Quote:
Originally Posted by joezzz
My conversation with Balmar,based solely on recharging of batteris indicated a larger alternator doesn't mean faster charging.
Why? As they told me, each series battery can only absorb a fixed amount of charging amps. So larger is not better. If your battery can only handle lets say 45 amps/hr. A 75 amp alternator will not charge it faster.
|
joe,
Not to seem to be piling on, but...
You're right, as far as it goes.
However, the
concept of a "larger" alternator is to reduce the heat and wear on the alternator and belt.
Regardless of battery types and generally sizes, the
concept in this example may be scaled:
Example:
400 ah house bank, AO goes to house bank, reserve or start bank charged via VSR
Statistics and reality meet [from years of my own operation and reading
Maine Sail!!!] and indicate that for a 50% SOC house bank, the battery acceptance CURRENT
for this sized wet cell house bank will be in the range of 50A, perhaps higher at first startup, but rapidly tapering off to that as the bulk phase does its work as the voltage rises to the setpoint and amperage is maximized.
Given that, does one choose a 45A alternator or a larger one? The 45A will "work" just fine, right at its max. But small case alternators, which most of us have, don't work well for very long at rated max load.
So, we buy larger alternators, amperage not size, separate topic, and find that they last longer because even at PEAK required output (i.e., 50A) they are running at half their designed COLD rated output.
For the coastal sailor with a traditional engine setup, the max load that a usual 3/8" belt can deal with without heavy belt dust and disintegration is this load and wrap around a 100A alternator. If the battery acceptance is higher than 50A because of going lower than 50% SOC or other reasons (a high use load when running the engine) the 100A alternator can handle it for a short period. Any time longer the belt squeaks and/or dies prematurely.
Of course, there are more sophisticated
electrical charging systems that many on this forum have employed, including all the other charging sources like
wind, solar and generators [which serve to decrease the discharge and increase the SOC and reduce the battery acceptance load when the engine starts]. And different battery types that, if they can accept more amperage, completely favor the larger alternator.
But this response has been deliberately focused on alternator sizing in response to your post, and why, within reason, bigger actually is better. And once the choice to buy an alternator is made, there is only an incremental difference in
price.
That's one of the Whys.