Custom Car Two Alternator Design

[NicholasGalassi]

I have a buddy that is building a custom car. I've been helping him with the electrical design. The engine is from a Hayabusa motorcycle and has a battery and alternator. The goal is to add additional systems, like A/C, radio, and window motors. The current alternators is only rated for 30 amps. So we have some options for upgrading the electrical system for the increased load. He has already purchased a 90A alternator. The initial thought was to put the two alternators in parallel. But after doing some research, it is sounding like there may be some issues with matching phases between the two alternators due to the rectified DC. Also, we would need to increase the conductor size to the battery and alternators to handle the additional current.

Does anyone have any experience with this? Are these valid concerns?

 

[shortbus=]

I haven't done it ,but a quick Google finds a place that has a way to use a GM one wire alternator with the Hayabusa engine. https://motormission.com/suzuki-hay...rnator-drive-and-stator-housing-for-charging/

Not sure about how the Hayabusa is but most bikes use a regulator that shunts the excess voltage to ground, because they use permanet magnets for the rotor. And car alternators use a regulator that varies the voltage to the rotor for regulation. So using one of each type together would probably cause problems, but that is just a guess.

 

[Nigel Goodwin]

Simple answer - ignore the old crude bike alternator and regulator, and use the proper car alternator on it's own.

 

[shortbus=]

and use the proper car alternator on it's own.

That is what the link was doing. But it takes some fabrication skills to make the adapter and drive. To change from the splines on the bike to the shaft of the car alternator and mounting bracket/housing. But if he is building a whole car it should be a snap, though today many people claim building a "custom" car is just putting a kit together.

 

[schmitt trigger]

From the mechanical point of view, I know that high performance motorcycle engines can rev up much, much higher than an automobile engines do.

Would the automobile alternator be able to sustain those higher RPMs without damage?

I don’t know, but suggest that you double check that.

 

[Nigel Goodwin]

From the mechanical point of view, I know that high performance motorcycle engines can rev up much, much higher than an automobile engines do.

Would the automobile alternator be able to sustain those higher RPMs without damage?

I don’t know, but suggest that you double check that.

I would imagine you'd take account of that in the drive system, so suitable sized pulleys and a belt - it's not as if cars drive them directly at engine speed either.

 

[Diver300]

I would imagine you'd take account of that in the drive system, so suitable sized pulleys and a belt - it's not as if cars drive them directly at engine speed either.

That's correct. The maximum rotational speed for alternators is often about 12,500 rpm to 15,000 rpm. They are geared up from the engine speed on cars, by 2 or 3 times. The gearing should be adjusted for a motorbike engine to respect the alternator's maximum speed.

When cars had dynamos, the maximum speed of the dynamo was much lower because the armature had to have the power windings. The gearing ratio was much lower, so at engine tick-over the dynamo didn't generate.

 

[crutschow]

I vote with Nigel.
Just use the added car alternator, and don't connect anything to the engine alternator.
It wouldn't work to connect them in parallel.

 

[shortbus=]

From the mechanical point of view, I know that high performance motorcycle engines can rev up much, much higher than an automobile engines do.

While true they don't normally operate at red line, at least not for long.

 

[Nigel Goodwin]

While true they don't normally operate at red line, at least not for long.

Neither do car engines

But regardless, the operating rev range of motor bike engines is usually a fair bit higher than car engines - but as we've all said, you simply take account of that in the gearing to the alternator, so it's of no concern.

 

[shortbus=]

Neither do car engines

What I was trying to say is they both operate in a similar RPM range while driving.

 

[Nigel Goodwin]

What I was trying to say is they both operate in a similar RPM range while driving.

Sorry, but I would disagree with that - as an ex-biker you certainly use more revs on a bike - or perhaps it's partly because I was younger

I had mostly two strokes, which are more lower revving than 4 stokes anyway, but certainly on the Japanese 4 stokes you need lot's of revs to get anywhere.

The red line on most of my two stroke bikes was 8000, where the four strokes were 13000-15000.

 

[crutschow]

What I was trying to say is they both operate in a similar RPM range while driving.

You still have to design for the maximum RPM of both the engine and the alternator.