Be very wary of well-meant but --- there's no other way to say it -- erroneous advice you may get in response to your question.
It would be good if you'd mention the model alternators you will be fitting, and whether they are internally or externally regulated.
You also didn't mention what type of batteries you have in the house bank: are they flooded, AGM
, gelled, or other?
However, even without those details it can be said that:
1. there's absolutely no way of furnishing your 880A house battery bank "too much charging current", unless in the unlikely event that the alternator's regulators allow the voltage
to exceed proper levels for the state-of-charge of the batteries. The batteries, given proper voltage control, will accept the charging current
they're going to accept, irrespective of the size of the charging source. Period. Even if you had 1,000 amp alternators they'd accept the same current
, provided that the charging voltage
were correct. And, that's the job of the regulators, internal or external.
2. You could wire both alternators directly to the house batteries, with appropriate size cable and with an ANL or MRBF fuse located near the batteries. This would work OK...not optimum, but OK.
3. The only concern might be about getting the most out of the alternators when in the acceptance charging stage. Since almost all regulators determine battery charging stage by the voltage of the batteries under charge, and since it is highly probable that one alternator would be putting out slightly higher voltage than the other, one regulator
would sense a higher voltage and be "tricked" into reducing its output. This is true of ANY charging source....solar, battery charger, alternator, wind generator
, etc. HOWEVER, by this time the battery's acceptance would likely have fallen sufficiently for either one of the alternators to provide as much current as they will accept. So, it really doesn't matter.
The above is true if you have flooded batteries
If you have gels or AGMs, their charging acceptance is much higher, and you'd want to try to get your alternators to be optimized for long-term output at high amperage levels.
Blue Sea Systems makes a charge controller called a "Centerfielder" which is specifically intended to make two alternators play nice with each other when charging a single
battery bank. This is a particularly good solution where AGMs or gels are used, but it's also good to have alternator temperature sensing set up -- or an alternate means to reduce the current output -- to be sure the batteries don't manage to overtax the alternators and burn them up.
4. As for automatic switching so the start batteries can be kept topped off, there are several ways to do it. The most elegant is to use a little voltage-follower device which senses a charge on the house batteries and bleeds off enough charging current to keep the start battery topped off. These products, e.g., the Xantrex EchoCharge or the Balmar
DuoCharge, are pretty simple to install. You'd need two of them if you have two starting batteries.
There are many threads on battery switch setup, charging, combining, etc. on this and other Forums