something you might consider doing, that is if you have sufficient hydro power available to give up maybe 50 watts or so
like everything in life compromises must be made, if you can't give up 50 watts or so, you might have to deal with biannual burnouts of somesort.
if you have sufficient power, i would replace the alternator with a standard wound field unit, and control the field with a balmar controller.
with the controller you get the 3 stage charging, you get programmable voltage setpoints which is nice, but also you get an amp manager as well
the amp manager function works to match your alternator to the amount of power you have available, you might find that this one function is the most useful of all functions because...
it might be that you run at 800 watts more or less continously, but have frequent excursions to over 1000 watts for suffient amount of time to cause your heating problem. the controller can make sure that does not happen.
a lot of folks get all anal about getting rid of the wound field in favor of magnets
in an effort to reclaim field current losses, this is really most important in small wind machines in light winds where most of what you generate is being used to drive the field, however
in an engine driven and hydro where you have consistant torque/rpm available, one might well be better served by keeping the wound field and not going the pm route.
the compromise being the loss of maybe 50 watts, but gaining control that you cannot have with pm alternators without sophisticated electronics. simple reostat control can limit output current or voltage but not both at the same time.
i would give it some serious thought if it were me, and i would give some thought to using a large frame hd truck alternator as well. i have a prototype alternator that i have been working with, it will produce 57.6 vdc at 70amps with no more than 45 watts of excitation current, no way am i to be persuaded to dump the wound field in favor of any magnets, 1% of output power going to field excitation is so low
that it is hard for me to conceptualize how magnets are going to save me anything
likely they would cost me in added eddy currents/hysterysis because of the shape of the magnet poles not being what they would need to be, added distortion likely would also cause issues and effect efficiency in a negative way... it just don't take much of a problem to equal 1% of output with the result being an alternator that ended up being less efficient that what it would have been had i left it well enuogh alone.
this is the problem i have with the claims of some of these folks that sell modified
delco alterntators, their claims might hold up in certain low wind applications but
they don't hold "water" in appications where you have consistant power/torque/rpm such as hydro, or engine drive.
i might also add the balmar controller also has an optional temp sensor for both the alternator and the battery bank,
the temp sensor for the batteries works to allow temp compensated charging of the batteries and also can shut down in case the batteries get too hot,
the temp sensor for the alternator monitors the alternator temp and if it gets over ~220 degree's it will go to half output, cutting the alternatot to half loading and allow it to cool off, or failing that cut the field off totally and allow the alternator to cool down. that too would save your alternator and allow for much longer run times.
if you are interested in controllers, do a search for
balmar regulators such as the mc612 and mc624
xantrex regulators such as the xar12 and xar 24
ample power makes a couple of very nice units as well
the english have at least 2 companies that make and sell their versions
as well for folks over the pond, look for marine controller/regulator
older units made by heart interface are also very good, if you can find a good one
hehr power also made a nice one that uses trim pots to control voltage, and amps
in my opinion the cadillac of cotrollers is the balmar MC612 or MC624, not sure they
make one for 48 volts yet, but there are simple work arounds for that issue.
sure would be nice to know what your resource is valued at? how much power is available from your hydro?
be even nicer to have your problem!
bob g
bob g