On 4/9/2013 1:50 PM, Michael A. Radtke wrote:
Contact Industries CT200C-12B1...
> 1) Is 200 amps enough?
It looks a little bit on the small side. But the price was right and you
already have it; so go ahead and give it a try!
You will certainly want the motor current to be able to exceed 200 amps,
or your acceleration will be abysmal. The Electravan is probably going
to draw 100 amps just to cruise at a constant speed (like 45 mph).
You're going to want at least 500 amps for accelerating, going faster,
and climbing hills.
But you shouldn't be running at these high currents for very long.
Contactors are good at handling high peak currents for minutes at a
time. You also won't (shouldn't!) be switching these high currents.
> 2) Why not change the jumpers so that both contactors are activated
> for reverse and neither for forward?
The normally-closed contact of relays and contactors have a lower
current rating. There is only a spring holding it closed, and it has to
be weaker than the coil's force (or the coil couldn't overcome the
spring to pull it in).
So, you don't want to use the normally-closed contacts to carry normal
forward current. If you're going to rewire it, wire it so you energize
both coils for forward, and neither coil for reverse.
One other thing: Be sure to wire it to reverse the field; not the
armature. When both coils are off, a reversing contactor typically
*snorts* the field. That's OK. But you do *not* want to let it short the
armature! You can get ruinously high currents if it shorts the armature
while the vehicle is moving!
--
An engineer can do for a nickel what any damn fool can do for a dollar.
-- Henry Ford
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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