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Re: (ET) 48v ET
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:
They also put in 30 amp fuses in 20amp fuse blocks. Bad idea; talk to
the guy who blew up his fuse panel. I wonder if the kit contains a 48
volt rated contactor in that series string; that could replace or
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.,
This however will not protect your contactor. Every time your contactor
opens or closes under load, there is an arc. Putting that arc out is the
job of the contactor. And when voltage gues up, the length of that arc
goes up as well.
On my solar panels, at 12 volts I get a little fitz when I measure
current by shorting the panels at the junction box (totally ok, can't
pull more than 12 amps). At 24 volts I get a nice spark. However at the
Elec-trak's 36 volt solar port I can pull a 1 inch spark with ease. I
think it gets better at 48 volts.
If your main contactor arcs and locks, how will you stop the tractor?
Probably with the main disconnect, but you might have already run over a
bush or into a parked car by the time you get it thrown.
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.