Universal motor requires speed control that will proportionally improve motor life. Please help.

I have an 1800 watt, brushed universal motor that is significantly stronger than I need a lot of the time. I would like to be able to control its output to buy more life. I am able to control the speed using phase control via a triac circuit, however, this hasn't actually bought me longer motor life.

Transformer Life

I have been able to get improved life using one motor on a transformer. This only gets me two speeds though. This is where I am at a loss. Am I missing something that can be used to limit power another way?

If this takes considerable thought or design time, i'd be happy to collaborate or potentially offer a reward if someone is able to resolve the issue in a way that gives results much like a transformer would (Half power approximately doubles life).

Thank you.

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Daniel Foster
UC Davis Mechanical Engineer. Trying to expand my electronics knowledge via various home improvement projects.