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Please help me use a PWM alternator for a project

hylo

Feb 7, 2024
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My goal is to mount an alternator to the lawn tractor's PTO shaft. The reason is to increase the amount of available power to operate 12v accessories, like winches, raising/lower a dump bed, or running an inverter for 110v. The battery I have is a small lawn tractor battery and it doesn't have the capacity for it. It will run down and its life will be significantly shortened. Additionally, the onboard charging system is not powerful enough to handle the job of recharging this battery in a timely manner, nor was it made to handle the kind of demand that I need. I have a used spare alternator I thought would do the job.

I may replace the current battery with a deep cycle one, but I don't want to spend the money at the moment, and without an adequate charging system it would be pointless anyway.

So far, I've successfully mounted and mechanically connected the alternator to the PTO output shaft via a v-belt. The alternator belt spindle has been replaced with a v-belt type. The alternator can be spun separately via the tractor's PTO switch.

My issues are with the electrical connections. My electronics knowledge is limited at best. I know the difference between volts and amps, what basic electronics components do, and I can do electrical connections. But designing an electrical system is out of my league. My day job is a software engineer, if that matters.

This is the alternator that I have:

Note that my alternator is a Motorcraft brand, but this is a direct replacement, so the interface should be the same.

The wiring diagram for this alternator is here: https://www.f150forum.com/attachmen...-wires-out-charging-system-wiring-diagram.pdf

Apparently this alternator takes in a PWM signal through wire 2 (GENCOM).

I don't have the ability to generate that in a purely analog system of a lawn tractor and I need the simplest way to make this alternator output 13-14v to keep the battery charged and feed any additional load that I may need. I am prepared to modify it if necessary. Using a different alternator would mean I would have to rebuild the mounting system which I don't really want to do, unless I have no choice.

What I have connected so far: The big red wire is connected to the battery positive. The alternator is grounded to the tractor chassis which is connected to the battery negative. I connected wire 1 to positive battery. I once connected wire 2 to negative (unintentionally, without spinning it, wire 1 was loose at that time) and then to positive (intentionally, with the engine on). At this point I am not sure if I damaged the alternator doing this. Then I read somewhere to connect wire 2 to wire 3. I thought that the GENMON signal sent might be similar enough to some acceptable form of a GENCOM signal to trick this thing into producing electricity. It wasn't or it's broken already. I don't know how to test this alternator. I don't even know if it was good to begin with as it was pulled from a junk truck. But let's assume it is, for the sake of progressing.

None of those combinations produced any voltage above 12.5v that I was reading at the battery terminals. I disconnected the tractor's charging system while I did this, to prevent interference. I don't know if I can run them safely at the same time, but would like to, because this alternator won't be activated at all times, only when I need a lot of power, and I don't want the battery to run down from normal use.
 

kellys_eye

Jun 25, 2010
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Would it not be simpler/easier to change the tractors existing alternator for one with a higher output rating?

I'm not familiar with that type of alternator but it looks to be fitted with internal electronics for monitoring speed, load, voltage etc via the CANBus system which means you need the relevant controllers that go with it. Bad purchase decision...... all the 'old' alternators work just as well, have just as much output but don't require fancy interfacing.

I recall that the CANBus comms is to allow the alternator to go 'dead' when there is no requirement for load therefore reducing the load on the engine and thus reduce fuel consumption - yeah, it's absolutely minimal in the scheme of things but that's how manufacturers have been pushed to keep average mpg up.

Either way, you could be messing with this for ages to see an output when a regular alternator swap would be 1 for 1 and fix all your issues.
 

Bluejets

Oct 5, 2014
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The wiring diagram for this alternator is here
Well actually that is the F150 wiring chart.
Alternator with an internal regulator is normally a relatively straight forward connection requirement.
Your description (unless I missed something in all the chit chat) seems to be connection of the new alternator to the existing battery as well as the original battery charging system which will not work.

I would have gone the direction kellys_eye suggested and fit a larger battery in place of the original and perhaps a larger alternator in place of the original.
Of course you do not mention the existing alternator output current capacity which is one important factor but one could take a guess at it being perhaps 35A.
Question there would be (once again not supplied "essential" info) current demand of any and all accessories, how you plan to use them i.e. all at once or one at a time etc.
 

hylo

Feb 7, 2024
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Would it not be simpler/easier to change the tractors existing alternator for one with a higher output rating?

I'm not familiar with that type of alternator but it looks to be fitted with internal electronics for monitoring speed, load, voltage etc via the CANBus system which means you need the relevant controllers that go with it. Bad purchase decision...... all the 'old' alternators work just as well, have just as much output but don't require fancy interfacing.

I recall that the CANBus comms is to allow the alternator to go 'dead' when there is no requirement for load therefore reducing the load on the engine and thus reduce fuel consumption - yeah, it's absolutely minimal in the scheme of things but that's how manufacturers have been pushed to keep average mpg up.

