There are a lot of other factors at play other than the simple distribution
of amps. Most of the GMC systems are not set for the larger alternator.
The wiring to the alternator should be increased if you really want the
increased amps.
The single belt should be changed to a dual or a serpentine to deliver
enough power for the load under a heavy charge. You are quite right that
you only get the load you are using but if you never need the extra amps no
real reason to increase to the larger alternator.
The diode isolators will increase their voltage drop with the higher
current load and therefor the power they waste in heat so they should be
increased in size.
If you are going to charge the batteries at a high current you should get a
smart alternator that also watches the temperature of the battery/s so that
you do not over charge them. (See Ample power and Heart systems)
If you want to recharge the house batteries quickly, it would prob be
better to crank up the 6000 watt Onan with the smart charger and use a
system designed for this function.
Most of the time when you are driving, the average run time is 4 hours
which is enough to recharge all of the batteries. In fact we are probably
over doing it at that since most of the alternators are supplying 14 +
volts which is too much for four hours if you do not have a smart
alternator. This would be the same with any alternator since our
batteries are seldom dead.
It has been reported here that most of the 100 amp plus alternators do not
supply that current. Some have speculated that the alternators are the
same just lower drop diodes. Since the output regulator is temperature
limited to really get a system that will provide these amps you should
design it with all the components not just change the alternator.
Not an easy answer---- not a clear need IMHO.
gene
>Sorry, but the energy required to drive the alternator is proportional to
>the output. Therefore a 80 and 140 amp alternator that are actually
>producing 60 amps each provide an equal load on the engine.
>
>I can also say that my experience with large battery banks has shown that a
>larger alternator is quite important get the system voltage up. Running
>systems undervoltage causes more internal heating of wiring and of the
>alternator components themselves.
>
>Everyone's needs are different. but if you are running a double set of golf
>cart batteries the battery bank is 470 amp hours. If that was somewhat
>discharged it might require 400 amp hours to recharge. If you run the 80
>amp alterator at full output on a continous basis it will definitely
>overheat. But that aside the GMC with its normal electrical demands could
>require 25 amps of that. That would leave 55 amps per hour left. So a full
>8 hour run would be required to recharge the bank. But the practicallity
>is that full continous oupt would be more like 60 amps and would leave
>only 35 amps per hour for recharge..
>
>I think that a larger capacity alternator is necessary if you are utilizing
>a large battery bank and/or an inverter
>
>Bill Hubert
>78 Royale
>
>>
>>
>>>Sirum, whose judgment I trust, 80 amps is big enough for the GMC. >>
>>
>>Dave - I agree with your statement. What would be running that would need
>>that much amps? An 80 amp alternator seems to sufficiently charge up my
>>batteries just fine. Also, one should not overlook the fact that a 145 amp
>>alternator will be drawing more horsepower from the engine than a 80 or 100
>>amp would.
>>
>>I suppose that if someone used an inverter to power a lot of things they
>>could fire up the engine to supplement the batteries but that would be the
>>exception among the GMcers that I know.
>>
>>Emery Stora
>>77 Kingsley
>>Santa Fe, NM
>>
>>
>
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/
