pnichols wrote:
I don't understand all this talk about being hard on vehicle alternators. Aren't they protected from burn-out regardless of how they're used?
It sure seems to me that's the way that they coulda/shoulda been designed in the first place. I assume that my RV's Ford 130 amp alternator can supply - if I spin it at high enough engine RPM - somehwere around 130 amps as long as I want it to, or until it's temperature protection and/or amperage protection kicks in .... whichever comes first. What am I missing here? :h
Per my Ford alternator's RPM versus amperage output curve, it can deliver around 60-70 amps at true engine idle. I assume it can do this forever, as the footnotes at the bottom of the curve say nothing about "intermittent use only".
Maybe alternators in the good old days could be burnt out - but modern ones have adequate protection? I can't anyway anyhow wrap my brain around being able to out smart the built in over-temperatue and/or over-current protection electronics in modern vehicle alternators.
Regarding long term idling of late model V8 and V10 engines .... I believe that Ford based (and probably Chevy based) ambulances and other emergency vehicles sit idling for hours at incident sites. And also, how about police cruisers .... they sit idling for hours along roads even in extreme heat with their air conditioners running, don't they?
A lot of mis-information in the above quote..
There IS NO "burn out protection" built into the alternators.
You DO have FUSEABLE "LINKS" involved with the stock vehicle wiring, but they are there to protect the wiring in case of a wiring short..
Inside a alternator you have one set of brushes with one "commutator" that the brushes ride on.. The brushes supply power to the rotor and that power magnetizes the rotor..
You have a built in "regulator" (older alternators used a separate regulator which was often mounted near the battery), many newer alternators also communicate with the vehicles BCM (Body Control Module) and the BCM will control the alternator rotor current and has charging curves that it will follow.
The rotor when powered and turning is energizing the stationary coils called a stator.
The stator output is three phase AC which can't be used with a battery..
So the output of the stator is connected to a full wave diode (AKA "rectifier") which converters the three phase AC into an unregulated/unfiltered choppy DC voltage.
You also have a pair of bearings rotating also..
You have ALL of the above mentioned items crammed into a space of a 50 pack spindle of CD or DVD blanks.
Here is a real nice cutaway drawing of an alternator from the website link below..
You will notice that the regulator, brushes and the diodes are located IN THE BACK of the alternator.. Newer alternators have a fan on the back of the stator to help cool those items.. older alternators do not..
Then add in that pretty much ALL vehicle manufacturers place the alternator ON TOP of the engine and if not on top on the side of the engine but basically in about THE HOTTEST PLACE YOU CAN FIND ON A ENGINE.. Not to mention the alternator ENDURES ALL the HOT AIR being pulled through the engine radiator/A/C condenser/transmission cooler and if equipped the power steering cooler..
So what can go wrong?
The alternator will easily get heat soaked just sitting still, then add in a very long term heavy load and you can easily over heat the regulator and or the diodes.. Not to mention the wear on the brushes and bearings..
Years ago I had someone pull off in my yard when the bearings in their alternator locked up and took out the serpentine belt.. They lost battery charging, power steering, engine cooling (no water pump turning)A/C and anything else driven by that belt.. Was a fairly new truck..
Should be pretty easy to see as to why it isn't a good idea..
GOOD DESCRIPTION OF AN ALTERNATORPer the website above.. (please pay attention the bolded section)
So what is the purpose of the alternator ?
An alternator is designed to maintain the state of charge of a cars battery while the car is being driven by providing the energy required to power the cars electrical system.
What are limitations of the alternator ?
ALTERNATORS ARE NOT DESIGNED TO RECHARGE A LOW OR DEAD BATTERY !
Charging a dead or low battery is the job of plug in battery charger only!
As stated above an alternator is designed to maintain the state of charge of a battery. Due to the huge power requirements of the normal operation of a cars electrical system today the alternator usually runs at or near its maximum output the entire time the car is driven. A dead or low battery adds to the work the alternator is required to do. There simply is no way for the alternator to recharge a low or dead battery and power the electrical system at the same time. Low or dead battery would happen to describe a RV battery which has been heavily discharged..
as for ambulance or emergency type vehicles that USE IS addressed by the vehicle manufacturer in a "ambulance/emergency use" option package and certifications.. Does not apply to non ambulance prepped vehicles..
Do what you want, it is your vehicle..
