Have alternators become more heavy duty?

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I know people suggest not to charge a dead battery with vehicle's alternator. I think a starter/alternator rebuilder even told me that years ago.

I know the alternator in my Ford truck is an extra heavy one, but the supplemental heater is a 115 amp load that comes on as soon as the vehicle is started and stays on until the engine is warm. Assuming it's cold and heat is on.

That just seems like a huge load for 15 or 20 minutes.
 
I know there is a big difference between the 91 and 97 Ford diesels of mine. 97 has a fuel filter heater and would think that's still on newer trucks too.
 
Yeah, it's a crazy amount of power. My Mercedes has a 180 amp alternator. Has heated seats and a bunch of other electronics.
 
Originally Posted By: Donald
I know people suggest not to charge a dead battery with vehicle's alternator. I think a starter/alternator rebuilder even told me that years ago.

I know the alternator in my Ford truck is an extra heavy one, but the supplemental heater is a 115 amp load that comes on as soon as the vehicle is started and stays on until the engine is warm. Assuming it's cold and heat is on.

That just seems like a huge load for 15 or 20 minutes.


In my experience the additional heaters don't stay on until the vehicle is fully warm, but rather until the coolant reaches about 100°F. It's not all the time the alternator that provides theload, chances are that it's actually the battery providing the power as few alternators can supply 115A at tickover.
 
So if a vehicle has a 150a alternator, how much of that capacity is used by the vehicle when it is running?

I assume most vehicles draw all 12v power off the battery for voltage regulation, but it doesn't make sense that the battery would be drawing a constant 150 amps during operation?
 
They put out more. But heat in the alternator increases with the square of current.
 
That heater (obviously an emissions tack-on thing-- yikes!) sounds like a good way to warm up the alternator, too!

I would worry more about the battery boiling than the alt frying. Battery won't take all 100 amps but it would take a bunch unless the alt control circuitry were smart enough to keep volts in the 13's.
 
Originally Posted By: Reddy45
So if a vehicle has a 150a alternator, how much of that capacity is used by the vehicle when it is running?

I assume most vehicles draw all 12v power off the battery for voltage regulation, but it doesn't make sense that the battery would be drawing a constant 150 amps during operation?


Whatever is needed. If there is a 10A load, it delivers 10A. If a 150A load, then 150A ... ignoring, for the moment, whatever part of the load that can be delivered by the storage battery, or in newer vehicles, supercapacitors, etc. Generally not much, or not for long, so safely ignored.

As the load (and therefore output) increases, the load on the engine (and therefore the HP required to drive the alternator) increases.

However, there is no correlation (within reason) between the maximum capacity of the alternator and the power it takes to drive it, or in other words the MPG your engine is achieving. It uses what it needs, no more. So installing a 300A alternator won't use more power than the 150A unit it replaced, as long as the demand remains at 150A or lower.

That is why electric oil pumps, water (coolant) pumps, and power steering pumps are showing up in newer vehicles. Since they are variable load pumps they are more efficient than the steady load mechanically driven units, including belt or chain driven units, they replace.

In particular the electric motors use much less engine power partly because the alternator that drives them is load dependent (via the voltage regulator), not engine RPM driven. The parasitic loss of water pump and engine fan increases as RPM increases, and can be many HP (60, 80 in a modern V8) versus a much lower load via the alternator, that can go to near zero if the electric load is lightened.
 
Originally Posted By: eljefino
That heater (obviously an emissions tack-on thing-- yikes!) sounds like a good way to warm up the alternator, too!

I would worry more about the battery boiling than the alt frying. Battery won't take all 100 amps but it would take a bunch unless the alt control circuitry were smart enough to keep volts in the 13's.


The in cabin supplemental heat is not an emissions thing. It allows the cabin to warm up faster. The fuel heater is pretty common on newer diesels. The Super Duty trucks have 2 batteries, usually 2 group 65 750CCA rated from factory.
 
Originally Posted By: eljefino
That heater (obviously an emissions tack-on thing-- yikes!) sounds like a good way to warm up the alternator, too!

I would worry more about the battery boiling than the alt frying. Battery won't take all 100 amps but it would take a bunch unless the alt control circuitry were smart enough to keep volts in the 13's.


The heater I am talking about is to heat me up. It's a 1500 watt heater in the air duct.
 
Not only can they crank out more amps, but I do believe regulation is now controlled by the ECU (or some similar fully electronic means). As far as I know, at least on some vehicles, one can query the ECU and see what the alternator load is--implying it knows what is full tilt, and can then limit alternator output. I don't believe old school units had that feature.

I have read that GM has a test facility out in AZ where they will part a car in front of a brick wall on a hot summer day, turn on everything, and leave it idling for the day. As a brutal heat-soak test.
 
Alternators do have more output these days then was once typical.
This may be the reason that they also seem to last longer.
Time was that I figured on an alternator replacement sometime not long after 100K.
Not these days where the alternators seem to last the life of the vehicle.
 
Pretty amazing how many amps a fast spinning alternator can produce nowadays, when commanded to do so via the voltage regulator that regulates the field current.

I have a digital ammeter on my alternator output (+) cable, as well as an ammeter showing what is flowing into or out of battery.

When my battery is 99% plus charged, it requires 8.2amps to run fuel pump and ignition, and 12.2 amps at 2000 rpm. Headlights are about 15 amps, blower motor on high ~18 amps.

I have seen 106 amps into heavily depleted batteries from my cool 120 amp alternator.

When idling hot, the alternator casing also heats up very fast( 180f+) when it is asked to produce 50+ amps, but at 65mph at 60 amps will struggle to get above 120F.

Heat is the alternator killer. Underhood airflow likely plays a huge part in its lifespan, along with its internal fan.

I have seen upto 8 amps of field current from my voltage regulator when maxing out the alternator via a depleted battery, all my loads turned on, and depleted battery able to suck up 60+ amps on its own.

My voltage regulator is adjustable, I have a potentiometer on the dashboard so i choose the voltage so I can prevent 14.9v on a fully charged battery and 13.7v from occurring when the battery is still depleted and greatly slow its recharging.
 
Originally Posted By: wrcsixeight
Heat is the alternator killer. Underhood airflow likely plays a huge part in its lifespan, along with its internal fan.


Absolutely this is the case. Alternators are a common failure item on 2003-2004 Mustang Cobras. When you look at where is it mounted, low on the driver's side they just cook themselves to death down there. I have seen both OEM and aftermarket setups with air ducting to the alternator.
 
my older BMWs had nifty ducts that brought fresh air up into the back of the internal fan. Seemed nice until they also directed dirt, leaves, and bees into the rear bearing. Every few years I'd blow out the critters and replace the bearing until I figured out to put a screen in the duct.

I don't think the 180 amp unit in my e90 works anywhere near capacity - no heated seats or steering wheel :-( I don't know how I'm surviving.
 
So what is the normal operating temp for an alternator?
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That's the real change right there, is that alternators are now designed to operate in a much hotter environment than days of past.

Not only do they have more output, but are designed to operate in more serious heat.

Why more heat? Engine bays are more sealed-off from non-radiator flow in the name of aerodynamics, thermostat temps got higher, AC use became more common, engine bays got a whole heck of a lot tighter.

The real revolution in alternator output was the advent of rear window defrosters. Once those came around, the 40-60 amp alternators were out of the window (for an average sized car). 100+ amp alternators showed up for the first time.

Any kind of electric heater is going to be a draw. For the Cummins engines, it's the grid heater that is used in lieu of glow plugs. That sucker can draw some ridiculous amperage.
 
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