Soft start a 12V DC motor, max 250A, possible?

[jpanhalt]

does anyone here really think OP can diy a 250 amp PWM motor controller?

I did.  It was my first project when I got back into the hobby in my late 50's.  The aforementioned controller for a 6-volt long-shaft Ford starter at 12V drew a lot of amperage (not legal for contests).  It was nowhere near adequate for continuous use, but quite capable for winch launching sailplanes of several kg and wingspans of 4m.

[BeBuLamar]

I suggested a motor drive (speed controller) but the OP said that it's too expensive and he only wants a soft starter. While I don't know of a soft starter for 12VDC motor I have used them for 480VAC 3 phase motor often. The application of soft starter is for the case when you would want to run the motor at full speed all the time and just want to limit the inrush current. Golf cart and most battery operated vehicles have motor drive to control their speed. You wouldn't want a golf cart to run only at full speed do you?
So when someone said to use a controller from the golf cart I asked do golf carts have soft start and not speed controller?

[jpanhalt]

I am not above scavenging junk yards, aka recycling centers.  I still think the TS's best option is the controller from a used or junked golf cart.  Here's the very first hit on ebay for golf cart controller: https://www.ebay.com/itm/276545575375?itmmeta=01J2HRC589DN8WVMGVQ5EC246T&hash=item40636699cf:g:Jx8AAOSwPABmjmqn&itmprp=enc%3AAQAJAAAA0CuaI5rCM41oRaddcR%2B8amB1BhH4N8HiXokUhC3Y3pPz0wNwsnjOdLrEm51eFIc7NaCEAzhyVeYLAsQ350q0lP1yTAZItSEFg4ErHBYiTjXd%2BfhNelfyNBXm6pkjHlxs%2BoBDdFIVHymItt4mUG8WShJQOrkgDiriAZXjIfZxn%2BUfWnTWYb9F894d3V2hAIbZ3wfV0OALQOaO1K9jI6CRxUKouzoraUTG9QrMI7fKehwcXbQ1cpMMZqbGG1P6c2YDQCdJSmDF%2B908hrGB25C8z1U%3D%7Ctkp%3ABk9SR5jUsLiUZA

That's new and less than $200 USD.  What would one from a junked cart cost?

Edit: Spelling

[Smokey]

The initial inrush on a brushed motor is huge.  It (often) quickly (25ms ish) tails off to the run current based on the load.  Go put a current probe on a car starter and watch that on the scope when you crank over your engine.  It's shocking the first time you see it.

The "simple" solution is you need an actual motor controller.  Something that does torque (current) control at a minimum.  This will limit the huge inrush peak until the thing gets spinning by actually regulating current. Measure your "run" current and size the controller for that, not the uncontrolled peaks. 

There is some stuff in the EV space that would probably work.  Check these out.
https://kellycontroller.com/controllers/brushed/