On Fri, 02 May 2008 06:42:53 +0000, Winston wrote:
Don Foreman wrote:
On Thu, 01 May 2008 19:05:20 -0600, gary556@... wrote:
I'm trying to wire a Freightliner to operate the tarp motor.
....
If you use starter solenoids, you'll need four of them if you want it
to run in both directions. The switch can be a SPDT center off or DPDT
center off toggle switch. The solenoids would be arranged in an H
with top of the H going to + battery and bottom of H going to ground or
- battery with the motor being the crossbar of the H.

-----------
| |
S1 S3
|--M--|
S4 S2
| |
-----------

The switch would then energize diagonally opposed pairs of solenoids S1
and S2 or S3 and S4, one set for up and the other set for down.
....
http://metalworking.com/dropbox/tarp.txt
http://metalworking.com/dropbox/tarp.JPG

On the right side you see a three position switch. Select 'Tarp On' and
the motor drives the tarp over the load. The limit switch stops the
motor when the tarp is in place. Select 'Tarp Off' and the motor removes
the tarp from the load. The other limit switch stops the motor when the
tarp is off.
....

Some other posts have said to just use a switch rather than switch +
relays; 20A 12V DPDT center-off switches are readily available, eg
http://www.parts-express.com/pe/show...number=060-376 or page
89 of http://www.delcity.net/delcity/docum...9_switches.pdf
if 20A is enough for the tarp motor. Of course if the limit switches
aren't heavy enough to switch the motor, you'd need relays anyway.

Note that in the dropbox/tarp.JPG diagram, the K3 and K4 coils are
shown backwards. Hooked up as shown, the internal diodes or the
wiring to them would burn up on first use.
-jiw