Shredding Alternator Belts Story

Just disintegrated my third alternator belt in 1800 miles, so something is up. I had what I thought were plausible reasons for the first two failures, but this third one has caused me to take a much closer look.

First some background: I converted my car from the original single 7M ALT/WP V belt to a dual belt setup so I could use the larger 11M V belt to drive a high output alternator (for an electric AC compressor). The 7M belt uses the stock water pump and crank pulley, with a factory tensioner assembly I sourced. This belt is working fine and seems very happy.

The 11M belt is driven from an existing V groove (formerly use to drive the AC compressor) located inboard of the 7M groove, and runs directly to the alternator with no idler pulley. Belt alignment and tension of the ALT belt do not appear to be the issue.

The ALT pulley, which is an eBay find, is I believe the culprit, as it's a generic 7/16" pulley with what appears to be the normal US 40 degree 'V'. From what I learned today from Gates belt specs (and roughly confirmed by measuring the angle on the new belt), the Gates Poly belts used on our cars require a 60 degree pulley. So clearly a mismatch which would not allow the belt to fully seat in the pulley, hence the slippage/melting/destruction. I'm somewhat embarrassed I didn't notice/figure this out sooner.

But how to resolve? Two questions:

Has anyone else done a similar 1 to 2 belt conversion and where did you source the alternator pulley? I've done a couple hours of internet searching without results thus far. Having one machined from scratch is definitely an option, but would prefer an off the shelf solution.

And: Is anyone successfully using a single 7M belt to drive a high output alternator under high current loads?
Probably not a good idea, but thought I would ask.

 

The photo is the remnants of belt #3 which melted during my drive to test my now functioning electric AC. I'm guessing the increased alternator load on the belt caused the extreme carnage.
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