Try it again with a subject line!

I started building an observatory with a roll off roof about 3 years ago.
The structure itself is finished.  The roof probably weighs about 2000 lbs
and rolls on steel wheels and while it can be pushed by hand, it takes a far
amount of force.  Not being fond of being cold, I constructed the mechanics
to roll the roof back using a couple of 24v dc motors.  The controller box
uses a 16F877 as the brains.  I am using (trying to at least) to use the PWM
to control the motors with.  The output of the PWM goes to a 220 ohm
resistor and then to the gate of an IRLZ44 (N-channel 60v 50A FET) which
between the motors and ground.  There are a pair of relays that reverse the
leads of the motors to change direction.  I am aware of back EMF and the
need for a blocking diode.  I have a blocking on each relay coil and another
diode between the +24v and the FET.  The FET works the first time, ramping
the motors up in speed, but after the relays switch the first time, the FET
becomes a dead short.  At first I thought the motors were drawing too much
current, so I tried two of the IRLZ44 paralleled - same result.  Anyone got
any suggestions?  I would really like to get this finished.

If the word pictured is not clear enough, I can place the schematic on my
web site.

Thanks to all,

David V. Fansler
DFansler@MindSpring.com
www.DV-Fansler.com

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