Alternator upgrade

[brianl703]

Originally Posted By: 440Magnum
OK, I'll admit I was wrong. Honda actually does use a current transformer to sense vehicle load in addition to monitoring voltage


Many other makes do this by monitoring the duty cycle of the field coil. The higher the duty cycle, the higher the electrical load. My Saab does this to measure the current consumption and if it's high will up the idle by 100RPM after several minutes.

Some GM vehicles had a current transformer to measure the battery charge current. This allows the ECU to cut back on the voltage output of the alternator as the battery reaches full charge, apparently to save a 1/10th of a mile per gallon or something like that.

 

[brianl703]

Originally Posted By: eljefino
I do recall the civic high-mileage version in the mid 90s would decrease system voltage from 14.x to 13.x under cruise conditions to boost MPG.


That's pretty normal, my 1988 Mustang GT does that. As the alternator heats up it cuts back on the voltage. So at cold start it may be 14.4V but when the engine is fully warmed it might only be 13.5V.

 

[PandaBear]

Originally Posted By: brianl703
That's pretty normal, my 1988 Mustang GT does that. As the alternator heats up it cuts back on the voltage. So at cold start it may be 14.4V but when the engine is fully warmed it might only be 13.5V.


I doubt that it is by design. What if you run the car in the death valley vs in Maine?

 

[Falcon_LS]

Thank you for the input. Learnt quite a number of things I didn't previously know.

I'll shop around for one that is a direct fit, with an upgraded output.

 

[brianl703]

Originally Posted By: PandaBear

I doubt that it is by design. What if you run the car in the death valley vs in Maine?


That IS by design. Study the charge voltage requirements of lead-acid cells vs. temperature. There's no good reason to continue putting 14+ volts into a battery after the engine, and therefore the battery, reach normal operating temperature.

 

[Steve S]

Originally Posted By: PandaBear
Originally Posted By: brianl703
That's pretty normal, my 1988 Mustang GT does that. As the alternator heats up it cuts back on the voltage. So at cold start it may be 14.4V but when the engine is fully warmed it might only be 13.5V.


I doubt that it is by design. What if you run the car in the death valley vs in Maine?
The cutback is because the Alternator and voltage regular is doing their jobs.

 

[mechtech2]

Alternators charge on demand.
There will be NO HP loss compared to stock unless you are fully utilizing the power it produces. And if you need that power, you need it.
Big sound systems and lots of lights or accessories can require a larger alternator to keep up.
If the car is stock, I would use the stock rating.

If you need more power at idle, get an overdrive pulley for the stock one. A large alt will not necessarily produce more at idle.

 

[meep]

Temp sense (intentional) SOME cars do this, not all. I know the chrysler variants actually put a thermistor below the battery box and adjust charge voltage setpoint per temp. Field voltage is controlled by ECU. Lots of GM cars use internally-regulated alts... if it's an alt w/ internal regulation then at best it would be an approximation based on underhood ambient temps.

Also, I don't think a transformer is used to monitor current. Transformers are strictly alternating current devices. Old school regulators ran the output current THROUGH a relay coil that would cut out the FC as output approached maximum, essentially lowering the voltage as the load hits the limit. Monitoring current in DC realm involves sending it through a shunt (really low value resistor) and reading the voltage difference... greater delta V = greater current.

I am not aware of any manufacturer doing this. Doesn't mean they don't, I've just never seen it. Besides, it'd be easier to monitor the duty cycle of the field coil (full cycle = full output for a given rpm) on an ECU-regulated alt. since it's already there in the ecu.

M

 

[brianl703]

Originally Posted By: meep

Also, I don't think a transformer is used to monitor current.


It's really a hall-effect sensor.

 

[meep]

ooooo.... so tell me more. how do they implement and which makes? (I'm not challenging you... I'm genuinely interested)

M

 

[meep]

hey but wait.. hall effect works on same principle and can detect changes in current, but not actual current, right? Or do they try to bias against say a perm mag at 90degrees or something like that?

M

 

[brianl703]

Originally Posted By: meep
ooooo.... so tell me more. how do they implement and which makes? (I'm not challenging you... I'm genuinely interested)


I've only seen them on GM vehicles for monitoring the battery charge current.

This link has details about how to use them for general current monitoring purposes:

http://scienceshareware.com/how-to-measure-AC-DC-current-with-a-hall-effect-clamp-.htm

I have a clamp-on AC/DC ammeter. Presumably it too has a hall effect sensor.

 

[brianl703]

Originally Posted By: meep
hey but wait.. hall effect works on same principle and can detect changes in current, but not actual current, right?


From what I read, hall effect detects magnetism. The output from the hall effect sensor increases as the strength of the magnetic field does.

 

[brianl703]

By the way the GM battery current sensor costs about $17 from gmpartsdirect, which is competitive with what Digi-Key wants for one. I thought about buying the GM one and using it to measure DC current on battery cables, but you probably can't get a datasheet for it...although it is waterproof and designed for underhood use.

(I don't think GM marks that particular part up very much).

 

[meep]

Hey thanks that's pretty cool. I'd never seen a HES used that way, always for a pulse train (cam/crank/distributor sensors). Superior than a shunt in several ways. Years ago I'd used a rack of parallel shunts (yea digikey) for a high-current digital ammeter. Would love to try an HES application.

Thanks!

Mike

 

[brianl703]

The clamp-on AC/DC ammeter is one of the most useful tools I've gotten. It'll measure up to 700A DC current.

 

[mechtech2]

Either by luck or design, alternators put out more when cooler.
Maybe a regulating component in some, and maybe internal resistance going up when hot in others.
But is sure is a consistent pattern.