I need to convert a 12v dc circuit to 6v dc to operate a power convertible top motor. I have not been able to find a regulator rated at more than 15A can I parallel ( 2) 15A regulators to get 30A

 

You can parallel regulators, but you must put some resistance in series with the regulators to prevent a situation called "current hogging". The amount of resistance depends on the regulators. Best to have the motor rewound for 12 volts. More info on the application like duration, frequency, ambient conditions, etc. might get you a better answer.

 

With linear regulators, half of your energy will be wasted as heat.
You may want to consider using a buck switching regulator instead.

 

What is the duty-cycle of the motor operation? A power convertible top motor likely will overheat if operated for more than a minute or so at a time.

 

I need to convert a 12v dc circuit to 6v dc to operate a power convertible top motor. I have not been able to find a regulator rated at more than 15A can I parallel ( 2) 15A regulators to get 30A

Take a look at the datasheet/appnotes for regulators such as the 78xx/LM317 etc, some show that you can put a series resistor in the input lead that develops a volt-drop when current is drawn. That voltage can be used to drive a PNP external pass transistor.

Download a few datasheets and you will find example circuits, you need a base resistor for the external transistor to protect the B/E junction - you can use multiple external pass transistors for more current, each transistor needs its base resistor for B/E protection and current sharing.

 

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