2021 E450 dual alternator

theoldwizard1 wrote:

pnichols wrote:
Large and reliable alternators will probably become more important as lithium coach batteries become more common in motorhomes. Supposedly lithium battery banks charge fast - but only if one has a charging method that can deliver the high currents that the batteries will accept. For dry camping - especially when many hours of enough solar aren't available - a large capacity alternator driven by an idling chassis engine might be very useful.

First, I would not want to try a put more than 100A into ANY battery for more than a few seconds. Bad things can happen and at that rate they will happen fast !

Second, you really should have a multi-stage charger to do the job properly !

Third, no automotive alternator is going to put out more than 13V "are idle". Typically it takes 1500-2000 RPM to get 14V. Buy a DC-DC charger.

I think that emergency service vehicles often have dual alternators.

And that is the only reason why someone would purchase a vehicle with 2 alternators !

For years (both the coach and chassis of my E450 Class C were manufactured as 2005 models) my idling V10 has spun it's alternator fast enough to, for a bit initialy, put out up to 70-75 amps into my ~50% discharged AGM coach batteries (I use 2 deep cycle 12V AGM batteries in parallel).

I watch coach battery in/out current flow rates on a shunt-based digital ammeter mounted on the driver's side cab dash.

The voltage of the chassis 12V system reads above 14 volts initiallly for a bit, and thereafter for 2-3 hours - as the coach batteries come up to full charge - this chassis voltage remains in the high 13.X volts range. When traveling, after the coach batteries have become fully charged, the chassis voltage usually remains around or above 13.5-13.6 volts.

I watch the above voltage levels on a couple of digital voltmeters mounted on the driver's side cab dash. One voltmeter shows chassis DC voltage and the other voltmeter shows coach DC voltage. Obviously, whenever the V10 is running, both voltages must at all times read very close to the same - if the chassis battery/coach battery interconnect solenoid is operating correclty and with no resistance in it's contacts.

The pulley size for the stock 130 amp alternator is such that the V10 always overdrives the alternator RPM at about 1.72 times faster than the engine crankshaft RPM. The stock 130 amp alternator output versus it's RPM and engine RPM published performance curves support what I see happening on my ammeter and voltmeters mounted on the cab dash.

There is one situation in which the alternator voltage applied simultaneously to the chassis and coach batteries reads in the low 13.X volts range ... that is when traveling in VERY HOT ambient air temperatures. It appears that the Ford systems are designed to provide just about perfect voltages to a lead acid based chassis battery versus ambient temperatures ... which winds up being also what the coach AGM batteries also require and get ... since both battery systems are connected together via the coach interconnect solenoid whenever the V10 is running.

These systems are performing just as Ford and Winnebago designed them to play together. Only the three digital meters that I installed on the dash are non-stock ... so that I know what's going on with these 12V systems as we camp and travel.