Alternator - Turning it On & Off ?

[MWP]

Hi guys,

So this is a bit of a strange one...

I'm designing the wiring for a 1.6L N/A class racing boat where every single HP matters.

I've been asked to have the ECU control when the alternator is enabled (charging) during competition.
Is this as simple as turning on & off the supply to the IG pin of the alternator (it's internally reg'ed) via a relay?

I gather he'll want the alternator disabled while at full-throttle, so it could potentially be turning on/off quite often... say every 10sec or so.

Can anyone foresee any issues with doing this?

Thanks

[elfturbomax]

I think it could depend on the particular alternator and where its voltage sense input is. That is, the outcome could vary between shutting it off or going over voltage, or somewhere in between.
But some alternators have a specific ecu control pin which allows the ecu to control charge to aid idle stability so one of them might be the go.

[BigJonWB]

How long are the races? Does it even need to charge the battery?

[chartreusehj]

This seems like a last resort thing after all normal methods of not losing power have been performed.

[Gin Kii]

Similar to how an ECU switches a smart alternator on and off ?

[MWP]

It's just a standard IG/L/S Toyota (Denso i guess) alternator.
He's already bought a new alternator, and milled up a nice ally bracket for it. I doubt he'll want to change type now.

There is a very short cable distance from alt to battery, so i was going to wire sense straight to the alt's batt lug.

How long are the races? Does it even need to charge the battery?

I'm not sure actually, but it's running quite a small battery.

[BigJonWB]

Maybe a better result would be a higher capacity lithium battery and no on board charging.

[Roy928tt]

No, always use a charging system. Otherwise at the end of the day the battery is going doughy the thing is reluctant to start and there isn't enough juice for the ignition system and fuel pump it breaks down at revs and you might as well throw the day away.

I suppose a micro switch to turn the alternator off at full throttle will do it.

[36]

Basic solution is to put a push button switch on the steering wheel to disconnect the alternator- relies on the driver being sensible with it. Will of course trigger the ignition light, so if it chucks a fan belt at the same time you don't get warning that the water pump has stopped..

All depends on the inputs - if the races are short enough, take your 2-3kg of alternator and put in a bigger battery and change/charge battery between runs.

How much time does a boat spend at full throttle? Is there "traction" style issues, during which its a good time to use excess power to charge the battery?

Personally, I prefer to have a charging system. Saves a lot of headaches.

[MWP]

It's hydroplane racing. These things: https://www.youtube.com/watch?v=JWL-rmWNdy0
So on the throttle 80% of the time I guess?

Turning the Alt off wont be a problem. I'll have spare ECU outputs that can deal with that.

My main concern is if turning it on & will cause voltage spikes, prematurely kill the alt, etc.

[36]

It's doable - plenty of cars do it these days - BiTurbo Rangers for instance. You probably don't want an alternator that big but might be able to work out what the widget is that makes it work.

[Gin Kii]

It's doable - plenty of cars do it these days - BiTurbo Rangers for instance. You probably don't want an alternator that big but might be able to work out what the widget is that makes it work.

Sounds like a dumb alternator has already been purchased and buying a smart one is not on the cards.

Will a dumb one cope with being switched on and off ?

[Do the safety dance.]

Is the ignition and fuel system gonna handle the drop in voltage?

[aerobrick]

^ good point - make sure the tuning is done at ~12.6v battery voltage and not 14.2v alternator voltage.

Sounds like something that will introduce a lot of gotchas.

[Aaron]

Surely unless the thing is piloted by a jockey already having the driver lay off the pies for a bit would be more effective than chasing 1hp of electrical load?