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oil pan 4 12-09-2015 10:52 PM

Schottky diode alternator
For this project I will be taking my old alternator and rebuilding the 3 phase bridge rectifier and trio voltage regulator rectifier with ultra high efficiency solar panel Schottky diodes.

But this isn't an alternator for any old vehicle electrical system.
This vehicle electrical system has a Lithium Iron Phosphate battery, 1000w pure sine inverter, 12v air compressor, lots of LED lights, electric coolant pump, electric fuel pump, solar panels, electric power steering and more.
So it has to be very hard working and efficient.
Common vehicle alternators are 1950s tech. Nothing it powers was even thought of as having 12v automotive application in the 1950s.

The alternator I am using is our of my suburban. I changed it out a few years ago because the alt wasn't really charging the battery. I think the voltage regulator was going bad. I just replaced it with a spare and put it on a shelf and didn't think about it for 8 years.

I am going to take it from this:
Typical GM alternator.

And turn it into this:
External rectifiers
Voltage adjustment
Exciter kill switch
Convert from 3 wire wye to 4 wire wye
Voltage sense going all the way to the relocated battery.

Why? Just to see what happens.

The original ideal to have an vehicle alternator use these ultra low forward voltage drop diodes came from serialk11r here:

me and my metro 12-09-2015 11:16 PM

Looks like a great project. Back about 20 years ago my city had an ambulance with a 200 amp Leese-Neville alternator. Only the rotor and the stator were in the case, all the diodes were mounted up front with big heat sinks. That was the only one we never had any problems with. Keep us posted.

DragBean 12-10-2015 02:35 AM

Turning Alternator into a motor to drive power steering
Nice car.
Are all the electric sub systems stock or aftermarket?

I'm doing something similar. Basically I'm unbelting the alternator and water pump from the engine. Then I'm going to drive the water pump with the alternator.

At this point i was just going to keep the field current constant, but I'm wondering if i can manipulate the already existing field voltage regulator on an alternator to improve the efficiency of the alternator motor?

Basically I'm going to have a potentiometer control the speef of the alternator.. Wonder if i can feed that or into to the field voltage to reduce it's voltage as rpms go up?

oil pan 4 12-10-2015 11:28 AM

I think it would be a lot easier to get a DC motor powered coolant pump and just run it off a PWM controller. I am using a $5 ebay PWM controller off ebay to power my big 7amp, 55gpm coolant pump.

oil pan 4 12-10-2015 03:01 PM

1 Attachment(s)
This is what the old GM alternators typically look like.

oil pan 4 12-10-2015 03:30 PM

1 Attachment(s)
Here is the alt with the diode trio and bridge rectifier removed. Alternator coils installed, new voltage regulator installed, old brushes reused, 4 wire conversion done, purple wire brings in power to the voltage rectifier from the remote schottky trio, gland seal strain relief installed.
I used 10 gauge wire for the lines and neutral because I bought 4 more partial 500 foot rolls of black and white 10 gauge for pennies on the dollar so for the foreseeable future I will be using 10 gauge wire as opposed to 12 gauge.
The motor brushes are being held back with a pin.

The purple wire will allow me to cut power to the exciter.

All the crimp connections are soldered because that's how it came from the factory and it seems to have worked well.

oil pan 4 12-19-2015 12:18 AM

The master plan is to install a 2000w samlex pure sine and 1000w Xantrex pure sine inverter into my suburban for remote build projects. This 2000w continuous, 4000watt surge inverter should be able power my mig welder, skill saw, pretty much everything but my plasma cutter and largest air compressors.
Finally got the deal I wanted on that samlex pure sine inverter.
Main problem was the 1000w would not power a skill saw well and had no where near the power to run the welder or 7 inch grinder.

Daox 09-29-2016 03:58 PM

How is this working out?

What was the reason you went to the 4 wye design vs 3 wye?

What diodes did you use for your setup?

I may be modifying an alternator soonish...

oil pan 4 09-30-2016 09:55 AM

According to my lineman's handbook going from a 3 wire wye to 4 wire wye system will allow a system to move something like 74% more power just by adding a neutral wire.

California98Civic 09-30-2016 10:26 AM

Way. Over. My. Head. ... subscribed.

Daox 09-30-2016 10:30 AM

Are there any modifications (besides rewinding) you know of to get higher charging voltages at lower rpms?

gumby79 10-01-2016 12:48 AM

Regear/reduce the od of the pulley. Im considering this on my Dodge, any one now of a cross reference for pulley od. and shaft size. As at idle the fild won't excit, to slow with a/c cluch and blower motor on hi.

gumby79 10-01-2016 09:08 PM

Yes, you can increase your alternators overall output as well as increase power output at engine idle speeds.
Check the size of the pulley on your alternator. If you are having problems with overall alternator output or charging at engine idle, maybe a smaller pulley is all you need. The most common pulleys on GM, Ford and Daimlier/Chrysler vehicles are the 6-groove 2-7/16, 2-3/8 and 2-1/4 inch pulleys, by reducing the pulley size to 2" or 1-7/8" your alternator will start producing power sooner and produce more power cruising down the boulevard or on the highway. Also, because your alternator is spinning faster the fan will move more cooling air through the alternator adding to component life, to little air flow can burn up an alternator.
?Will this help ?
?What is the point of loss due to over speed?
Oil Pan ?what do you anticipate the %gain in efficiency to be?

Watch out for voltage drop causing a bad voltage signal from the relocated battery . Dodge used to small a gage wire for there remote voltage regulator on the fire wall in there pick ups, result the lights flicker/pulse voltage gage bounces .

oil pan 4 10-02-2016 01:58 PM


Originally Posted by Daox (Post 523835)
Are there any modifications (besides rewinding) you know of to get higher charging voltages at lower rpms?

Start with a wye wound stator. Looks like the cut in voltage is as low as 1,000 to 1,200 alternator rpm where delta cut in voltage is around 2,000rpm.
Other ways to get more voltage at lower rpm would be to swap in a lower resistance rotor, or boost the voltage going to the rotor.

serialk11r 06-15-2021 05:22 PM

So as of 2021, it seems like a 50A active diode costs around 20 bucks shipped from Alibaba, and you would need 12 of them for an alternator, which is pretty expensive (not to mention they are bulky).

As an alternative, I found this:

0.5V drop is respectable, and the package is compact so you can screw 6 of them onto an aluminum heatsink and hang it off the side of the alternator. 30V max reverse voltage may or may not be a problem, I'm not sure. Maybe some zener diodes to absorb voltage spikes would be a good call.

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