alternator question

As an example of an alternator output curve, here in this .pdf on page 6 of 7 are output curves for the 130 amp alternator in our 2005 E450 Ford V10 motorhome.

These curves show alternator output in amps versus temperature versus alternator RPM. Note in the chart just above the curves that our V10 engine alternator is OVERDRIVEN above engine RPM by a ratio of 2.72 to 1. This means that when the engine is idling at around, say, only 600 RPM - the alternator is actually spinning much faster than this. To determine approximate maximum alternator output at any given engine RPM, multiply engine RPM by 2.72, then use this RPM on the chart to see what amperage the alternator is capable of putting out at that engine RPM:

https://www.fleet.ford.com/truckBBAS/non-html/2005/vs_pdf/05elect.pdf

For our case I estimate off the curves that when the V10 is idling, the alternator is capable of providing 60 - 70 amps in combination to the chassis electrical system and the motorhome's batteries. I have seen the alternator providing up to 50 amps into partically depleted coach batteries while the engine is idling. (I have an ammeter permanently mounted on the cab's dash that monitors current into and out of the coach batteries.)

Don, with the electric fuel pump, an electric fan, an electric AC clutch, ignition, et al, it may indeed be thirty amps. Add cabin fans, lights, action, camera, and the total may jump to 50 amperes.

Who says fast idle is not possible on Gas Engines? (It is, however, an add on, not a stock item in most cases)

The amps is at cruising speeds or at Maximum speeds depending on who rated it, at full idle it may drop to zero.

Hi,

So we have 90 amps to work with. But--how many are used by the engine to keep running? 30?

Yeah, think about those poor bearings when an engine is wound tight, going uphill or passing somebody.

18,000 RPM. Woo Woo !

Thanks for the replies

MEX you answered the question.
I never thought about the alt going 2.5 tims RPM
Dave after years of being a F150 fan,my next truck will be F250 w/camper pac
Can you give me the true MPG for the 6.2.I would like to get aleast what I get with my old 5.4/4speed witch is 16.5-17 hiway empty and 13.4 w camper,7550 gvw

RWD, I put one on my 2012 Ford gasser. Ya just plug it into the OBD port and hook up a couple of wires under the dash.

I have it set to idle the engine at 900 and it is energized by 12 Volt input which I supply from the #3 Upfitter switch.

RWDIII wrote:
If an alternator is rated 200 amps,why cant they tell you at what RPM this rating is good.

The world is at your fingertips.

I know the rambodubuilder.com site has the outputs for Ram products.