Those of us with recent Cummins engines (since they started using air preheaters) will notice that the factory alternators are actually pretty respectable. My 2000 270Bs come with 105A Delco alternators. You would think this means I can charge at over 200A with the two installed in Dirona. Well, it turns out that the 105A specification is more of a marketing number than an engineering specification. Yes, they can produce 105A of output. However, they can’t do this for more than a few minutes at a time, which is close to useless. Now that we know that they can’t really produce 105A continuously, what can they do?
Sometime back I wrote up an article investigating what charging rates can be produced continuously and reliably and how to achieve that number at minimum cost and hassle. It was published in the May 2007 PassageMaker and we just put it up online at: http://www.mvdirona.com/TechnicalArticles/ChargingSystem.htm. I’ve found that you can reliably get 70 to 80A and the alternators will run trouble free for years configured that way. The article documents the investigation, discusses the limiting factors and shows how to configure your charging systems to get good results.