cummins 6b5.9 alternator failures

96bounder wrote:
Why didn't they take pulley off and remove the fan instead of whacking it up like that.also 10 si and 15 si are same size unit.
Difference is internal 10 si units are 66 amps at best.the 15 si are generally 78 amp and with proper internal parts can be built to a 94 amp.
As for the OPs question.,if your installer is not properly charging your batteries that is destroying your alternators.They are not designed to charge weak batteries but more so to maintain what you have.
I own a starter/alternator rebuild shop and will gladly provide any info I can to solve your problem .

Thanks for the thoughts and offer ... I can't really answer the 'why' question. I can guess that they needed a spacer to put the pulley in line with the others (it is ...) and that was as easy a way as any for them.

The one time that I changed an alternator on my previous MH, I noted that the prior owner had replaced about 10k mi earlier. And I also had noticed that every time I left a campground the fan belt tended to squeal for at least 10's of minutes. When I made the mental connection to asking the alternator to charge up a bunch of deep cycle batteries, I started running the genny in the AM before we'd leave and give them a bit of charge. That alternator was still fine after another 30k mi when we sold. When we bought this Winnie and had the alternator replaced shortly after, I defeated Winnie's coach battery charging relays - I put an additional switch in series with the solenoid windings so that I chose when to connect motor and coach batteries. I only energize now when the motor battery is too pooped to start. So this alternator has virtually never charged anything but the motor battery and auto systems (headlights, etc.)

The easiest answer to my situation would be an alternator with the same form factor as the 15SI, but internal fans so as to avoid contact with the belt tensioner. From what I can see, the Delco CS130 has the same form factor and uses both an internal fan for the diodes and regulator and an external fan for the windings. As an apparent bolt-in this might at least have a better chance of survival with the external fan mutilated, given the internal fan. It's not shown in the pics that Don posted for me, but there is a 3rd mounting point on the back side with a bracket mounted from the exhaust manifold bolt. It looks like the CS130 has the matching tapped hole and thus would be a direct bolt in.

But I'd still worry about a CS130 with only the internal fan. Probably better than what I have had, but I'm aiming for the last alternator this rig will require. So there is the Delco CS130D, which has 2 internal fans. BUT ... the standard CS130D case has more distance between the mounting ears than the 15SI or CS130. I found a site that claims to have CS130D with 6.6" between the ears, so maybe that could be OK. However, none of those appear to have the grounding hole on the backside that Cummins used as a 3rd mounting point. I'm assuming Cummins added that brace in order to support the alternator against the belt loading of the big radiator fan, so I'm reluctant to delete it.

Would you have a suggestion then for an alternator with the same form factor as the 15SI that doesn't require an external fan? It would also need to put the pulley in the same position along the motor axis as the 15SI, to maintain pulley alignment with the rest of the pulleys in the system. Otherwise, I'd need to make new brackets anyway and instead I'd probably just space the existing brackets further away from the motor (simple spacers ...)and use another 15SI

Thanks
Gary