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Discussion Starter · #1 ·
This is on a 2015 Lexus RX350. Is it nice/good/efficient for it's size....? Anyone know a lot about alternators?

I think I see 2 stators....wired in Wye configuration with 12 diodes? Nice? (I believe it is rated at "160A" by Lexus)


Capture-schem.PNG
 

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If it is a 160A machine, I'd consider that quite adequate, unless you are multi Kw SPL type.

Looks like it is battery sensed, which I always find preferable. If the diagram is correct, it looks like a straight forward alternator & regulator, with no ECU control over output = simplicity.

The dual stator/single field and rectifier configuration is not that common, although my alternator knowledge is mainly on heavy duty 24V machines.

What sort of load are you going to be putting on it?
 

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Discussion Starter · #3 ·
What does the dual stator set-up do for me? More current output capability for given mechanical size?

Yeah agree, the controls look pretty straight forward. The ECU monitors the field voltage, but that's about it (woo-hoo!).

I would be asking something like ~150A load for the subwoofer amp on the music peaks, 3x 500W subs. I'm planning to run some tests on the alternator to see how much current it can output before it drops voltage. To test the alternator out on the car. I am not expecting too much out of it.

I have been monitoring the voltage via the OBD2 port on my daily drive, and turning loads on in the car.... once the engine/alternator is warmed up (after around 30min) I can get the voltage to dip down to ~12.5V - 12.7V when the engine is at idle by turning on a lot of loads..... the window de-fogger, heated seats, high beams, etc. I'm not sure how much current is being drawn in those cases yet, but yeah.
 

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I've no idea what the advantages of a dual stator arrangement will give, but as they have individual rectifiers perhaps the total capacity (160A) is split between each. If so, that will put less stress on the rectifier diodes and should yield more output for a given case size.

I'd love to put a scope on the output to see if any smoothing or other advantages occur with that set up.

150A from music should be achievable with your alternator, but the 160A rating is at high alternator RPM, not "normal" driving engine RPM.

Looking again at the diagram, there is an 'M' terminal, where does that go/come from?
 

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The easiest way to find what your alternator is rated is to shop for an alternator and see what spec it is. For example: Genuine Lexus RX350 Alternator
Put in the rest of your car info and it should show you the right one.

The diagram you linked shows 140A with a smaller 7.5A.
 

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It
What does the dual stator set-up do for me? More current output capability for given mechanical size?
...
If Google doesn’t help, it may result in less voltage ripple (as the extra lobes can be humped out of phase with the first triad of humps...)
 

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Good point, if the stators are arranged accordingly, it would be a 6ph generator, and as Holmz said, will reduce ripple on the B+ output.
 

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Discussion Starter · #8 ·
Thanks you guys. Good to know, appreciate the info. I can throw the scope on the alternator B+ and see how it looks. I got a new scope recently, that I need to try out :)

I know the alternator is fused for 140A, but the Lexus literature claims it is a 160A alternator with the tow package. We'll see how much current it can put out, when I get to testing it in the future.

I believe the M wire is the "field" output wire. It looks like it connects to the ECU module. I think it is a way for the ECU to monitor the alternator health/behavior in some manner. I can throw a scope on that wire too.

Looking again at the diagram, there is an 'M' terminal, where does that go/come from?
 

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Discussion Starter · #9 ·
I took some scope captures of my alternator voltage and current. It looks like the ripple on the alternator at idle is ~80mV and doubled to ~160mV when the alt heated up and was sourcing decent amount of current, all at idle. Is this good...? 100mV-200mV feels "pretty" okay-good, but I don't have a lot of experience with good/okay/bad alternator performance. Let me know your thoughts! See waveforms below.

I think my alternator output at idle might be maxing out at around 70A-80A, as the voltage was coming down to ~12.7V-12.9V at that point. I hope do do some more testing on this parameter in the future!

