Dynastarter vs alternator (MD2B) electrical question

[imported_Jimmy]

While investigating the rat's nest of wires in my old wooden boat prior to re-wiring it I have noticed that both the Dynastarter and the Alternator (each with its own voltage regulator) are wired to charge the same batteries at the same time. The wiring diagram for the engine shows them each charging their own separate battery. The question is: in this arrangement are they just fighting each other or can they get along? I know it is common practice to give up on the charging capability of the Dynastarter and rely on the alternator, but it seems like it would be good to have the redundancy. Especially since the isolation diode on my alternator keeps blowing (which is one of the reasons I am looking at the wiring). How have other people wired their MD2Bs?

[imported_Conrad]

Not a good idea. Since they both balance their output against the battery voltage, which is assumed to be below the regulator's cut out point, each "fools" the other into thinking voltage is first high, then low, setting up a rapidly occilating cycle. No wonder the diodes keep blowing! Either go back to two completely isolated batteries, or disconnect one charging source. You can leave the redundant system in place as a spare if you want. Personally, I'd go with the alternator and let the starter just do the starting!

[Andrew Craig-Bennett]

There is no point in wasting time with the Dynastart's feeble generating capacity; it makes a fine starter motor, however! 20 years ago I added an alternator to my MD2 and left the Dynastart as a starter motor. The set up is still working nicely.

[imported_Jimmy]

Thanks, I'll try to figure out how to rewire it so that the dynastarter isn't charging, but can be used if the alernator fails again. I think it was wired as just a starter before I bought it, but the boat yard that "fixed" it as a condition of sale dug the voltage regulator out of a box and hooked it up "properly" and I've had nothing but trouble since. Thanks

[imported_Jimmy]

For the benefit of anyone searching the archives it does seem as though there isn't any easy way to have both the dynastarter and alternator charging the same battery bank. Information on how to have both in the same system are difficult to find, however, the solutions to this problem seem to be:
1. wiring them to completely separate batteries (as the wiring diagram shows) so the systems are separate. This solution is quite sensible since you would use 1 battery only for starting and couldn't easily use it for house power. However, since you could accidently have the battery switch for the alternator sstem turned off when you start the engine you could wreck your alternator so you need to have a clever way of preventing this.
2. you can also disconnect the charging capability of the dynastarter. This isn't quite as easy as it sounds since the voltage regulator is also a starting relay in this system. You can replace it with a regular starting relay, but then you wouldn't be able to use the charging capability if you wreck your alternator (that would be frustrating). It looks like if you just disconnect the wire that goes to the field windings in the dynastarter (or put in a switch) everything will operate normally,but the dynastarter will not generate any electricity. (that is what I am thinking of doing, if I'm wrong I would appreciate it if somebody would correct me, thanks)