My Ford diesel alternators were rated at 3000 rpm, so I assumed the difference between gas and diesel was higher output at lower rpm (diesel)
The alternator RPM rating is the RPM of the spindle shaft, not the vehicle's engine. The stated output rating of an alternator as stamped (or printed) on the alternator itself is always at 6,000 RPM. It may be that 3,000 RPMs on the engine is where the alternator is at 6,000 RPMs. The only real difference between a gas alternator and a diesel alternator is the pulley diameter and the shaft length (sometimes). It has to do with horsepower and torque of the engine driving the alternator. But they are all rated the same way to the same ISO and SAE standards.
My current Ram Van 130 amp has over 400,000 on it between 2 vans, and works correctly for accessories and battery charging.
It's almost certainly not putting out the same voltage and amperage that it did when new, but it's obviously putting out enough of both so that it's still working. But the diodes wear out (or burn out and fail), the brushes wear out just like any other wear part (but gradually, think shock absorbers wearing out over time) and the contact rings get worn. Road grime, salt and engine oil and coolant speed up the wear. 400,000 miles is a really lot on an alternator, as most have a lifespan of 100,000 to 150,000 miles (or 8-10 years, whichever comes first).
I had the clutch pulley fail on mine once, so I changed it out then, but otherwise I change mine out when the charging voltage is weaker than it should be or the amps going back to the house bank is lower than normal. That ends up being about every 150,000 miles. I could probably let it go for another 50,000 to 75,000 miles and it would still work, though.
Everything is trouble-free right up until it starts giving you trouble. It's like one guy I know with a Sprinter who used some high dollar AGM batteries for his house bank. They were trouble-free, worked great. He didn't believe me that he'd have to replace them within 2 years because they wouldn't have any capacity left. But they were trouble-free, right up until they were nothing but trouble. The problem was, AGM and wet cell batteries require difference charging voltages, and the alternator is always going to put out what the cranking battery and system voltage requires, which is less than that of AGM batteries. So, for 2 years he was chronically undercharging his battery bank. which results in sulfation and lowered capacity, until eventually the batteries were dead.
Now with the 1000 watt class A amplifier, JL sub and 160w Pioneer deck, Galaxy CB and Espar, I may have to rethink things...I planned to use battery bank to absorb spikes and provide entertainment when parked...got a 27 Icd flatscreen with no current home as well...
The Espar will only draw on average about an amp per hour, so that's not a lot of concern. You need to figure out the input amperage or each device and add it up. A 1000 Watt Class A amp will pull 125 amps or so. Great sound, but astonishingly inefficient.
Just an idea...if I put in a proper deep cycle charger, like a solar type but 12 volt, would that limit the alternator draw to the rating of the charger, Eg. 30 amp? Then I could wire all the extra goodies to the batteries and not care, they'd let me know if it was too much when the batteries discharged...keeping stock alternator and fuel mileage the same..
Well, first, you'll never be able to put enough solar panels on the roof of the van to get anywhere near 30 amps out of them. Second, a bigger alternator or one that's outputting at or near max output will give you a fuel mileage hit, but it's minimal. five percent at most. I wouldn't get too concerned about that.
There are alternatives to just raw charging from the alternator. One is the battery-to-battery chargers such as the
marine battery chargers where you connect the charger to the starting battery and it piggybacks the current off that from the alternator. Another way, and it the ideal best way, is to use a
Sterling Power alternator-to-battery charger, which connects directly to the alternator, and then from the charger you connect the house bank and the starting battery. It will charge each battery independently and you can program the correct voltage for each, allowing you to use AGMs for the house bank and a standard wet cell for the cranking battery.
RLENT has that system installed, so if you want some detailed information about it, he's the one to contact.
As for the "...they'd let me know if it was too much when the batteries discharged..." is concerned, visualize a picture of a face palm here.
How to rapidly decrease the life of a battery (or, Batteries Don't Die, Their Owners Kill Them)
Undercharging: consistently failing to fully recharge batteries leaves them with lead sulfate that hardens on their plates—they become sulfated—and gradually lose their ability to perform. Increased resistance when charging causes falsely elevated voltage readings, essentially fooling the battery charger, leading to further undercharging, in a downward spiral. Beyond a certain point, a sulfated battery cannot be returned to a healthy state, and you need a replacement. Keep your batteries charged, and equalize your wet cell batteries every six to eight weeks in temperate climates, and more frequently in the South and in the summer.
People run stuff off their batteries until lights dim, inverters scream or shut down, then crank the engine for 15 or 30 minutes and think they've recharged the battery. Newp. If you have a 100Ah battery and draw 50 amps out of it, you'll put back approximately 35% of its capacity after one hour charging at 20 amps (never charge a wet cell battery at more than 2 times its capacity). It'll take another 3 or 4 hours to get the battery up to 85% of capacity, and another 5-8 hours to finally push that final 15% back into the battery. In other words, it takes 6-14 hours to recharge a battery at 50%, more if it's less than 50% discharged. Even if just 20 amps were pulled from the 100Ah battery, it'll take 3-8 hours to fully recharge. Stop short of full and sulfation begins to occur.
Overcharging: especially fatal to Gel and AGM batteries, consistent overcharging (NOT equalization) boils the electrolyte out of the cells, and can even lead to thermal runaway, with the battery becoming hotter and hotter (and can catch on fire or explode - which is really bad when it happens on a boat).
Excessive deep discharge: don’t completely discharge a deep cycle battery if it can be avoided. The deeper the discharge the less life you will get from the battery. The ideal method is to charge and discharge the batteries through the middle range (50 percent to 85 percent) of their capacity and, if they are flooded batteries, to equalize them periodically. Leaving the battery in a fully-discharged state, for example during winter storage, causes it to become sulfated. When you discharge the batteries to the point where things stop working, you've long ago passed the point where you should have stopped discharging.
Excessive deep discharge and chronic undercharging, which is what most people do, is the surest way to just murder your batteries. They'll last 12-18 months instead of 5-8 years.
If you're serious about a house bank for use other than recharging a laptop, a light or two, Espar heater, roof vent fan, and a few small accessories, you need a
battery monitor. A battery monitor keeps track of all amps in and all amps out, and thus the state of charge of the bank. It's literally a fuel gauge for the battery bank. It will let you know the amp draw at any given time, and more importantly let you know when you're discharged down to 50% and thus need to recharge. The alternative is to become Rainman, or just guess.
but after researching house batteries im more confused than when I started.