Waveform 1: Ripple=80mV, V=13.7V-13.8V, Current=20A, Temp=cool/ambient, RPM=idle
Waveform 2: Ripple=160mV, V=13.4V-13.6V, Current=55A, Temp=hot, RPM=idle
Waveform 3: Ripple=160mV, V=12.7V-12.9V, Current=75A, Temp=hot, RPM=idle

The yellow waveform (ch1) is alternator voltage right on the alternator to it's case.
The purple waveform (ch2) is alternator current measured on the (+) wire of the alternator.
The blue & green waveforms are currents at the battery terminals.


Capture-Lexus-RX350-OEM-Alt-Voltage-1-Idle-Amb-20A.PNG


Capture-Lexus-RX350-OEM-Alt-Voltage-2-Idle-Hot-55A.PNG


Capture-Lexus-RX350-OEM-Alt-Voltage-3-Idle-Hot-75A.PNG
 

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Discussion Starter · #10 ·
I found this article about alternator ripple, it seems like my results are inline with others, maybe a little better. It appears that ripple increases with load current and RPM, in some cases ripple doubles with RPM. So maybe I'll look at taking same more data, see how this alt matches up with the results in this article, article is from ~2010.

Article:
"Updating Your Ripple Voltage Tutorial By Juan Grube"
Link:
"https://www.scannerdanner.com/media/kunena/attachments/4419/updatingyourripplevoltagetutorial.pdf"
 

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I took some scope captures of my alternator voltage and current. It looks like the ripple on the alternator at idle is ~80mV and doubled to ~160mV when the alt heated up and was sourcing decent amount of current, all at idle. Is this good...? 100mV-200mV feels "pretty" okay-good, but I don't have a lot of experience with good/okay/bad alternator performance. Let me know your thoughts! See waveforms below.

I think my alternator output at idle might be maxing out at around 70A-80A, as the voltage was coming down to ~12.7V-12.9V at that point. I hope do do some more testing on this parameter in the future!

1sr - Nice data.

Is there are problem you are trying to solve?
 

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Discussion Starter · #12 ·
Thx!

No problem to solve, just wondering about the 2 stators in the schematic..... also wanted to try out my new scope/probes, honestly.

Also, learn about alternators a little. DIY!
 

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Ripple measurements look very good, perhaps that is due to the dual stator.

When your voltage drops to 12.8-12.9v then you are at maximum output. Out of interest, how are you applying load when testing?
 

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What was the RPM?
what are the X the divisions?

It should be possible to see 3 sets of diodes… or 6 if is two stators in a staggered arrangement.
 

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Discussion Starter · #15 ·
Good to know. I was adding electrical loads by turning features on in the car. It looked like there was around 20A draw without anything extra/special on. I assume that is the vehicle's fuel system and engine control electronics. That number jumped around a little. So I'll just say in that range.

Then I turned on high beam headlights (19A), rear window defogger (17A), air conditioner + radiator fans (15A), and heated seats (6A). All of these together with the ~20A engine electronics totaled pretty close to 75A. The loads add up fast! Real world, probably would never drive like that..... but you know, just to add loads. And once things got hot.... this started to tax the alternator as the voltage got down to 12.7V-12.8V-12.9V range as you can see in the waveform #3 above.

This is my end goal...... What I would like to do eventually, (not too distant future) is add loads in a more controlled manner. So my plan is to use a larger mono subwoofer style audio amplifier and tune the gain/amp to pull variable amount of current for controlled amounts of time. So should be able to pull 50A for 5 seconds. Then try 100A for 2 seconds, etc. I would plan to use larger amp that can pull ~200-300A.

Ripple measurements look very good, perhaps that is due to the dual stator.

When your voltage drops to 12.8-12.9v then you are at maximum output. Out of interest, how are you applying load when testing?
 

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Discussion Starter · #16 · (Edited)
This is a fun little discussion.

Vehicle was at idle, I think the engine runs at 700-800 RPM when it warms up, alt RPM should be 3x --> 2100-2400 RPM (i think).
Next time I take some measurements, I'll be sure to log the engine RPM.

