Alternator

pnichols wrote:

Chum lee wrote:
To a certain extent, your chassis alternator output (voltage and current) is dependent on the current state of charge of your chassis battery(s) and the loads placed on the alternator by the VEHICLES electrical system. If your chassis battery is fully charged, expect the alternator output to be a fraction of it's maximum rated capacity until the existing loads drop the charge in the chassis battery. Ford engineers designed their charging system that way to improve fuel mileage and to prevent people from doing what they want to do . . . . . charge the batteries in their camper with the chassis alternator.
Chum lee

I not talking about a pickup truck here ... but with respect to our small Class C motorhome on an E450 V10 chassis with "only" a 130 amp alternator: The V10 engine battery I have installed is an overkill Ford OEM battery model intended for their diesel trucks. The coach has two 115 AH Group 31 AGM batteries wired in balanced parallel.

Whenever the V10 is running, the two coach batteries and one engine battery are all connected together in direct parallel via a high amperage continuous duty 12V solenoid. I know this because I have an engine battery readout voltmeter mounted on the dash and a coach battery readout voltmeter also mounted on the dash - and they both read nearly the same all the time - which means that all three batteries are connected in direct parallel when the engine is running. There appears to be no isolation diodes involved between the engine battery and coach batteries.

I've also mounted on the dash an ammeter that reads the current going into, or out of, the coach batteries.

After drycamping a bit, whenever the coach batteries are down to around 50% (12.0-12.1V reading on their dash voltmeter), I sometimes start up the V10 and idle it for an hour or so to conveniently and very quietly to partially top up the two coach batteries. The coach battery ammeter (on the dash) will sometimes spike to as high as 80 amps at first (V10 idling), and then gradually taper down as the coach batteries are being boost and bulk charged via the 130 amp Ford alternator. The voltage output of the alternator (as indicated by the voltmeter on the dash) will start out at 14.X volts at first, and then gradually taper down as the coach batteries charge up.

So the bottom line is ... yes, some stock engine alternator systems can indeed be used to charge camper battery systems just fine.

As a sidenote, the performance curve for our V10's 130 amp Ford alternator indicates that it can indeed output around 70-80 amps at engine idle RPM speeds, so it's performing as expected ... at least in our 2005 E450 based motorhome. Even though the engine itself may be idling at only 550-650 RPM, the pulley system powering the alternator spins it a lot faster. In order for an engine alternator to output high currents at low engine speeds, the engine merely has to be able to delivery enough horsepower at idle so as to spin the alternator at whatever RPM the alternator's power vs RPM curve requires for the desired amperage output in the application. It may be difficult to locate the power-vs-rpm graphs for many alternators, however.

Yes, my '99 F53 (V10) does the same thing and on some mornings I often run the engine at idle to put a little charge (little is the key word) in the house batteries. As theoldwizard1 mentioned, the newer vehicles are more sensitive to charging conditions. The problem is, when idling with the alternator putting out close to the maximum voltage/current, even though the alternator is over driven, the cooling fan on the alternator needs to be able to dissipate the additional heat generated with the engine at idle. Since the idle is stabilized, available horsepower isn't the issue, . . . . IMO, cooling is. I'm not saying that it will fail overnight, it just gets hotter. Heat kills, . . . . . more heat kills more quickly.

Chum lee