All good info. Before we did our cable upgrade we did some checking with a couple mechanics as well as posted on a couple of forums to see how a 130 amp alternator (what we have in our E350 based motorhome according to the specs and my mechanic) would hold up to a 40 to 50 amp load current for an hour or two. General consensus from those who had experience with large competition type sound systems, large external light units (4 X 4's etc) and others with everything from trailers full of freezers to pump setups. etc. Anyway, the one caution was to be sure to monitor the current for excessive loads, eg, starting out with dead batteries either on the additional apparatus or the truck/van battery. However, if the van battery was already charged, none had any problem with the 130 amp alternator supporting 40 to 50 amp extended loads. We generally see mid to high 30's at idle, more when the toaster or microwave is on. In my case it is never more than an hour as the two group 31 AGM's take a charge easy and once it starts to drop off below 15 or 20 amps I shut it down. Our primary (off grid) charge source is the 320 watt(ish) solar array. However sometimes the weather doesn't cooperate and its nice to have a back up. In our case a generator is out of the question. We have been doing this for 7 or 8 years but not a lot. A bad year might be 20 hours, not so much most years. Depends. We are already over 180K on the odometer and all is well. If I blow up the alternator someday I'll probably put a 160 amp in there. Have to watch the batteries acceptance though. When the dometic fridge dies a residential or 12 volt compressor type will go in and we will put in a couple more AGM's. Meanwhile, if anyone wants to cite a success story of using the alternator as a good backup high current charge source, we are it.
On edit, keep in mind that during the charging of the coach AGM's there are no lights, fans, heaters etc on. Really most of the current heads for the AGM's.
