PWM Alternators

[Mikey G]

I'm currently building a kit car based around the Focus ST170 engine and gearbox in the rear. I'm looking to re locate the alternator to the front of the engine (lower r/h side as you look at the crank pulley) also going electric water pump so the belt only has that to drive.
Anyway the ECU I have purchased has the option to drive a smart or PWM/PID based alternator which I would like to use if possible. With the relocation I am looking to purchase a smaller alternator to replace the huge ST170 one fitted originaly to the engine, one of the options is a Toyota Yaris alternator which seems popular but i'm finding it difficult getting information on how this alternator is controlled.

Also looking for suggestions on alternative alternators that I could adapt to fit the engine with this method of control? I'm assuming most of them would be quite big due to the method of operation?
I have guestimated my current consumption would max out around the 50-60A mark if I was to drive at night. So a 70-90 amp alternator should be more than enough.

[stevieturbo]

Keep it simple...small cheap basic alternator that requires no controls.

[annodomini2]

PWM based alternators offer, minor efficiency savings great for modern production car emission standards, ineffectual realistically for a kit car, just more to go wrong.

Find a solid reliable std alternator sized for the car.

[Mikey G]

I knew I wouldnt get the answer here, I fully know the benifits of keeping things simple, but thats boring.
If i wanted to keep the car simple I wouldnt be running an EWP, modifying the engine for more power, running a digidash on canbus and end up using the standard ecu or running carbs, but i'm not.

[Evoluzione]

Posting up on here is like putting penetrating oil on rusty nuts & bolts, you know you'll end up cutting them off, but spray some on anyhow 'just in case'.

[stevieturbo]

Yes, simple, reliable and effective is boring.

So much fun being broken down at the roadside when things don't work lol

[Penelope Stopit]

annodomini2 said:

PWM based alternators offer, minor efficiency savings great for modern production car emission standards, ineffectual realistically for a kit car, just more to go wrong.

Find a solid reliable std alternator sized for the car.

The above just about sums it up

PWM alternators and control circuits aren't about reliability or even evolution, they are all about how manufacturers are competing for better fuel consumption figures and minimising pollution

Appreciate that you're attempting to use as much high tech electronics as possible yet feel you've not delved deep enough into the reasons for some alternator control circuits

In attempting to move forward you are inadvertently moving backwards

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Shorter version

PWM alternators aren't for kit cars

[Mikey G]

Well, i'm not going to get anything here am I. I'll do some more research on the matter and look elsewhere. I want to do it as more of a technical excercise for myself also, as you say modern cars all run smart alternators and one day I may well be driving a 15 year old daily with such a device that may leave me stranded so getting to know how one works properly and its benefits will be nice to know. Also whatever alternator I choose to fit i'll need to know its primary control anyway.

[annodomini2]

Running a 50A alternator, turning it off under full load acceleration your peak gains are going to be about 1.2hp.

You'd be better off in investing the cash in improving the engine.

[100SRV]

Mikey G said:

Well, i'm not going to get anything here am I. I'll do some more research on the matter and look elsewhere. I want to do it as more of a technical excercise for myself also, as you say modern cars all run smart alternators and one day I may well be driving a 15 year old daily with such a device that may leave me stranded so getting to know how one works properly and its benefits will be nice to know. Also whatever alternator I choose to fit i'll need to know its primary control anyway.

Could you rent a similar car to the one the alternator is used on, instrument it up and record the behaviour?

I am thinking that monitoring alternator load current and system Voltage with an oscilloscope watching the alternator control lines.
Vary electrical loads and, if you have a portable set of kit take it on a representative drive cycle.
That way you can get a loose correlation of alternator loads and control system responses.

[Mikey G]

100SRV said:

Could you rent a similar car to the one the alternator is used on, instrument it up and record the behaviour?

I am thinking that monitoring alternator load current and system Voltage with an oscilloscope watching the alternator control lines.
Vary electrical loads and, if you have a portable set of kit take it on a representative drive cycle.
That way you can get a loose correlation of alternator loads and control system responses.

Funny enough I was thinking of doing that to my daily Merc via OBD to see how it behaves as I have a feeling that has a smart alternator.
I have found out that smart alternators are not that new, some cars from before 2010 are running them like ecoboost Fiesta's etc.
I have already got a small AGM battery for the kit car anyway and looking at the software you can control the target voltage at different times, I feel this may also help with the life of the battery. There is currently no control over target voltages when accelarating/decelarating so that side of it is pointless at the moment anyway.
With regards to tthe argument of spendiing the money elsewhere I have to buy an alternator anyway, looking at the prices online its neither here nor there with the extra cost being minimal to nothing compared to a good Lucas A127.

[stevieturbo]

100SRV said:

Could you rent a similar car to the one the alternator is used on, instrument it up and record the behaviour?

I am thinking that monitoring alternator load current and system Voltage with an oscilloscope watching the alternator control lines.
Vary electrical loads and, if you have a portable set of kit take it on a representative drive cycle.
That way you can get a loose correlation of alternator loads and control system responses.

It's easy to datalog current in the system these days. In fact a lot of modern stuff do monitor actual current draw via a small hall effect current transformer