all the time; the lift is run at 18+ V but is used at 12+ in a 
car.  The rating of the 
plug for the mower is 30 A, as is the tiller an blower.  I have seen well 
over that.  The rating 
is for the temperature rise due to current; the saving grace is that the 
ET is a constant voltage 
source; and as things get hot the resistance INCREASES which lowers the 
current.  The relation is:

Delta R(T)/R(20C)=Alpha*Delta T, where Alpha is the temperature 
coefficient of resistivity of copper, 
or 4.07E-3/Deg. C.  The limits for the silver contacts on the contactor 
are different because the 
coefficient is different for silver, but most of the elements even there 
are copper.  On the plug 
the temperature in question is where the vinyl on the plug begins to 
soften; in a winding it's the 
190C that the varnish can take.  This is giving me more reason to 
re-design the ET controls from 
scratch with 3mOhm FET's... what one would use today.  Nah, I don't have 
the time, but it would be fun.,

Larry Elie


-----Original Message-----
From: Christopher Zach [mailto:czach computer org]
Sent: Tuesday, June 01, 2004 11:17 AM
To: Elie, Larry (L.D.)
Cc: Elec-trak list
Subject: Re: (ET) 48v ET


> The real problem with raising the voltage is that the current goes high 
> (more or less constant resistance... 
> well, the resistance increases with temperature, the RTD effect) which 
> causes things to get very hot.  It's 
> the CURRENT that produces torque, not the voltage, but you need voltage 
> to get the current up.

There's also the little issue that the parts of an Elec-Trak are rated 
for 36 volts. Bumping things up to 48 may not seem like much, but it 
could eventually weld a contactor. That would be bad.

The other truth is resistance: The wires in an Elec-Trak put a *LOT* of 
resistance under heavy load. I was actually kind of shocked to see that 
my little sensor does not trip the lights when attached directly to the 
battery, but does trip when attached to the other end of the battery 
wires from the back pack forward. There is a volt drop under full load 
there; that's about 100 watts of power wasted into cable.

If you're building a dragster class Elec-Trak, upgrade the battery 
connect wire runs to 4 gauge wire or something really thick. It's a limit.

Chris