what solenoid to use

[whiteloc32]

I have 1985 ezgo 36v system so what is the difference between which solenoid to use coud i use just the 50a or the 100a

[scottyb]

Here is some handy info from alltrax.com ....


Contactors (called Solenoids)
A contactor is basically an “electromagnetically
driven switch” capable of carry large amounts of
current. Inside the contactor are a set of fixed
contacts and a set of moving contacts. When the coil
is energized, a magnet either pushes or pulls a metal
rod and the contacts against the current carrying
components.
Contactors used in EV applications:
The contactor must be wired so it is only energizes
when the throttle pedal is depressed. Once the
contactor is energized, battery current can flow to the
controller. When the throttle is off in the “rest
position”, the throttle switch opens and the contactor
turns off, thereby removing battery power to the
controller. This prevents the cart from moving until the
operator is ready. AXE and DCX controller products
handle this function differently which will be described
later.
The contactor also functions as a primary
disconnect in an emergency… If something
happens, the driver’s first instinct is take their foot off
the throttle and step on the brake. When the contactor
is wired through the throttle (foot switch), the
contactor is very fast and will open long before the
driver’s foot actually touches brake pedal.
To ensure the proper operation of the contactor, its
ratings are very important:
• Coil Voltage
• Carry Current (continuous current)
• Break current (or called disconnect current)
• Contact material and plating (the durability of
the contact surface)
The coil of the contactor is a electromagnet device
which provides a strong enough field to keep the
contacts closed while the vehicle is being jostled
around. When turned off, the return spring in the
contactor must be strong enough to “break” the
current flow in case something goes wrong.
The coil voltage rating is important – use the
correct contactor voltage rating! Using 24 volts to
drive a 48 volt coil does not generate the required
force necessary to hold the contacts in place during
operation. Too much voltage will burn – or cook - the
coil wiring of which the contacts may not separate
when turned off. Contactor plunger binding or self
arcing will cause controller failure.
Choosing the correct current rating of a contactor
is just as critical as choosing the right size wire for the
motor and battery connections. The carrying current is
determined by the size and plating of the contacts
inside of the contactor.
Why are Contactor Ratings So Important?
OEM style cars are very cost conscience and use
lower current ratings and fairly small copper contacts
without the costly contact plating material on the
contacts. Adding a 500 amp controller to a stock OEM
70amp contactor will cause controller failure and could
weld the contacts closed causing severe damage.
When the foot pedal is released, the contactor MUST
open. If it fails to open, the battery current will
continue to be fed to the controller. In the case of a
controller failure or the motor commutator flashes over
– a small or undersized contactor may weld closed and
not open when the foot switch is opened, thereby
continuing to feed the plasma arc.
• AXE controllers (for Series wound motors),
closing of the foot switch activates the
controller and the contactor.
• DCX controllers, (for Shunt wound motors),
the foot switch switches applies pack
voltage to pin 5 and the controller applies a
ground to pin 7 and energizes the contactor.
P/N: Doc120-046-A_TN010-Contactor-Fuse-Diode-Lessons-Learned Page 4 of 9
© Alltrax Inc. 2007
All Rights Reserved
Technical Note 010: Lessons Learned, Why are Fuses and
Solenoid Disconnects So Important?
Contactor Design:
Lets discuss the contactor ratings, physical design,
and differences between Stock OEM and Performance
(or called Heavy Duty) contactors.
Breaking current is the “maximum disconnect
current” the contacts can handle and still able to
separate the contacts.
In high performance or modified EV applications
using larger controllers, motors, or heavy duty pulling
or mud buggies, you must use oversized contactors. A
contactor that is undersized not only affects
performance but is a safety hazard! If the contactor is
overloaded and can not handle the current, it will weld
itself together and the contacts will not be able to
separate in case of an emergency.
Stock OEM 70amp or 100amp contactors
typically use plain copper contacts without any plating
material. These contactors are susceptible to arcing,
carbon deposits, or contact pitting when used with high
current controllers and motors.
OEM –Vs- Performance contactors (see example
below) utilize larger contacts than the stock OEM
70amp versions. Performance and Heavy duty
contactors use special plating material on the contact
surface called silver-cadmium oxide (AgCdO) alloy. This
helps prevent pitting and carbon deposits during arcing
and increases the amount of current the contact can
make or break.
Contactor Analysis
The Prestolite SBC-4801B (Also Ametek) contactor
was used in an application with a 500 amp controller.
The contactor welded closed and the arcing during that
event caused the controller to fail. The welded
contactor could not disconnect and subsequently, the
vehicle burned. The stock OEM contactor, the
Prestolite, SBC-4801B was made for 75 amp
controllers (Curtis 1204 with 75amp continuous run
current).
Prestolite SBC-4801B – an inside view.
The contacts shown below are made of standard
copper and copper alloy, prone to arcing under
conditions outside their rated capacity. The break
current rating (i.e. the current the contactor can safely
disconnect) is rated as 75amps, but with higher
temperatures, this rating is obviously reduced with plain
copper contacts. (See manufacturing data)