Time divisions are 500 micro seconds. I think I am getting 1.5 peaks/"ripples"/rectified sines per division.

If I did have the 2 stators/12 diodes, wouldn't I see 12x peaks/"ripples"/rectified sines per alt rotation....? Or does it not work like that?
I am not sure how the sine timing matches exactly here.

edit.... updated math.
If I was at lets say .... 2400 alt RPM... that would be one alt rotation every 25 milli seconds? (help me out here)
In the scope capture I have 20 peaks/"ripples"/rectified sines in 7 milli seconds, so I would have ~71 peaks/"ripples"/rectified in 1 rotation (25 milli seconds).
Is that right?... feels like I might be off somewhere there.

Capture-Lexus-RX350-OEM-Alt-Voltage-4-Idle-Hot-75A.PNG


What was the RPM?
what are the X the divisions?

It should be possible to see 3 sets of diodes… or 6 if is two stators in a staggered arrangement.
 

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This is a fun little discussion.
….

edit.... updated math.
If I was at lets say .... 2400 alt RPM... that would be one alt rotation every 25 milli seconds? (help me out here)
In the scope capture I have 20 peaks/"ripples"/rectified sines in 7 milli seconds, so I would have ~71 peaks/"ripples"/rectified in 1 rotation (25 milli seconds).
Is that right?... feels like I might be off somewhere there.
2400 RPM is using pulley ratios?

Then divide by 60 to get to RPS and we get 40/sec.
so 3 stators would be 120/sec and 6 would be 240/sec. (8 amd 4 milisec)

There is also probably a factor of 2 as the negative voltage get put upright with the diodes… so 4 and 2 milliseconds respectively.

To get from 2 to 25/71 requires something like a 6:1 pulley ratio??
 
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Discussion Starter · #18 ·
Thanks, I think our maths agree. I feel like we are just off by a factor of 2x or 3x or 4x. That's pretty close right? ;)

What makes the voltage peaks/"ripples"? It is the physical passing of a the rotor magnet pole passed a stator coil, correct? And then the negative voltage gets put upright with the diodes, so 2x peaks/"ripples" each time a magnet pole passes a stator coil. So the number of peaks/"ripples" per given time period is related to the RPM/RPS of the alternator, and also the physical # of rotor magnet poles and the # of stator coils..... hmmmm. Maybe? Could you multiple these together 2x to get the number of expected peaks/"ripples"?

2400 RPM is using pulley ratios?

Then divide by 60 to get to RPS and we get 40/sec.
so 3 stators would be 120/sec and 6 would be 240/sec. (8 amd 4 milisec)

There is also probably a factor of 2 as the negative voltage get put upright with the diodes… so 4 and 2 milliseconds respectively.

To get from 2 to 25/71 requires something like a 6:1 pulley ratio??
 

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Thanks, I think our maths agree. I feel like we are just off by a factor of 2x or 3x or 4x. That's pretty close right? ;)
...
In cosmology it is exact!


...
What makes the voltage peaks/"ripples"? It is the physical passing of a the rotor magnet pole passed a stator coil, correct? And then the negative voltage gets put upright with the diodes, so 2x peaks/"ripples" each time a magnet pole passes a stator coil. So the number of peaks/"ripples" per given time period is related to the RPM/RPS of the alternator, and also the physical # of rotor magnet poles and the # of stator coils..... hmmmm. Maybe? Could you multiple these together 2x to get the number of expected peaks/"ripples"?
I think a generator has magnets and an alternator uses coils to create a magnetic like a magnet would... then they can change the strength of it to make the output go higher or lower?

If there is 2 or 3 of the “magnets” (stator or rotor coils) then it would make 2 or 3 peaks.

The sharp edges, and spikes, may come the diodes?

And packing more in, and using more pulley ratio, makes the ripples closer and probably lower amplitude.. (lower if one runs a capacitor somewhere.)
 
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