Either way, you could be messing with this for ages to see an output when a regular alternator swap would be 1 for 1 and fix all your issues.

The tractor's alternator is underneath the flywheel, there is no room for modification and that would be far harder. This alternator I bought as a backup for my truck and had it sitting around when I decided to do this.

I saw some threads online about modifying these alternators, replacing their existing regulators with "4 wire regulators" I don't really understand most of it, I am hoping someone comes along that has knowledge of how they internally work and what my options are.
 

hylo

Feb 7, 2024
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Well actually that is the F150 wiring chart.
Alternator with an internal regulator is normally a relatively straight forward connection requirement.
Your description (unless I missed something in all the chit chat) seems to be connection of the new alternator to the existing battery as well as the original battery charging system which will not work.

If you're suggesting that I just directly connect what I have then yes it would not work, I am aware of that. I don't have the internal wiring chart of the alternator. I was hoping there was someone here with knowledge of PWM alternators that have been around for some years now that can explain to me how this needs to be modified.
 

Bluejets

Oct 5, 2014
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Never heard of a PWM alternator..........seen many alternators in my time with either internal or external regulators which, as I said, are relatively easy to connect.
If you have gone out on a whim and bought some high follutin" wiz-bang alternator with bells and whistles, then you'll need to find info on that particular device rather than how it connects to a Ford F150. kapich???
Personally, I would have visited a wreckers and picked up an old Mazda, Honda, Hyundai or whatever everyday run-of-the-mill unit for $10 and at least experiment with that first.
Over and out.....:rolleyes:
 

crutschow

May 7, 2021
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From all I've read, that smart alternator requires a PWM signal from the PCM to control it's output voltage, so don't see how you can use that alternator for what you want to do, unless you can determine how to generate that required signal. :(
 

hylo

Feb 7, 2024
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From all I've read, that smart alternator requires a PWM signal from the PCM to control it's output voltage, so don't see how you can use that alternator for what you want to do, unless you can determine how to generate that required signal. :(

Yeah I guess what I was hoping for was a way to attach some simpler controller to the basic alternator underneath the PWM regulator. I was reading this post here (How to make a PWM alternator work? - LS1TECH - Camaro and Firebird Forum Discussion ) and apparently for this GM alternator there is a way to go back to a 4 pin (analog) from a 2 pin (PWM) via a part. There doesn't seem to be a part for a Ford alternator and even if there was it would probably be $50. At that point I could just go to a junkyard and find an analog alternator but like I said I don't want to reengineer the mounting system. I went through quite a lot of trouble finding the right belt size, the right pulley, welding shut some holes in the frame, etc...

So after some more research last night I am going to try to generate the signal via this part (https://www.amazon.com/dp/B07HKHW98L)
This post describes the Ford GENMON system input requirements: Ford PCM controlled alternator testing - ScannerDanner Forum - SCANNERDANNER

This video gave me that solution:

I'll let you guys know how it goes once I get the part in.
 

kellys_eye

Jun 25, 2010
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Whilst that PWM generator will deliver an output it won't be able to REGULATE the output without some from of feedback from the load. The output voltage will vary with the load. That's where the CANBus solution comes into its own.

If that load happens to vary widely you might end up setting the unit for too high an output (and boil the battery) under low/no load or too low for a high/heavy load which will just drain the battery - same issue as you already have.

If that module accepts a 'modulation' input (voltage) I suppose you can find the right attenuation values to ensure it does what it should.

The KISS principle applies here - and very much so - a conventional alternator of the same physical dimensions/mounting points would make things easier.
 

crutschow

May 7, 2021
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I am going to try to generate the signal via this part
Since that is an open-loop adjustment, I trust you realize that you will need to connect a voltmeter to adjust the battery charging voltage to the desired value.
 

hylo

Feb 7, 2024
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Whilst that PWM generator will deliver an output it won't be able to REGULATE the output without some from of feedback from the load. The output voltage will vary with the load. That's where the CANBus solution comes into its own.

That makes sense, and my solution to this is to add a voltmeter to the dashboard and manually regulate it. One day I might get into programming microcontrollers, at that point I can replace this whole thing entirely with something much more powerful and customizable.

The good news is the part I ordered did the trick and I was able to generate a bit over 14v with 90Hz and 20% duty cycle with battery voltage. I didn't go higher than that as I didn't want to damage my battery. The engine stalls out when engaging the PTO even at full throttle when I'm asking for 14v. So there's a procedure to switch things on in the right order. The engine might also be worn out as I'm getting a bit of blow by with crankcase pressure, so it might need a rebuilt. It's a 20HP, that should be enough to drive an alternator, right?

I also connected the engine's stator as well and it didn't fry anything. I think they work OK in unison. So I'm going to call this one solved and leave this for the internets, just like those posts helped me put this together, one day someone might find this useful.

Next steps is to add that voltmeter, secure all these connections, add some switches and make room for an RV deep cycle battery. I also want to add an inverter and generate 120v to use powertools away from the house.
 
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